Why is the combined gas–steam cycle more efficient than

Problem 1P Why is the Carnot cycle not a realistic model for steam power plants?

Problem 134P Stack gases exhausting from electrical power plants are at approximately 150°C. Design a basic Rankine cycle that uses water, refrigerant-134a, or ammonia as the working fluid and that produces the maximum amount of work from this energy source while rejecting heat to the ambient air at 40°C. You are to use a turbine whose efficiency is 92 percent and whose exit quality cannot be less than 85 percent.

Problem 2P Water enters the boiler of a steady-flow Carnot engine as a saturated liquid at 400 psia and leaves with a quality of 0.95. Steam leaves the turbine at a pressure of 20 psia. Show the cycle on a T-s diagram relative to the saturation lines, and determine (a) the thermal efficiency, (b) the quality at the end of the isothermal heat-rejection process, and (c) the net work output.

A steady-flow Carnot cycle uses water as the working fluid. Water changes from saturated liquid to saturated vapor as heat is transferred to it from a source at 250°C. Heat rejection takes place at a pressure of 20 kPa. Show the cycle on a T-s diagram relative to the saturation lines, and determine (a) the thermal efficiency, (b) the amount of heat rejected, and (c) the net work output.

Problem 4P Repeat Prob. 10–3 for a heat rejection pressure of l0 kPa.

Problem 5P Consider a steady-flow Carnot cycle with water as the working fluid. The maximum and minimum temperatures in the cycle are 350 and 60°C. The quality of water is 0.891 at the beginning of the heat-rejection process and 0.1 at the end. Show the cycle on a T-s diagram relative to the saturation lines, and determine (a) the thermal efficiency, (b) the pressure at the turbine inlet, and (c) the net work output.

Problem 9P How do actual vapor power cycles differ from idealized ones?

Problem 6P Consider a simple ideal Ranking cycle with fixed turbine inlet conditions.What is the effect of lowering the condenser pressure on Pump work input: (a) increases, (b) decreases, (c) remains the same Turbine work output: (a) increases, (b) decreases, (c) remains the same Heat supplied: (a) increases, (b) decreases, (c) remains the same Heat rejected: (a) increases, (b) decreases, (c) remains the same Cycle efficiency: (a) increases, (b) decreases, (c) remains the same Moisture content at turbine exit: (a) increases, (b) decreases, (c) remains the same

Problem 10P The entropy of steam increases in actual steam turbines as a result of irreversibilities. In an effort to control entropy increase, it is proposed to cool the steam in the turbine by running cooling water around the turbine casing. It is argued that this will reduce the entropy and the enthalpy of the steam at the turbine exit and thus increase the work output. How would you evaluate this proposal?

Problem 11P Is it possible to maintain a pressure of 10 kPa in a condenser that is being cooled by river water entering at 20°C?

Problem 7P Consider a simple ideal Rankine cycle with fixed turbine inlet temperature and condenser pressure. What is the effect of increasing the boiler pressure on Pump work input: (a) increases, (b) decreases, (c) remains the same Turbine work output: (a) increases, (b) decreases, (c) remains the same Heat supplied: (a) increases, (b) decreases, (c) remains the same Heat rejected: (a) increases, (b) decreases, (c) remains the same Cycle efficiency: (a) increases, (b) decreases, (c) remains the same Moisture content at turbine exit: (a) increases, (b) decreases, (c) remains the same

Problem 8P Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. What is the effect of superheating the steam to a higher temperature on Pump work input: (a) increases, (b) decreases, (c) remains the same Turbine work output: (a) increases, (b) decreases, (c) remains the same Heat supplied: (a) increases, (b) decreases, (c) remains the same Heat rejected: (a) increases, (b) decreases, (c) remains the same Cycle efficiency: (a) increases, (b) decreases, (c) remains the same Moisture content at turbine exit: (a) increases, (b) decreases, (c) remains the same

Problem 12P A steam power plant operates on a simple ideal Rankine cycle between the pressure limits of 3 MPa and 50 kPa. The temperature of the steam at the turbine inlet is 300°C, and the mass flow rate of steam through the cycle is 35 kg/s. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the thermal efficiency of the cycle and (b) the net power output of the power plant.

A simple ideal Rankine cycle which uses water as the working fluid operates its condenser at \(40^{\circ} \mathrm{C}\) and its boiler at \(300^{\circ} \mathrm{C}\). Calculate the work produced by the turbine, the heat supplied in the boiler, and the thermal efficiency of this cycle when the steam enters the turbine without any superheating. Equation Transcription: Text Transcription: 40°C 300°C

Problem 15P A simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of 2500 psia in the boiler and 5 psia in the condenser. What is the minimum temperature required at the turbine inlet such that the quality of the steam leaving the turbine is not below 80 percent. When operated at this temperature, what is the thermal efficiency of this cycle?

Problem 16P Consider a 210-MW steam power plant that operates on a simple ideal Rankine cycle. Steam enters the turbine at 10 MPa and 500°C and is cooled in the condenser at a pressure of 10 kPa. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the quality of the steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.

Problem 18P A steam Rankine cycle operates between the pressure limits of 1500 psia in the boiler and 2 psia in the condenser. The turbine inlet temperature is 800°F. The turbine isentropic efficiency is 90 percent, the pump losses are negligible, and the cycle is sized to produce 2500 kW of power. Calculate the mass flow rate through the boiler, the power produced by the turbine, the rate of heat supply in the boiler, and the thermal efficiency.

Problem 13P Refrigerant-134a is used as the working fluid in a simple ideal Rankine cycle which operates the boiler at 2000 kPa and the condenser at 24°C. The mixture at the exit of the turbine has a quality of 93 percent. Determine the turbine inlet temperature, the cycle thermal efficiency, and the back-work ratio of this cycle.

Problem 17P Repeat Prob. 10–16 assuming an isentropic efficiency of 85 percent for both the turbine and the pump. Problem 10–16 Consider a 210-MW steam power plant that operates on a simple ideal Rankine cycle. Steam enters the turbine at 10 MPa and 500°C and is cooled in the condenser at a pressure of 10 kPa. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the quality of the steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.

Problem 20P A steam power plant operates on a simple ideal Rankine cycle between the pressure limits of 1250 and 2 psia. The mass flow rate of steam through the cycle is 75 lbm/s. The moisture content of the steam at the turbine exit is not to exceed 10 percent. Show the cycle on a T-sdiagram with respect to saturation lines, and determine (a) the minimum turbine inlet temperature, (b) the rate of heat input in the boiler, and (c) the thermal efficiency of the cycle.

Problem 24P The net work output and the thermal efficiency for the Carnot and the simple ideal Rankine cycles with steam as the working fluid are to be calculated and compared. Steam enters the turbine in both cases at 5 MPa as a saturated vapor, and the condenser pressure is 50 kPa. In the Rankine cycle, the condenser exit state is saturated liquid and in the Carnot cycle, the boiler inlet state is saturated liquid. Draw the T-s diagrams for both cycles.

Problem 21P Repeat Prob. 10–20E assuming an isentropic efficiency of 85 percent for both the turbine and the pump. Problem 10–20E A steam power plant operates on a simple ideal Rankine cycle between the pressure limits of 1250 and 2 psia. The mass flow rate of steam through the cycle is 75 lbm/s. The moisture content of the steam at the turbine exit is not to exceed 10 percent. Show the cycle on a T-sdiagram with respect to saturation lines, and determine (a) the minimum turbine inlet temperature, (b) the rate of heat input in the boiler, and (c) the thermal efficiency of the cycle.

Problem 22P A simple Rankine cycle uses water as the working fluid. The boiler operates at 6000 kPa and the condenser at 50 kPa. At the entrance to the turbine, the temperature is 450°C. The isentropic efficiency of the turbine is 94 percent, pressure and pump losses are negligible, and the water leaving the condenser is subcooled by 6.3°C. The boiler is sized for a mass flow rate of 20 kg/s. Determine the rate at which heat is added in the boiler, the power required to operate the pumps, the net power produced by the cycle, and the thermal efficiency.

Problem 19P Reconsider Prob. 10–18E. How much error is caused in the thermal efficiency if the power required by the pump were completely neglected? Problem 10–18E A steam Rankine cycle operates between the pressure limits of 1500 psia in the boiler and 2 psia in the condenser. The turbine inlet temperature is 800°F. The turbine isentropic efficiency is 90 percent, the pump losses are negligible, and the cycle is sized to produce 2500 kW of power. Calculate the mass flow rate through the boiler, the power produced by the turbine, the rate of heat supply in the boiler, and the thermal efficiency.

Problem 26P Consider a coal-fired steam power plant that produces 175 MW of electric power. The power plant operates on a simple ideal Rankine cycle with turbine inlet conditions of 7 MPa and 550°C and a condenser pressure of 15 kPa. The coal has a heating value (energy released when the fuel is burned) of 29,300 kJ/kg. Assuming that 85 percent of this energy is transferred to the steam in the boiler and that the electric generator has an efficiency of 96 percent, determine (a) the overall plant efficiency (the ratio of net electric power output to the energy input as fuel) and (b) the required rate of coal supply.

Problem 27P Show the ideal Rankine cycle with three stages of reheating on a T-s diagram. Assume the turbine inlet temperature is the same for all stages. How does the cycle efficiency vary with the number of reheat stages?

Problem 30P An ideal reheat Rankine cycle with water as the working fluid operates the boiler at 15,000 kPa, the reheater 2000 kPa, and the condenser at 100 kPa. The temperature is 450°C at the entrance of the high-pressure and low-pressure turbines. The mass flow rate through the cycle is 1.74 kg/s. Determine the power used by pumps, the power produced by the cycle, the rate of heat transfer in. the reh1eater, and the thermal efficiency of this system.

Problem 29P Consider a simple ideal Rankine cycle and an ideal Rankine cycle with three reheat stages. Both cycles operate between the same pressure limits. The maximum temperature is 700°C in the simple cycle and 450°C in the reheat cycle. Which cycle do you think will have a higher thermal efficiency?

Problem 28P How do the following quantities change when a simple ideal Rankine cycle is modified with reheating? Assume the mass flow rate is maintained the same. Pump work input: (a) increases, (b) decreases, (c) remains the same Turbine work output: (a) increases, (b) decreases, (c) remains the same Heat supplied: (a) increases, (b) decreases, (c) remains the same Heat rejected: (a) increases, (b) decreases, (c) remains the same Moisture content at turbine exit: (a) increases, (b) decreases, (c) remains the same

Problem 33P Steam enters the high-pressure turbine of a steam power plant that operates on the ideal reheat Rankine cycle at 800 psia and 900°F and leaves as saturated vapor. Steam is then reheated to 800°F before it expands to a pressure of 1 psia. Heat is transferred to the steam in the boiler at a rate of 6 × 104 Btu/s. Steam is cooled in the condenser by the cooling water from a nearby river, which enters the condenser at 45°F. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the pressure at which reheating takes place, (b) the net power output and thermal efficiency, and (c) the minimum mass flow rate of the cooling water required.

Consider a steam power plant that operates on the ideal reheat Rankine cycle. The plant maintains the boiler at \(5000 k P a \), the reheat section at \(1200 k P a\), and the condenser at \(20 k P a). The mixture quality at the exit of both turbines is 96 percent. Determine the temperature at the inlet of each turbine and the cycle’s thermal efficiency. FIGURE P10–34 Equation Transcription: Text Transcription: 5000 kPa 1200 kPa 20 kPa

A steam power plant operates on the ideal reheat Rankine cycle. Steam enters the high-pressure turbine at \(6 M P a \text { and } 400^{\circ} \mathrm{C}\) and leaves at \(2 M P a\). Steam is then reheated at constant pressure to \(400^{\circ} \mathrm{C}\) before it expands to \(20 k P a\) in the low-pressure turbine. Determine the turbine work output, in , and the thermal efficiency of the cycle. Also, show the cycle on a \(T-s\) diagram with respect to saturation lines. Equation Transcription: Text Transcription: 6MPa and 400°C 2MPa 400°C 20kPa T-s

Problem 35P A steam power plant operates on an ideal reheat Rankine cycle between the pressure limits of 15 MPa and 10 kPa. The mass flow rate of steam through the cycle is 12 kg/s. Steam enters both stages of the turbine at 500°C. If the moisture content of the steam at the exit of the low-pressure turbine is not to exceed 10 percent, determine (a) the pressure at which reheating takes place, (b) the total rate of heat input in the boiler, and (c) the thermal efficiency of the cycle. Also, show the cycle on a T-s diagram with respect to saturation lines.

Problem 37P Consider a steam power plant that operates on a reheat Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 500°C and the low-pressure turbine at 1 MPa and 500°C. Steam leaves the condenser as a saturated liquid at a pressure of 10 kPa. The isentropic efficiency of the turbine is 80 percent, and that of the pump is 95 percent. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the quality (or temperature, if superheated) of the steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.

Problem 38P Repeat Prob. 10–37 assuming both the pump and the turbine are isentropic Problem 10–37 Consider a steam power plant that operates on a reheat Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 500°C and the low-pressure turbine at 1 MPa and 500°C. Steam leaves the condenser as a saturated liquid at a pressure of 10 kPa. The isentropic efficiency of the turbine is 80 percent, and that of the pump is 95 percent. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the quality (or temperature, if superheated) of the steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.

A steam power plant operates on the reheat Rankine cycle. Steam enters the high-pressure turbine at \(12.5 \mathrm{MP} a and 550^{\circ} \mathrm{C}\) at a rate of \(7.7 \mathrm{~kg} / \mathrm{s}\) and leaves at \(2 M P a\). Steam is then reheated at constant pressure to \(450^{\circ} C\) before it expands in the low-pressure turbine. The isentropic efficiencies of the turbine and the pump are 85 percent and 90 percent, respectively. Steam leaves the condenser as a saturated liquid. If the moisture content of the steam at the exit of the turbine is not to exceed 5 percent, determine (a) the condenser pressure, (b) the net power output, and the thermal efficiency. Answers: (a) , (b) , (c) percent. Equation Transcription: Text Transcription: 12.5MPa and 550°C 7.7 kg/s 2MPa 450°C

Problem 40P Consider a simple ideal Rankine cycle and an ideal regenerative Rankine cycle with one open feedwater heater. The two cycles are very much alike, except the feedwater in the regenerative cycle is heated by extracting some steam just before it enters the turbine. How would you compare the efficiencies of these two cycles?

Problem 39P During a regeneration process, some steam is extracted from the turbine and is used to heat the liquid water leaving the pump. This does not seem like a smart thing to do since the extracted steam could produce some more work in the turbine. How do you justify this action?

Problem 41P How do open feedwater heaters differ from closed feedwater heaters?

Problem 43P Turbine bleed steam enters an open feedwater heater of a regenerative Rankine cycle at 40 psia and 280°F while the cold feedwater enters at 110°F. Determine the ratio of the bleed steam mass flow rate to the inlet feedwater mass flow rate required to heat the feedwater to 250°F.

Problem 42P How do the following quantities change when the simple ideal Rankine cycle is modified with regeneration? Assume the mass flow rate through the boiler is the same. Turbine work output: (a) increases, (b) decreases, (c) remains the same Heat supplied: (a) increases, (b) decreases, (c) remains the same Heat rejected: (a) increases, (b) decreases, (c) remains the same Moisture content at turbine exit: (a) increases, (b) decreases, (c) remains the same

Problem 47P A steam power plant operates on an ideal regenerative Rankine cycle with two open feedwater heaters. Steam enters the turbine at 8 MPa and 550°C and exhausts to the condenser at 10 kPa. Steam is extracted from the turbine at 0.6 and 0.2 MPa. Water leaves both feedwater heaters as a saturated liquid. The mass flow rate of steam through the boiler is 16 kg/s. Show the cycle on a T-s diagram, and determine (a) the net power output of the power plant and (b) the thermal efficiency of the cycle.

The closed feedwater heater of a regenerative Rankine cycle is to heat \(7000 \mathrm{kPa}\) feedwater from \(260^{\circ} \mathrm{C}\) to a saturated liquid. The turbine supplies bleed steam at \(6000 \mathrm{kP} \text { a and } 325^{\circ} \mathrm{C}\) to this unit. This steam is condensed to a saturated liquid before entering the pump. Calculate the amount of bleed steam required to heat of feedwater in this unit. Answer: \(0.0779 \mathrm{~kg} / \mathrm{s}\) Equation Transcription: Text Transcription: 7000kPa 260°C 6000kPa and 325°C 0.0779 kg/s

Reconsider Prob. 10–48. Using EES (or other) software, determine the optimum bleed pressure for the closed feedwater heater that maximizes the thermal efficiency of the cycle. Answer: \(220 \mathrm{kPa}\) Equation Transcription: Text Transcription: 220 kPa

Consider a steam power plant that operates on the ideal regenerative Rankine cycle with a closed feedwater heater as shown in the figure. The plant maintains the turbine inlet at \(3000 \mathrm{kP} a and 350^{\circ} \mathrm{C}\); and operates the condenser at \(20 \mathrm{kPa}\) Steam is extracted at \(1000 k P a\) to serve the closed feedwater heater, which discharges into the condenser after being throttled to condenser pressure. Calculate the work produced by the turbine, the work consumed by the pump, and the heat supply in the boiler for this cycle per unit of boiler flow rate. Answers: \(741 \mathrm{~kJ} / \mathrm{kg}, 3.0 \mathrm{~kJ} / \mathrm{kg}, 2353 \mathrm{~kJ} / \mathrm{kg}\) Equation Transcription: Text Transcription: 3000kPa and 350°C 20kPa 1000kPa 741 kJ/kg, 3.0 kJ/kg, 2353 kJ/kg

Problem 50P Determine the thermal efficiency of the regenerative Rankine cycle of Prob. 10–53 when the isentropic efficiency of the turbine is 90 percent before and after steam extraction point.

Problem 46P Repeat Prob. 10–45 by replacing the open feedwater heater with a closed feedwater heater. Assume that the feedwater leaves the heater at the condensation temperature of the extracted steam and that the extracted steam leaves the heater as a saturated liquid and is pumped to the line carrying the feedwater. Problem 10–45 A steam power plant operates on an ideal regenerative Rankine cycle. Steam enters the turbine at 6 MPa and 450°C and is condensed in the condenser at 20 kPa. Steam is extracted from the turbine at 0.4 MPa to heat the feedwa- ter in an open feedwater heater. Water leaves the feedwater heater as a saturated liquid. Show the cycle on a T-s diagram, and determine (a) the net work output per kilogram of steam flowing through the boiler and (b) the thermal efficiency of the cycle.

Problem 51P Determine the thermal efficiency of the regenerative Rankine cycle of Prob. 10–53 when the isentropic efficiency of the turbine before and after steam extraction point is 90 percent and the condenser condensate is subcooled by 10°C.

Consider an ideal steam regenerative Rankine cycle with two feedwater heaters, one closed and one open. Steam enters the turbine at \(10 M P \text { a and } 600^{\circ} \mathrm{C}\) and exhausts to the condenser at \(10 k P a\). Steam is extracted from the turbine at \(1.2 M P a\) for the closed feedwater heater and at MPa for the open one. The feedwater is heated to the condensation temperature of the extracted steam in the closed feedwater heater. The extracted steam leaves the closed feedwater heater as a saturated liquid, which is subsequently throttled to the open feedwater heater. Show the cycle on a -s diagram with respect to saturation lines, and determine the mass flow rate of steam through the boiler for a net power output of and the thermal efficiency of the cycle. Equation Transcription: Text Transcription: 10MPa and 600°C 10kPa 1.2 MPa

Reconsider Prob. 10–48. Using EES (or other) software, determine how much additional heat must be supplied to the boiler when the turbine isentropic efficiency before and after the extraction point is 90 percent and there is a \(10 \mathrm{kPa}\) pressure drop across the boiler? Equation Transcription: Text Transcription: 10 kPa

Problem 58P Determine the exergy destruction associated with each of the processes of the Rankine cycle described in Prob. 10–12, assuming a source temperature of 1500 K and a sink temperature of 290 K. Problem 10–12 A steam power plant operates on a simple ideal Rankine cycle between the pressure limits of 3 MPa and 50 kPa. The temperature of the steam at the turbine inlet is 300°C, and the mass flow rate of steam through the cycle is 35 kg/s. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the thermal efficiency of the cycle and (b) the net power output of the power plant.

Problem 59P Determine the exergy destruction associated with each of the processes of the Rankine cycle described in Prob. 10–16, assuming a source temperature of 1500 K and a sink temperature of 290 K. Problem 10–16 Consider a 210-MW steam power plant that operates on a simple ideal Rankine cycle. Steam enters the turbine at 10 MPa and 500°C and is cooled in the condenser at a pressure of 10 kPa. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the quality of the steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.

Problem 45P A steam power plant operates on an ideal regenerative Rankine cycle. Steam enters the turbine at 6 MPa and 450°C and is condensed in the condenser at 20 kPa. Steam is extracted from the turbine at 0.4 MPa to heat the feedwa- ter in an open feedwater heater. Water leaves the feedwater heater as a saturated liquid. Show the cycle on a T-s diagram, and determine (a) the net work output per kilogram of steam flowing through the boiler and (b) the thermal efficiency of the cycle.

Repeat Prob. 10–55, but replace the open feedwater heater with a closed feedwater heater. Assume that the feedwater leaves the heater at the condensation temperature of the extracted steam and that the extracted steam leaves the heater as a saturated liquid and is pumped to the line carrying the feedwater.

Problem 60P Determine the exergy destruction associated with each of the processes of the reheat Rankine cycle described in Prob. 10–35. Assume a source temperature of 1500 K and a sink temperature of 295 K.

Problem 62P Determine the exergy destruction associated with the heat addition process and the expansion process in Prob. 10–37. Assume a source temperature of 1600 K and a sink temperature of 285 K. Also, determine the exergy of the steam at the boiler exit. Take P0 = 100 kPa. Problem 10–37 Consider a steam power plant that operates on a reheat Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 500°C and the low-pressure turbine at 1 MPa and 500°C. Steam leaves the condenser as a saturated liquid at a pressure of 10 kPa. The isentropic efficiency of the turbine is 80 percent, and that of the pump is 95 percent. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the quality (or temperature, if superheated) of the steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.

10-57 An ideal Rankine steam cycle modified with two closed feedwater heaters is shown below. The power cycle receives \(75 \mathrm{~kg} / \mathrm{s}\) of steam at the high pressure inlet to the turbine. The feedwater heater exit states for the boiler feedwater and the condensed steam are the normally assumed ideal states. The fraction of mass entering the high pressure turbine at state 5 that is extracted for the feedwater heater operating at \(1400 \mathrm{kP} \text { a is } y=0.1446\) Use the data provided in the tables given below to (a) Sketch the -s diagram for the ideal cycle. (b) Determine the fraction of mass, , that is extracted for the closed feedwater heater operating at the extraction pressure. Equation Transcription: Text Transcription: 75 kg/s 1400kPa is y=0.1446

Problem 63P Determine the exergy destruction associated with the regenerative cycle described in Prob. 10–45. Assume a source temperature of 1500 K and a sink temperature of 290 K. Problem 10–45 A steam power plant operates on an ideal regenerative Rankine cycle. Steam enters the turbine at 6 MPa and 450°C and is condensed in the condenser at 20 kPa. Steam is extracted from the turbine at 0.4 MPa to heat the feedwa- ter in an open feedwater heater. Water leaves the feedwater heater as a saturated liquid. Show the cycle on a T-s diagram, and determine (a) the net work output per kilogram of steam flowing through the boiler and (b) the thermal efficiency of the cycle.

Problem 66P How is the utilization factor ?u for cogeneration plants defined? Could ?u be unity for a cogeneration plant that does not produce any power?

Problem 64P Determine the exergy destruction associated with the reheating and regeneration processes described in Prob. 10–55. Assume a source temperature of 1800 K and a sink temperature of 290 K. Problem 10–55 A steam power plant operates on an ideal reheat- regenerative Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 550°C and leaves at 0.8 MPa. Some steam is extracted at this pressure to heat the feedwater in an open feedwater heater. The rest of the steam is reheated to 500°C and is expanded in the low-pressure turbine to the condenser pressure of 10 kPa. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the mass flow rate of steam through the boiler and (b) the thermal efficiency of the cycle.

Problem 67P Consider a cogeneration plant for which the utilization factor is 1. Is the irreversibility associated with this cycle necessarily zero? Explain.

The schematic of a single-flash geothermal power plant with state numbers is given in Fig. P10-65. Geothermal resource exists as saturated liquid at \(230^{\circ} \mathrm{C}\). The geothermal liquid is withdrawn from the production well at a rate of \(230 \mathrm{~kg} / \mathrm{s}\) and is flashed to a pressure of \(500 k P a\) by an essentially isenthalpic flashing process where the resulting vapor is separated from the liquid in a separator and is directed to the turbine. The steam leaves the turbine at \(10 k P a\) with a moisture content of 5 percent and enters the condenser where it is condensed; it is routed to a reinjection well along with the liquid coming off the separator. Determine the power output of the turbine and the thermal efficiency of the plant, the exergy of the geothermal liquid at the exit of the flash chamber, and the exergy destructions and the second-law efficiencies for the turbine and the entire plant. Answers: (a) , Equation Transcription: Text Transcription: 230°C 230 kg/s 500kPa 10kPa

Steam enters the turbine of a cogeneration plant at \(4 M P a \text { and } 500^{\circ} \mathrm{C}\). One-fourth of the steam is extracted from the turbine at \(1200-k P a\)pressure for process heating. The remaining steam continues to expand to . The extracted steam is then condensed and mixed with feed water at constant pressure and the mixture is pumped to the boiler pressure of . The mass flow rate of steam through the boiler is . Disregarding any pressure drops and heat losses in the piping, and assuming the turbine and the pump to be isentropic, determine the net power produced and the utilization factor of the plant. Equation Transcription: Text Transcription: 4MPa and 500°C 1200-kPa

Problem 70P A large food-processing plant requires 1.5 lbm/s of saturated or slightly superheated steam at 140 psia, which is extracted from the turbine of a cogeneration plant. The boiler generates steam at 800 psia and 1000°F at a rate of 10 lbm/s, and the condenser pressure is 2 psia. Steam leaves the process heater as a saturated liquid. It is then mixed with the feedwater at the same pressure and this mixture is pumped to the boiler pressure. Assuming both the pumps and the turbine have isentropic efficiencies of 86 percent, determine (a) the rate of heat transfer to the boiler and (b) the power output of the cogeneration plant.

Problem 68P Consider a cogeneration plant for which the utilization factor is 0.5. Can the exergy destruction associated with this plant be zero? If yes, under what conditions?

Consider a cogeneration power plant modified with regeneration. Steam enters the turbine at \(9 M P \text { a and } 400^{\circ} \mathrm{C}\) and expands to a pressure of . At this pressure, 35 percent of the steam is extracted from the turbine, and the remainder expands to 10 kPa. Part of the extracted steam is used to heat the feedwater in an open feedwater heater. The rest of the extracted steam is used for process heating and leaves the process heater as a saturated liquid at 1.6 MPa. It is subsequently mixed with the feedwater leaving the feedwater heater, and the mixture is pumped to the boiler pressure. Assuming the turbines and the pumps to be isentropic, show the cycle on a T-s diagram with respect to saturation lines, and determine the mass flow rate of steam through the boiler for a net power output of 25 MW. ________________ Equation Transcription: Text Transcription: 9MPa and 400°C

Problem 75P In combined gas–steam cycles, what is the energy source for the steam?

Problem 76P Why is the combined gas–steam cycle more efficient than either of the cycles operated alone?

Problem 74P Steam is generated in the boiler of a cogeneration plant at 600 psia and 650°F at a rate of 32 lbm/s. The plant is to produce power while meeting the process steam requirements for a certain industrial application. One-third of the steam leaving the boiler is throttled to a pressure of 120 psia and is routed to the process heater. The rest of the steam is expanded in an isentropic turbine to a pressure of 120 psia and is also routed to the process heater. Steam leaves the process heater at 240°F. Neglecting the pump work, determine (a) the net power produced, (b) the rate of process heat supply, and (c) the utilization factor of this plant.

Problem 77P The gas-turbine portion of a combined gas-steam power plant has a pressure ratio of 16. Air enters the compressor at 300 K at a rate of 14 kg/s and is heated to 1500 K in the combustion chamber. The combustion gases leaving the gas turbine are used to heat the steam to 400°C at 10 MPa in a heat exchanger. The combustion gases leave the heat exchanger at 420 K. The steam leaving the turbine is condensed at 15 kPa. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate of the steam, (b) the net power output, and (c) the thermal efficiency of the combined cycle. For air, assume constant specific heats at room temperature.

Problem 71P Steam is generated in the boiler of a cogeneration plant at 10 MPa and 450°C at a steady rate of 5 kg/s. In normal operation, steam expands in a turbine to a pressure of 0.5 MPa and is then routed to the process heater, where it supplies the process heat. Steam leaves the process heater as a saturated liquid and is pumped to the boiler pressure. In this mode, no steam passes through the condenser, which operates at 20 kPa. (a) Determine the power produced and the rate at which process heat is supplied in this mode. ________________ (b) Determine the power produced and the rate of process heat supplied if only 60 percent of the steam is routed to the process heater and the remainder is expanded to the condenser pressure.

Problem 80P Repeat Prob. 10–78 assuming isentropic efficiencies of 100 percent for the pump, 82 percent for the compressor, and 86 percent for the gas and steam turbines. Problem 10–78 Consider a combined gas?steam power plant that has a net power output of 450 MW. The pressure ratio of the gas-turbine cycle is 14. Air enters the compressor at 300 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 8 MPa to 400°C in a heat exchanger. The combustion gases leave the heat exchanger at 460 K. An open feedwater heater incorporated with the steam cycle operates at a pressure of 0.6 MPa. The condenser pressure is 20 kPa. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate ration of air to steam, (b) the required rate of heat input in the combustion chamber, and (c) thermal efficiency of the combined cycle.

Problem 82P Consider a combined gas-steam power plant that has a net power output of 280 MW. The pressure ratio of the gas-turbine cycle is 11. Air enters the compressor at 300 K and the turbine at 1100 K. The combustion gases leaving the gas turbine are used to heat the steam at 5 MPa to 350°C in a heat exchanger. The combustion gases leave the heat exchanger at 420 K. An open feedwater heater incorporated with the steam cycle operates at a pressure of 0.8 MPa. The condenser pressure is 10 kPa. Assuming isentropic efficiences of 100 percent for the pump, 82 percent for the compressor, and 86 percent for the gas and steam turbines, determine (a) the mass flow rate ratio of air to steam, (b) the required rate of heat input in the combustion chamber, and (c) the thermal efficiency of the combined cycle.

Consider a combined gas–steam power plant that has a net power output of 450 MW. The pressure ratio of the gas-turbine cycle is 14. Air enters the compressor at 300 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 8 MPa to 4008C in a heat exchanger. The combustion gases leave the heat exchanger at 460 K. An open feedwater heater incorporated with the steam cycle operates at a pressure of 0.6 MPa. The condenser pressure is 20 kPa. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate ration of air to steam, (b) the required rate of heat input in the combustion chamber, and (c) thermal efficiency of the combined cycle.

Problem 85P Why is steam not an ideal working fluid for vapor power cycles?

10-84 Consider a combined gas-steam power cycle. The topping cycle is a simple Brayton cycle that has a pressure ratio of 7 . Air enters the compressor at \(15^{\circ} \mathrm{C}\) at a rate of \(40 \mathrm{~kg} / \mathrm{s} 950^{\circ} \mathrm{C}\) and the gas turbine at . The bottoming cycle is a reheat Rankine cycle between the pressure limits of and . Steam is heated in a heat exchanger at a rate of by the exhaust gases leaving the gas turbine, and the exhaust gases leave the heat exchanger at \(200^{\circ} \mathrm{C}\). Steam leaves the high-pressure turbine at and is reheated to \(400^{\circ} \mathrm{C}\) in the heat exchanger before it expands in the low-pressure turbine. Assuming 80 percent isentropic efficiency for all pumps and turbines, determine the moisture content at the exit of the low-pressure turbine, the steam temperature at the inlet of the high-pressure turbine, the net power output and the thermal efficiency of the combined plant. Equation Transcription: Text Transcription: 15°C 40 kg/s 950°C 200°C 400°C

Problem 86P What is a binary power cycle? What is its purpose?

Problem 88P Why is mercury a suitable working fluid for thetopping portion of a binary vapor cycle but not for the bottoming cucle?

Problem 87P What is the difference between the binary vapor power cycle and the combined gas-steam power cycle?

Problem 89P By writing an energy balance on the heat exchanger of a binary vapor power cycle, obtain a relation for the ratio of mass flow rates of two fluids in terms of their enthalpies.

Problem 90P Steam enters the turbine of a steam power plant that operates on a simple ideal Rankine cycle at a pressure of 6 MPa, and it leaves as a saturated vapor at 7.5 kPa. Heat is transferred to the steam in the boiler at a rate of 40,000 kJ/s. Steam is cooled in the condenser by the cooling water from a nearby river, which enters the condenser at 15°C. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the turbine inlet temperature, (b) the net power output and thermal efficiency, and (c) the minimum mass flow rate of the cooling water required.

Problem 91P A steam power plant operating on a simple ideal Rankine cycle maintains the boiler at 6000 kPa, the turbine inlet at 600°C, and the condenser at 50 kPa. Compare the thermal efficiency of this cycle when it is operated so that the liquid enters the pump as a saturated liquid against that when the liquid enters the pump 11.3°C cooler than a saturated liquid at the condenser pressure.

Problem 92P A steam power plant operates on an ideal Rankine cycle with two stages of reheat and has a net power output of 75 MW. Steam enters all three stages of the turbine at 550°C. The maximum pressure in the cycle is 10 MPa, and the minimum pressure is 30 kPa. Steam is reheated at 4 MPa the first time and at 2 MPa the second time. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the thermal efficiency of the cycle, and (b) the mass flow rate of the steam.

Problem 93P Consider a steam power plant operating on the ideal Rankine cycle with reheat between the pressure limits of 30 MPa and 10 kPa with a maximum cycle temperature of 700°C and a moisture content of 5 percent at the turbine exit. For a reheat temperature of 700°C, determine the reheat pressures of the cycle for the cases of (a) single and (b) double reheat.

10-94 Consider a steam power plant that operates on a regenerative Rankine cycle and has a net power output of . Steam enters the turbine at \(10 M P a \text { and } 500^{\circ} \mathrm{C}\) and the condenser at . The isentropic efficiency of the turbine is 80 percent, and that of the pumps is 95 percent. Steam is extracted from the turbine at 0.5 MPa to heat the feedwater in an open feedwater heater. Water leaves the feedwater heater as a saturated liquid. Show the cycle on a T-s diagram, and determine (a) the mass flow rate of steam through the boiler, and (b) the thermal efficiency of the cycle. Also, determine the exergy destruction associated with the regeneration process. Assume a source temperature of 1300 K and a sink temperature of 303 K. Equation Transcription: Text Transcription: 10 M P a \text { and } 500^{\circ} \mathrm{C}

Problem 95P Repeat Prob. 10–100 assuming both the pump and the turbine are isentropic.

Problem 97P Repeat Prob. 10–102 assuming an isentropic efficiency of 84 percent for the turbines and 100 percent for the pumps.

Problem 98P Steam is to be supplied from a boiler to a high- pressure turbine whose isentropic efficiency is 85 percent at conditions to be determined. The steam is to leave the high- pressure turbine as a saturated vapor at 1.4 MPa, and the turbine is to produce 5.5 MW of power. Steam at the turbine exit is extracted at a rate of 1000 kg/min and routed to a process heater while the rest of the steam is supplied to a low- pressure turbine whose isentropic efficiency is 80 percent. The low-pressure turbine allows the steam to expand to 10 kPa pressure and produces 1.5 MW of power. Determine the temperature, pressure, and the flow rate of steam at the inlet of the high-pressure turbine.

Problem 96P Consider an ideal reheat-regenerative Rankine cycle with one open feedwater heater. The boiler pressure is 10 MPa, the condenser pressure is 15 kPa.the reheater pressure is 1 MPa, and the feedwater pressure is 0.6 MPa. Steam enters both the high- and low-pressure turbines at 500°C. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the fraction of steam extracted for regeneration and (b) the thermal efficiency of the cycle.

Consider a cogeneration power plant that is modified with reheat and that produces of power and supplies of process heat. Steam enters the high-pressure turbine at and \(500^{\circ} \mathrm{C}\) and expands to a pressure of 1 MPa. At this pressure, part of the steam is extracted from the turbine and routed to the process heater, while the remainder is reheated to \(500^{\circ} \mathrm{C}\) and expanded in the low-pressure turbine to the condenser pressure of . The condensate from the condenser is pumped to and is mixed with the extracted steam, which leaves the process heater as a compressed liquid at \(120^{\circ} \mathrm{C}\). The mixture is then pumped to the boiler pressure. Assuming the turbine to be isentropic, show the cycle on a diagram with respect to saturation lines, and disregarding pump work, determine the rate of heat input in the boiler and the fraction of steam extracted for process heating. Equation Transcription: Text Transcription: 500°C 500°C 120°C

Problem 101P Atmospheric air enters the air compressor of a simple combined gas-steam power system at 14.7 psia and 80°F. The air compressor’s compression ratio is 10; the gas cycle’s maximum temperature is 2100°F; and the air compressor and turbine have an isentropic efficiency of 90 percent. The gas leaves the heat exchanger 50°F hotter than the saturation temperature of the steam in the heat exchanger. The steam pressure in the heat exchanger is 800 psia, and the steam leaves the heat exchanger at 600°F. The steam-condenser pressure is 5 psia and the isentropic efficiency of the steam turbine is 95 percent. Determine the overall thermal efficiency of this combined cycle. For air, use constant specific heats at room temperature.

10-99 A textile plant requires \(4 \mathrm{~kg} / \mathrm{s}\) of saturated steam at MPa, which is extracted from the turbine of a cogeneration plant. Steam enters the turbine at and \(500^{\circ} \mathrm{C}\) at a rate of \(11 \mathrm{~kg} / \mathrm{s}\) and leaves at . The extracted steam leaves the process heater as a saturated liquid and mixes with the feedwater at constant pressure. The mixture is pumped to the boiler pressure. Assuming an isentropic efficiency of 88 percent for both the turbine and the pumps, deter- mine the rate of process heat supply, the net power output, and the utilization factor of the plant. Equation Transcription: Text Transcription: 4 kg/s 500°C 11 kg/s

Problem 103P During winter, the system of Prob. 10–109E must supply 2 ×106 Btu/h of heat to the buildings. What is the mass flow rate of air through the air compressor and the system’s total electrical power production in winter?

Problem 105P Repeat Prob. 10?104 assuming isentropic efficiencies of 100 percent for the pump, 85 percent for the compressor, and 90 percent for the gas and steam turbines. Problem 10?104 The gas-turbine cycle of a combined gas?steam power plant has a pressure ratio of 12. Air enters the compressor at 310 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 12.5 MPa to 500°C in a heat exchanger. The combustion gases leave the heat exchanger at 247°C. Steam expands in a high-pressure turbine to a pressure of 2.5 MPa and is reheated in the combustion chamber to 550°C before it expands in a low-pressure turbine to 10 kPa. The mass flow rate of steam is 12 kg/s. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate of air in the gas-turbine cycle, (b) the rate of total heat input, and (c) the thermal efficiency of the combined cycle.

Problem 104P The gas-turbine cycle of a combined gas-steam power plant has a pressure ratio of 12. Air enters the compressor at 310 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 12.5 MPa to 500°C in a heat exchanger. The combustion gases leave the heat exchanger at 247°C. Steam expands in a high-pressure turbine to a pressure of 2.5 MPa and is reheated in the combustion chamber to 550°C before it expands in a low-pressure turbine to 10 kPa. The mass flow rate of steam is 12 kg/s. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate of air in the gas-turbine cycle, (b) the rate of total heat input, and (c) the thermal efficiency of the combined cycle.

Using EES (or other) software, investigate the effect of the condenser pressure on the performance of a simple ideal Rankine cycle. Turbine inlet conditions of steam are maintained constant at 10 MPa and \(550^{\circ} \mathrm{C}\) while the condenser pressure is varied from 5 to 100 kPa. Determine the thermal efficiency of the cycle and plot it against the condenser pressure, and discuss the results. Equation Transcription: Text Transcription: 550°C

10-112 Show the thermal efficiency of a combined gas-steam power plant \(\eta_{c c}\) can be expressed as \(\eta_{c c}=\eta_{g}+\eta_{s}-\eta_{g} \eta_{s}\) where \(\eta_{g}=W_{g} / Q_{\text {in }} \text { and } \eta_{s}=W_{s} / Q_{g, \text { out }}\) are the thermal efficiencies of the gas and steam cycles, respectively. Using this relation, determine the thermal efficiency of a combined power cycle that consists of a topping gas-turbine cycle with an efficiency of 40 percent and a bottoming steam-turbine cycle with an efficiency of 30 percent. Equation Transcription: Text Transcription: \eta_c c \eta_c c=\eta_g+\eta_s-\eta_g \eta_s \eta_g=W_g / Q_in and \eta_s=W_s / Q_g, out

10-113 It can be shown that the thermal efficiency of a combined gas-steam power plant \(\eta_{c c}\) can be expressed in terms of the thermal efficiencies of the gas- and the steamturbine cycles as \(\eta_{c c}=\eta_{g}+\eta_{s}-\eta_{g} \eta_{s}\) Prove that the value of \(\eta_{c c}\) is greater than either of \(\eta_{g} \text { or } \eta_{s}\) That is, the combined cycle is more efficient than either of the gas-turbine or steam-turbine cycles alone. Equation Transcription: Text Transcription: \eta_{c c} \eta_{c c}=\eta_{g}+\eta_{s}-\eta_{g} \eta_{s} \eta_{c c} \eta_{g} or \eta_{s}

Problem 115P A solar collector system delivers heat to a power plant. It is well known that the thermal collection efficiency ?sc of a solar collector diminishes with increasing solar collection output temperature TH, or ?sc = A – BTH where A and B are known constants. The thermal efficiency of the power plant hth is a fixed fraction of the Carnot thermal efficiency, such that ?th = F(1 – TL/TH) where Fis a known constant assumed here independent of temperatures and TL is the condenser temperature, also constant for this problem. Here, the solar collection temperature TH is also taken to be the source temperature for the power plant. (a) At what temperature TH should the solar collector be operated to obtain the maximum overall system efficiency? ________________ (b) Develop an expression for the maximum overall system efficiency.

10-107 A steam power plant operates on an ideal reheatregenerative Rankine cycle with one reheater and two feedwater heaters, one open and one closed. Steam enters the high-pressure turbine at \(15 \mathrm{MP} \text { a and } 600^{\circ} \mathrm{C}\) and the low-pressure turbine at and \(500^{\circ} \mathrm{C}\). The condenser pressure is . Steam is extracted from the turbine at for the closed feedwater heater and at for the open feedwater heater. In the closed feedwater heater, the feedwater is heated to the condensation temperature of the extracted steam. The extracted steam leaves the closed feedwater heater as a saturated liquid, which is subsequently throttled to the open feedwater heater. Show the cycle on a diagram with respect to saturation lines. Determine the fraction of steam extracted from the turbine for the open feedwater heater, the thermal efficiency of the cycle, and the net power output for a mass flow rate of through the boiler. Equation Transcription: Text Transcription: 15MPa and 600°C 500°C

10-106 An ideal Rankine steam cycle modified with two closed feedwater heaters and one open feedwater heater is shown below. The power cycle receives of steam at the high pressure inlet to the turbine. The feedwater heater exit states for the boiler feedwater and the condensed steam are the normally assumed ideal states. Use the data provided in the tables given below to (a) Sketch the diagram for the ideal cycle. (b) Determine the fraction of mass extracted for the open feedwater heater. (c) If, in addition to your result from part , the fraction of mass entering the high pressure turbine at state 7 extracted for the closed feedwater heater operating at is \(z=0.0655\), and at the extraction fraction is , determine the cooling water temperature rise in the condenser, in \({ }^{\circ} \mathrm{C}\), when the cooling water flow rate is . Assume \(c_{p}=4.18 \mathrm{~kJ} / \mathrm{kg} \cdot K\) for cooling water. (d) Determine the rate of heat rejected in the condenser and the thermal efficiency of the plant. Process states and selected data State 1 20 2 620 3 620 4 620 5 5000 6 5000 7 5000 700 3900 8 1910 3515 9 620 3154 10 140 2799 11 20 2478 Saturation data 20 251 140 458 620 676 1910 898 5000 1154 Equation Transcription: Text Transcription: z=0.0655 °C cp=4.18 kJ/kgK

Problem 114P Starting with Eq. 10–20, show that the exergy destruction associated with a simple ideal Rankine cycle can be expressed as i = qin(?th,Carnot ? ?th), where ?th is efficiency of the Rankine cycle and ?th,Carnot is the efficiency of the Carnot cycle operating between the same temperature limits.

Problem 118P Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. If the cycle is modified with reheating, (a) the turbine work output will decrease. ________________ (b) the amount of heat rejected will decrease. ________________ (c) the pump work input will decrease. ________________ (d) the moisture content at turbine exit will decrease. ________________ (e) the amount of heat input will decrease.

Problem 116P Consider a simple ideal Rankine cycle. If the condenser pressure is lowered while keeping turbine inlet state the same, (a) the turbine work output will decrease. ________________ (b) the amount of heat rejected will decrease. ________________ (c) the cycle efficiency will decrease. ________________ (d) the moisture content at turbine exit will decrease. ________________ (e) the pump work input will decrease.

Problem 117P Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. If the steam is superheated to a higher temperature, (a) the turbine work output will decrease. ________________ (b) the amount of heat rejected will decrease. ________________ (c) the cycle efficiency will decrease. ________________ (d) the moisture content at turbine exit will decrease. ________________ (e) the amount of heat input will decrease.

Problem 120P Consider a steady-flow Carnot cycle with water as the working fluid executed under the saturation dome between the pressure limits of 3 MPa and 10 kPa. Water changes from saturated liquid to saturated vapor during the heat addition process. The net work output of this cycle is (a) 666 kJ/kg ________________ (b) 888kJ/kg ________________ (c) 1040 kJ/kg ________________ (d) 1130kJ/kg ________________ (e) 1440 kJ/kg

Problem 121P A simple ideal Rankine cycle operates between the pressure limits of 10 kPa and 3 MPa, with a turbine inlet temperature of 600°C. Disregarding the pump work, the cycle efficiency is (a) 24 percent ________________ (b) 37 percent ________________ (c) 52 percent ________________ (d) 63 percent ________________ (e) 71 percent

Problem 122P A simple ideal Rankine cycle operates between the pressure limits of 10 kPa and 5 MPa, with a turbine inlet temperature of 600°C. The mass fraction of steam that condenses at the turbine exit is (a) 6 percent ________________ (b) 9 percent ________________ (c) 12 percent ________________ (d) 15 percent ________________ (e) 18 percent

Problem 119P Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. If the cycle is modified with regeneration that involves one open feedwater heater (select the correct statement per unit mass of steam flowing through the boiler), (a) the turbine work output will decrease. ________________ (b) the amount of heat rejected will increase. ________________ (c) the cycle thermal efficiency will decrease. ________________ (d) the quality of steam at turbine exit will decrease. ________________ (e) the amount of heat input will increase.

Problem 123P A steam power plant operates on the simple ideal Rankine cycle between the pressure limits of 10 kPa and 5 MPa, with a turbine inlet temperature of 600°C. The rate of heat transfer in the boiler is 300 kJ/s. Disregarding the pump work, the power output of this plant is (a) 93 kW ________________ (b) 118 kW ________________ (c) 190 kW ________________ (d) 216 kW ________________ (e) 300 kW

Problem 126P Pressurized feedwater in a steam power plant is to be heated in an ideal open feedwater heater that operates at a pressure of 2 MPa with steam extracted from the turbine. If the enthalpy of feedwater is 252 kJ/kg and the enthalpy of extracted steam is 2810 kJ/kg, the mass fraction of steam extracted from the turbine is (a) 10 percent ________________ (b) 14 percent ________________ (c) 26 percent ________________ (d) 36 percent ________________ (e) 50 percent

Problem 124P Consider a combined gas-steam power plant. Water for the steam cycle is heated in a well-insulated heat exchanger by the exhaust gases that enter at 800 K at a rate of 60 kg/s and leave at 400 K. Water enters the heat exchanger at 200°C and 8 MPa and leaves at 350°C and 8 MPa. If the exhaust gases are treated as air with constant specific heats at room temperature, the mass flow rate of water through the heat exchanger becomes (a) 11 kg/s ________________ (b) 24 kg/s ________________ (c) 46 kg/s ________________ (d) 53 kg/s ________________ (e) 60 kg/s

Problem 127P Consider a steam power plant that operates on the regenerative Rankine cycle with one open feedwater heater. The enthalpy of the steam is 3374 kJ/kg at the turbine inlet, 2797 kJ/kg at the location of bleeding, and 2346 kJ/kg at the turbine exit. The net power output of the plant is 120 MW, and the fraction of steam bled off the turbine for regeneration is 0.172. If the pump work is negligible, the mass flow rate of steam at the turbine inlet is (a) 117 kg/s ________________ (b) 126 kg/s ________________ (c) 219 kg/s ________________ (d) 268 kg/s ________________ (e) 679 kg/s

Problem 125P An ideal reheat Rankine cycle operates between the pressure limits of 10 kPa and 8 MPa, with reheat occurring at 4 MPa. The temperature of steam at the inlets of both turbines is 500°C, and the enthalpy of steam is 3185 kJ/kg at the exit of the high-pressure turbine, and 2247 kJ/kg at the exit of the low-pressure turbine. Disregarding the pump work, the cycle efficiency is (a) 29 percent ________________ (b) 32 percent ________________ (c) 36 percent ________________ (d) 41 percent ________________ (e) 49 percent

10-128 Consider a cogeneration power plant modified with regeneration. Steam enters the turbine at and at a rate of and expands to a pressure of . At this pressure, 60 percent of the steam is extracted from the turbine, and the remainder expands to a pressure of . Part of the extracted steam is used to heat feedwater in an open feedwater heater. The rest of the extracted steam is used for process heating and leaves the process heater as a saturated liquid at . It is subsequently mixed with the feedwater leaving the feedwater heater, and the mixture is pumped to the boiler pressure. The steam in the condenser is cooled and condensed by the cooling water from a nearby river, which enters the adiabatic condenser at a rate of 1. The total power output of the turbine is (a) (b) (c) (d) (e) 2. The temperature rise of the cooling water from the river in the condenser is (a) (b) (c) (d) (e) 3. The mass flow rate of steam through the process heater is (a) (b) (c) (d) (e) 4. The rate of heat supply from the process heater per unit mass of steam passing through it is (a) (b) (c) (d) (e) 5. The rate of heat transfer to the steam in the boiler is (a) (b) (c) (d) (e)

A binary geothermal power plant uses geothermal water at \(160^{\circ} \mathrm{C}\) as the heat source. The cycle operates on the simple Rankine cycle with isobutane as the working fluid. Heat is transferred to the cycle by a heat exchanger in which geothermal liquid water enters at \(160^{\circ} \mathrm{C}\) at a rate of \(555.9 \mathrm{~kg} / \mathrm{s}\) and leaves at \(90^{\circ} \mathrm{C}\) Isobutane enters the turbine at and \(147^{\circ} \mathrm{C} \) at a rate of \(305.6 \mathrm{~kg} / \mathrm{s}\), and leaves at \(79.5^{\circ} \mathrm{C}\) and . Isobutane is condensed in an air-cooled condenser and pumped to the heat exchanger pressure. Assuming the pump to have an isentropic efficiency of 90 percent, determine the isentropic efficiency of the turbine, the net power output of the plant, and the thermal efficiency of the cycle. The properties of isobutane may be obtained from EES. Equation Transcription: Text Transcription: 160°C 160°C 555.9 kg/s 90°C 147°C 305.6 kg/s 79.5°C

Problem 55P A steam power plant operates on an ideal reheat- regenerative Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 550°C and leaves at 0.8 MPa. Some steam is extracted at this pressure to heat the feedwater in an open feedwater heater. The rest of the steam is reheated to 500°C and is expanded in the low-pressure turbine to the condenser pressure of 10 kPa. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the mass flow rate of steam through the boiler and (b) the thermal efficiency of the cycle.

Problem 102P It has been suggested that the steam passing through the condenser of the combined cycle in Prob. 10–108E be routed to buildings during the winter to heat them. When this is done, the pressure in the heating system where the steam is now condensed will have to be increased to 10 psia. How does this change the overall thermal efficiency of the combined cycle?

Why is the Carnot cycle not a realistic model for steam power plants?

It has been suggested that the steam passing through the condenser of the combined cycle in Prob. 10–101E be routed to buildings during the winter to heat them. When this is done, the pressure in the heating system where the steam is now condensed will have to be increased to . How does this change the overall thermal efficiency of the combined cycle?

During winter, the system of Prob. 10–102E must supply of heat to the buildings. What is the mass flow rate of air through the air compressor and the system’s total electrical power production in winter?

The gas-turbine cycle of a combined gas–steam power plant has a pressure ratio of 12. Air enters the compressor at and the turbine at . The combustion gases leaving the gas turbine are used to heat the steam at to in a heat exchanger. The combustion gases leave the heat exchanger at . Steam expands in a high-pressure turbine to a pressure of and is reheated in the combustion chamber to before it expands in a low-pressure turbine to . The mass flow rate of steam is . Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate of air in the gas-turbine cycle, (b) the rate of total heat input, and (c) the thermal efficiency of the combined cycle.

Repeat Prob. 10–104 assuming isentropic efficiencies of 100 percent for the pump, 85 percent for the compressor, and 90 percent for the gas and steam turbines

Step 1 of 8 A rankine steam cycle modified with two closed feedwater heaters and one open feedwater heater is considered. The T-s diagram for the ideal cycle is to be sketched. The fraction of mass extracted for the open feedwater heater y and the cooling water flow temperature rise are to be determined. Also, the rate of heat rejected in the condenser with the thermal efficiency of the plant is to be determined. Assumptions are 1. Steady operating conditions exist 2. kinetic and potential energy changes are negligible. Step 2 of 8 (a)Sketch the T-s diagram for the ideal cycle as below. Step 3 of 8 (b) Using the data from the problem statement, the enthalpies at various states are Step 4 of 8 An energy balance on the open feedwater heater gives Where $$y$$ is the fraction of steam extracted from the low-pressure turbine. Solving for y, Step 5 of 8 ( C) An energy balance on the condenser gives Solving for the temperature rise of cooling water, and substituting with correct units, Step 6 of 8 (d) The rate of heat rejected in the condenser is Step 7 of 8 The rate of heat input in the boiler is Step 8 of 8 The thermal efficiency is then ________________

Consider a simple ideal Rankine cycle with fixed turbine inlet temperature and condenser pressure. What is the effect of increasing the boiler pressure on

Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. What is the effect of superheating the steam to a higher temperature on

How do actual vapor power cycles differ from idealized ones?

The entropy of steam increases in actual steam turbines as a result of irreversibilities. In an effort to control entropy increase, it is proposed to cool the steam in the turbine by running cooling water around the turbine casing. It is argued that this will reduce the entropy and the enthalpy of the steam at the turbine exit and thus increase the work output. How would you evaluate this proposal?

Is it possible to maintain a pressure of in a condenser that is being cooled by river water entering at ?

A steam power plant operates on a simple ideal Rankine cycle between the pressure limits of and . The temperature of the steam at the turbine inlet is , and the mass flow rate of steam through the cycle is 35 kg/s. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the thermal efficiency of the cycle and (b) the net power output of the power plant.

Refrigerant-134a is used as the working fluid in a simple ideal Rankine cycle which operates the boiler at and the condenser at . The mixture at the exit of the turbine has a quality of 93 percent. Determine the turbine inlet temperature, the cycle thermal efficiency, and the back-work ratio of this cycle.

A simple ideal Rankine cycle which uses water as the working fluid operates its condenser at and its boiler at . Calculate the work produced by the turbine, the heat supplied in the boiler, and the thermal efficiency of this cycle when the steam enters the turbine without any superheating.

A simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of in the boiler and in the condenser. What is the minimum temperature required at the turbine inlet such that the quality of the steam leaving the turbine is not below 80 percent. When operated at this temperature, what is the thermal efficiency of this cycle?

Consider a 210-MW steam power plant that operates on a simple ideal Rankine cycle. Steam enters the turbine at and and is cooled in the condenser at a pressure of . Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the quality of the steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.

Repeat Prob. 10-16 assuming an isentropic efficiency of 85 percent for both the turbine and the pump.

A steam Rankine cycle operates between the pressure limits of in the boiler and in the condenser. The turbine inlet temperature is . The turbine isentropic efficiency is 90 percent, the pump losses are negligible, and the cycle is sized to produce of power. Calculate the mass flow rate through the boiler, the power produced by the turbine, the rate of heat supply in the boiler, and the thermal efficiency.

Reconsider Prob. 1018E. How much error is caused in the thermal efficiency if the power required by the pump were completely neglected?

A steam power plant operates on a simple ideal Rankine cycle between the pressure limits of 1250 and . The mass flow rate of steam through the cycle is . The moisture content of the steam at the turbine exit is not to exceed 10 percent. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the minimum turbine inlet temperature, (b) the rate of heat input in the boiler, and (c) the thermal efficiency of the cycle.

Repeat Prob. 1020E assuming an isentropic efficiency of 85 percent for both the turbine and the pump.

A simple Rankine cycle uses water as the working fluid. The boiler operates at and the condenser at . At the entrance to the turbine, the temperature is . The isentropic efficiency of the turbine is 94 percent, pressure and pump losses are negligible, and the water leaving the condenser is subcooled by . The boiler is sized for a mass flow rate of 20 kg/s. Determine the rate at which heat is added in the boiler, the power required to operate the pumps, the net power produced by the cycle, and the thermal efficiency.

Using EES (or other) software, determine how much the thermal efficiency of the cycle in Prob. 1022 would change if there were a 50 kPa pressure drop across the boiler.

The net work output and the thermal efficiency for the Carnot and the simple ideal Rankine cycles with steam as the working fluid are to be calculated and compared. Steam enters the turbine in both cases at 5 MPa as a saturated vapor, and the condenser pressure is 50 kPa. In the Rankine cycle, the condenser exit state is saturated liquid and in the Carnot cycle, the boiler inlet state is saturated liquid. Draw the T-s diagrams for both cycles.

A binary geothermal power plant uses geothermal water at 1608C as the heat source. The cycle operates on the simple Rankine cycle with isobutane as the working fluid. Heat is transferred to the cycle by a heat exchanger in which geothermal liquid water enters at 1608C at a rate of 555.9 kg/s and leaves at 908C. Isobutane enters the turbine at 3.25 MPa and 1478C at a rate of 305.6 kg/s, and leaves at 79.58C and 410 kPa. Isobutane is condensed in an air-cooled condenser and pumped to the heat exchanger pressure. Assuming the pump to have an isentropic efficiency of 90 percent, determine (a) the isentropic efficiency of the turbine, (b) the net power output of the plant, and (c) the thermal efficiency of the cycle. The properties of isobutane may be obtained from EES.

Consider a coal-fired steam power plant that produces 175 MW of electric power. The power plant operates on a simple ideal Rankine cycle with turbine inlet conditions of 7 MPa and 5508C and a condenser pressure of 15 kPa. The coal has a heating value (energy released when the fuel is burned) of 29,300 kJ/kg. Assuming that 85 percent of this energy is transferred to the steam in the boiler and that the electric generator has an efficiency of 96 percent, determine (a) the overall plant efficiency (the ratio of net electric power output to the energy input as fuel) and (b) the required rate of coal supply.

Show the ideal Rankine cycle with three stages of reheating on a T-s diagram. Assume the turbine inlet temperature is the same for all stages. How does the cycle efficiency vary with the number of reheat stages?

How do the following quantities change when a simple ideal Rankine cycle is modified with reheating? Assume the mass flow rate is maintained the same.

Consider a simple ideal Rankine cycle and an ideal Rankine cycle with three reheat stages. Both cycles operate between the same pressure limits. The maximum temperature is 7008C in the simple cycle and 4508C in the reheat cycle. Which cycle do you think will have a higher thermal efficiency?

An ideal reheat Rankine cycle with water as the working fluid operates the boiler at 15,000 kPa, the reheater at 2000 kPa, and the condenser at 100 kPa. The temperature is 4508C at the entrance of the high-pressure and lowpressure turbines. The mass flow rate through the cycle is 1.74 kg/s. Determine the power used by pumps, the power produced by the cycle, the rate of heat transfer in the reheater, and the thermal efficiency of this system.

A steam power plant operates on the ideal reheat Rankine cycle. Steam enters the highpressure turbine at 6 MPa and 4008C and leaves at 2 MPa. Steam is then reheated at constant pressure to 4008C before it expands to 20 kPa in the low-pressure turbine. Determine the turbine work output, in kJ/kg, and the thermal efficiency of the cycle. Also, show the cycle on a T-s diagram with respect to saturation lines.

Reconsider Prob. 1031. Using EES (or other) software, solve this problem by the diagram window data entry feature of EES. Include the effects of the turbine and pump efficiencies and also show the effects of reheat on the steam quality at the lowpressure turbine exit. Plot the cycle on a T-s diagram with respect to the saturation lines. Discuss the results of your parametric studies.

Steam enters the high-pressure turbine of a steam power plant that operates on the ideal reheat Rankine cycle at 800 psia and 9008F and leaves as saturated vapor. Steam is then reheated to 8008F before it expands to a pressure of 1 psia. Heat is transferred to the steam in the boiler at a rate of 6 3 104 Btu/s. Steam is cooled in the condenser by the cooling water from a nearby river, which enters the condenser at 458F. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the pressure at which reheating takes place, (b) the net power output and thermal efficiency, and (c) the minimum mass flow rate of the cooling water required.

Consider a steam power plant that operates on the ideal reheat Rankine cycle. The plant maintains the boiler at 5000 kPa, the reheat section at 1200 kPa, and the condenser at 20 kPa. The mixture quality at the exit of both turbines is 96 percent. Determine the temperature at the inlet of each turbine and the cycles thermal efficiency.

A steam power plant operates on an ideal reheat Rankine cycle between the pressure limits of 15 MPa and 10 kPa. The mass flow rate of steam through the cycle is 12 kg/s. Steam enters both stages of the turbine at 5008C. If the moisture content of the steam at the exit of the lowpressure turbine is not to exceed 10 percent, determine (a) the pressure at which reheating takes place, (b) the total rate of heat input in the boiler, and (c) the thermal efficiency of the cycle. Also, show the cycle on a T-s diagram with respect to saturation lines.

A steam power plant operates on the reheat Rankine cycle. Steam enters the high-pressure turbine at 12.5 MPa and 5508C at a rate of 7.7 kg/s and leaves at 2 MPa. Steam is then reheated at constant pressure to 4508C before it expands in the low-pressure turbine. The isentropic efficiencies of the turbine and the pump are 85 percent and 90 percent, respectively. Steam leaves the condenser as a saturated liquid. If the moisture content of the steam at the exit of the turbine is not to exceed 5 percent, determine (a) the condenser pressure, (b) the net power output, and (c) the thermal efficiency.

Consider a steam power plant that operates on a reheat Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 5008C and the low-pressure turbine at 1 MPa and 5008C. Steam leaves the condenser as a saturated liquid at a pressure of 10 kPa. The isentropic efficiency of the turbine is 80 percent, and that of the pump is 95 percent. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the quality (or temperature, if superheated) of the steam at the turbine exit, (b) the thermal efficiency of the cycle, and (c) the mass flow rate of the steam.

Repeat Prob. 1037 assuming both the pump and the turbine are isentropic.

During a regeneration process, some steam is extracted from the turbine and is used to heat the liquid water leaving the pump. This does not seem like a smart thing to do since the extracted steam could produce some more work in the turbine. How do you justify this action?

Consider a simple ideal Rankine cycle and an ideal regenerative Rankine cycle with one open feedwater heater. The two cycles are very much alike, except the feedwater in the regenerative cycle is heated by extracting some steam just before it enters the turbine. How would you compare the efficiencies of these two cycles?

How do open feedwater heaters differ from closed feedwater heaters?

How do the following quantities change when the simple ideal Rankine cycle is modified with regeneration? Assume the mass flow rate through the boiler is the same.

Turbine bleed steam enters an open feedwater heater of a regenerative Rankine cycle at 40 psia and 2808F while the cold feedwater enters at 1108F. Determine the ratio of the bleed steam mass flow rate to the inlet feedwater mass flow rate required to heat the feedwater to 2508F.

The closed feedwater heater of a regenerative Rankine cycle is to heat 7000 kPa feedwater from 2608C to a saturated liquid. The turbine supplies bleed steam at 6000 kPa and 3258C to this unit. This steam is condensed to a saturated liquid before entering the pump. Calculate the amount of bleed steam required to heat 1 kg of feedwater in this unit.

A steam power plant operates on an ideal regenerative Rankine cycle. Steam enters the turbine at 6 MPa and 4508C and is condensed in the condenser at 20 kPa. Steam is extracted from the turbine at 0.4 MPa to heat the feedwater in an open feedwater heater. Water leaves the feedwater heater as a saturated liquid. Show the cycle on a T-s diagram, and determine (a) the net work output per kilogram of steam flowing through the boiler and (b) the thermal efficiency of the cycle.

Repeat Prob. 1045 by replacing the open feedwater heater with a closed feedwater heater. Assume that the feedwater leaves the heater at the condensation temperature of the extracted steam and that the extracted steam leaves the heater as a saturated liquid and is pumped to the line carrying the feedwater.

A steam power plant operates on an ideal regenerative Rankine cycle with two open feedwater heaters. Steam enters the turbine at 8 MPa and 5508C and exhausts to the condenser at 10 kPa. Steam is extracted from the turbine at 0.6 and 0.2 MPa. Water leaves both feedwater heaters as a saturated liquid. The mass flow rate of steam through the boiler is 16 kg/s. Show the cycle on a T-s diagram, and determine (a) the net power output of the power plant and (b) the thermal efficiency of the cycle.

Consider a steam power plant that operates on the ideal regenerative Rankine cycle with a closed feedwater heater as shown in the figure. The plant maintains the turbine inlet at 3000 kPa and 3508C; and operates the condenser at 20 kPa. Steam is extracted at 1000 kPa to serve the closed feedwater heater, which discharges into the condenser after being throttled to condenser pressure. Calculate the work produced by the turbine, the work consumed by the pump, and the heat supply in the boiler for this cycle per unit of boiler flow rate.

Reconsider Prob. 1048. Using EES (or other) software, determine the optimum bleed pressure for the closed feedwater heater that maximizes the thermal efficiency of the cycle.

Determine the thermal efficiency of the regenerative Rankine cycle of Prob. 1048 when the isentropic efficiency of the turbine is 90 percent before and after steam extraction point.

Determine the thermal efficiency of the regenerative Rankine cycle of Prob. 1048 when the isentropic efficiency of the turbine before and after steam extraction point is 90 percent and the condenser condensate is subcooled by 108C.

Reconsider Prob. 1048. Using EES (or other) software, determine how much additional heat must be supplied to the boiler when the turbine isentropic efficiency before and after the extraction point is 90 percent and there is a 10 kPa pressure drop across the boiler?

Consider an ideal steam regenerative Rankine cycle with two feedwater heaters, one closed and one open. Steam enters the turbine at 10 MPa and 6008C and exhausts to the condenser at 10 kPa. Steam is extracted from the turbine at 1.2 MPa for the closed feedwater heater and at 0.6 MPa for the open one. The feedwater is heated to the condensation temperature of the extracted steam in the closed feedwater heater. The extracted steam leaves the closed feedwater heater as a saturated liquid, which is subsequently throttled to the open feedwater heater. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the mass flow rate of steam through the boiler for a net power output of 400 MW and (b) the thermal efficiency of the cycle.

Reconsider Prob. 1053. Using EES (or other) software, investigate the effects of turbine and pump efficiencies as they are varied from 70 percent to 100 percent on the mass flow rate and thermal efficiency. Plot the mass flow rate and the thermal efficiency as a function of turbine efficiency for pump efficiencies of 70, 85, and 100 percent, and discuss the results. Also plot the T-s diagram for turbine and pump efficiencies of 85 percent.

A steam power plant operates on an ideal reheat regenerative Rankine cycle and has a net power output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 5508C and leaves at 0.8 MPa. Some steam is extracted at this pressure to heat the feedwater in an open feedwater heater. The rest of the steam is reheated to 5008C and is expanded in the low-pressure turbine to the condenser pressure of 10 kPa. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the mass flow rate of steam through the boiler and (b) the thermal efficiency of the cycle.

Repeat Prob. 1055, but replace the open feedwater heater with a closed feedwater heater. Assume that the feedwater leaves the heater at the condensation temperature of the extracted steam and that the extracted steam leaves the heater as a saturated liquid and is pumped to the line carrying the feedwater.

An ideal Rankine steam cycle modified with two closed feedwater heaters is shown below. The power cycle receives 75 kg/s of steam at the high pressure inlet to the turbine. The feedwater heater exit states for the boiler feedwater and the condensed steam are the normally assumed ideal states. The fraction of mass entering the high pressure turbine at state 5 that is extracted for the feedwater heater operating at 1400 kPa is y 5 0.1446. Use the data provided in the tables given below to (a) Sketch the T-s diagram for the ideal cycle. (b) Determine the fraction of mass, z, that is extracted for the closed feedwater heater operating at the 245 kPa extraction pressure. (c) Determine the required cooling water flow rate, in kg/s, to keep the cooling water temperature rise in the condenser to 108C. Assume cp 5 4.18 kJ/kgK for cooling water. (d) Determine the net power output and the thermal efficiency of the plant.

Determine the exergy destruction associated with each of the processes of the Rankine cycle described in Prob. 1012, assuming a source temperature of 1500 K and a sink temperature of 290 K.

Determine the exergy destruction associated with each of the processes of the Rankine cycle described in Prob. 1016, assuming a source temperature of 1500 K and a sink temperature of 290 K.

Determine the exergy destruction associated with each of the processes of the reheat Rankine cycle described in Prob. 1031. Assume a source temperature of 1500 K and a sink temperature of 295 K.

Reconsider Prob. 1060. Using EES (or other) software, solve this problem by the diagram window data entry feature of EES. Include the effects of the turbine and pump efficiencies to evaluate the irreversibilities associated with each of the processes. Plot the cycle on a T-s diagram with respect to the saturation lines. Discuss the results of your parametric studies.

Determine the exergy destruction associated with the heat addition process and the expansion process in Prob. 1037. Assume a source temperature of 1600 K and a sink temperature of 285 K. Also, determine the exergy of the steam at the boiler exit. Take P0 5 100 kPa.

Determine the exergy destruction associated with the regenerative cycle described in Prob. 1045. Assume a source temperature of 1500 K and a sink temperature of 290 K.

Determine the exergy destruction associated with the reheating and regeneration processes described in Prob. 1055. Assume a source temperature of 1800 K and a sink temperature of 290 K.

The schematic of a single-flash geothermal power plant with state numbers is given in Fig. P1065. Geothermal resource exists as saturated liquid at 2308C. The geothermal liquid is withdrawn from the production well at a rate of 230 kg/s and is flashed to a pressure of 500 kPa by an essentially isenthalpic flashing process where the resulting vapor is separated from the liquid in a separator and is directed to the turbine. The steam leaves the turbine at 10 kPa with a moisture content of 5 percent and enters the condenser where it is condensed; it is routed to a reinjection well along with the liquid coming off the separator. Determine (a) the power output of the turbine and the thermal efficiency of the plant, (b) the exergy of the geothermal liquid at the exit of the flash chamber, and the exergy destructions and the second-law efficiencies for (c) the turbine and (d) the entire plant.

How is the utilization factor Pu for cogeneration plants defined? Could Pu be unity for a cogeneration plant that does not produce any power?

Consider a cogeneration plant for which the utilization factor is 1. Is the irreversibility associated with this cycle necessarily zero? Explain.

Consider a cogeneration plant for which the utilization factor is 0.5. Can the exergy destruction associated with this plant be zero? If yes, under what conditions?

Steam enters the turbine of a cogeneration plant at 4 MPa and 5008C. One-fourth of the steam is extracted from the turbine at 1200-kPa pressure for process heating. The remaining steam continues to expand to 10 kPa. The extracted steam is then condensed and mixed with feedwater at constant pressure and the mixture is pumped to the boiler pressure of 7 MPa. The mass flow rate of steam through the boiler is 55 kg/s. Disregarding any pressure drops and heat losses in the piping, and assuming the turbine and the pump to be isentropic, determine the net power produced and the utilization factor of the plant.

A large food-processing plant requires 1.5 lbm/s of saturated or slightly superheated steam at 140 psia, which is extracted from the turbine of a cogeneration plant. The boiler generates steam at 800 psia and 10008F at a rate of 10 lbm/s, and the condenser pressure is 2 psia. Steam leaves the process heater as a saturated liquid. It is then mixed with the feedwater at the same pressure and this mixture is pumped to the boiler pressure. Assuming both the pumps and the turbine have isentropic efficiencies of 86 percent, determine (a) the rate of heat transfer to the boiler and (b) the power output of the cogeneration plant.

Steam is generated in the boiler of a cogeneration plant at 10 MPa and 4508C at a steady rate of 5 kg/s. In normal operation, steam expands in a turbine to a pressure of 0.5 MPa and is then routed to the process heater, where it supplies the process heat. Steam leaves the process heater as a saturated liquid and is pumped to the boiler pressure. In this mode, no steam passes through the condenser, which operates at 20 kPa. (a) Determine the power produced and the rate at which process heat is supplied in this mode. (b) Determine the power produced and the rate of process heat supplied if only 60 percent of the steam is routed to the process heater and the remainder is expanded to the condenser pressure.

Consider a cogeneration power plant modified with regeneration. Steam enters the turbine at 9 MPa and 4008C and expands to a pressure of 1.6 MPa. At this pressure, 35 percent of the steam is extracted from the turbine, and the remainder expands to 10 kPa. Part of the extracted steam is used to heat the feedwater in an open feedwater heater. The rest of the extracted steam is used for process heating and leaves the process heater as a saturated liquid at 1.6 MPa. It is subsequently mixed with the feedwater leaving the feedwater heater, and the mixture is pumped to the boiler pressure. Assuming the turbines and the pumps to be isentropic, show the cycle on a T-s diagram with respect to saturation lines, and determine the mass flow rate of steam through the boiler for a net power output of 25 MW.

Reconsider Prob. 1072. Using EES (or other) software, investigate the effect of the extraction pressure for removing steam from the turbine to be used for the process heater and open feedwater heater on the required mass flow rate. Plot the mass flow rate through the boiler as a function of the extraction pressure, and discuss the results.

Steam is generated in the boiler of a cogeneration plant at 600 psia and 6508F at a rate of 32 lbm/s. The plant is to produce power while meeting the process steam requirements for a certain industrial application. One-third of the steam leaving the boiler is throttled to a pressure of 120 psia and is routed to the process heater. The rest of the steam is expanded in an isentropic turbine to a pressure of 120 psia and is also routed to the process heater. Steam leaves the process heater at 2408F. Neglecting the pump work, determine (a) the net power produced, (b) the rate of process heat supply, and (c) the utilization factor of this plant.

In combined gassteam cycles, what is the energy source for the steam?

Why is the combined gassteam cycle more efficient than either of the cycles operated alone?

The gas-turbine portion of a combined gassteam power plant has a pressure ratio of 16. Air enters the compressor at 300 K at a rate of 14 kg/s and is heated to 1500 K in the combustion chamber. The combustion gases leaving the gas turbine are used to heat the steam to 4008C at 10 MPa in a heat exchanger. The combustion gases leave the heat exchanger at 420 K. The steam leaving the turbine is condensed at 15 kPa. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate of the steam, (b) the net power output, and (c) the thermal efficiency of the combined cycle. For air, assume constant specific heats at room temperature.

Consider a combined gassteam power plant that has a net power output of 450 MW. The pressure ratio of the gas-turbine cycle is 14. Air enters the compressor at 300 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 8 MPa to 4008C in a heat exchanger. The combustion gases leave the heat exchanger at 460 K. An open feedwater heater incorporated with the steam cycle operates at a pressure of 0.6 MPa. The condenser pressure is 20 kPa. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate ration of air to steam, (b) the required rate of heat input in the combustion chamber, and (c) thermal efficiency of the combined cycle.

Reconsider Prob. 1078. Using EES (or other) software, study the effects of the gas cycle pressure ratio as it is varied from 10 to 20 on the ratio of gas flow rate to steam flow rate and cycle thermal efficiency. Plot your results as functions of gas cycle pressure ratio, and discuss the results.

Repeat Prob. 1078 assuming isentropic efficiencies of 100 percent for the pump, 82 percent for the compressor, and 86 percent for the gas and steam turbines.

Reconsider Prob. 1080. Using EES (or other) software, study the effects of the gas cycle pressure ratio as it is varied from 10 to 20 on the ratio of gas flow rate to steam flow rate and cycle thermal efficiency. Plot your results as functions of gas cycle pressure ratio, and discuss the results.

Consider a combined gassteam power plant that has a net power output of 280 MW. The pressure ratio of the gasturbine cycle is 11. Air enters the compressor at 300 K and the turbine at 1100 K. The combustion gases leaving the gas turbine are used to heat the steam at 5 MPa to 3508C in a heat exchanger. The combustion gases leave the heat exchanger at 420 K. An open feedwater heater incorporated with the steam cycle operates at a pressure of 0.8 MPa. The condenser pressure is 10 kPa. Assuming isentropic efficiences of 100 percent for the pump, 82 percent for the compressor, and 86 percent for the gas and steam turbines, determine (a) the mass flow rate ratio of air to steam, (b) the required rate of heat input in the combustion chamber, and (c) the thermal efficiency of the combined cycle.

Reconsider Prob. 1082. Using EES (or other) software, study the effects of the gas cycle pressure ratio as it is varied from 10 to 20 on the ratio of gas flow rate to steam flow rate and cycle thermal efficiency. Plot your results as functions of gas cycle pressure ratio, and discuss the results.

Consider a combined gassteam power cycle. The topping cycle is a simple Brayton cycle that has a pressure ratio of 7. Air enters the compressor at 158C at a rate of 40 kg/s and the gas turbine at 9508C. The bottoming cycle is a reheat Rankine cycle between the pressure limits of 6 MPa and 10 kPa. Steam is heated in a heat exchanger at a rate of 4.6 kg/s by the exhaust gases leaving the gas turbine, and the exhaust gases leave the heat exchanger at 2008C. Steam leaves the high-pressure turbine at 1.0 MPa and is reheated to 4008C in the heat exchanger before it expands in the low-pressure turbine. Assuming 80 percent isentropic efficiency for all pumps and turbines, determine (a) the moisture content at the exit of the low-pressure turbine, (b) the steam temperature at the inlet of the high-pressure turbine, (c) the net power output and the thermal efficiency of the combined plant.

Why is steam not an ideal working fluid for vapor power cycles?

What is a binary power cycle? What is its purpose?

What is the difference between the binary vapor power cycle and the combined gassteam power cycle?

Why is mercury a suitable working fluid for the topping portion of a binary vapor cycle but not for the bottoming cycle?

By writing an energy balance on the heat exchanger of a binary vapor power cycle, obtain a relation for the ratio of mass flow rates of two fluids in terms of their enthalpies.

Steam enters the turbine of a steam power plant that operates on a simple ideal Rankine cycle at a pressure of 6 MPa, and it leaves as a saturated vapor at 7.5 kPa. Heat is transferred to the steam in the boiler at a rate of 40,000 kJ/s. Steam is cooled in the condenser by the cooling water from a nearby river, which enters the condenser at 158C. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the turbine inlet temperature, (b) the net power output and thermal efficiency, and (c) the minimum mass flow rate of the cooling water required.

A steam power plant operating on a simple ideal Rankine cycle maintains the boiler at 6000 kPa, the turbine inlet at 6008C, and the condenser at 50 kPa. Compare the thermal efficiency of this cycle when it is operated so that the liquid enters the pump as a saturated liquid against that when the liquid enters the pump 11.38C cooler than a saturated liquid at the condenser pressure.

A steam power plant operates on an ideal Rankine cycle with two stages of reheat and has a net power output of 75 MW. Steam enters all three stages of the turbine at 5508C. The maximum pressure in the cycle is 10 MPa, and the minimum pressure is 30 kPa. Steam is reheated at 4 MPa the first time and at 2 MPa the second time. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the thermal efficiency of the cycle, and (b) the mass flow rate of the steam.

Consider a steam power plant operating on the ideal Rankine cycle with reheat between the pressure limits of 30 MPa and 10 kPa with a maximum cycle temperature of 7008C and a moisture content of 5 percent at the turbine exit. For a reheat temperature of 7008C, determine the reheat pressures of the cycle for the cases of (a) single and (b) double reheat.

Consider a steam power plant that operates on a regenerative Rankine cycle and has a net power output of 150 MW. Steam enters the turbine at 10 MPa and 5008C and the condenser at 10 kPa. The isentropic efficiency of the turbine is 80 percent, and that of the pumps is 95 percent. Steam is extracted from the turbine at 0.5 MPa to heat the feedwater in an open feedwater heater. Water leaves the feedwater heater as a saturated liquid. Show the cycle on a T-s diagram, and determine (a) the mass flow rate of steam through the boiler, and (b) the thermal efficiency of the cycle. Also, determine the exergy destruction associated with the regeneration process. Assume a source temperature of 1300 K and a sink temperature of 303 K.

Repeat Prob. 1094 assuming both the pump and the turbine are isentropic.

Consider an ideal reheatregenerative Rankine cycle with one open feedwater heater. The boiler pressure is 10 MPa, the condenser pressure is 15 kPa, the reheater pressure is 1 MPa, and the feedwater pressure is 0.6 MPa. Steam enters both the high- and low-pressure turbines at 5008C. Show the cycle on a T-s diagram with respect to saturation lines, and determine (a) the fraction of steam extracted for regeneration and (b) the thermal efficiency of the cycle.

Repeat Prob. 1096 assuming an isentropic efficiency of 84 percent for the turbines and 100 percent for the pumps.

Steam is to be supplied from a boiler to a highpressure turbine whose isentropic efficiency is 85 percent at conditions to be determined. The steam is to leave the highpressure turbine as a saturated vapor at 1.4 MPa, and the turbine is to produce 5.5 MW of power. Steam at the turbine exit is extracted at a rate of 1000 kg/min and routed to a process heater while the rest of the steam is supplied to a lowpressure turbine whose isentropic efficiency is 80 percent. The low-pressure turbine allows the steam to expand to 10 kPa pressure and produces 1.5 MW of power. Determine the temperature, pressure, and the flow rate of steam at the inlet of the high-pressure turbine.

A textile plant requires 4 kg/s of saturated steam at 2 MPa, which is extracted from the turbine of a cogeneration plant. Steam enters the turbine at 8 MPa and 5008C at a rate of 11 kg/s and leaves at 20 kPa. The extracted steam leaves the process heater as a saturated liquid and mixes with the feedwater at constant pressure. The mixture is pumped to the boiler pressure. Assuming an isentropic efficiency of 88 percent for both the turbine and the pumps, determine (a) the rate of process heat supply, (b) the net power output, and (c) the utilization factor of the plant.

Consider a cogeneration power plant that is modified with reheat and that produces 3 MW of power and supplies 7 MW of process heat. Steam enters the high-pressure turbine at 8 MPa and 5008C and expands to a pressure of 1 MPa. At this pressure, part of the steam is extracted from the turbine and routed to the process heater, while the remainder is reheated to 5008C and expanded in the low-pressure turbine to the condenser pressure of 15 kPa. The condensate from the condenser is pumped to 1 MPa and is mixed with the extracted steam, which leaves the process heater as a compressed liquid at 1208C. The mixture is then pumped to the boiler pressure. Assuming the turbine to be isentropic, show the cycle on a T-s diagram with respect to saturation lines, and disregarding pump work, determine (a) the rate of heat input in the boiler and (b) the fraction of steam extracted for process heating.

Atmospheric air enters the air compressor of a simple combined gas-steam power system at 14.7 psia and 808F. The air compressors compression ratio is 10; the gas cycles maximum temperature is 21008F; and the air compressor and turbine have an isentropic efficiency of 90 percent. The gas leaves the heat exchanger 508F hotter than the saturation temperature of the steam in the heat exchanger. The steam pressure in the heat exchanger is 800 psia, and the steam leaves the heat exchanger at 6008F. The steam-condenser pressure is 5 psia and the isentropic efficiency of the steam turbine is 95 percent. Determine the overall thermal efficiency of this combined cycle. For air, use constant specific heats at room temperature.

It has been suggested that the steam passing through the condenser of the combined cycle in Prob. 10101E be routed to buildings during the winter to heat them. When this is done, the pressure in the heating system where the steam is now condensed will have to be increased to 10 psia. How does this change the overall thermal efficiency of the combined cycle?

During winter, the system of Prob. 10102E must supply 2 3 106 Btu/h of heat to the buildings. What is the mass flow rate of air through the air compressor and the systems total electrical power production in winter?

The gas-turbine cycle of a combined gassteam power plant has a pressure ratio of 12. Air enters the compressor at 310 K and the turbine at 1400 K. The combustion gases leaving the gas turbine are used to heat the steam at 12.5 MPa to 5008C in a heat exchanger. The combustion gases leave the heat exchanger at 2478C. Steam expands in a high-pressure turbine to a pressure of 2.5 MPa and is reheated in the combustion chamber to 5508C before it expands in a low-pressure turbine to 10 kPa. The mass flow rate of steam is 12 kg/s. Assuming all the compression and expansion processes to be isentropic, determine (a) the mass flow rate of air in the gas-turbine cycle, (b) the rate of total heat input, and (c) the thermal efficiency of the combined cycle.

Repeat Prob. 10104 assuming isentropic efficiencies of 100 percent for the pump, 85 percent for the compressor, and 90 percent for the gas and steam turbines.

An ideal Rankine steam cycle modified with two closed feedwater heaters and one open feedwater heater is shown below. The power cycle receives 100 kg/s of steam at the high pressure inlet to the turbine. The feedwater heater exit states for the boiler feedwater and the condensed steam are the normally assumed ideal states. Use the data provided in the tables given below to (a) Sketch the T-s diagram for the ideal cycle. (b) Determine the fraction of mass y extracted for the open feedwater heater. (c) If, in addition to your result from part (b), the fraction of mass entering the high pressure turbine at state 7 extracted for the closed feedwater heater operating at 140 kPa is z 5 0.0655, and at 1910 kPa the extraction fraction is w 5 0.0830, determine the cooling water temperature rise in the condenser, in 8C, when the cooling water flow rate is 4200 kg/s. Assume cp 5 4.18 kJ/kgK for cooling water. (d) Determine the rate of heat rejected in the condenser and the thermal efficiency of the plant.

A steam power plant operates on an ideal reheat regenerative Rankine cycle with one reheater and two feedwater heaters, one open and one closed. Steam enters the high-pressure turbine at 15 MPa and 6008C and the low- pressure turbine at 1 MPa and 5008C. The condenser pressure is 5 kPa. Steam is extracted from the turbine at 0.6 MPa for the closed feedwater heater and at 0.2 MPa for the open feedwater heater. In the closed feedwater heater, the feedwater is heated to the condensation temperature of the extracted steam. The extracted steam leaves the closed feedwater heater as a saturated liquid, which is subsequently throttled to the open feedwater heater. Show the cycle on a T-s diagram with respect to saturation lines. Determine (a) the fraction of steam extracted from the turbine for the open feedwater heater, (b) the thermal efficiency of the cycle, and (c) the net power output for a mass flow rate of 42 kg/s through the boiler

Using EES (or other) software, investigate the effect of the boiler pressure on the performance of a simple ideal Rankine cycle. Steam enters the turbine at 5008C and exits at 10 kPa. The boiler pressure is varied from 0.5 to 20 MPa. Determine the thermal efficiency of the cycle and plot it against the boiler pressure, and discuss the results.

Using EES (or other) software, investigate the effect of the condenser pressure on the performance of a simple ideal Rankine cycle. Turbine inlet conditions of steam are maintained constant at 10 MPa and 5508C while the condenser pressure is varied from 5 to 100 kPa. Determine the thermal efficiency of the cycle and plot it against the condenser pressure, and discuss the results.

Using EES (or other) software, investigate the effect of reheat pressure on the performance of an ideal Rankine cycle. The maximum and minimum pressures in the cycle are 15 MPa and 10 kPa, respectively, and steam enters both stages of the turbine at 5008C. The reheat pressure is varied from 12.5 to 0.5 MPa. Determine the thermal efficiency of the cycle and plot it against the reheat pressure, and discuss the results.

Using EES (or other) software, investigate the effect of extraction pressure on the performance of an ideal regenerative Rankine cycle with one open feedwater heater. Steam enters the turbine at 15 MPa and 6008C and the condenser at 10 kPa. Determine the thermal efficiency of the cycle, and plot it against extraction pressures of 12.5, 10, 7, 5, 2, 1, 0.5, 0.1, and 0.05 MPa, and discuss the results.

Show that the thermal efficiency of a combined gassteam power plant hcc can be expressed as hcc 5 hg 1 hs 2 hghs where hg 5 Wg /Qin and hs 5 Ws /Qg,out are the thermal efficiencies of the gas and steam cycles, respectively. Using this relation, determine the thermal efficiency of a combined power cycle that consists of a topping gas-turbine cycle with an efficiency of 40 percent and a bottoming steam-turbine cycle with an efficiency of 30 percent.

It can be shown that the thermal efficiency of a combined gassteam power plant hcc can be expressed in terms of the thermal efficiencies of the gas- and the steamturbine cycles as hcc 5 hg 1 hs 2 hghs Prove that the value of hcc is greater than either of hg or hs. That is, the combined cycle is more efficient than either of the gas-turbine or steam-turbine cycles alone.

Starting with Eq. 1020, show that the exergy destruction associated with a simple ideal Rankine cycle can be expressed as xdest 5 qin(hth,Carnot 2 hth), where hth is efficiency of the Rankine cycle and hth,Carnot is the efficiency of the Carnot cycle operating between the same temperature limits.

A solar collector system delivers heat to a power plant. It is well known that the thermal collection efficiency hsc of a solar collector diminishes with increasing solar collection output temperature TH , or hsc = A 2 BTH where A and B are known constants. The thermal efficiency of the power plant hth is a fixed fraction of the Carnot thermal efficiency, such that hth = F(1 2 TL/TH) where F is a known constant assumed here independent of temperatures and TL is the condenser temperature, also constant for this problem. Here, the solar collection temperature TH is also taken to be the source temperature for the power plant. (a) At what temperature TH should the solar collector be operated to obtain the maximum overall system efficiency? (b) Develop an expression for the maximum overall system efficiency.

Consider a simple ideal Rankine cycle. If the condenser pressure is lowered while keeping turbine inlet state the same, (a) the turbine work output will decrease. (b) the amount of heat rejected will decrease. (c) the cycle efficiency will decrease. (d) the moisture content at turbine exit will decrease. (e) the pump work input will decrease.

Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. If the steam is superheated to a higher temperature, (a) the turbine work output will decrease. (b) the amount of heat rejected will decrease. (c) the cycle efficiency will decrease. (d) the moisture content at turbine exit will decrease. (e) the amount of heat input will decrease.

Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. If the cycle is modified with reheating, (a) the turbine work output will decrease. (b) the amount of heat rejected will decrease. (c) the pump work input will decrease. (d) the moisture content at turbine exit will decrease. (e) the amount of heat input will decrease.

Consider a simple ideal Rankine cycle with fixed boiler and condenser pressures. If the cycle is modified with regeneration that involves one open feedwater heater (select the correct statement per unit mass of steam flowing through the boiler), (a) the turbine work output will decrease. (b) the amount of heat rejected will increase. (c) the cycle thermal efficiency will decrease. (d) the quality of steam at turbine exit will decrease. (e) the amount of heat input will increase.

Consider a steady-flow Carnot cycle with water as the working fluid executed under the saturation dome between the pressure limits of 3 MPa and 10 kPa. Water changes from saturated liquid to saturated vapor during the heat addition process. The net work output of this cycle is (a) 666 kJ/kg (b) 888 kJ/kg (c) 1040 kJ/kg (d) 1130 kJ/kg (e) 1440 kJ/kg

A simple ideal Rankine cycle operates between the pressure limits of 10 kPa and 3 MPa, with a turbine inlet temperature of 6008C. Disregarding the pump work, the cycle efficiency is (a) 24 percent (b) 37 percent (c) 52 percent (d) 63 percent (e) 71 percent

A simple ideal Rankine cycle operates between the pressure limits of 10 kPa and 5 MPa, with a turbine inlet temperature of 6008C. The mass fraction of steam that condenses at the turbine exit is (a) 6 percent (b) 9 percent (c) 12 percent (d) 15 percent (e) 18 percent

A steam power plant operates on the simple ideal Rankine cycle between the pressure limits of 10 kPa and 5 MPa, with a turbine inlet temperature of 6008C. The rate of heat transfer in the boiler is 300 kJ/s. Disregarding the pump work, the power output of this plant is (a) 93 kW (b) 118 kW (c) 190 kW (d) 216 kW (e) 300 kW

Consider a combined gas-steam power plant. Water for the steam cycle is heated in a well-insulated heat exchanger by the exhaust gases that enter at 800 K at a rate of 60 kg/s and leave at 400 K. Water enters the heat exchanger at 2008C and 8 MPa and leaves at 3508C and 8 MPa. If the exhaust gases are treated as air with constant specific heats at room temperature, the mass flow rate of water through the heat exchanger becomes (a) 11 kg/s (b) 24 kg/s (c) 46 kg/s (d) 53 kg/s (e) 60 kg/s

An ideal reheat Rankine cycle operates between the pressure limits of 10 kPa and 8 MPa, with reheat occurring at 4 MPa. The temperature of steam at the inlets of both turbines is 5008C, and the enthalpy of steam is 3185 kJ/kg at the exit of the high-pressure turbine, and 2247 kJ/kg at the exit of the low-pressure turbine. Disregarding the pump work, the cycle efficiency is (a) 29 percent (b) 32 percent (c) 36 percent (d) 41 percent (e) 49 percent

Pressurized feedwater in a steam power plant is to be heated in an ideal open feedwater heater that operates at a pressure of 2 MPa with steam extracted from the turbine. If the enthalpy of feedwater is 252 kJ/kg and the enthalpy of extracted steam is 2810 kJ/kg, the mass fraction of steam extracted from the turbine is (a) 10 percent (b) 14 percent (c) 26 percent (d) 36 percent (e) 50 percent

Consider a steam power plant that operates on the regenerative Rankine cycle with one open feedwater heater. The enthalpy of the steam is 3374 kJ/kg at the turbine inlet, 2797 kJ/kg at the location of bleeding, and 2346 kJ/kg at the turbine exit. The net power output of the plant is 120 MW, and the fraction of steam bled off the turbine for regeneration is 0.172. If the pump work is negligible, the mass flow rate of steam at the turbine inlet is (a) 117 kg/s (b) 126 kg/s (c) 219 kg/s (d) 268 kg/s (e) 679 kg/s

Consider a cogeneration power plant modified with regeneration. Steam enters the turbine at 6 MPa and 4508C at a rate of 20 kg/s and expands to a pressure of 0.4 MPa. At this pressure, 60 percent of the steam is extracted from the turbine, and the remainder expands to a pressure of 10 kPa. Part of the extracted steam is used to heat feedwater in an open feedwater heater. The rest of the extracted steam is used for process heating and leaves the process heater as a saturated liquid at 0.4 MPa. It is subsequently mixed with the feedwater leaving the feedwater heater, and the mixture is pumped to the boiler pressure. The steam in the condenser is cooled and condensed by the cooling water from a nearby river, which enters the adiabatic condenser at a rate of 463 kg/s. 1. The total power output of the turbine is (a) 17.0 MW (b) 8.4 MW (c) 12.2 MW (d) 20.0 MW (e) 3.4 MW 2. The temperature rise of the cooling water from the river in the condenser is (a) 8.08C (b) 5.28C (c) 9.68C (d) 12.98C (e) 16.28C 3. The mass flow rate of steam through the process heater is (a) 1.6 kg/s (b) 3.8 kg/s (c) 5.2 kg/s (d) 7.6 kg/s (e) 10.4 kg/s 4. The rate of heat supply from the process heater per unit mass of steam passing through it is (a) 246 kJ/kg (b) 893 kJ/kg (c) 1344 kJ/kg (d) 1891 kJ/kg (e) 2060 kJ/kg 5. The rate of heat transfer to the steam in the boiler is (a) 26.0 MJ/s (b) 53.8 MJ/s (c) 39.5 MJ/s (d) 62.8 MJ/s (e) 125.4 MJ/s

Design a steam power cycle that can achieve a cycle thermal efficiency of at least 40 percent under the conditions that all turbines have isentropic efficiencies of 85 percent and all pumps have isentropic efficiencies of 60 percent. Prepare an engineering report describing your design. Your design report must include, but is not limited to, the following: (a) Discussion of various cycles attempted to meet the goal as well as the positive and negative aspects of your design. (b) System figures and T-s diagrams with labeled states and temperature, pressure, enthalpy, and entropy information for your design. (c) Sample calculations.

A natural gasfired furnace in a textile plant is used to provide steam at 1308C. At times of high demand, the furnace supplies heat to the steam at a rate of 30 MJ/s. The plant also uses up to 6 MW of electrical power purchased from the local power company. The plant management is considering converting the existing process plant into a cogeneration plant to meet both their process-heat and power requirements. Your job is to come up with some designs. Designs based on a gas turbine or a steam turbine are to be considered. First decide whether a system based on a gas turbine or a steam turbine will best serve the purpose, considering the cost and the complexity. Then propose your design for the cogeneration plant complete with pressures and temperatures and the mass flow rates. Show that the proposed design meets the power and process-heat requirements of the plant.

Design the condenser of a steam power plant that has a thermal efficiency of 40 percent and generates 10 MW of net electric power. Steam enters the condenser as saturated vapor at 10 kPa, and it is to be condensed outside horizontal tubes through which cooling water from a nearby river flows. The temperature rise of the cooling water is limited to 88C, and the velocity of the cooling water in the pipes is limited to 6 m/s to keep the pressure drop at an acceptable level. From prior experience, the average heat flux based on the outer surface of the tubes can be taken to be 12,000 W/m2 . Specify the pipe diameter, total pipe length, and the arrangement of the pipes to minimize the condenser volume.

Several geothermal power plants are in operation in the United States and more are being built since the heat source of a geothermal plant is hot geothermal water, which is free energy. An 8-MW geothermal power plant is being considered at a location where geothermal water at 1608C is available. Geothermal water is to serve as the heat source for a closed Rankine power cycle with refrigerant-134a as the working fluid. Specify suitable temperatures and pressures for the cycle, and determine the thermal efficiency of the cycle. Justify your selections.

A photographic equipment manufacturer uses a flow of 64,500 lbm/h of steam in its manufacturing process. Presently the spent steam at 3.8 psia and 2248F is exhausted to the atmosphere. Do the preliminary design of a system to use the energy in the waste steam economically. If electricity is produced, it can be generated about 8000 h/yr and its value is $0.08/kWh. If the energy is used for space heating, the value is also $0.08/kWh, but it can only be used about 3000 h/yr (only during the heating season). If the steam is condensed and the liquid H2O is recycled through the process, its value is $0.70/100 gal. Make all assumptions as realistic as possible. Sketch the system you propose. Make a separate list of required components and their specifications (capacity, efficiency, etc.). The final result will be the calculated annual dollar value of the energy use plan (actually a saving because it will replace electricity or heat and/or water that would otherwise have to be purchased).

Stack gases exhausting from electrical power plants are at approximately 1508C. Design a basic Rankine cycle that uses water, refrigerant-134a, or ammonia as the working fluid and that produces the maximum amount of work from this energy source while rejecting heat to the ambient air at 408C. You are to use a turbine whose efficiency is 92 percent and whose exit quality cannot be less than 85 percent.

Contact your power company and obtain information on the thermodynamic aspects of their most recently built power plant. If it is a conventional power plant, find out why it is preferred over a highly efficient combined power plant.

Steam boilers have long been used to provide process heat as well as to generate power. Write an essay on the history of steam boilers and the evolution of modern supercritical steam power plants. What was the role of the American Society of Mechanical Engineers in this development?