Develop an expression for the higher heating value of a

Problem 2P Is the number of atoms of each element conserved during a chemical reaction? How about the total number of moles?

Problem 4P Is the air-fuel ratio expressed on a mole basis identical to the air-fuel ratio expressed on a mass basis?

Problem 6P Trace amounts of sulfur (S) in coal are burned in the presence of diatomic oxygen (O2) to form sulfur dioxide (SO2). Determine the minimum mass of oxygen required in the reactants and the mass of sulfur dioxide in the products when 1 kg of sulfur is burned.

Problem 1P How does the presence of N2 in air affect the outcome of a combustion process?

Problem 130P A fuel is burned during a steady-flow combustion process. Heat is lost to the surroundings at 300 K at a rate of 1120 kW. The entropy of the reactants entering per unit time is 17 kW/K and that of the products is 15 kW/K. The total rate of exergy destruction during this combustion process is (a) 520 kW ________________ (b) 600 kW ________________ (c) 1120 kW ________________ (d) 340kW ________________ (e) 739kW

Problem 5P What does the dew-point temperature of the product gases represent? How is it determined?

Problem 3P What is the air-fuel ratio? How is it related to the fuel-air ratio?

Problem 7P Methane (CH4) is burned in the presence of diatomic oxygen. The combustion products consist of water vapor and carbon dioxide gas. Determine the mass of water vapor generated when 1 lbm of methane is burned.

Problem 8P What does 100 percent theoretical air represent?

Problem 12P Which is more likely to be found in the products of an incomplete combustion of a hydrocarbon fuel, CO or OH? Why?

Propane fuel \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) is burned in the presence of air. Assuming that the combustion is theoretical-that is, only nitrogen \(\left(\mathrm{N}_{2}\right)v, water vapor \(\left(\mathrm{H}_{2} \mathrm{O}\right)\), and carbon dioxide \(\left(\mathrm{CO}_{2}\right)\) are present in the products - determine (a) the mass fraction of carbon dioxide and (b) the mole and mass fractions of the water vapor in the products. Equation Transcription: Text Transcription: (C_3H_8) (N_2) (H_2O) (CO_2)

Problem 10P Are complete combustion and theoretical combustion identical? If not, how do they differ?

Problem 13P Methane (CH4) is burned with stoichiometric amount of air during a combustion process. Assuming complete combustion, determine the air–fuel and fuel–air ratios.

Problem 9P Consider a fuel that is burned with (a) 130 percent theoretical air and (b) 70 percent excess air. In which case is the fuel burned with more air?

Problem 11P What are the causes of incomplete combustion?

Problem 15P n-Octane (C8H18) is burned with stoichiometric amount of air. Calculate the mass fraction of each product and the mass of water in the products per unit mass of fuel burned. Also, calculate the mass fraction of each reactant.

Problem 16P Acetylene (C2H2) is burned with 25 percent excess oxygen in a cutting torch. Determine the mass fraction of each of the products. Calculate the mass of oxygen used per unit mass of acetylene burned.

Problem 21P Ethylene (C2H4) is burned with 175 percent theoretical air during a combustion process. Assuming complete combustion and a total pressure of 14.5 psia, determine (a) the air-fuel ratio and (b) the dew-point temperature of the products.

Problem 18P n-Octane (C8H18) is burned with 50 percent excess air. Calculate the mass fraction of each product and the mass of water in the products per unit mass of fuel burned. Also, calculate the mass fraction of each reactant.

Problem 17P Propal alcohol (C3H7OH) is burned with 50 percent excess air. Write the balanced reaction equation for complete combustion and determine the air-to-fuel ratio.

Problem 22P One kilogram of butane (C4H10) is burned with 25 kg of air that is at 30°C and 90 kPa. Assuming that the combustion is complete and the pressure of the products is 90 kPa, determine (a) the percentage of theoretical air used and (b) the dew-point temperature of the products.

Problem 19P In a combustion chamber, ethane (C2H6) is burned at a rate of 8 kg/h with air that enters the combustion chamber at a rate of 176 kg/h. Determine the percentage of excess air used during this process.

Problem 20P One kmol of ethane (C2H6) is burned with an unknown amount of air during a combustion process. An analysis of the combustion products reveals that the combustion is complete, and there are 3 kmol of free O2 in the products. Determine (a) the air–fuel ratio and (b) the percentage of theoretical air used during this process.

Problem 24P Butane (C4H10) is burned in 200 percent theoretical air. For complete combustion, how many kmol of water must be sprayed into the combustion chamber per kmol of fuel if the products of combustion are to have a dew-point temperature of 50°C when the product pressure is 100 kPa?

Problem 25P A fuel mixture of 60 percent by mass methane (CH4) and 40 percent by mass ethanol (C2H6O), is burned completely with theoretical air. If the total flow rate of the fuel is 10 kg/s, determine the required flow rate of air.

Problem 23P One lbm of butane (C4H10) is burned with 25 lbm of air that is at 90°F and 14.7 psia. Assuming that the combustion is complete and the pressure of the products is 14.7 psia, determine (a) the percentage of theoretical air used and (b) the dew-point temperature of the products.

Problem 28P A gaseous fuel with a volumetric analysis of 45 percent CH4,35 percent H2, and 20 percent N2 is burned to completion with 130 percent theoretical air. Determine (a) the air-fuel ratio and (b) the fraction of water vapor that would condense if the product gases were cooled to 25 °C at 1 atm.

Problem 30P Methane (CH4) is burned with dry air. The volumetric analysis of the products on a dry basis is 5.20 percent CO2, 0.33 percent CO, 11.24 percent O2, and 83.23 percent N2. Determine (a) the air-fuel ratio and (b) the percentage of theoretical air used.

Problem 32P n-Octane (C8H18) is burned with 60 percent excess air with 15 percent of the carbon in the fuel forming carbon monoxide. Calculate the mole fractions of the products and the dew-point temperature of the water vapor in the products when the products are at 1 atm pressure.

Reconsider Prob. 15-28. Using EES (or other) software, study the effects of varying the percentages of \(\mathrm{CH}_{4}, \mathrm{H}_{2}\), and \(\mathrm{N}_{2}\) making up the fuel and the product gas temperature in the range 5 to \(150^{\circ} \mathrm{C}\). Equation Transcription: Text Transcription: CH_4,H_4,H_2,N_2 150^circC

Problem 26P A certain natural gas, has the following volumetric analysis: 65 percent CH4, 8 percent H2, 18 percent N2, 3 percent O2, and 6 percent CO2. This gas is now burned completely with the stoichiometric amount of dry air. What is the air-fuel ratio for this combustion process?

Problem 27P Repeat Prob. 15–26 by replacing the dry air by moist air that enters the combustion chamber at 25°C, 1 atm, and 70 percent relative humidity. Problem 15–26 A certain natural gas has the following volumetric analysis: 65 percent CH4, 8 percent H2, 18 percent N2, 3 percent O2, and 6 percent CO2. This gas is now burned completely with the stoichiometric amount of dry air. What is the air?fuel ratio for this combustion process?

Problem 31P Octane (C8H18) is burned with dry air. The volumetric analysis of the products on a dry basis is 9.21 percent CO2, 0.61 percent CO, 7.06 percent O2, and 83.12 percent N2. Determine (a) the air–fuel ratio and (b) the percentage of theoretical air used.

Problem 34P Ethyl alcohol (C2H5OH) is burned with stoichiometric amount of air. The combustion is incomplete with 5 percent (by volume) of the carbon in the fuel forming carbon monoxide and 5 percent of the hydrogen forming OH. Calculate the apparent molecular weight of the products.

Methyl alcohol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\) is burned with 100 percent excess air. During the combustion process, 60 percent of the carbon in the fuel is converted to \(\mathrm{CO}_{2}\) and 40 percent is converted to \(\mathrm{CO}\). Write the balanced reaction equation and determine the air-fuel ratio. Equation Transcription: Text Transcription: (CH_3OH) CO_2 CO

A coal from Illinois which has an ultimate analysis (by mass) as 67.40 percent C, 5.31 percent \(\mathrm{H}_{2}\), 15.11 percent \(\mathrm{O}_{2}\), 1.44 percent \(\mathrm{N}_{2}\), 2.36 percent S, and 8.38 percent ash (non-combustibles) is burned with 40 percent excess air. Calculate the mass of air required per unit mass of coal burned and the apparent molecular weight of the product gas neglecting the ash constituent. Equation Transcription: Text Transcription: H_2 O_2 N_2

Problem 36P A certain coal has the following analysis on a mass basis: 82 percent C, 5 percent H2O, 2 percent H2, 1 percent O2, and 10 percent ash. The coal is burned with 50 percent excess air. Determine the air–fuel ratio.

Problem 38P What is enthalpy of combustion? How does it differ from the enthalpy of reaction?

Problem 37P What is enthalpy of formation? How does it differ from the enthalpy of combustion?

Problem 39P What are the higher and the lower heating values of a fuel? How do they differ? How is the heating value of a fuel related to the enthalpy of combustion of that fuel?

The \(\bar{h}_{f}^{\circ}\) of \(\mathrm{N}_{2}\) is listed as zero. Does this mean that \(\mathrm{N}_{2}\) contains no chemical energy at the standard reference state? Equation Transcription: Text Transcription: bar h _f ^circ N_2 N_2

Problem 41P Which contains more chemical energy, 1 kmol of H2 or l kmol of H2O?

Problem 46P Ethane (C2H6) is burned at atmospheric pressure with stoichiometric amount of air as the oxidizer. Determine the heat rejected, in kJ/kmol fuel, when the products and reactants are at 25°C, and the water appears in the products as water vapor.

Problem 47P What is the minimum pressure of the products of Prob. 15–49 which will assure that the water in the products will be in vapor form?

Repeat Prob. 15 –42 for gaseous ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{8}\right)\). Equation Transcription: Text Transcription: (C_H_6)

Problem 49P Calculate the higher and lower heating values of a coal from Illinois which has an ultimate analysis (by mass) as 67.40 percent C, 5.31 percent H2, 15.11 percent O2, 1.44 percent N2, 2.36 percent S, and 8.38 percent ash (non-combustibles). The enthalpy of formation of SO2 is ?297,100 kJ/kmol.

Calculate the \(\mathrm{HHV}\) and \(\mathrm{LHV}\) of liquid propane fuel \(\left(\mathrm{C}_{3} \mathrm{H}_{3}\right)\). Compare your results with the values in Table A-27. Equation Transcription: Text Transcription: HHV LHV (C_3H_8)

Problem 50P Consider a complete combustion process during which both the reactants and the products are maintained at the same state. Combustion is achieved with (a) 100 percent theoretical air, (b) 200 percent theoretical air, and (c) the chemically correct amount of pure oxygen. For which case will the amount of heat transfer be the highest? Explain.

Determine the enthalpy of combustion of methane \(\left(\mathrm{CH}_{4}\right)\)at \(25^{\circ} \mathrm{C}\) and \(1 \mathrm{~atm}\), using the enthalpy of formation data from Table A-26. Assume that the water in the products is in the liquid form. Compare your result to the value listed in Table A-27. Equation Transcription: Text Transcription: (CH_4) 25^circC 1 atm

Repeat Prob. 15 –42 for liquid octane \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\). Equation Transcription: Text Transcription: (C_8H_18)

Problem 52P Derive an energy balance relation for a reacting closed system undergoing a quasi-equilibrium constant pressure expansion or compression process.

Problem 51P Consider a complete combustion process during which the reactants enter the combustion chamber at 20°C and the products leave at 700°C. Combustion is achieved with (a) 100 percent theoretical air, (b) 200 percent theoretical air, and (c) the chemically correct amount of pure oxygen. For which case will the amount of heat transfer be the lowest? Explain.

Problem 53P Acetylene gas (C2H2) is burned completely with 20 percent excess air during a steady-flow combustion process. The fuel and air enter the combustion chamber at 25°C, and the products leave at 1500 K. Determine (a) the air–fuel ratio and (b) the heat transfer for this process.

Problem 54P Liquid propane (C3H8) enters a combustion chamber at 77°F at a rate of 0.75 lbm/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 40°F. If the combustion is complete and the exit temperature of the combustion gases is 1800 R, determine (a) the mass flow rate of air and (b) the rate of heat transfer from the combustion chamber.

n-Octane gas \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\) is burned with 80 percent excess air in a constant pressure burner. The air and fuel enter this burner steadily at standard conditions and the products of combustion leave at \(217^{\circ} \mathrm{C}\). Calculate the heat transfer, in \(\mathrm{kJ} /\) \(\mathrm{kg}\) fuel, during this combustion. Equation Transcription: Text Transcription: (C_8H_18) 217^circC kJ/kg

Hydrogen \(\left(\mathrm{H}_{2}\right)\) is burned completely with the stoichiometric amount of air during a steady-flow combustion process. If both the reactants and the products are maintained at \(25^{\circ} \mathrm{C}\) and \(1 \mathrm{~atm}\) and the water in the products exists in the liquid form, determine the heat transfer from the combustion chamber during this process. What would your answer be if combustion were achieved with 50 percent excess air? Equation Transcription: Text Transcription: (H_2) 25^circC 1 atm

Problem 55P Propane fuel (C3H8) is burned with an air–fuel ratio of 25 in an atmospheric pressure heating furnace. Determine the heat transfer per kilogram of fuel burned when the temperature of the products is such that liquid water just begins to form in the products.

Octane gas \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\) at \(25^{\circ} \mathrm{C}\) is burned steadily with 80 percent excess air at \(25^{\circ} \mathrm{C}, 1 \mathrm{~atm}\), and 40 percent relative humidity. Assuming combustion is complete and the products leave the combustion chamber at \(1000 \mathrm{~K}\), determine the heat transfer for this process per unit mass of octane. Equation Transcription: Text Transcription: (C_8H_18) 25^circC, 1 atm 1000 K

Reconsider Prob. 15–59. Using EES (or other) software, investigate the effect of the amount of excess air on the heat transfer for the combustion process. Let the excess air vary from 0 to 200 percent. Plot the heat transfer against excess air, and discuss the results.

Problem 61P Diesel fuel (C12H26) at 25°C is burned in a steady-flow combustion chamber with 20 percent excess air that also enters at 25°C. The products leave the combustion chamber at 500 K. Assuming combustion is complete, determine the required mass flow rate of the diesel fuel to supply heat at a rate of 2000 kJ/s.

Problem 58P A coal from Texas which has an ultimate analysis (by mass) as 39.25 percent C, 6.93 percent H2,41.11 percent O2, 0.72 percent N2, 0.79 percent S, and 11.20 percent ash (non-combustibles) is burned steadily with 40 percent excess air in a power plant boiler. The coal and air enter this boiler at standard conditions and the products of combustion in the smokestack are at 127°C. Calculate the heat transfer, in kJ/kg fuel, in this boiler. Include the effect of the sulfur in the energy analysis by noting that sulfur dioxide has an enthalpy of formation of ?297,100 kJ/kmol and an average specific heat at constant pressure of cp=41.7 kJ/kmol?K.

Problem 62P Liquid ethyl alcohol (C2H5OH(?)) at 25°C is burned in a steady-flow combustion chamber with 40 percent excess air that also enters at 25°C. The products leave the combustion chamber at 600 K. Assuming combustion is complete, determine the required volume flow rate of the liquid ethyl alcohol, to supply heat at a rate of 2000 kJ/s. At 25°C the density of liquid ethyl alcohol is 790 kg/m3, the specific heat at a constant pressure is 114.08 kJ/kmol · K, and the enthalpy of vaporization is 42,340 kJ/kmol.

A gaseous fuel mixture that is 40 percent propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) and 60 percent methane \(\left(\mathrm{CH}_{4}\right)\) by volume is mixed with the theoretical amount of dry air and burned in a steady-flow, constant pressure process at \(100 \mathrm{kPa}\). Both the fuel and air enter the combustion chamber at \(298 \mathrm{~K}\) and undergo a complete combustion process. The products leave the combustion chamber at \(423 \mathrm{~K}\). Determine (a) the balanced combustion equation, (b) the amount of water vapor condensed from the products, and (c) the required air flow rate, in \(\mathrm{kg} / \mathrm{h}\), when the combustion process produces a heat transfer output of \(140,000 \mathrm{~kJ} / \mathrm{h}\). Equation Transcription: Text Transcription: (C_3H_8) (CH_4) 100 kPa 298 K 423 K kg/h 140,000 kJ/h

Problem 65P A constant-volume tank contains a mixture of 120 g of methane (CH4) gas and 600 g of O2 at 25°C and 200 kPa. The contents of the tank are now ignited, and the methane gas burns completely. If the final temperature is 1200 K, determine (a) the final pressure in the tank and (b) the heat transfer during this process.

Gaseous E10 fuel is 10 percent ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{8} \mathrm{O}\right)\) and 90 percent octane \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\) on a kmol basis. This fuel is burned with 110 percent theoretical air. During the combustion process, 90 percent of the carbon in the fuel is converted to \(\mathrm{CO}_{2}\) and 10 percent is converted to \(\mathrm{CO}\). Determine (a) the balanced combustion equation, (b) the dew-point temperature of the products, in \({ }^{\circ} \mathrm{C}\), for a product pressure of \(100 \mathrm{kPa}\), (c) the heat transfer for the process, in \(\mathrm{kJ}\), after \(2.5 \mathrm{~kg}\) of fuel are burned and the reactants and products are at \(25^{\circ} \mathrm{C}\) with the water in the products remaining a gas, and (d) the relative humidity of atmospheric air for the case where the atmospheric air is at \(258 \mathrm{C}\) and \(100 \mathrm{kPa}\) and the products are found to contain \(9.57 \mathrm{kmol}\) of water vapor per kmol of fuel burned. Equation Transcription: Text Transcription: (C_2H_6O) (C_8H_18) CO_2 CO ^circC 100 kPa kJ 2.5 kg 25^circC 258^circC 100 kPa 9.57kmol

Reconsider Prob. 15-65. Using EES (or other) software, investigate the effect of the final temperature on the final pressure and the heat transfer for the combustion process. Let the final temperature vary from 500 to \(1500 \mathrm{~K}\). Plot the final pressure and heat transfer against the final temperature, and discuss the results. Equation Transcription: Text Transcription: 1500 K

One \(\mathrm{lbmol}\) of methane \(\left(\mathrm{CH}_{4}\right)\) undergoes complete combustion with stoichiometric amount of air in a rigid container. Initially, the air and methane are at 14.4 psia and \(77^{\circ} \mathrm{F}\). The products of combustion are at \(800^{\circ} \mathrm{F}\). How much heat is rejected from the container, in Btu/lbmol fuel? Equation Transcription: Text Transcription: lbmol (CH_4) 77^circF 800^circ F

Problem 68P A closed combustion chamber is designed so that it maintains a constant pressure of 300 kPa during a combus-tion process. The combustion chamber has an initial volume of 0.5 m3 and contains a stoichiometric mixture of octane (C8H18) gas and air at 25°C. The mixture is now ignited, and the product gases are observed to be at 1000 K at the end of the combustion process. Assuming complete combustion, and treating both the reactants and the products as ideal gases, determine the heat transfer from the combustion chamber during this process.

Problem 69P To supply heated air to a house, a high-efficiency gas furnace burns gaseous propane (C3H8) with a combustion efficiency of 96 percent. Both the fuel and 140 percent theoretical air are supplied to the combustion chamber at 25°C and 100 kPa, and the combustion is complete. Because this is a high-efficiency furnace, the product gases are cooled to 25°C and 100 kPa before leaving the furnace. To maintain the house at the desired temperature, a heat transfer rate of 31,650 kJ/h is required from the furnace. Determine the volume of water condensed from the product gases per day.

Problem 71P A fuel at 25°C is burned in a well-insulated steady-flow combustion chamber with air that is also at 25°C. Under what conditions will the adiabatic flame temperature of the combustion process be a maximum?

Problem 70P A fuel is completely burned first with the stoichiometric amount of air and then with the stoichiometric amount of pure oxygen. For which case will the adiabatic flame temperature be higher?

Problem 72P Estimate the adiabatic flame temperature of an acetylene (C2H2) cutting torch, in °C, which uses a stoichiometric amount of pure oxygen.

Problem 73P Compare the adiabatic flame temperature of propane fuel (C3H8) when it is burned with stoichiometric amount of air and when it is burned with 20 percent excess air. The reactants are at 25°C and 1 atm.

Problem 74P Acetylene gas (C2H2) at 25°C is burned during a steady-flow combustion process with 30 percent excess air at 27°C. It is observed that 75,000 kJ of heat is being lost from the combustion chamber to the surroundings per kmol of acetylene. Assuming combustion is complete, determine the exit temperature of the product gases.

Problem 75P Octane gas (C8H18) at 25°C is burned steadily with 30 percent excess air at 25°C, 1 atm, and 60 percent relative humidity. Assuming combustion is complete and adiabatic, calculate the exit temperature of the product gases.

A coal from Pennsylvania has an ultimate analysis (by mass) as 84.36 percent C, 1.89 percent \(\mathrm{H}_{2}, 4.40\) percent \(\mathrm{O}_{2}, 0.63\) percent \(\mathrm{N}_{2}\), 0.89 percent \(\mathrm{S}\), and 7.83 percent ash (non-combustibles) is burned in an industrial boiler with 100 percent excess air. This combustion is incomplete with 3 percent (by volume) of the carbon in the products forming carbon monoxide. What is the impact of the incomplete combustion on the adiabatic flame temperature, in \({ }^{\circ} \mathrm{C}$, as compared to when the combustion is complete? Neglect the effect of the sulfur on the energy balance. Equation Transcription: Text Transcription: H_2 O_2 N_2 S ^circC

Problem 78P An adiabatic constant-volume tank contains a mixture of 1 kmol of hydrogen (H2) gas and the stoichiometric amount of air at 25°C and 1 atm. The contents of the tank are now ignited. Assuming complete combustion, determine the final temperature in the tank.

Problem 79P Methane (CH4) is burned with 200 percent excess air in an adiabatic constant volume container. Initially, air and methane are at 1 atm and 25°C. Assuming complete combustion, determine the final pressure and temperature of the combustion products.

Problem 80P Express the increase of entropy principle for chemically reacting systems.

What does the Gibbs function of formation \(\bar{g}_{f}^{\circ}\) of a compound represent? Equation Transcription: Text Transcription: Bar g _f ^circ

Liquid octane \(\left(\mathrm{C}_{3} \mathrm{H}_{18}\right)\)\) enters a steady-flow combustion chamber at \(25^{\circ} \mathrm{C}$ and \(1 \mathrm{~atm}\) at a rate of \(0.25 \mathrm{~kg} / \mathrm{min}\). It is burned with 50 percent excess air that also enters at \(25^{\circ} \mathrm{C}\) and \(1 \mathrm{~atm}\). After combustion, the products are allowed to cool to \(25^{\circ} \mathrm{C}\). Assuming complete combustion and that all the \(\mathrm{H}_{2} \mathrm{O}\) in the products is in liquid form, determine (a) the heat transfer rate from the combustion chamber, (b) the entropy generation rate, and (c) the exergy destruction rate. Assume that \(T_{0}=298 \mathrm{~K}\) and the products leave the combustion chamber at \(1 \mathrm{~atm}\) pressure. Equation Transcription: Text Transcription: (C_8H_18) 25^circC 0.25 kg/min 25^circC 1 atm 25^circC H2O T0=298 K 1 atm

Problem 81P How are the absolute entropy values of ideal gases at pressures different from 1 atm determined?

Problem 84P Benzene gas (C6H6) at 1 atm and 77°F is burned during a steady-flow combustion process with 90 percent theoretical air that enters the combustion chamber at 77°F and 1 atm. All the hydrogen in the fuel burns to H2O, but part of the carbon burns to CO. Heat is lost to the surroundings at 77°F, and the products leave the combustion chamber at 1 atm and 1900 R. Determine (a) the heat transfer from the combustion chamber and (b) the exergy destruction.

Problem 87P n-Octane (C8H18) is burned in the constant pressure combustor of an aircraft engine with 70 percent excess air. Air enters this combustor at 600 kPa and 327°C, liquid fuel is injected at 25°C, and the products of combustion leave at 600 kPa and 1067°C. Determine the entropy generation and exergy destruction per unit mass of fuel during this combustion process. Take T0 = 25°C.

Problem 89P A steady-flow combustion chamber is supplied with CO gas at 37°C and 110 kPa at a rate of 0.4 m3/min and air at 25°C and 110 kPa at a rate of 1.5 kg/min. Heat is transferred to a medium at 800 K, and the combustion products leave the combustion chamber at 900 K. Assuming the combustion is complete and T0 = 25°C, determine (a) the rate of heat transfer from the combustion chamber and (b) the rate of exergy destruction.

An automobile engine uses methyl alcohol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\) as fuel with 200 percent excess air. Air enters this engine at \(1 \mathrm{~atm}$ and \(25^{\circ} \mathrm{C\). Liquid fuel at \(25^{\circ} \mathrm{C}\) is mixed with this air before combustion. The exhaust products leave the exhaust system at \(1 \mathrm{~atm}\) and \(77^{\circ} \mathrm{C}\). What is the maximum amount of work, in \(\mathrm{kJ} / \mathrm{kg}\) fuel, that can be produced by this engine? Take \(T_{0}=25^{\circ} \mathrm{C}\). Equation Transcription: Text Transcription: (CH_3OH) 1 atm 25^circC 25^circC 77^circC kJ/kg T_0=25^circC

Liquid propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) enters a steady-flow combustion chamber at \(25^{\circ} \mathrm{C}\) and \(1 \mathrm{~atm}\) at a rate of \(0.4 \mathrm{~kg} / \mathrm{min}\) where it is mixed and burned with 150 percent excess air that enters the combustion chamber at \(12^{\circ} \mathrm{C}\). If the combustion products leave at \(1200 \mathrm{~K}\) and \(1 \mathrm{~atm}\), determine (a) the mass flow rate of air, (b) the rate of heat transfer from the combustion chamber, and (c) the rate of entropy generation during this process. Assume \(T_{0}=25^{\circ} \mathrm{C}\). Equation Transcription: Text Transcription: (C_3H_8) 25^circC 1 atm 0.4 kg/min 12^circC 1200 K 1 atm T_0=25^circC

Problem 90P Acetylene gas (C2H2) is burned completely with 20 percent excess air during a steady-flow combustion process. The fuel and the air enter the combustion chamber separately at 25°C and 1 atm, and heat is being lost from the combustion chamber to the surroundings at 25°C at a rate of 300,000 kJ/kmol C2H2. The combustion products leave the combustion chamber at 1 atm pressure. Determine (a) the temperature of the products, (b) the total entropy change per kmol of C2H2, and (c) the exergy destruction during this process.

Problem 91P A 1-g sample of a certain fuel is burned in a bomb calorimeter that contains 2 kg of water in the presence of 100 g of air in the reaction chamber. If the water temperature rises by 2.5°C when equilibrium is established, determine the heating value of the fuel, in kJ/kg.

Reconsider Prob. 15-85. Using EES (or other) software, study the effect of varying the surroundings temperature from 0 to \(38^{\circ} \mathrm{C}\) on the rate of exergy destruction, and plot it as a function of surroundings temperature Equation Transcription: Text Transcription: 38^circC

Propane fuel \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) is burned with stoichiometric amount of air in a water heater. The products of combustion are at \(1 \mathrm{~atm}\) pressure and \(120^{\circ} \mathrm{F}\). What fraction of the water vapor in the products is vapor? Equation Transcription: Text Transcription: (C_3H_8) 1 atm 120^circF

Problem 95P A coal from Utah which has an ultimate analysis (by mass) as 61.40 percent C, 5.79 percent H2, 25.31 percent O2, 1.09 percent N2, 1.41 percent S, and 5.00 percent ash (non-combustibles) is burned with 25 percent excess air in an industrial boiler. Assuming complete combustion and that the pressure in the boiler smokestack is 1 atm, calculate the minimum temperature, in °C, of the combustion products before liquid water begins to form in the smokestack.

Problem 97P A mixture of 40 percent by volume methane (CH4), and 60 percent by volume propane (C3H8), is burned completely with theoretical air and leaves the combustion chamber at 100°C. The products have a pressure of 100 kPa and are cooled at constant pressure to 39°C. Sketch the T-s diagram for the water vapor that does not condense, if any. How much of the water formed during the combustion process will be condensed, in kmol H2O/kmol fuel?

Problem 92P A gaseous fuel with 80 percent CH4, 15 percent N2, and 5 percent O2 (on a mole basis) is burned to completion with 120 percent theoretical air that enters the combustion chamber at 30°C, 100 kPa, and 60 percent relative humidity. Determine (a) the air–fuel ratio and (b) the volume flow rate of air required to burn fuel at a rate of 2 kg/min.

Problem 96P Methane fuel (CH4) is burned with 15 percent excess air in a space-heating furnace. The pressure in the chimney is 1 atm. Presuming complete combustion, determine the temperature of the combustion products at which liquid water will begin to form in the chimney.

Problem 93P Hydrogen (H2) is burned with 100 percent excess air that enters the combustion chamber at 80°F, 14.5 psia, and 60 percent relative humidity. Assuming complete combustion, determine (a) the air–fuel ratio and (b) the volume flow rate of air required to burn the hydrogen at a rate of 40 lbm/h.

Problem 99P A liquid-gas fuel mixture consists of 90 percent octane (C8H18), and 10 percent alcohol (C2H5OH), by moles. This fuel is burned with 200 percent theoretical dry air. Write the balanced reaction equation for complete combustion of this fuel mixture. Determine (a) the theoretical air–fuel ratio for this reaction, (b) the product-fuel ratio for this reaction, (c) the air-flow rate for a fuel mixture flow rate of 5 kg/s, and (d) the lower heating value of the fuel mixture with 200 percent theoretical air at 25°C.

Problem 98P A gaseous fuel mixture of 60 percent propane (C3H8), and 40 percent butane (C4H10), on a volume basis is burned in air such that the air–fuel ratio is 19 kg air/kg fuel when the combustion process is complete. Determine (a) the moles of nitrogen in the air supplied to the combustion process, in kmol/kmol fuel, (b) the moles of water formed in the combustion process, in kmol/kmol fuel, and (c) the moles of oxygen in the product gases in kmol/kmol fuel.

Ethanol gas \(\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}\right)\) is burned with 110 percent theoretical air. During the combustion process, 90 percent of the carbon in the fuel is converted to \(\mathrm{CO}_{2}\) and 10 percent is converted to \(\mathrm{CO}\). Determine (a) the theoretical kmols of \(\mathrm{O}_{2}\) required for complete combustion of one kmol of ethanol, (b) the balanced combustion equation for the incomplete combustion process, and (c) the rate of heat transfer from the combustion process, in kW, when \(3.5 \mathrm{~kg} / \mathrm{h}\) of fuel are burned when the reactants and products are at \(25^{\circ} \mathrm{C}\) with the water in the products remaining a gas. Equation Transcription: Text Transcription: (C_2H_6O) CO_2 CO O_2 3.5 kg/h 25^circC

Problem 100P A steady-flow combustion chamber is supplied with CO gas at 37°C and 110 kPa at a rate of 0.4 m3/min and air at 25°C and 110 kPa at a rate of 1.5 kg/min. The combustion products leave the combustion chamber at 900 K. Assuming combustion is complete, determine the rate of heat transfer from the combustion chamber.

Problem 104P Determine the highest possible temperature that can be obtained when liquid gasoline (assumed C8H18) at 25°C is burned steadily with air at 25°C and 1 atm. What would your answer be if pure oxygen at 25 °C were used to burn the fuel instead of air?

Problem 101P A 6-m3 rigid tank initially contains a mixture of 1 kmol of hydrogen (H2) gas and the stoichiometric amount of air at 25°C. The contents of the tank are ignited, and all the hydrogen in the fuel burns to H2O. If the combustion products are cooled to 25°C, determine (a) the fraction of the H2O that condenses and (b) the heat transfer from the combustion chamber during this process.

Problem 105P Liquid propane (C3H8(?)) enters a combustion chamber at 25°C and 1 atm at a rate of 0.4 kg/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 25°C. The heat transfer from the combustion process is 53 kW. Write the balanced combustion equation and determine (a) the mass flow rate of air; (b) the average molar mass (molecular weight) of the product gases; (c) the average specific heat at constant pressure of the product gases; and (d) the temperature of the products of combustion.

Problem 103P Propane gas (C3H8) enters a steady-flow combustion chamber at 1 atm and 25°C and is burned with air that enters the combustion chamber at the same state. Determine the adiabatic flame temperature for (a) complete combustion with 100 percent theoretical air, (b) complete combustion with 200 percent theoretical air, and (c) incomplete combustion (some CO in the products) with 90 percent theoretical air.

Problem 106P Determine the work potential of 1 lbmol of diesel fuel (C12H26) at 77°F and 1 atm in an environment at the same state.

Problem 107P n-Octane (C8H18) is burned with 30 percent excess air, with 10 percent of the carbon forming carbon monoxide. Determine the maximum work that can be produced, in kJ/kg fuel, when the air, fuel products are all at 25°C and 1 atm.

Problem 108P A steam boiler heats liquid water at 200°C to superheated steam at 4 MPa and 400°C. Methane fuel (CH4) is burned at atmospheric pressure with 50 percent excess air. The fuel and air enter the boiler at 25°C and the products of combustion leave at 227°C. Calculate (a) the amount of steam generated per unit of fuel mass burned, (b) the change in the exergy of the combustion streams, in kJ/kg fuel, (c) the change in the exergy of the steam stream, in kJ/kg steam, and (d) the lost work potential, in kJ/kg fuel. Take T0 =25°C.

Problem 111P Develop an expression for the higher heating value of a gaseous alkane CnH2n+2 in terms of n.

Problem 109P Repeat Prob. 15–115 using a coal from Utah which has an ultimate analysis (by mass) as 61.40 percent C, 5.79 percent H2, 25.31 percent O2, 1.09 percent N2, 1.41 percent S, and 5.00 percent ash (non-combustibles). Neglect the effect of the sulfur in the energy and entropy balances.

Problem 110P Liquid octane (C8H18) enters a steady-flow combustion chamber at 25°C and 8 atm at a rate of 0.8 kg/min. It is burned with 200 percent excess air that is compressed and preheated to 500 K and 8 atm before entering the combustion chamber. After combustion, the products enter an adiabatic turbine at 1300 K and 8 atm and leave at 950 K and 2 atm. Assuming complete combustion and T0 = 25°C, determine (a) the heat transfer rate from the combustion chamber, (b) the power output of the turbine, and (c) the reversible work and exergy destruction for the entire process.

Consider the combustion of hydrocarbon fuel, \(\mathrm{C}_{n} \mathrm{H}_{\mathrm{m}}\), with excess theoretical air and incomplete combustion according to the chemical reaction as follows: \(\begin{aligned}&\mathrm{C}_{n} \mathrm{H}_{m}+(1+B) A_{\mathrm{th}}\left(\mathrm{O}_{2}+3.76 \mathrm{~N}_{2}\right) \rightarrow \\&\quad D \mathrm{CO}_{2}+E \mathrm{CO}+F \mathrm{H}_{2} \mathrm{O}+G \mathrm{O}_{2}+J \mathrm{~N}_{2}\end{aligned}\) where \(\mathrm{A}_{\mathrm{th}}\) is the theoretical \(\mathrm{O}_{2}\) required for this fuel and \(\mathrm{B}\) is the excess amount of air in decimal form. If a is the fraction of carbon in the fuel converted to carbon dioxide and \(b\) is the remaining fraction converted to carbon monoxide, determine the coefficients \(A_{\text {th }}, D, E, F, G\), and \(J\) for a fixed \(B\) amount of excess air. Write the coefficients \(D, E, F, G\), and \(J\) as functions of \(n, m, a, b\), \(B\), and \(A_{\text {th }}\) in the simplest correct forms. Equation Transcription: Text Transcription: C_nH_m C_nH_m+(1+B)A_th(O_2+3.76N_2) DCO_2+ECO+FH_2O+GO_2+J N_ A_th O_2 A_th,D,E,F,G,J D,E,F,G,J n,m,a,b,B A_th

Consider the combustion of a mixture of an alcohol, \(\mathrm{C}_{n} \mathrm{H}_{m} \mathrm{O}_{x}\), and a hydrocarbon fuel, \(\mathrm{C}_{w} \mathrm{H}_{z}\), with excess theoretical air and incomplete combustion according to the chemical reaction as follows: \(\begin{array}{r}y_{1} \mathrm{C}_{n} \mathrm{H}_{m} \mathrm{O}_{x}+y_{2} \mathrm{C}_{1} \mathrm{H}_{2}+(1+B) A_{\mathrm{th}}\left(\mathrm{O}_{2}+3.76 \mathrm{~N}_{2}\right) \rightarrow \\\quad D \mathrm{CO}_{2}+E \mathrm{CO}+F \mathrm{H}_{2} \mathrm{O}+G \mathrm{O}_{2}+J \mathrm{~N}_{2}\end{array}\) where \(y_{1}\) and \(y_{2}\) are the mole fractions of the fuel mixture, \(A_{\text {th }}\) is the theoretical\(\mathrm{O}_{2}\) required for this fuel, and \(B\) is the excess amount of air in decimal form. If a is the fraction of carbon in the fuel converted to carbon dioxide and \(b\) is the remaining fraction converted to carbon monoxide, determine the coefficients \(A_{\mathrm{th}}, D, E, F, G\), and \(J\) for a fixed \(B\)amount of excess air. Write the coefficients \(D, E, F, G\), and \(J\) as functions of \(y_{1}, y_{2}, n, m, x, w, z, a, b, B\), and \(A_{t h}\) in the simplest correct forms. Equation Transcription: Text Transcription: C_nH_mO_x C_wH_z y_1C_nH_m+y_2C_nH_z+(1+B)A_th(O_2+3.76N_2) DCO_2+ECO+FH_2O+GO_2+J N_2 y_1 y_2 A_th O_2 B A_th,D,E,F,G,J B D,E,F,G,J y_1,y_2,n,m,x,w,z,a,b,B,A_th

Using EES (or other) software, determine the effect of the amount of air on the adiabatic flame temperature of liquid octane \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\). Assume both the air and the octane are initially at \(25^{\circ} \mathrm{C}\). Determine the adiabatic flame temperature for 75,90,100,120,150,200,300,500, and 800 percent theoretical air. Assume the hydrogen in the fuel always burns \(\mathrm{H}_{2} \mathrm{O}\) and the carbon \(\mathrm{CO}_{2}\) except when there is a deficiency of air. In the latter case, assume that part of the carbon forms \(\mathrm{CO}\). Plot the adiabatic flame temperature against the percent theoretical air, and discuss the results. Equation Transcription: Text Transcription: (C_8H_18) 25^circC H_2O CO_2 CO

Problem 121P A fuel is burned steadily in a combustion chamber. The combustion temperature will be the highest except when (a) the fuel is preheated. ________________ (b) the fuel is burned with a deficiency of air. ________________ (c) the air is dry. ________________ (d) the combustion chamber is well insulated. ________________ (e) the combustion is complete.

Problem 124P One kmol of methane (CH4) is burned with an unknown amount of air during a combustion process. If the combustion is complete and there are 1 kmol of free O2 in the products, the air-fuel mass ratio is (a) 34.6 ________________ (b) 25.7 ________________ (c) 17.2 ________________ (d) 14.3 ________________ (e) 11.9

Problem 123P Propane (C3H8) is burned with 150 percent theoretical air. The air-fuel mass ratio for this combustion process is (a) 5.3 ________________ (b) 10.5 ________________ (c) 15.7 ________________ (d) 23.4 ________________ (e) 39.3

Problem 122P A fuel is burned with 70 percent theoretical air. This is equivalent to (a) 30% excess air ________________ (b) 70% excess air ________________ (c) 30% deficiency of air ________________ (d) 70% deficiency of air ________________ (e) stoichiometric amount of air

Problem 125P An equimolar mixture of carbon dioxide and water vapor at 1 atm and 60°C enter a dehumidifying section where the entire water vapor is condensed and removed from the mixture, and the carbon dioxide leaves at 1 atm and 60°C. The entropy change of carbon dioxide in the dehumidifying section is (a) -2.8 kJ/kg·K ________________ (b) -0.13 kJ/kg·K ________________ (c) 0 ________________ (d) 0.13 kJ/kg·K ________________ (e) 2.8 kJ/kg·K

Problem 126P Methane (CH4) is burned completely with 80 percent excess air during a steady-flow combustion process. If both the reactants and the products are maintained at 25°C. and 1 atm and the water in the products exists in the liquid form, the heat transfer from the combustion chamber per unit mass of methane is (a) 890 MJ/kg ________________ (b) 802 MJ/kg ________________ (c) 75 MJ/kg ________________ (d) 56 MJ/kg ________________ (e) 50 MJ/kg

Problem 127P The higher heating value of a hydrocarbon fuel Cn, Hm with m= 8 is given to be 1560 MJ/kmol of fuel. Then its lower heating value is (a) 1384 MJ/kmol ________________ (b) 1208 MJ/kmol ________________ (c) 1402 MJ/kmol ________________ (d) 1514 MJ/kmol ________________ (e) 1551 MJ/kmol

Problem 128P Acetylene gas (C2H2) is burned completely during a steady-flow combustion process. The fuel and the air enter the combustion chamber at 25°C, and the products leave at 1500 K. If the enthalpy of the products relative to the standard reference state is ?404 MJ/kmol of fuel, the heat transfer from the combustion chamber is (a) 177 MJ/kmol ________________ (b) 227 MJ/kmol ________________ (c) 404 MJ/kmol ________________ (d) 631 MJ/kmol ________________ (e) 751 MJ/kmol

How does the presence of in air affect the outcome of a combustion process?

Is the number of atoms of each element conserved during a chemical reaction? How about the total number of moles?

What is the air–fuel ratio? How is it related to the fuel–air ratio?

Is the air-fuel ratio expressed on a mole basis identical to the air-fuel ratio expressed on a mass basis?

What does the dew-point temperature of the product gases represent? How is it determined?

Trace amounts of sulfur in coal are burned in the presence of diatomic oxygen to form sulfur dioxide . Determine the minimum mass of oxygen required in the reactants and the mass of sulfur dioxide in the products when of sulfur is burned.

Methane is burned in the presence of diatomic oxygen. The combustion products consist of water vapor and carbon dioxide gas. Determine the mass of water vapor generated when of methane is burned.

What does 100 percent theoretical air represent?

Consider a fuel that is burned with (a) 130 percent theoretical air and (b) 70 percent excess air. In which case is the fuel burned with more air?

Are complete combustion and theoretical combustion identical? If not, how do they differ?

What are the causes of incomplete combustion?

Which is more likely to be found in the products of an incomplete combustion of a hydrocarbon fuel, CO or OH? Why?

Methane ( ) is burned with stoichiometric amount of air during a combustion process. Assuming complete combustion, determine the air-fuel and fuel-air ratios.

Propane fuel ( ) is burned in the presence of air. Assuming that the combustion is theoretical-that is, only nitrogen ( ), water vapor ( ), and carbon dioxide (CO2) are present in the product-determine (a) the mass fraction of carbon dioxide and (b) the mole and mass fractions of the water vapor in the products.

n-Butane ( ) is burned with stoichiometric amount of oxygen. Determine the mole fraction of carbon dioxide and water in the products. Also, calculate the mole number of carbon dioxide in the products per unit mole of fuel burned.

Acetylene ( ) is burned with 25 percent excess oxygen in a cutting torch. Determine the mass fraction of each of the products. Calculate the mass of oxygen used per unit mass of acetylene burned

Propal alcohol ( ) is burned with 50 percent excess air. Write the balanced reaction equation for complete combustion and determine the air-to-fuel ratio.

n-Octane is burned with 50 percent excess air. Calculate the mass fraction of each product and the mass of water in the products per unit mass of fuel burned. Also, calculate the mass fraction of each reactant.

In a combustion chamber, ethane is burned at a rate of with air that enters the combustion chamber at a rate of . Determine the percentage of excess air used during this process.

One kmol of ethane is burned with an unknown amount of air during a combustion process. An analysis of the combustion products reveals that the combustion is complete, and there are of free in the products. Determine (a) the air-fuel ratio and (b) the percentage of theoretical air used during this process.

Ethylene is burned with 175 percent theoretical air during a combustion process. Assuming complete combustion and a total pressure of determine (a) the air-fuel ratio and (b) the dew-point temperature of the products.

One kilogram of butane is burned with 25 kg of air that is at and . Assuming that the combustion is complete and the pressure of the products is , determine (a) the percentage of theoretical air used and (b) the dew-point temperature of the products.

One lbm of butane (C4H10) is burned with 25 lbm of air that is at 908F and 14.7 psia. Assuming that the combustion is complete and the pressure of the products is 14.7 psia, determine (a) the percentage of theoretical air used and (b) the dew-point temperature of the products.

Butane (C4H10) is burned in 200 percent theoretical air. For complete combustion, how many kmol of water must be sprayed into the combustion chamber per kmol of fuel if the products of combustion are to have a dew-point temperature of 508C when the product pressure is 100 kPa?

A fuel mixture of 60 percent by mass methane (CH4) and 40 percent by mass ethanol (C2H6O), is burned completely with theoretical air. If the total flow rate of the fuel is 10 kg/s, determine the required flow rate of air.

A certain natural gas has the following volumetric analysis: 65 percent CH4, 8 percent H2, 18 percent N2, 3 percent O2, and 6 percent CO2. This gas is now burned completely with the stoichiometric amount of dry air. What is the airfuel ratio for this combustion process?

Repeat Prob. 1526 by replacing the dry air by moist air that enters the combustion chamber at 258C, 1 atm, and 70 percent relative humidity.

A gaseous fuel with a volumetric analysis of 45 percent CH4, 35 percent H2, and 20 percent N2 is burned to completion with 130 percent theoretical air. Determine (a) the airfuel ratio and (b) the fraction of water vapor that would condense if the product gases were cooled to 258C at 1 atm.

Reconsider Prob. 1528. Using EES (or other) software, study the effects of varying the percentages of CH4, H2, and N2 making up the fuel and the product gas temperature in the range 5 to 1508C.

Methane (CH4) is burned with dry air. The volumetric analysis of the products on a dry basis is 5.20 percent CO2, 0.33 percent CO, 11.24 percent O2, and 83.23 percent N2. Determine (a) the airfuel ratio and (b) the percentage of theoretical air used.

Octane (C8H18) is burned with dry air. The volumetric analysis of the products on a dry basis is 9.21 percent CO2, 0.61 percent CO, 7.06 percent O2, and 83.12 percent N2. Determine (a) the air-fuel ratio and (b) the percentage of theoretical air used.

n-Octane (C8H18) is burned with 60 percent excess air with 15 percent of the carbon in the fuel forming carbon monoxide. Calculate the mole fractions of the products and the dew-point temperature of the water vapor in the products when the products are at 1 atm pressure.

Methyl alcohol (CH3OH) is burned with 100 percent excess air. During the combustion process, 60 percent of the carbon in the fuel is converted to CO2 and 40 percent is converted to CO. Write the balanced reaction equation and determine the air-fuel ratio.

Ethyl alcohol (C2H5OH) is burned with stoichiometric amount of air. The combustion is incomplete with 5 percent (by volume) of the carbon in the fuel forming carbon monoxide and 5 percent of the hydrogen forming OH. Calculate the apparent molecular weight of the products.

A coal from Illinois which has an ultimate analysis (by mass) as 67.40 percent C, 5.31 percent H2, 15.11 percent O2, 1.44 percent N2, 2.36 percent S, and 8.38 percent ash (non-combustibles) is burned with 40 percent excess air. Calculate the mass of air required per unit mass of coal burned and the apparent molecular weight of the product gas neglecting the ash constituent. A

A certain coal has the following analysis on a mass basis: 82 percent C, 5 percent H2O, 2 percent H2, 1 percent O2, and 10 percent ash. The coal is burned with 50 percent excess air. Determine the airfuel ratio.

What is enthalpy of formation? How does it differ from the enthalpy of combustion?

What is enthalpy of combustion? How does it differ from the enthalpy of reaction?

What are the higher and the lower heating values of a fuel? How do they differ? How is the heating value of a fuel related to the enthalpy of combustion of that fuel?

The h8 f of N2 is listed as zero. Does this mean that N2 contains no chemical energy at the standard reference state?

Which contains more chemical energy, 1 kmol of H2 or 1 kmol of H2O?

Determine the enthalpy of combustion of methane (CH4) at 258C and 1 atm, using the enthalpy of formation data from Table A26. Assume that the water in the products is in the liquid form. Compare your result to the value listed in Table A27.

Reconsider Prob. 1542. Using EES (or other) software, study the effect of temperature on the enthalpy of combustion. Plot the enthalpy of combustion as a function of temperature over the range 25 to 6008C.

Repeat Prob. 15 42 for gaseous ethane (C2H6).

Repeat Prob. 15 42 for liquid octane (C8H18).

Ethane (C2H6) is burned at atmospheric pressure with stoichiometric amount of air as the oxidizer. Determine the heat rejected, in kJ/kmol fuel, when the products and reactants are at 258C, and the water appears in the products as water vapor.

What is the minimum pressure of the products of Prob. 1546 which will assure that the water in the products will be in vapor form?

Calculate the HHV and LHV of liquid propane fuel (C3H8). Compare your results with the values in Table A-27.

Calculate the higher and lower heating values of a coal from Illinois which has an ultimate analysis (by mass) as 67.40 percent C, 5.31 percent H2, 15.11 percent O2, 1.44 percent N2, 2.36 percent S, and 8.38 percent ash (non-combustibles). The enthalpy of formation of SO2 is 2297,100 kJ/kmol.

Consider a complete combustion process during which both the reactants and the products are maintained at the same state. Combustion is achieved with (a) 100 percent theoretical air, (b) 200 percent theoretical air, and (c) the chemically correct amount of pure oxygen. For which case will the amount of heat transfer be the highest? Explain.

Consider a complete combustion process during which the reactants enter the combustion chamber at 208C and the products leave at 7008C. Combustion is achieved with (a) 100 percent theoretical air, (b) 200 percent theoretical air, and (c) the chemically correct amount of pure oxygen. For which case will the amount of heat transfer be the lowest? Explain.

Derive an energy balance relation for a reacting closed system undergoing a quasi-equilibrium constant pressure expansion or compression process.

Acetylene gas (C2H2) is burned completely with 20 percent excess air during a steady-flow combustion process. The fuel and air enter the combustion chamber at 258C, and the products leave at 1500 K. Determine (a) the airfuel ratio and (b) the heat transfer for this process.

Liquid propane (C3H8) enters a combustion chamber at 778F at a rate of 0.75 lbm/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 408F. If the combustion is complete and the exit temperature of the combustion gases is 1800 R, determine (a) the mass flow rate of air and (b) the rate of heat transfer from the combustion chamber

Propane fuel (C3H8) is burned with an air-fuel ratio of 25 in an atmospheric pressure heating furnace. Determine the heat transfer per kilogram of fuel burned when the temperature of the products is such that liquid water just begins to form in the products.

Hydrogen (H2) is burned completely with the stoichiometric amount of air during a steady-flow combustion process. If both the reactants and the products are maintained at 258C and 1 atm and the water in the products exists in the liquid form, determine the heat transfer from the combustion chamber during this process. What would your answer be if combustion were achieved with 50 percent excess air?

n-Octane gas (C8H18) is burned with 80 percent excess air in a constant pressure burner. The air and fuel enter this burner steadily at standard conditions and the products of combustion leave at 2178C. Calculate the heat transfer, in kJ/ kg fuel, during this combustion.

A coal from Texas which has an ultimate analysis (by mass) as 39.25 percent C, 6.93 percent H2, 41.11 percent O2, 0.72 percent N2, 0.79 percent S, and 11.20 percent ash (noncombustibles) is burned steadily with 40 percent excess air in a power plant boiler. The coal and air enter this boiler at standard conditions and the products of combustion in the smokestack are at 1278C. Calculate the heat transfer, in kJ/kg fuel, in this boiler. Include the effect of the sulfur in the energy analysis by noting that sulfur dioxide has an enthalpy of formation of 2297,100 kJ/kmol and an average specific heat at constant pressure of cp 5 41.7 kJ/kmol K.

Octane gas (C8H18) at 258C is burned steadily with 80 percent excess air at 258C, 1 atm, and 40 percent relative humidity. Assuming combustion is complete and the products leave the combustion chamber at 1000 K, determine the heat transfer for this process per unit mass of octane.

Reconsider Prob. 1559. Using EES (or other) software, investigate the effect of the amount of excess air on the heat transfer for the combustion process. Let the excess air vary from 0 to 200 percent. Plot the heat transfer against excess air, and discuss the results.

Diesel fuel (C12H26) at 258C is burned in a steadyflow combustion chamber with 20 percent excess air that also enters at 258C. The products leave the combustion chamber at 500 K. Assuming combustion is complete, determine the required mass flow rate of the diesel fuel to supply heat at a rate of 2000 kJ/s.

Liquid ethyl alcohol (C2H5OH(,)) at 258C is burned in a steady-flow combustion chamber with 40 percent excess air that also enters at 258C. The products leave the combustion chamber at 600 K. Assuming combustion is complete, determine the required volume flow rate of the liquid ethyl alcohol, to supply heat at a rate of 2000 kJ/s. At 258C the density of liquid ethyl alcohol is 790 kg/m3 , the specific heat at a constant pressure is 114.08 kJ/kmol ? K, and the enthalpy of vaporization is 42,340 kJ/kmol.

A gaseous fuel mixture that is 40 percent propane (C3H8) and 60 percent methane (CH4) by volume is mixed with the theoretical amount of dry air and burned in a steadyflow, constant pressure process at 100 kPa. Both the fuel and air enter the combustion chamber at 298 K and undergo a complete combustion process. The products leave the combustion chamber at 423 K. Determine (a) the balanced combustion equation, (b) the amount of water vapor condensed from the products, and (c) the required air flow rate, in kg/h, when the combustion process produces a heat transfer output of 140,000 kJ/h.

Gaseous E10 fuel is 10 percent ethanol (C2H6O) and 90 percent octane (C8H18) on a kmol basis. This fuel is burned with 110 percent theoretical air. During the combustion process, 90 percent of the carbon in the fuel is converted to CO2 and 10 percent is converted to CO. Determine (a) the balanced combustion equation, (b) the dew-point temperature of the products, in 8C, for a product pressure of 100 kPa, (c) the heat transfer for the process, in kJ, after 2.5 kg of fuel are burned and the reactants and products are at 258C with the water in the products remaining a gas, and (d) the relative humidity of atmospheric air for the case where the atmospheric air is at 258C and 100 kPa and the products are found to contain 9.57 kmol of water vapor per kmol of fuel burned.

A constant-volume tank contains a mixture of 120 g of methane (CH4) gas and 600 g of O2 at 258C and 200 kPa. The contents of the tank are now ignited, and the methane gas burns completely. If the final temperature is 1200 K, determine (a) the final pressure in the tank and (b) the heat transfer during this process.

Reconsider Prob. 1565. Using EES (or other) software, investigate the effect of the final temperature on the final pressure and the heat transfer for the combustion process. Let the final temperature vary from 500 to 1500 K. Plot the final pressure and heat transfer against the final temperature, and discuss the results.

One lbmol of methane (CH4) undergoes complete combustion with stoichiometric amount of air in a rigid container. Initially, the air and methane are at 14.4 psia and 778F. The products of combustion are at 8008F. How much heat is rejected from the container, in Btu/lbmol fuel?

A closed combustion chamber is designed so that it maintains a constant pressure of 300 kPa during a combustion process. The combustion chamber has an initial volume of 0.5 m3 and contains a stoichiometric mixture of octane (C8H18) gas and air at 258C. The mixture is now ignited, and the product gases are observed to be at 1000 K at the end of the combustion process. Assuming complete combustion, and treating both the reactants and the products as ideal gases, determine the heat transfer from the combustion chamber during this process.

To supply heated air to a house, a high-efficiency gas furnace burns gaseous propane (C3H8) with a combustion efficiency of 96 percent. Both the fuel and 140 percent theoretical air are supplied to the combustion chamber at 258C and 100 kPa, and the combustion is complete. Because this is a high-efficiency furnace, the product gases are cooled to 258C and 100 kPa before leaving the furnace. To maintain the house at the desired temperature, a heat transfer rate of 31,650 kJ/h is required from the furnace. Determine the volume of water condensed from the product gases per day.

A fuel is completely burned first with the stoichiometric amount of air and then with the stoichiometric amount of pure oxygen. For which case will the adiabatic flame temperature be higher?

A fuel at 258C is burned in a well-insulated steadyflow combustion chamber with air that is also at 258C. Under what conditions will the adiabatic flame temperature of the combustion process be a maximum?

Estimate the adiabatic flame temperature of an acetylene (C2H2) cutting torch, in 8C, which uses a stoichiometric amount of pure oxygen. A

Compare the adiabatic flame temperature of propane fuel (C3H8) when it is burned with stoichiometric amount of air and when it is burned with 20 percent excess air. The reactants are at 258C and 1 atm.

Acetylene gas (C2H2) at 258C is burned during a steady-flow combustion process with 30 percent excess air at 278C. It is observed that 75,000 kJ of heat is being lost from the combustion chamber to the surroundings per kmol of acetylene. Assuming combustion is complete, determine the exit temperature of the product gases.

Octane gas (C8H18) at 258C is burned steadily with 30 percent excess air at 258C, 1 atm, and 60 percent relative humidity. Assuming combustion is complete and adiabatic, calculate the exit temperature of the product gases.

Reconsider Prob. 1575. Using EES (or other) software, investigate the effect of the relative humidity on the exit temperature of the product gases. Plot the exit temperature of the product gases as a function of relative humidity for 0 , f , 100 percent.

A coal from Pennsylvania has an ultimate analysis (by mass) as 84.36 percent C, 1.89 percent H2, 4.40 percent O2, 0.63 percent N2, 0.89 percent S, and 7.83 percent ash (non-combustibles) is burned in an industrial boiler with 100 percent excess air. This combustion is incomplete with 3 percent (by volume) of the carbon in the products forming carbon monoxide. What is the impact of the incomplete combustion on the adiabatic flame temperature, in 8C, as compared to when the combustion is complete? Neglect the effect of the sulfur on the energy balance.

An adiabatic constant-volume tank contains a mixture of 1 kmol of hydrogen (H2) gas and the stoichiometric amount of air at 258C and 1 atm. The contents of the tank are now ignited. Assuming complete combustion, determine the final temperature in the tank.

Methane (CH4) is burned with 200 percent excess air in an adiabatic constant volume container. Initially, air and methane are at 1 atm and 258C. Assuming complete combustion, determine the final pressure and temperature of the combustion products.

Express the increase of entropy principle for chemically reacting systems.

How are the absolute entropy values of ideal gases at pressures different from 1 atm determined?

What does the Gibbs function of formation g8 f of a compound represent?

Liquid octane (C8H18) enters a steady-flow combustion chamber at 258C and 1 atm at a rate of 0.25 kg/min. It is burned with 50 percent excess air that also enters at 258C and 1 atm. After combustion, the products are allowed to cool to 258C. Assuming complete combustion and that all the H2O in the products is in liquid form, determine (a) the heat transfer rate from the combustion chamber, (b) the entropy generation rate, and (c) the exergy destruction rate. Assume that T0 5 298 K and the products leave the combustion chamber at 1 atm pressure.

Benzene gas (C6H6) at 1 atm and 778F is burned during a steady-flow combustion process with 90 percent theoretical air that enters the combustion chamber at 778F and 1 atm. All the hydrogen in the fuel burns to H2O, but part of the carbon burns to CO. Heat is lost to the surroundings at 778F, and the products leave the combustion chamber at 1 atm and 1900 R. Determine (a) the heat transfer from the combustion chamber and (b) the exergy destruction.

Liquid propane (C3H8) enters a steady-flow combustion chamber at 258C and 1 atm at a rate of 0.4 kg/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 128C. If the combustion products leave at 1200 K and 1 atm, determine (a) the mass flow rate of air, (b) the rate of heat transfer from the combustion chamber, and (c) the rate of entropy generation during this process. Assume T0 5 258C.

Reconsider Prob. 1585. Using EES (or other) software, study the effect of varying the surroundings temperature from 0 to 388C on the rate of exergy destruction, and plot it as a function of surroundings temperature

n-Octane (C8H18) is burned in the constant pressure combustor of an aircraft engine with 70 percent excess air. Air enters this combustor at 600 kPa and 3278C, liquid fuel is injected at 258C, and the products of combustion leave at 600 kPa and 10678C. Determine the entropy generation and exergy destruction per unit mass of fuel during this combustion process. Take T0 5 258C.

An automobile engine uses methyl alcohol (CH3OH) as fuel with 200 percent excess air. Air enters this engine at 1 atm and 258C. Liquid fuel at 258C is mixed with this air before combustion. The exhaust products leave the exhaust system at 1 atm and 778C. What is the maximum amount of work, in kJ/kg fuel, that can be produced by this engine? Take T0 5 258C.

A steady-flow combustion chamber is supplied with CO gas at 378C and 110 kPa at a rate of 0.4 m3 /min and air at 258C and 110 kPa at a rate of 1.5 kg/min. Heat is transferred to a medium at 800 K, and the combustion products leave the combustion chamber at 900 K. Assuming the combustion is complete and T0 5 258C, determine (a) the rate of heat transfer from the combustion chamber and (b) the rate of exergy destruction.

Acetylene gas (C2H2) is burned completely with 20 percent excess air during a steady-flow combustion process. The fuel and the air enter the combustion chamber separately at 258C and 1 atm, and heat is being lost from the combustion chamber to the surroundings at 258C at a rate of 300,000 kJ/kmol C2H2. The combustion products leave the combustion chamber at 1 atm pressure. Determine (a) the temperature of the products, (b) the total entropy change per kmol of C2H2, and (c) the exergy destruction during this process.

A 1-g sample of a certain fuel is burned in a bomb calorimeter that contains 2 kg of water in the presence of 100 g of air in the reaction chamber. If the water temperature rises by 2.58C when equilibrium is established, determine the heating value of the fuel, in kJ/kg.

A gaseous fuel with 80 percent CH4, 15 percent N2, and 5 percent O2 (on a mole basis) is burned to completion with 120 percent theoretical air that enters the combustion chamber at 308C, 100 kPa, and 60 percent relative humidity. Determine (a) the airfuel ratio and (b) the volume flow rate of air required to burn fuel at a rate of 2 kg/min.

Hydrogen (H2) is burned with 100 percent excess air that enters the combustion chamber at 808F, 14.5 psia, and 60 percent relative humidity. Assuming complete combustion, determine (a) the airfuel ratio and (b) the volume flow rate of air required to burn the hydrogen at a rate of 40 lbm/h.

Propane fuel (C3H8) is burned with stoichiometric amount of air in a water heater. The products of combustion are at 1 atm pressure and 1208F. What fraction of the water vapor in the products is vapor?

A coal from Utah which has an ultimate analysis (by mass) as 61.40 percent C, 5.79 percent H2, 25.31 percent O2, 1.09 percent N2, 1.41 percent S, and 5.00 percent ash (non-combustibles) is burned with 25 percent excess air in an industrial boiler. Assuming complete combustion and that the pressure in the boiler smokestack is 1 atm, calculate the minimum temperature, in 8C, of the combustion products before liquid water begins to form in the smokestack.

Methane fuel (CH4) is burned with 15 percent excess air in a space-heating furnace. The pressure in the chimney is 1 atm. Presuming complete combustion, determine the temperature of the combustion products at which liquid water will begin to form in the chimney.

A mixture of 40 percent by volume methane (CH4), and 60 percent by volume propane (C3H8), is burned completely with theoretical air and leaves the combustion chamber at 1008C. The products have a pressure of 100 kPa and are cooled at constant pressure to 398C. Sketch the T-s diagram for the water vapor that does not condense, if any. How much of the water formed during the combustion process will be condensed, in kmol H2O/kmol fuel?

A gaseous fuel mixture of 60 percent propane (C3H8), and 40 percent butane (C4H10), on a volume basis is burned in air such that the airfuel ratio is 19 kg air/kg fuel when the combustion process is complete. Determine (a) the moles of nitrogen in the air supplied to the combustion process, in kmol/kmol fuel, (b) the moles of water formed in the combustion process, in kmol/kmol fuel, and (c) the moles of oxygen in the product gases in kmol/kmol fuel.

A liquidgas fuel mixture consists of 90 percent octane (C8H18), and 10 percent alcohol (C2H5OH), by moles. This fuel is burned with 200 percent theoretical dry air. Write the balanced reaction equation for complete combustion of this fuel mixture. Determine (a) the theoretical airfuel ratio for this reaction, (b) the productfuel ratio for this reaction, (c) the air-flow rate for a fuel mixture flow rate of 5 kg/s, and (d) the lower heating value of the fuel mixture with 200 percent theoretical air at 258C.

A steady-flow combustion chamber is supplied with CO gas at 378C and 110 kPa at a rate of 0.4 m3 /min and air at 258C and 110 kPa at a rate of 1.5 kg/min. The combustion products leave the combustion chamber at 900 K. Assuming combustion is complete, determine the rate of heat transfer from the combustion chamber.

A 6-m3 rigid tank initially contains a mixture of 1 kmol of hydrogen (H2) gas and the stoichiometric amount of air at 258C. The contents of the tank are ignited, and all the hydrogen in the fuel burns to H2O. If the combustion products are cooled to 258C, determine (a) the fraction of the H2O that condenses and (b) the heat transfer from the combustion chamber during this process.

Ethanol gas (C2H6O) is burned with 110 percent theoretical air. During the combustion process, 90 percent of the carbon in the fuel is converted to CO2 and 10 percent is converted to CO. Determine (a) the theoretical kmols of O2 required for complete combustion of one kmol of ethanol, (b) the balanced combustion equation for the incomplete combustion process, and (c) the rate of heat transfer from the combustion process, in kW, when 3.5 kg/h of fuel are burned when the reactants and products are at 258C with the water in the products remaining a gas.

Propane gas (C3H8) enters a steady-flow combustion chamber at 1 atm and 258C and is burned with air that enters the combustion chamber at the same state. Determine the adiabatic flame temperature for (a) complete combustion with 100 percent theoretical air, (b) complete combustion with 200 percent theoretical air, and (c) incomplete combustion (some CO in the products) with 90 percent theoretical air

Determine the highest possible temperature that can be obtained when liquid gasoline (assumed C8H18) at 258C is burned steadily with air at 258C and 1 atm. What would your answer be if pure oxygen at 258C were used to burn the fuel instead of air?

Liquid propane (C3H8(,)) enters a combustion chamber at 258C and 1 atm at a rate of 0.4 kg/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 258C. The heat transfer from the combustion process is 53 kW. Write the balanced combustion equation and determine (a) the mass flow rate of air; (b) the average molar mass (molecular weight) of the product gases; (c) the average specific heat at constant pressure of the product gases; and (d) the tem per ature of the products of combustion.

Determine the work potential of 1 lbmol of diesel fuel (C12H26) at 778F and 1 atm in an environment at the same state.

n-Octane (C8H18) is burned with 30 percent excess air, with 10 percent of the carbon forming carbon monoxide. Determine the maximum work that can be produced, in kJ/kg fuel, when the air, fuel products are all at 258C and 1 atm.

A steam boiler heats liquid water at 2008C to superheated steam at 4 MPa and 4008C. Methane fuel (CH4) is burned at atmospheric pressure with 50 percent excess air. The fuel and air enter the boiler at 258C and the products of combustion leave at 2278C. Calculate (a) the amount of steam generated per unit of fuel mass burned, (b) the change in the exergy of the combustion streams, in kJ/kg fuel, (c) the change in the exergy of the steam stream, in kJ/kg steam, and (d) the lost work potential, in kJ/kg fuel. Take T0 5 258C.

Repeat Prob. 15108 using a coal from Utah which has an ultimate analysis (by mass) as 61.40 percent C, 5.79 percent H2, 25.31 percent O2, 1.09 percent N2, 1.41 percent S, and 5.00 percent ash (non-combustibles). Neglect the effect of the sulfur in the energy and entropy balances.

Liquid octane (C8H18) enters a steady-flow combustion chamber at 258C and 8 atm at a rate of 0.8 kg/min. It is burned with 200 percent excess air that is compressed and preheated to 500 K and 8 atm before entering the combustion chamber. After combustion, the products enter an adiabatic turbine at 1300 K and 8 atm and leave at 950 K and 2 atm. Assuming complete combustion and T0 5 258C, determine (a) the heat transfer rate from the combustion chamber, (b) the power output of the turbine, and (c) the reversible work and exergy destruction for the entire process.

Develop an expression for the higher heating value of a gaseous alkane CnH2n12 in terms of n.

The furnace of a particular power plant can be considered to consist of two chambers: an adiabatic combustion chamber where the fuel is burned completely and adiabatically, and a heat exchanger where heat is transferred to a Carnot heat engine isothermally. The combustion gases in the heat exchanger are well-mixed so that the heat exchanger is at a uniform temperature at all times that is equal to the temperature of the exiting product gases, Tp. The work output of the Carnot heat engine can be expressed as W 5 QhC 5 Qa1 2 T0 Tp b where Q is the magnitude of the heat transfer to the heat engine and T0 is the temperature of the environment. The work output of the Carnot engine will be zero either when Tp 5 Taf (which means the product gases will enter and exit the heat exchanger at the adiabatic flame temperature Taf, and thus Q 5 0) or when Tp 5 T0 (which means the temperature of the product gases in the heat exchanger will be T0, and thus hC 5 0), and will reach a maximum somewhere in between. Treating the combustion products as ideal gases with constant specific heats and assuming no change in their composition in the heat exchanger, show that the work output of the Carnot heat engine will be maximum when Tp 5 "TafT0 Also, show that the maximum work output of the Carnot engine in this case becomes Wmax 5 CTafa1 2 T0 Taf b 2 where C is a constant whose value depends on the composition of the product gases and their specific heats.

Consider the combustion of hydrocarbon fuel, CnHm, with excess theoretical air and incomplete combustion according to the chemical reaction as follows: CnHm 1 (1 1 B)Ath(O2 1 3.76 N2) S D CO2 1 E CO 1 F H2O 1 G O2 1 J N2 where Ath is the theoretical O2 required for this fuel and B is the excess amount of air in decimal form. If a is the fraction of carbon in the fuel converted to carbon dioxide and b is the remaining fraction converted to carbon monoxide, determine the coefficients Ath, D, E, F, G, and J for a fixed B amount of excess air. Write the coefficients D, E, F, G, and J as functions of n, m, a, b, B, and Ath in the simplest correct forms.

Consider the combustion of a mixture of an alcohol, CnHmOx, and a hydrocarbon fuel, CwHz, with excess theoretical air and incomplete combustion according to the chemical reaction as follows: y1CnHmOx 1 y2CwHz 1 (1 1 B)Ath(O2 1 3.76 N2) S D CO2 1 E CO 1 F H2O 1 G O2 1 J N2 where y1 and y2 are the mole fractions of the fuel mixture, Ath is the theoretical O2 required for this fuel, and B is the excess amount of air in decimal form. If a is the fraction of carbon in the fuel converted to carbon dioxide and b is the remaining fraction converted to carbon monoxide, determine the coefficients Ath, D, E, F, G, and J for a fixed B amount of excess air. Write the coefficients D, E, F, G, and J as functions of y1, y2, n, m, x, w, z, a, b, B, and Ath in the simplest correct forms.

Using EES (or other) software, determine the adiabatic flame temperature of the fuels CH4(g), C2H2(g), CH3OH(g), C3H8(g), C8H18(,). Assume both the fuel and the air enter the steady-flow combustion chamber at 258C.

Using EES (or other) software, determine the effect of the amount of air on the adiabatic flame temperature of liquid octane (C8H18). Assume both the air and the octane are initially at 258C. Determine the adiabatic flame temperature for 75, 90, 100, 120, 150, 200, 300, 500, and 800 percent theoretical air. Assume the hydrogen in the fuel always burns H2O and the carbon CO2, except when there is a deficiency of air. In the latter case, assume that part of the carbon forms CO. Plot the adiabatic flame temperature against the percent theoretical air, and discuss the results.

Using EES (or other) software, determine the fuel among CH4(g), C2H2(g), C2H6(g), C3H8(g), C8H18(,) that gives the highest temperature when burned completely in an adiabatic constant-volume chamber with the theoretical amount of air. Assume the reactants are at the standard reference state.

Using EES (or other) software, write a general program to determine the heat transfer during the complete combustion of a hydrocarbon fuel (CnHm) at 258C in a steady-flow combustion chamber when the percent of excess air and the temperatures of air and the products are specified. As a sample case, determine the heat transfer per unit mass of fuel as liquid propane (C3H8) is burned steadily with 50 percent excess air at 258C and the com bustion products leave the combustion chamber at 1800 K.

Using EES (or other) software, determine the rate of heat transfer for the fuels CH4(g), C2H2(g), CH3OH(g), C3H8(g), and C8H18(,) when they are burned completely in a steady-flow combustion chamber with the theoretical amount of air. Assume the reactants enter the combustion chamber at 298 K and the products leave at 1200 K.

Using EES (or other) software, repeat Prob. 15119 for (a) 50, (b) 100, and (c) 200 percent excess air.

A fuel is burned steadily in a combustion chamber. The combustion temperature will be the highest except when (a) the fuel is preheated. (b) the fuel is burned with a deficiency of air. (c) the air is dry. (d) the combustion chamber is well insulated. (e) the combustion is complete.

A fuel is burned with 70 percent theoretical air. This is equivalent to (a) 30% excess air (b) 70% excess air (c) 30% deficiency of air (d) 70% deficiency of air (e) stoichiometric amount of air

Propane (C3H8) is burned with 150 percent theoretical air. The airfuel mass ratio for this combustion process is (a) 5.3 (b) 10.5 (c) 15.7 (d) 23.4 (e) 39.3

One kmol of methane (CH4) is burned with an unknown amount of air during a combustion process. If the combustion is complete and there are 1 kmol of free O2 in the products, the airfuel mass ratio is (a) 34.6 (b) 25.7 (c) 17.2 (d ) 14.3 (e) 11.9

An equimolar mixture of carbon dioxide and water vapor at 1 atm and 608C enter a dehumidifying section where the entire water vapor is condensed and removed from the mixture, and the carbon dioxide leaves at 1 atm and 608C. The entropy change of carbon dioxide in the dehumidifying section is (a) 22.8 kJ/kgK (b) 20.13 kJ/kgK (c) 0 (d) 0.13 kJ/kgK (e) 2.8 kJ/kgK

Methane (CH4) is burned completely with 80 percent excess air during a steady-flow combustion process. If both the reactants and the products are maintained at 258C and 1 atm and the water in the products exists in the liquid form, the heat transfer from the combustion chamber per unit mass of methane is (a) 890 MJ/kg (b) 802 MJ/kg (c) 75 MJ/kg (d) 56 MJ/kg (e) 50 MJ/kg

The higher heating value of a hydrocarbon fuel CnHm with m 5 8 is given to be 1560 MJ/kmol of fuel. Then its lower heating value is (a) 1384 MJ/kmol (b) 1208 MJ/kmol (c) 1402 MJ/kmol (d) 1514 MJ/kmol (e) 1551 MJ/kmol

Acetylene gas (C2H2) is burned completely during a steady-flow combustion process. The fuel and the air enter the combustion chamber at 258C, and the products leave at 1500 K. If the enthalpy of the products relative to the standard reference state is 2404 MJ/kmol of fuel, the heat transfer from the combustion chamber is (a) 177 MJ/kmol (b) 227 MJ/kmol (c) 404 MJ/kmol (d) 631 MJ/kmol (e) 751 MJ/kmol

Benzene gas (C6H6) is burned with 95 percent theoretical air during a steady-flow combustion process. The mole fraction of the CO in the products is (a) 8.3% (b) 4.7% (c) 2.1% (d) 1.9% (e) 14.3%

A fuel is burned during a steady-flow combustion process. Heat is lost to the surroundings at 300 K at a rate of 1120 kW. The entropy of the reactants entering per unit time is 17 kW/K and that of the products is 15 kW/K. The total rate of exergy destruction during this combustion process is (a) 520 kW (b) 600 kW (c) 1120 kW (d) 340 kW (e) 739 kW

Design a combustion process suitable for use in a gas-turbine engine. Discuss possible fuel selections for the several applications of the engine.

A promising method of power generation by direct energy conversion is through the use of magnetohydrodynamic (MHD) generators. Write an essay on the current status of MHD generators. Explain their operation principles and how they differ from conventional power plants. Discuss the problems that need to be overcome before MHD generators can become economical

What is oxygenated fuel? How would the heating value of oxygenated fuels compare to those of comparable hydrocarbon fuels on a unit-mass basis? Why is the use of oxygenated fuels mandated in some major cities in winter months?

The safe disposal of hazardous waste material is a major environmental concern for industrialized societies and creates challenging problems for engineers. The disposal methods commonly used include landfilling, burying in the ground, recycling, and incineration or burning. Incineration is frequently used as a practical means for the disposal of combustible waste such as organic materials. The EPA regulations require that the waste material be burned almost completely above a specified temperature without polluting the environment. Maintaining the temperature above a certain level, typically about 11008C, necessitates the use of a fuel when the combustion of the waste material alone is not sufficient to obtain the minimum specified temperature. A certain industrial process generates a liquid solution of ethanol and water as the waste product at a rate of 10 kg/s. The mass fraction of ethanol in the solution is 0.2. This solution is to be burned using methane (CH4) in a steady-flow combustion chamber. Propose a combustion process that will accomplish this task with a minimal amount of methane. State your assumptions.

Constant-volume vessels that contain flammable mixtures of hydrocarbon vapors and air at low pressures are frequently used. Although the ignition of such mixtures is very unlikely as there is no source of ignition in the tank, the Safety and Design Codes require that the tank withstand four times the pressure that may occur should an explosion take place in the tank. For operating gauge pressures under 25 kPa, determine the pressure for which these vessels must be designed in order to meet the requirements of the codes for (a) acetylene C2H2(g), (b) propane C3H8(g), and (c) n-octane C8H18(g). Justify any assumptions that you make.

An electrical utility uses a Pennsylvania coal which has an ultimate analysis (by mass) as 84.36 percent C, 1.89 percent H2, 4.40 percent O2, 0.63 percent N2, 0.89 percent S, and 7.83 percent ash (non-combustibles) as fuel for its boilers. The utility is changing from the Pennsylvania coal to an Illinois coal which has an ultimate analysis (by mass) as 67.40 percent C, 5.31 percent H2, 15.11 percent O2, 1.44 percent N2, 2.36 percent S, and 8.38 percent ash (non-combustibles) as fuel for its boilers. With the Pennsylvania coal, the boilers used 15 percent excess air. Develop a schedule for the new coal showing the heat released, the smokestack dew-point temperature, adiabatic flame temperature, and carbon dioxide production for various amount of excess air. Use this schedule to determine how to operate with the new coal as closely as possible to the conditions of the old coal. Is there anything else that will have to be changed to use the new coal?