Solved: What is sensible heat? How is the sensible heat

Problem 3P Can the water vapor in air be treated as an ideal gas? Explain.

Problem 5P Is it possible to obtain saturated air from unsaturated air without adding any moisture? Explain.

Problem 1P What is the difference between dry air and atmospheric air?

Problem 149P Air at a total pressure of 90 kPa, 15°C, and 75 percent relative humidity is heated and humidified to 25°C and 75 percent relative humidity by introducing water vapor. If the mass flow rate of dry air is 4 kg/s, the rate at which steam is added to the air is (a) 0.032 kg/s ________________ (b) 0.013 kg/s ________________ (c) 0.019 kg/s ________________ (d) 0.0079 kg/s ________________ (e) 0 kg/s

Problem 2P What is the difference between the specific humidity and the relative humidity?

Problem 6P Moist air is passed through a cooling section where it is cooled and dehumidified. How do (a) the specific humidity and (b) the relative humidity of air change during this process?

Problem 4P Is the relative humidity of saturated air necessarily 100 percent?

Problem 7P How will (a) the specific humidity and (b) the relative humidity of the air contained in a well-sealed room change as it is heated?

Problem 8P How will (a) the specific humidity and (b) the relative humidity of the air contained in a well-sealed room change as it is cooled?

Problem 9P Consider a tank that contains moist air at 3 atm and whose walls are permeable to water vapor. The surrounding air at 1 atm pressure also contains some moisture. Is it possible for the water vapor to flow into the tank from surroundings? Explain.

Problem 10P Why are the chilled water lines always wrapped with vapor barrier jackets?

Problem 11P A tank contains 15 kg of dry air and 0.17 kg of water vapor at 30°C and 100 kPa total pressure. Determine (a) the specific humidity, (b) the relative humidity, and (c) the volume of the tank.

Problem 14P Repeat Prob. 14–15 for a pressure of 85kPa.

Problem 15P A room contains air at 85°F and 13.5 psia at a relative humidity of 60 percent. Determine (a) the partial pressure of dry air, (b) the specific humidity, and (c) the enthalpy per unit mass of dry air.

Problem 16P An 8 m3-tank contains saturated air at 30°C, 105 kPa. Determine (a) the mass of dry air, (b) the specific humidity, and (c) the enthalpy of the air per unit mass of the dry air.

Problem 17P Determine the masses of dry air and the water vapor contained in a 90-m3 room at 93 kPa, 26°C, and 50 percent relative humidity.

Problem 12P Repeat Prob. 14–11 for a temperature of 20°C. Problem 14–11 A tank contains 15 kg of dry air and 0.17 kg of water vapor at 30°C and 100 kPa total pressure. Determine (a) the specific humidity, (b) the relative humidity, and (c) the volume of the tank.

Humid air at 100 kPa, \(20^{\circ} \mathrm{C}\), and 90 percent relative humidity is compressed in a steady-flow, isentropic compressor to 800 kPa. What is the relative humidity of the air at the compressor outlet? Equation Transcription: Text Transcription: 20°C

Problem 19P What is the dew-point temperature?

Problem 13P A room contains air at 20°C and 98 kPa at a relative humidity of 85 percent. Determine (a) the partial pressure of dry air, (b) the specific humidity of the air, and (c) the enthalpy per unit mass of dry air.

Problem 20P Andy and Wendy both wear glasses. On a cold winter day, Andy comes from the cold outside and enters the warm house while Wendy leaves the house and goes outside. Whose glasses are more likely to be fogged? Explain.

Problem 21P In summer, the outer surface of a glass filled with iced water frequently “sweats.” How can you explain this sweating?

Problem 22P In some climates, cleaning the ice off the windshield of a car is a common chore on winter mornings. Explain how ice forms on the windshield during some nights even when there is no rain or snow.

Problem 23P When are the dry-bulb and dew-point temperatures identical?

Problem 25P After a long walk in the 12?C outdoors, a person wearing glasses enters a room at 25?C and 55 percent relative humidity. Determine whether the glasses will become fogged.

Problem 24P When are the adiabatic saturation and wet-bulb temperatures equivalent for atmospheric air?

Problem 26P Repeat Prob. 14?28 for a relative humidity of 30 percent.

Problem 27P A thirsty woman opens the refrigerator and picks up a cool canned drink at 40°F. Do you think the can will "sweat" as she enjoys the drink in a room at 70°F and 38 percent relative humidity?

Problem 29P The air in a room has a dry-bulb temperature of 26°C and a wet-bulb temperature of 21°C. Assuming a pressure of 100 kPa, determine (a) the specific humidity, (b) the relative humidity, and (c) the dew-point temperature.

Reconsider Prob. 14–29. Determine the required properties using EES (or other) software. What would the property values be at a pressure of 300 kPa?

Problem 28P The dry- and wet-bulb temperatures of atmospheric air at 95 kPa are 25 and 17°C, respectively. Determine (a) the specific humidity, (b) the relative humidity, and (c) the enthalpy of the air, in kJ/kg dry air.

Problem 32P Atmospheric air at 35°C flows steadily into an adiabatic saturation device and leaves as a saturated mixture at 25°C. Makeup water is supplied to the device at 25°C. Atmospheric pressure is 98 kPa. Determine the relative humidity and specific humidity of the air.

Problem 31P The air in a room has a dry-bulb temperature of 75°F and a wet-bulb temperature of 65°F. Assuming a pressure of 14.3 psia, determine (a) the specific humidity, (b) the relative humidity, and (c) the dew-point temperature.

Problem 33P How do constant-enthalpy and constant-wet-bulb-temperature lines compare on the psychrometric chart?

Problem 34P At what states on the psychrometric chart are the dry-bulb, wet-bulb, and dew-point temperatures identical?

Problem 35P How is the dew-point temperature at a specified state determined on the psychrometric chart?

Problem 36P Can the enthalpy values- determined from a psychrometric chart at sea level be used at higher elevations?

Problem 39P The air in a room has a pressure of 1 atm, a dry-bulb temperature of 24°C, and a wet-bulb temperature of 17°C. Using the psychrometric chart, determine (a) the specific humidity, (b) the enthalpy, in kJ/kg dry air, (c) the relative humidity, (d) the dew-point temperature, and (e) the specific volume of the air, in m3/kg dry air.

Reconsider Prob. 14–39. Determine the required properties using EES (or other) software instead of the psychrometric chart. What would the property values be at a location at 3000 m altitude?

Problem 37P A room contains air at 1 atm, 82°F, and 70 percent relative humidity. Using the psychrometric chart, determine (a) the specific humidity, (b) the enthalpy (in Btu/lbm dry air), (c) the wet-bulb temperature, (d) the dew-point temperature, and (e) the specific volume of the air (in ft3/lbm dry air).

Atmospheric air at a pressure of 1 atm and dry-bulb temperature of \(28^{\circ} \mathrm{C}\) has a wet-bulb temperature of \(20^{\circ} \mathrm{C}\). Using the psychrometric chart, determine (a) the relative humidity, (b) the humidity ratio, (c) the enthalpy, (d) the dew-point temperature, and (e) the water vapor pressure. Equation Transcription: Text Transcription: 28°C 20°C

Determine the adiabatic saturation temperature of the humid air in Prob. 14–41.

Determine the adiabatic saturation temperature of the humid air in Prob. 14–43E.

Problem 45P What does a modern air-conditioning system do besides heating or cooling the air? ,

Problem 43P Atmospheric air at a pressure of 1 atm and dry-bulb temperature of 90°F has a dew-point temperature of 75°F. Using the psychrometric chart, determine (a) the relative humidity, (b) the humidity ratio, (c) the enthalpy, (d) the wet-bulb temperature, and (e) the water vapor pressure.

Problem 46P How does the human body respond to (a) ho weather, (b) cold weather, and (c) hot and humid weather?

Problem 47P What is the radiation effect? How does it affect human comfort?

Problem 50P Why do you think little babies are more susceptible to cold?

Problem 49P Consider a tennis match in cold weather where both players and spectators wear the same clothes. Which group of people will feel colder? Why?

Problem 48P How does the air motion in the vicinity of the human body affect human comfort?

Problem 52P What are humidification and dehumidification?

Problem 51P How does humidity affect human comfort?

Problem 53P What is metabolism? What is the range of metabolic rate for an average man? Why are we interested in the metabolic rate of the occupants of a building when we deal with heating and air-conditioning?

Problem 54P What is sensible heat? How is the sensible heat loss from a human body affected by the (a) skin temperature, (b) environment temperature, and (c) air motion?

Problem 55P What is latent heat? How is the latent heat loss from the human body affected by the (a) skin wettedness and (b) relative humidity of the environment? How is the rate of evaporation from the body related to the rate of latent heat loss? ,

Problem 59P Repeat Prob. 14–58 for an infiltration rate of 1.8 ACH. Problem 14–58 For an infiltration rate of 1.2 air changes per hour (ACH), determine sensible, latent, and total infiltration heat load of a building at sea level, in kW, that is 20 m long, 13 m wide, and 3 m high when the outdoor air is at 32°C and 35 percent relative humidity. The building is maintained at 24°C and 55 percent relative humidity at all times.

Problem 60P An average person produces 0.25 kg of moisture while taking a shower and 0.05 kg while bathing in a tub. Consider a family of four who each shower once a day in a bathroom that is not ventilated. Taking the heat of vaporization of water to be 2450 kJ/kg, determine the contribution of showers to the latent heat load of the air conditioner per day in summer.

Problem 56P A department store expects to have 225 customers and 20 employees at peak times in summer. Determine the contribution of people to the total cooling load of the store.

Problem 57P In a movie theater in winter, 500 people, each generating sensible heat at a rate of 70 W, are watching a movie. The heat losses through the walls, windows, and the roof are estimated to be 130,000 Btu/h. Determine if the theater needs to be heated or cooled.

Problem 58P For an infiltration rate of 1.2 air changes per hour (ACH), determine sensible, latent, and total infiltration heat load of a building at sea level, in kW, that is 20 m long, 13 m wide, and 3 m high when the outdoor air is at 32°C and 35 percent relative humidity. The building is maintained at 24°C and 55 percent relative humidity at all times.

Problem 61P An average (1.82 kg or 4.0 Ibm) chicken has a basal metabolic rate of 5:47 W and an average metabolic rate of 10.2 W (3.78 W sensible and 6.42 W latent) during normal activity. If there are 100 chickens in a breeding room, determine the rate of total heat generation and the rate of moisture production in the room. Take the heat of vaporization of water to be 2430 kJ/kg.

Problem 62P How do relative and specific humidities change during a simple heating process? Answer the same question for a simple cooling process.

Problem 63P Why does a simple heating or cooling process appear as a horizontal line on the psychrometric chart?

Problem 65P Humid air at 1 atm, 35°C, and 45 percent relative humidity is cooled at constant pressure to the dew-point temperature. Determine the cooling, in kJ/kg dry air, required for this process.

Problem 64P Air enters a heating section at 95 kPa, 12°C, and 30 percent relative humidity at a rate of 6 m3/min, and it leaves at 25°C. Determine (a) the rate of heat transfer in the heating section and (b) the relative humidity of the air at the exit.

Air enters a 30-cm-diameter cooling section at 1 atm, \(35^{\circ} \mathrm{C}\), and 45 percent relative humidity at \(18 \mathrm{~m} / \mathrm{s}\). Heat is removed from the air at a rate of \(750 \mathrm{~kJ} / \mathrm{min}\). Determine (a) the exit temperature, (b) the exit relative humidity of the air, and (c) the exit velocity. Equation Transcription: Text Transcription: 35°C 18 m/s 750 kJ/min

Problem 66P Humid air at 40 psia, 50°F, and 90 percent relative humidity is heated in a pipe at constant pressure to 120°F. Calculate the relative humidity at the pipe outlet and the amount of heat, in Btu/lbm dry air, required.

Problem 68P Repeat Prob. 14–67 for a heat removal rate of 950 kJ/min. Problem 14–67 Air enters a 30-cm-diameter cooling section at 1 atm, 35°C, and 45 percent relative humidity at 18 m/s. Heat is removed from the air at a rate of 750 kJ/min. Determine (a) the exit temperature, (b) the exit relative humidity of the air, and (c) the exit velocity.

Problem 69P A heating section consists of a 15-in-diameter duct that houses a 4-kW electric resistance heater. Air enters the heating section at 14.7 psia, 50°F, and 40 percent relative humidity at a velocity of 25 ft/s. Determine (a) the exit temperature, (b) the exit relative humidity of the air, and (c) the exit velocity.

Problem 70P Why is heated air sometimes humidified?

Problem 72P Air at 14.7 psia, 35°F, and 50 percent relative humidity is first heated to 65°F in a heating section and then humidified by introducing water vapor. The air leaves the humidifying section at 75°F and 55 percent relative humidity. Determine (a) the amount of steam added to the air, in lbm H2O/lbm dry air, and (b) the amount of heat transfer to the air in the heating section, in Btu/lbm dry air.

Problem 71P Air at 1 atm, 15°C, and 60 percent relative humidity is first heated to 20°C in a heating section and then humidified by introducing water vapor. The air leaves the humidifying section at 25°C and 65 percent relative humidity. Determine (a) the amount of steam added to the air, and (b) the amount of heat transfer to the air in the heating section.

Problem 74P Repeat Prob. 14–78 for a total pressure of 95 kPa for the airstream.

Problem 75P Why is cooled air sometimes reheated in summer before it is discharged to a room?

An air-conditioning system operates at a total pressure of \(1 \mathrm{~atm}\) and consists of a heating section and a humidifier that supplies wet steam (saturated water vapor) at \(100^{\circ} \mathrm{C}\). Air enters the heating section at \(10^{\circ} \mathrm{C}\) and 70 percent relative humidity at a rate of \(35 \mathrm{~m}^{3} / \mathrm{min}\), and it leaves the humidifying section at \(208 \mathrm{C}\) and 60 percent relative humidity. Determine (a) the temperature and relative humidity of air when it leaves the heating section, (b) the rate of heat transfer in the heating section, and (c) the rate at which water is added to the air in the humidifying section. Equation Transcription: Text Transcription: 1 atm 100^circC 10^circC 35 m^3/min 208 C

Problem 76P Air enters a window air conditioner at 1 atm, 32°C, and 70 percent relative humidity at a rate of 2 m3/min, and it leaves as saturated air at 15°C. Part of the moisture in the air that condenses during the process is also removed at 15°C. Determine the rates of heat and moisture removal from the air.

Problem 80P Repeat Prob. 14–86 for a total pressure of 95 kPa for air.

Humid atmospheric air at \(1 \mathrm{~atm}, 90^{\circ} \mathrm{F}\), and 90 percent relative humidity is cooled to \(50^{\circ} \mathrm{F}\) while the mixture pressure remains constant. Calculate the amount of water, in \(\mathrm{lbm} / \mathrm{lbm}\) dry air, removed from the air and the cooling requirement, in Btu/lbm dry air, when the liquid water leaves the system at \(60^{\circ} \mathrm{F}\). Equation Transcription: Text Transcription: 1 atm 90^circF 50^circF lbm/lbm 60^circF

Problem 81P Air enters a 1-ft-diameter cooling section at 14.7 psia, 90°F, and 60 percent relative humidity at 600 ft/min. The air is cooled by passing it over a cooling coil through which cold water flows. The water experiences a temperature rise of 14°F. The air leaves the cooling section saturated at 70°F. Determine (a) the rate of heat transfer, (b) the mass flow rate of the water, and (c) the exit velocity of the airstream.

Problem 83P Repeat Prob. 14–81E for a total pressure of 14.4 psia for air. Problem 14–81E Air enters a 1-ft-diameter cooling section at 14.7 psia, 90°F, and 60 percent relative humidity at 600 ft/min. The air is cooled by passing it over a cooling coil through which cold water flows. The water experiences a temperature rise of 14°F. The air leaves the cooling section saturated at 70°F. Determine (a) the rate of heat transfer, (b) the mass flow rate of the water, and (c) the exit velocity of the airstream.

Air enters a 40 -cm-diameter cooling section at \(1 \mathrm{~atm}, 32^{\circ} \mathrm{C}\), and 70 percent relative humidity at \(120 \mathrm{~m} / \mathrm{min}\). The air is cooled by passing it over a cooling coil through which cold water flows. The water experiences a temperature rise of \(6^{\circ} \mathrm{C}\). The air leaves the cooling section saturated at \(20^{\circ} \mathrm{C}\). Determine (a) the rate of heat transfer, (b) the mass flow rate of the water, and (c) the exit velocity of the airstream. Equation Transcription: Text Transcription: 1 atm 32^circC 120 m/min 36^circC 20^circC

Problem 84P Air from a workspace enters an air conditioner unit at 30°C dry bulb and 20°C wet bulb. The air leaves the air conditioner and returns to the space at 20°C dry-bulb and 6.5°C dew-point temperature. If there is any, the condensate leaves the air conditioner at the temperature of the air leaving the cooling coils. The volume flow rate of the air returned to the workspace is 800 m3/min. Atmospheric pressure is 101 kPa. Determine the heat transfer rate from the air, in kW, and the mass flow rate of condensate water, if any, in kg/h.

Atmospheric air from the inside of an automobile enters the evaporator section of the air conditioner at \(1 \mathrm{~atm}, 27^{\circ} \mathrm{C}\) and 50 percent relative humidity. The air returns to the automobile at \(10^{\circ} \mathrm{C}\) and 90 percent relative humidity. The passenger compartment has a volume of \(2 \mathrm{~m}^{3}\) and 5 air changes per minute are required to maintain the inside of the automobile at the desired comfort level. Sketch the psychrometric diagram for the atmospheric air flowing through the air conditioning process. Determine the dew point and wet bulb temperatures at the inlet to the evaporator section, in \({ }^{\circ} \mathrm{C}\). Determine the required heat transfer rate from the atmospheric air to the evaporator fluid, in kW. Determine the rate of condensation of water vapor in the evaporator section, in \(\mathrm{kg} / \mathrm{min}\). Equation Transcription: Text Transcription: 1 atm 27^circC 10^circC 2 m^3 ^circC kg/min

Atmospheric air at \(1 \mathrm{~atm}, 32^{\circ} \mathrm{C}\), and 95 percent relative humidity is cooled to \(24^{\circ} \mathrm{C}\) and 60 percent relative humidity. A simple ideal vapor-compression refrigeration system using refrigerant-134a as the working fluid is used to provide the cooling required. It operates its evaporator at \(4^{\circ} \mathrm{C}$\) and its condenser at a saturation temperature of \(39.4^{\circ} \mathrm{C}\). The condenser rejects its heat to the atmospheric air. Calculate the exergy destruction, in kJ, in the total system per \(1000 \mathrm{~m}^{3}\) of dry air processed. Equation Transcription: Text Transcription: 1 atm 32^circC 24^circC 4^circC 39.4^circC 1000 m^3

Humid air is to be conditioned in a constant pressure process at \(1 \mathrm{~atm}\) from \(39^{\circ} \mathrm{C}\) dry bulb and 50 percent relative humidity to \(17^{\circ} \mathrm{C}\) dry bulb and \(10.8^{\circ} \mathrm{C}\) wet bulb. The air is first passed over cooling coils to remove all of the moisture necessary to achieve the final moisture content and then is passed over heating coils to achieve the final state. (a) Sketch the psychometric diagram for the process. (b) Determine the dew point temperature of the mixture at the inlet of the cooling coils and at the inlet of the heating coils. (c) What is the net heat transfer for the entire process for this process, in kJ/kg dry air? Equation Transcription: Text Transcription: 1 atm 39^circC 17^circC 10.8^circC

Problem 88P What is evaporative cooling? Will it work in humid climates?

Problem 89P During evaporation from awater body to air, under what conditions will the latent heat of vaporization be equal to the heat transfer from the air?

Problem 91P Air enters an evaporative cooler at 95 kPa, 40°C, and 25 percent relative humidity and exits saturated. Determine the exit temperature of air.

Problem 90P Does an evaporation process have to involve heat transfer? Describe a process that involves both heat and mass transfer.

Problem 92P Air enters an evaporative cooler at 14.5 psia, 93°F, and 30 percent relative humidity and exits saturated. Determine the exit temperature of air.

Problem 93P Air enters an evaporative cooler at 1 atm, 40°C, and 20 percent relative humidity at a rate of 7 m3/min, and it leaves with a relative humidity of 90 percent. Determine (a) the exit temperature of the air and (b) the required rate of water supply to the evaporative cooler.

Problem 96P Two unsaturated airstreams are mixed adiabatically. It is observed that some moisture condenses during the mixing process. Under what conditions will this be the case?

Problem 98P During an air-conditioning process, 900 ft3/min of conditioned air at 65°F and 30 percent relative humidity is mixed adiabatically with 300 ft3/min of outside air at 80°F and 90 percent relative humidity at a pressure of 1 atm. Determine (a) the temperature, (b) the specific humidity, and (c) the relative humidity of the mixture.

Problem 97P Consider the adiabatic mixing of two airstreams. Does the state of the mixture on the psychrometric chart have to be on the straight line connecting the two states?

Problem 95P Air at 1atm, 20°C, and 50 percent relative humidity is first heated to 35°C in a heating section and then passed through an evaporative cooler where its temperature drops to 25°C. Determine (a) the exit relative humidity and (b) the amount of water added to air, in kg H2O/kg dry air.

Two airstreams are mixed steadily and adiabatically. The first stream enters at \(35^{\circ} \mathrm{C}\) and 30 percent relative humidity at a rate of \(15 \mathrm{~m}^{3} / \mathrm{min}\), while the second stream enters at \(12^{\circ} \mathrm{C}\) and 90 percent relative humidity at a rate of \(25 \mathrm{~m}^{3} / \mathrm{min}\). Assuming that the mixing process occurs at a pressure of \(1 \mathrm{~atm}\), determine the specific humidity, the relative humidity, the dry-bulb temperature, and the volume flow rate of the mixture. Equation Transcription: Text Transcription: 35^circC 15 m^3/min 125^circC 25 m^3/min 1 atm

Problem 94P Air enters an evaporative cooler at 1 atm, 32°C, and 30 percent relative humidity at a rate of 5 m3/min and leaves at22°C. Determine (a) the final relative humidity and (b) the amount ofwater added to air.

Problem 102P A stream of warm air with a dry-bulb temperature of 36°C and a wet-bulb temperature of 30°C is mixed adiabatically with a stream of saturated cool air at 12°C. The dry air mass flow rates of the warm and cool airstreams are 8 and 10 kg/s, respectively. Assuming a total pressure of 1 atm, determine (a) the temperature, (b) the specific humidity, and (c) the relative humidity of the mixture.

Problem 104P Saturated humid air at 1 atm and 50°F is to be mixed with atmospheric air at 1 atm, 90°F, and 80 percent relative humidity, to form air at 70°F Determine the proportions at which these two streams are to be mixed and the relative humidity of the resulting air.

Repeat Prob. 14-100 for a total mixing-chamber pressure of \(90 \mathrm{kPa}\). Equation Transcription: Text Transcription: 90 kPa

Problem 106P What is a spray pond? How does its performance compare to the performance of a wet cooling tower?

Problem 105P How does a natural-draft wet cooling tower work?

Problem 107P he cooling water from the condenser of a power plant enters a wet cooling tower at 40°C at a rate of 90 kg/s. The water is cooled to 25°C in the cooling tower by air that enters the tower at 1 atm, 23°C, and 60 percent relative humidity and leaves saturated at 32°C. Neglecting the power input to the fan, determine (a) the volume flow rate of air into the cooling tower and (b) the mass flow rate of the required makeup water.

Problem 108P The cooling water from the condenser of a power plant enters a wet cooling tower at 110°F at a rate of 100 lbm/s. Water is cooled to 80°F in the cooling tower by air that enters the tower at 1 atm, 76°F, and 60 percent relative humidity and leaves saturated at 95°F. Neglecting the power input to the fan, determine (a) the volume flow rate of air into the cooling tower and (b) the mass flow rate of the required makeup water

Problem 110P A wet cooling tower is to cool 25 kg/s of cooling water from 40 to 30°C at a location where the atmospheric pressure is 96 kPa. Atmospheric air enters the tower at 20°C and 70 percent relative humidity and leaves saturated at 35°C. Neglecting the power input to the fan, determine (a) the volume flow rate of air into the cooling tower and (b) the mass flow rate of the required makeup water.

Problem 111P Water enters a cooling tower at 95?F and at a rate of 3 lbm/s, and leaves at 80?F. Humid air enters this tower at 1 atm and 65?F with a relative humidity of 30 percent and leaves at 75?F with relative humidity of 80 percent. Determine the mass flow rate of dry air through this tower.

Problem 112P How much work potential, in Btu/lbm dry air, is lost in the cooling tower of Prob. 14-118E. Take To =65?F.

Problem 113P Dry air whose molar analysis is 78.1 percent N2, 20.9 percent O2, and 1 percent Ar flows over a water body until it is saturated. If the pressure and temperature of air remain constant at 1 atm and 25°C during the process, determine (a) the molar analysis of the saturated air and (b) the density of air before and after the process. What do you conclude from your results?

A wet cooling tower is to cool \(60 \mathrm{~kg} / \mathrm{s}\) of water from 40 to \(33^{\circ} \mathrm{C}\). Atmospheric air enters the tower at \(1 \mathrm{~atm}\) with dry-and wet-bulb temperatures of 22 and \(16^{\circ} \mathrm{C}\), respectively, and leaves at \(30^{\circ} \mathrm{C}\) with a relative humidity of 95 percent. Using the psychrometric chart, determine (a) the volume flow rate of air into the cooling tower and (b) the mass flow rate of the required makeup water. Equation Transcription: Text Transcription: 60 kg/s 33^circC 1 atm 16^circC 30^circC

Problem 115P The condensation of the water vapor in compressed-air lines is a major concern in industrial facilities, and the compressed air is often dehumidified to avoid the problems associated with condensation. Consider a compressor that compresses ambient air from the local atmospheric pressure of 92 kPa to a pressure of 800 kPa (absolute). The compressed air is then cooled to the ambient temperature as it flows through the compressed-air lines. Disregarding any pressure losses, determine if there will be any condensation in the compressed-air lines on a day when the ambient air is at 20°C and 50 percent relative humidity.

Problem 114P The relative humidity of air at 80°F and 14.7 psia is increased from 25 to 75 percent during a humidification process at constant temperature and pressure. Determine the percent error involved in assuming the density of air to have remained constant.

Problem 117P A cooling tower with a cooling capacity of 30 tons (105 kW) is claimed to evaporate 4000 kg of water per day. Is this a reasonable claim?

Problem 116P The capacity of evaporative coolers is usually expressed in terms of the flow rate of air in ft3/min (or cfm), and a practical way of determining the required size of an evaporative cooler for an 8-ft-high house is to multiply the floor area of the house by 4 (by 3 in dry climates and by 5 in humid climates). For example, the capacity of an evaporative cooler for a 30-ft-long, 40-ft-wide house is 1200 × 4 = 4800 cfm. Develop an equivalent rule of thumb for the selection of an evaporative cooler in SI units for 2.4-m-high houses whose floor areas are given in m2.

Problem 119P The thermostat setting of a house can be lowered by 2°F by wearing a light long-sleeved sweater, or by 4°F by level of comfort. If each °F reduction in thermostat setting reduces the heating cost of a house by 4 percent at a particular location, determine how much the heating costs of a house can be reduced by wearing heavy sweaters if the annual heating cost of the house is $600.

Problem 120P A typical winter day in Moscow has a temperature of 0°C and a relative humidity of 40 percent. What is the relative humidity inside a dacha that has air that has been heated to 18°C?

Problem 118P The air-conditioning costs of a house can be reduced by up to 10 percent by installing the outdoor unit (the condenser) of the air conditioner at a location shaded by trees and shrubs. If the air-conditioning costs of a house are $500 a year, determine how much the trees will save the home owner in the 20-year life of the system.

Problem 121P The relative humidity inside dacha of Prob. 14–120 is to be brought to 50 percent by evaporating water at 20°C. How much heat, in kJ, is required for this purpose per m3 of air in the dacha?

During a summer day in Phoenix, Arizona, the air is at \(1 \mathrm{~atm}, 110^{\circ} \mathrm{F}\), and 15 percent relative humidity. Water at \(70^{\circ} \mathrm{F}\) is evaporated into this air to produce air at \(75^{\circ} \mathrm{F}\) and 80 percent relative humidity. How much water, in \(\mathrm{lbm} / \mathrm{lbm}\) dry air, is required and how much cooling, in Btu/lbm dry air, has been produced? Equation Transcription: Text Transcription: 1 atm 110^circF 70^circF 75^circF lbm/lbm

Problem 124P A 1.8-m3 tank contains saturated air at 20°C and 90 kPa. Determine (a) the mass of the dry air, (b) the specific humidity, and (c) the enthalpy of the air per unit mass of the dry air.

Problem 123P If the system of Prob. 14-129E is operated as an adiabatic system and the air produced by this system has a relative humidity of 70 percent, what is the temperature of the air produced?

Reconsider Prob. 14-124. Using EES (or other) software, determine the properties of the air at the initial state. Study the effect of heating the air at constant volume until the pressure is \(110 \mathrm{kPa}\). Plot the required heat transfer, in \(\mathrm{kJ}\), as a function of pressure. Equation Transcription: Text Transcription: 110 kPa kJ

Problem 127P Air flows steadily through an isentropic nozzle. The air enters the nozzle at 35°C, 200 kPa and 50 percent relative humidity. If no condensation is to occur during the expansion process, determine the pressure, temperature, and velocity of the air at the nozzle exit.

Problem 126P Air at 15 psia, 60°F, and 70 percent relative humidity flows in an 6-in diameter duct at a velocity of 35 ft/s. Determine (a) the dew-point temperature, (b) the volume flow rate of air, and (c) the mass flow rate of dry air.

Problem 128P Air enters a cooling section at 97 kPa, 35°C, and 30 percent relative humidity at a rate of 6 m3/min, where it is cooled until the moisture in the air starts condensing. Determine (a) the temperature of the air at the exit and (b) the rate of heat transfer in the cooling section.

Problem 129P Outdoor air enters an air-conditioning system at 10°C and 70 percent relative humidity at a steady rate of 26 m3/min, and it leaves at 25°C and 55 percent relative humidity. The outdoor air is first heated to 18°C in the heating section and then humidified by the injection of hot steam in the humidifying section. Assuming the entire process takes place at a pressure of 1 atm, determine (a) the rate of heat supply in the heating section and (b) the mass flow rate of steam required in the humidifying section.

Problem 131P Air enters an air-conditioning system that uses refrigerant-134a at 30°C and 70 percent relative humidity at a rate of 4 m3/min. The refrigerant enters the cooling section at 700 kPa with a quality of 20 percent and leaves as saturated vapor. The air is cooled to 20°C at a pressure of 1 atm. Determine (a) the rate of dehumidification, (b) the rate of heat transfer, and (c) the mass flow rate of the refrigerant.

Humid air at \(101.3 \mathrm{kPa}, 36^{\circ} \mathrm{C}\) dry bulb and 65 percent relative humidity is cooled at constant pressure to a temperature \(10^{\circ} \mathrm{C}\) below its dew-point temperature. Sketch the psychrometric diagram for the process and determine the heat transfer from the air, in \(\mathrm{kJ} / \mathrm{kg} \mathrm{dry}\) air. Equation Transcription: Text Transcription: 101.3 kPa, 36^circC 10^circ C kJ/kg

Problem 132P Repeat Prob. 14–131 for a total pressure of 90 kPa for air. Problem 14–131 Air enters an air-conditioning system that uses refrigerant-134a at 30°C and 70 percent relative humidity at a rate of 4 m3/min. The refrigerant enters the cooling section at 700 kPa with a quality of 20 percent and leaves as saturated vapor. The air is cooled to 20°C at a pressure of 1 atm. Determine (a) the rate of dehumidification, (b) the rate of heat transfer, and (c) the mass flow rate of the refrigerant.

Problem 133P An air-conditioning system operates at a total pressure of 1 atm and consists of a heating section and an evaporative cooler. Air enters the heating section at 15°C and 55 percent relative humidity at a rate of 30 m3/min, and it leaves the evaporative cooler at 25 °C and 45 percent relatively humidity. Determine (a) the temperature and relative humidity of the air when it leaves the heating section, (b) the rate of heat transfer in the heating section, and (c) the rate of water added to air in the evaporative cooler.

Problem 135P Repeat Prob. 14–140 for a total pressure of 96 kPa.

A natural-draft cooling tower is to remove \(70 \mathrm{MW}\) of waste heat from the cooling water that enters the tower at \(42^{\circ} \mathrm{C}\) and leaves at \(30^{\circ} \mathrm{C}\). Atmospheric air enters the tower at \(1 \mathrm{~atm}\) with dry- and wet-bulb temperatures of 23 and \(16^{\circ} \mathrm{C}\), respectively, and leaves saturated at \(32^{\circ} \mathrm{C}\). Determine (a) the mass flow rate of the cooling water, (b) the volume flow rate of air into the cooling tower, and (c) the mass flow rate of the required makeup water. Equation Transcription: Text Transcription: 70 MW 42^circC 30^circC 1 atm 16^circC 32^circC

Problem 136P Conditioned air at 13°C and 90 percent relative humidity is to be mixed with outside air at 34°C and 40 percent relative humidity at 1 atm. If it is desired that the mixture have a relative humidity of 60 percent, determine (a) the ratio of the dry air mass flow rates of the conditioned air to the outside air and (b) the temperature of the mixture.

(a) Derive Eq. (9.12) by combining Eqs. (9.7) and (9.11) to eliminate t. (b) The angular velocity of an airplane propeller increases from 12.0 rad/s to 16.0 rad/s while turning through 7.00 rad. What is the angular acceleration in \(\mathrm{rad} / \mathrm{s}^{2} ?\)

Problem 142P A 40-m3 room contains air at 30°C and a total pressure of 90 kPa with a relative humidity of 75 percent. The mass of dry air in the room is (a) 24.7 kg ________________ (b) 29.9 kg ________________ (c) 39.9 kg ________________ (d) 41.4 kg ________________ (e) 52.3 kg

Problem 141P A room contains 65 kg of dry air and 0.6 kg of water vapor at 25°C and 90 kPa total pressure. The relative humidity of air in the room is (a) 3.5% ________________ (b) 41.5% ________________ (c) 55.2% ________________ (d) 60.9% ________________ (e) 73.0%

Problem 143P A room contains air at 30°C and a total pressure of 96.0 kPa with a relative humidity of 75 percent. The partial pressure of dry air is (a) 82.0 kPa ________________ (b) 85.8 kPa ________________ (c ) 92.8 kPa ________________ (d) 90.6 kPa ________________ (e) 72.0 kPa

Problem 147P An air stream at a specified temperature and relative humidity undergoes evaporative cooling by spraying water into it at about the same temperature. The lowest temperature the air stream can be cooled to is (a) the dry bulb temperature at the given state ________________ (b) the wet bulb temperature at the given state ________________ (c) the dew point temperature at the given state ________________ (d) the saturation temperature corresponding to the humidity ratio at the given state ________________ (e) the triple point temperature of water

Problem 145P On the psychrometric chart, a cooling and dehumidification process appears as a line that is (a) horizontal to the left ________________ (b) vertical downward ________________ (c) diagonal upwards to the right (NE direction) ________________ (d) diagonal upwards to the left (NW direction) ________________ (e) diagonal downwards to the left (SW direction)

Problem 146P On the psychrometric chart, a heating and humidification process appears as a line that is (a) horizontal to the right ________________ (b) vertical upward ________________ (c) diagonal upwards to the right (NE direction) ________________ (d) diagonal upwards to the left (NW direction) ________________ (e) diagonal downwards to the right (SE direction)

Problem 144P The air in a house is at 25°C and 65 percent relative humidity. Now the air is cooled at constant pressure. The temperature at which the moisture in the air will start condensing is (a) 7.4°C ________________ (b) 16.3°C ________________ (c) 18.0°C ________________ (d)11.3°C ________________ (e)20.2°C

Problem 148P Air is cooled and dehumidified as it flows over the coils of a refrigeration system at 85 kPa from 35°C and a humidity ratio of 0.023 kg/kg dry air to 15 °C and a humidity ratio of 0.015 kg/kg dry air. If the mass flow rate of dry air is 0.4 kg/s, the rate of heat removal from the air is (a) 4 kJ/s ________________ (b) 8 kJ/s ________________ (c) 12 kJ/s ________________ (d) 16kJ/s ________________ (e) 20 kJ/s

What is the difference between dry air and atmospheric air?

What is the difference between the specific humidity and the relative humidity?

Can the water vapor in air be treated as an ideal gas? Explain.

Is the relative humidity of saturated air necessarily 100 percent?

Is it possible to obtain saturated air from unsaturated air without adding any moisture? Explain.

On the psychrometric chart, a heating and humidification process appears as a line that is (a) horizontal to the right, (b) vertical upward, (c) diagonal upwards to the right (NE direction) (d) diagonal upwards to the left (NW direction) (e) diagonal downwards to the right (SE direction)

An air stream at a specified temperature and relative humidity undergoes evaporative cooling by spraying water into it at about the same temperature. The lowest temperature the air stream can be cooled to is (a) the dry bulb temperature at the given state (b) the wet bulb temperature at the given state (c) the dew point temperature at the given state (d) the saturation temperature corresponding to the humidity ratio at the given state (e) the triple point temperature of water

How will (a) the specific humidity and (b) the relative humidity of the air contained in a well-sealed room change as it is cooled?

Consider a tank that contains moist air at and whose walls are permeable to water vapor. The surrounding air at Pressure also contains some moisture. Is it possible for the water vapor to flow into the tank from surroundings? Explain.

Why are the chilled water lines always wrapped with vapor barrier jackets?

A tank contains 15 kg of dry air and 0.17 kg of water vapor at and total pressure. Determine (a) the specific humidity, (b) the relative humidity, and (c) the volume of the tank.

Repeat Prob. 14-11 for a temperature of .

A room contains air at and at a relative humidity of 85 percent. Determine (a) the partial pressure of dry air, (b) the specific humidity of the air, and (c) the enthalpy per unit mass of dry air.

Repeat Prob. 14-13 for a pressure of .

A room contains air at and at a relative humidity of 60 percent. Determine (a) the partial pressure of dry air, (b) the specific humidity, and (c) the enthalpy per unit mass of dry air.

An -tank contains saturated air at , . Determine (a) the mass of dry air, (b) the specific humidity, and (c) the enthalpy of the air per unit mass of the dry air.

Determine the masses of dry air and the water vapor contained in a room at , , and 50 percent relative humidity.

Humid air at , , and 90 percent relative humidity is compressed in a steady-flow, isentropic compressor to . What is the relative humidity of the air at the compressor outlet?

What is the dew-point temperature?

Andy and Wendy both wear glasses. On a cold winter day, Andy comes from the cold outside and enters the warm house while Wendy leaves the house and goes outside. Whose glasses are more likely to be fogged? Explain.

In summer, the outer surface of a glass filled with iced water frequently sweats. How can you explain this sweating?

In some climates, cleaning the ice off the windshield of a car is a common chore on winter mornings. Explain how ice forms on the windshield during some nights even when there is no rain or snow.

When are the dry-bulb and dew-point temperatures identical?

When are the adiabatic saturation and wet-bulb temperatures equivalent for atmospheric air?

After a long walk in the 128C outdoors, a person wearing glasses enters a room at 258C and 55 percent relative humidity. Determine whether the glasses will become fogged.

Repeat Prob. 1425 for a relative humidity of 30 percent.

A thirsty woman opens the refrigerator and picks up a cool canned drink at 408F. Do you think the can will sweat as she enjoys the drink in a room at 708F and 38 percent relative humidity?

The dry- and wet-bulb temperatures of atmospheric air at 95 kPa are 25 and 178C, respectively. Determine (a) the specific humidity, (b) the relative humidity, and (c) the enthalpy of the air, in kJ/kg dry air

The air in a room has a dry-bulb temperature of 268C and a wet-bulb temperature of 218C. Assuming a pressure of 100 kPa, determine (a) the specific humidity, (b) the relative humidity, and (c) the dew-point temperature.

Reconsider Prob. 1429. Determine the required properties using EES (or other) software. What would the property values be at a pressure of 300 kPa?

The air in a room has a dry-bulb temperature of 758F and a wet-bulb temperature of 658F. Assuming a pressure of 14.3 psia, determine (a) the specific humidity, (b) the relative humidity, and (c) the dew-point temperature.

Atmospheric air at 358C flows steadily into an adiabatic saturation device and leaves as a saturated mixture at 258C. Makeup water is supplied to the device at 258C. Atmospheric pressure is 98 kPa. Determine the relative humidity and specific humidity of the air

How do constant-enthalpy and constant-wet-bulbtemperature lines compare on the psychrometric chart?

At what states on the psychrometric chart are the dry-bulb, wet-bulb, and dew-point temperatures identical?

How is the dew-point temperature at a specified state determined on the psychrometric chart?

Can the enthalpy values determined from a psychrometric chart at sea level be used at higher elevations?

A room contains air at 1 atm, 828F, and 70 percent relative humidity. Using the psychrometric chart, determine (a) the specific humidity, (b) the enthalpy (in Btu/lbm dry air), (c) the wet-bulb temperature, (d ) the dew-point temperature, and (e) the specific volume of the air (in ft3 /lbm dry air).

Reconsider Prob. 1437E. Determine the required properties using EES (or other) software instead of the psychrometric chart. What would the property values be at a location at 5000 ft altitude?

The air in a room has a pressure of 1 atm, a dry-bulb temperature of 248C, and a wet-bulb temperature of 178C. Using the psychrometric chart, determine (a) the specific humidity, (b) the enthalpy, in kJ/kg dry air, (c) the relative humidity, (d) the dew-point temperature, and (e) the specific volume of the air, in m3 /kg dry air.

Reconsider Prob. 1439. Determine the required properties using EES (or other) software instead of the psychrometric chart. What would the property values be at a location at 3000 m altitude?

Atmospheric air at a pressure of 1 atm and drybulb temperature of 288C has a wet-bulb temperature of 208C. Using the psychrometric chart, determine (a) the relative humidity, (b) the humidity ratio, (c) the enthalpy, (d) the dew-point temperature, and (e) the water vapor pressure.

Determine the adiabatic saturation temperature of the humid air in Prob. 1441.

Atmospheric air at a pressure of 1 atm and drybulb temperature of 908F has a dew-point temperature of 758F. Using the psychrometric chart, determine (a) the relative humidity, (b) the humidity ratio, (c) the enthalpy, (d) the wet-bulb temperature, and (e) the water vapor pressure.

Determine the adiabatic saturation temperature of the humid air in Prob. 1443E.

What does a modern air-conditioning system do besides heating or cooling the air?

How does the human body respond to (a) hot weather, (b) cold weather, and (c) hot and humid weather?

What is the radiation effect? How does it affect human comfort?

How does the air motion in the vicinity of the human body affect human comfort?

Consider a tennis match in cold weather where both players and spectators wear the same clothes. Which group of people will feel colder? Why?

Why do you think little babies are more susceptible to cold?

How does humidity affect human comfort?

What are humidification and dehumidification?

What is metabolism? What is the range of metabolic rate for an average man? Why are we interested in the metabolic rate of the occupants of a building when we deal with heating and air-conditioning?

What is sensible heat? How is the sensible heat loss from a human body affected by the (a) skin temperature, (b) environment temperature, and (c) air motion?

What is latent heat? How is the latent heat loss from the human body affected by the (a) skin wettedness and (b) relative humidity of the environment? How is the rate of evaporation from the body related to the rate of latent heat loss?

A department store expects to have 225 customers and 20 employees at peak times in summer. Determine the contribution of people to the total cooling load of the store.

In a movie theater in winter, 500 people, each generating sensible heat at a rate of 70 W, are watching a movie. The heat losses through the walls, windows, and the roof are estimated to be 130,000 Btu/h. Determine if the theater needs to be heated or cooled.

For an infiltration rate of 1.2 air changes per hour (ACH), determine sensible, latent, and total infiltration heat load of a building at sea level, in kW, that is 20 m long, 13 m wide, and 3 m high when the outdoor air is at 328C and 35 percent relative humidity. The building is maintained at 248C and 55 percent relative humidity at all times.

Repeat Prob. 1458 for an infiltration rate of 1.8 ACH.

An average person produces 0.25 kg of moisture while taking a shower and 0.05 kg while bathing in a tub. Consider a family of four who each shower once a day in a bathroom that is not ventilated. Taking the heat of vaporization of water to be 2450 kJ/kg, determine the contribution of showers to the latent heat load of the air conditioner per day in summer.

An average (1.82 kg or 4.0 lbm) chicken has a basal metabolic rate of 5.47 W and an average metabolic rate of 10.2 W (3.78 W sensible and 6.42 W latent) during normal activity. If there are 100 chickens in a breeding room, determine the rate of total heat generation and the rate of moisture production in the room. Take the heat of vaporization of water to be 2430 kJ/kg.

How do relative and specific humidities change during a simple heating process? Answer the same question for a simple cooling process.

Why does a simple heating or cooling process appear as a horizontal line on the psychrometric chart?

Air enters a heating section at 95 kPa, 128C, and 30 percent relative humidity at a rate of 6 m3 /min, and it leaves at 258C. Determine (a) the rate of heat transfer in the heating section and (b) the relative humidity of the air at the exit.

Humid air at 1 atm, 358C, and 45 percent relative humidity is cooled at constant pressure to the dew-point temperature. Determine the cooling, in kJ/kg dry air, required for this process.

Humid air at 40 psia, 508F, and 90 percent relative humidity is heated in a pipe at constant pressure to 1208F. Calculate the relative humidity at the pipe outlet and the amount of heat, in Btu/lbm dry air, required.

Air enters a 30-cm-diameter cooling section at 1 atm, 358C, and 45 percent relative humidity at 18 m/s. Heat is removed from the air at a rate of 750 kJ/min. Determine (a) the exit temperature, (b) the exit relative humidity of the air, and (c) the exit velocity.

Repeat Prob. 1467 for a heat removal rate of 950 kJ/min.

A heating section consists of a 15-in-diameter duct that houses a 4-kW electric resistance heater. Air enters the heating section at 14.7 psia, 508F, and 40 percent relative humidity at a velocity of 25 ft/s. Determine (a) the exit temperature, (b) the exit relative humidity of the air, and (c) the exit velocity.

Why is heated air sometimes humidified?

Air at 1 atm, 158C, and 60 percent relative humidity is first heated to 208C in a heating section and then humidified by introducing water vapor. The air leaves the humidifying section at 258C and 65 percent relative humidity. Determine (a) the amount of steam added to the air, and (b) the amount of heat transfer to the air in the heating section.

Air at 14.7 psia, 358F, and 50 percent relative humidity is first heated to 658F in a heating section and then humidified by introducing water vapor. The air leaves the humidifying section at 758F and 55 percent relative humidity. Determine (a) the amount of steam added to the air, in lbm H2O/lbm dry air, and (b) the amount of heat transfer to the air in the heating section, in Btu/lbm dry air

An air-conditioning system operates at a total pressure of 1 atm and consists of a heating section and a humidifier that supplies wet steam (saturated water vapor) at 1008C. Air enters the heating section at 108C and 70 percent relative humidity at a rate of 35 m3 /min, and it leaves the humidifying section at 208C and 60 percent relative humidity. Determine (a) the temperature and relative humidity of air when it leaves the heating section, (b) the rate of heat transfer in the heating section, and (c) the rate at which water is added to the air in the humidifying section.

Repeat Prob. 1473 for a total pressure of 95 kPa for the airstream.

Why is cooled air sometimes reheated in summer before it is discharged to a room?

Air enters a window air conditioner at 1 atm, 328C, and 70 percent relative humidity at a rate of 2 m3 /min, and it leaves as saturated air at 158C. Part of the moisture in the air that condenses during the process is also removed at 158C. Determine the rates of heat and moisture removal from the air.

Humid atmospheric air at 1 atm, 908F, and 90 percent relative humidity is cooled to 508F while the mixture pressure remains constant. Calculate the amount of water, in lbm/lbm dry air, removed from the air and the cooling requirement, in Btu/lbm dry air, when the liquid water leaves the system at 608F.

Air enters a 40-cm-diameter cooling section at 1 atm, 328C, and 70 percent relative humidity at 120 m/min. The air is cooled by passing it over a cooling coil through which cold water flows. The water experiences a temperature rise of 68C. The air leaves the cooling section saturated at 208C. Determine (a) the rate of heat transfer, (b) the mass flow rate of the water, and (c) the exit velocity of the airstream.

Reconsider Prob. 1478. Using EES (or other) software, develop a general solution of the problem in which the input variables may be supplied and parametric studies performed. For each set of input variables for which the pressure is atmospheric, show the process on the psychrometric chart.

Repeat Prob. 1478 for a total pressure of 95 kPa for air.

Air enters a 1-ft-diameter cooling section at 14.7 psia, 908F, and 60 percent relative humidity at 600 ft/min. The air is cooled by passing it over a cooling coil through which cold water flows. The water experiences a temperature rise of 148F. The air leaves the cooling section saturated at 708F. Determine (a) the rate of heat transfer, (b) the mass flow rate of the water, and (c) the exit velocity of the airstream.

Reconsider Prob. 1481E. Using EES (or other) software, study the effect of the total pressure of the air over the range 14.3 to 15.2 psia on the required results. Plot the required results as functions of air total pressure.

Repeat Prob. 1481E for a total pressure of 14.4 psia for air

Air from a workspace enters an air conditioner unit at 308C dry bulb and 208C wet bulb. The air leaves the air conditioner and returns to the space at 208C dry-bulb and 6.58C dew-point temperature. If there is any, the condensate leaves the air conditioner at the temperature of the air leaving the cooling coils. The volume flow rate of the air returned to the workspace is 800 m3 /min. Atmospheric pressure is 101 kPa. Determine the heat transfer rate from the air, in kW, and the mass flow rate of condensate water, if any, in kg/h.

Atmospheric air from the inside of an automobile enters the evaporator section of the air conditioner at 1 atm, 278C and 50 percent relative humidity. The air returns to the automobile at 108C and 90 percent relative humidity. The passenger compartment has a volume of 2 m3 and 5 air changes per minute are required to maintain the inside of the automobile at the desired comfort level. Sketch the psychrometric diagram for the atmospheric air flowing through the air conditioning process. Determine the dew point and wet bulb temperatures at the inlet to the evaporator section, in 8C. Determine the required heat transfer rate from the atmospheric air to the evaporator fluid, in kW. Determine the rate of condensation of water vapor in the evaporator section, in kg/min.

Atmospheric air at 1 atm, 328C, and 95 percent relative humidity is cooled to 248C and 60 percent relative humidity. A simple ideal vapor-compression refrigeration system using refrigerant-134a as the working fluid is used to provide the cooling required. It operates its evaporator at 48C and its condenser at a saturation temperature of 39.48C. The condenser rejects its heat to the atmospheric air. Calculate the exergy destruction, in kJ, in the total system per 1000 m3 of dry air processed.

Humid air is to be conditioned in a constant pressure process at 1 atm from 398C dry bulb and 50 percent relative humidity to 178C dry bulb and 10.88C wet bulb. The air is first passed over cooling coils to remove all of the moisture necessary to achieve the final moisture content and then is passed over heating coils to achieve the final state. (a) Sketch the psychometric diagram for the process. (b) Determine the dew point temperature of the mixture at the inlet of the cooling coils and at the inlet of the heating coils. (c) What is the net heat transfer for the entire process for this process, in kJ/kg dry air?

What is evaporative cooling? Will it work in humid climates?

During evaporation from a water body to air, under what conditions will the latent heat of vaporization be equal to the heat transfer from the air?

Does an evaporation process have to involve heat transfer? Describe a process that involves both heat and mass transfer.

Air enters an evaporative cooler at 95 kPa, 408C, and 25 percent relative humidity and exits saturated. Determine the exit temperature of air.

Air enters an evaporative cooler at 14.5 psia, 938F, and 30 percent relative humidity and exits saturated. Determine the exit temperature of air.

Air enters an evaporative cooler at 1 atm, 408C, and 20 percent relative humidity at a rate of 7 m3 /min, and it leaves with a relative humidity of 90 percent. Determine (a) the exit temperature of the air and (b) the required rate of water supply to the evaporative cooler.

Air enters an evaporative cooler at 1 atm, 328C, and 30 percent relative humidity at a rate of 5 m3 /min and leaves at 228C. Determine (a) the final relative humidity and (b) the amount of water added to air.

Air at 1 atm, 208C, and 50 percent relative humidity is first heated to 358C in a heating section and then passed through an evaporative cooler where its temperature drops to 258C. Determine (a) the exit relative humidity and (b) the amount of water added to air, in kg H2O/kg dry air.

Two unsaturated airstreams are mixed adiabatically. It is observed that some moisture condenses during the mixing process. Under what conditions will this be the case?

Consider the adiabatic mixing of two airstreams. Does the state of the mixture on the psychrometric chart have to be on the straight line connecting the two states?

During an air-conditioning process, 900 ft3 /min of conditioned air at 658F and 30 percent relative humidity is mixed adiabatically with 300 ft3 /min of outside air at 808F and 90 percent relative humidity at a pressure of 1 atm. Determine (a) the temperature, (b) the specific humidity, and (c) the relative humidity of the mixture.

Reconsider Prob. 1498E. Using EES (or other) software, develop a general solution of the problem in which the input variables may be supplied and parametric studies performed. For each set of input variables for which the pressure is atmospheric, show the process on the psychrometric chart.

Two airstreams are mixed steadily and adiabatically. The first stream enters at 358C and 30 percent relative humidity at a rate of 15 m3 /min, while the second stream enters at 128C and 90 percent relative humidity at a rate of 25 m3 /min. Assuming that the mixing process occurs at a pressure of 1 atm, determine the specific humidity, the relative humidity, the dry-bulb temperature, and the volume flow rate of the mixture.

Repeat Prob. 14100 for a total mixing-chamber pressure of 90 kPa.

A stream of warm air with a dry-bulb temperature of 368C and a wet-bulb temperature of 308C is mixed adiabatically with a stream of saturated cool air at 128C. The dry air mass flow rates of the warm and cool airstreams are 8 and 10 kg/s, respectively. Assuming a total pressure of 1 atm, determine (a) the temperature, (b) the specific humidity, and (c) the relative humidity of the mixture.

Reconsider Prob. 14102. Using EES (or other) software, determine the effect of the mass flow rate of saturated cool air stream on the mixture temperature, specific humidity, and relative humidity. Vary the mass flow rate of saturated cool air from 0 to 16 kg/s while maintaining the mass flow rate of warm air constant at 8 kg/s. Plot the mixture temperature, specific humidity, and relative humidity as functions of the mass flow rate of cool air, and discuss the results.

Saturated humid air at 1 atm and 508F is to be mixed with atmospheric air at 1 atm, 908F, and 80 percent relative humidity, to form air at 708F. Determine the proportions at which these two streams are to be mixed and the relative humidity of the resulting air.

How does a natural-draft wet cooling tower work?

What is a spray pond? How does its performance compare to the performance of a wet cooling tower?

The cooling water from the condenser of a power plant enters a wet cooling tower at 408C at a rate of 90 kg/s. The water is cooled to 258C in the cooling tower by air that enters the tower at 1 atm, 238C, and 60 percent relative humidity and leaves saturated at 328C. Neglecting the power input to the fan, determine (a) the volume flow rate of air into the cooling tower and (b) the mass flow rate of the required makeup water.

The cooling water from the condenser of a power plant enters a wet cooling tower at 1108F at a rate of 100 lbm/s. Water is cooled to 808F in the cooling tower by air that enters the tower at 1 atm, 768F, and 60 percent relative humidity and leaves saturated at 958F. Neglecting the power input to the fan, determine (a) the volume flow rate of air into the cooling tower and (b) the mass flow rate of the required makeup water.

A wet cooling tower is to cool 60 kg/s of water from 40 to 338C. Atmospheric air enters the tower at 1 atm with dryand wet-bulb temperatures of 22 and 168C, respectively, and leaves at 308C with a relative humidity of 95 percent. Using the psychrometric chart, determine (a) the volume flow rate of air into the cooling tower and (b) the mass flow rate of the required makeup water.

A wet cooling tower is to cool 25 kg/s of cooling water from 40 to 308C at a location where the atmospheric pressure is 96 kPa. Atmospheric air enters the tower at 208C and 70 percent relative humidity and leaves saturated at 358C. Neglecting the power input to the fan, determine (a) the volume flow rate of air into the cooling tower and (b) the mass flow rate of the required makeup water.

Water enters a cooling tower at 958F and at a rate of 3 lbm/s, and leaves at 808F. Humid air enters this tower at 1 atm and 658F with a relative humidity of 30 percent and leaves at 758F with relative humidity of 80 percent. Determine the mass flow rate of dry air through this tower.

How much work potential, in Btu/lbm dry air, is lost in the cooling tower of Prob. 14-111E. Take T0 5 658F.

Dry air whose molar analysis is 78.1 percent N2, 20.9 percent O2, and 1 percent Ar flows over a water body until it is saturated. If the pressure and temperature of air remain constant at 1 atm and 258C during the process, determine (a) the molar analysis of the saturated air and (b) the density of air before and after the process. What do you conclude from your results?

The relative humidity of air at 808F and 14.7 psia is increased from 25 to 75 percent during a humidification process at constant temperature and pressure. Determine the percent error involved in assuming the density of air to have remained constant.

The condensation of the water vapor in compressedair lines is a major concern in industrial facilities, and the compressed air is often dehumidified to avoid the problems associated with condensation. Consider a compressor that compresses ambient air from the local atmospheric pressure of 92 kPa to a pressure of 800 kPa (absolute). The compressed air is then cooled to the ambient temperature as it flows through the compressed-air lines. Disregarding any pressure losses, determine if there will be any condensation in the compressed-air lines on a day when the ambient air is at 208C and 50 percent relative humidity.

The capacity of evaporative coolers is usually expressed in terms of the flow rate of air in ft3 /min (or cfm), and a practical way of determining the required size of an evaporative cooler for an 8-ft-high house is to multiply the floor area of the house by 4 (by 3 in dry climates and by 5 in humid climates). For example, the capacity of an evaporative cooler for a 30-ft-long, 40-ft-wide house is 1200 3 4 5 4800 cfm. Develop an equivalent rule of thumb for the selection of an evaporative cooler in SI units for 2.4-m-high houses whose floor areas are given in m2 .

A cooling tower with a cooling capacity of 30 tons (105 kW) is claimed to evaporate 4000 kg of water per day. Is this a reasonable claim?

The air-conditioning costs of a house can be reduced by up to 10 percent by installing the outdoor unit (the condenser) of the air conditioner at a location shaded by trees and shrubs. If the air-conditioning costs of a house are $500 a year, determine how much the trees will save the home owner in the 20-year life of the system.

The thermostat setting of a house can be lowered by 28F by wearing a light long-sleeved sweater, or by 48F by wearing a heavy long-sleeved sweater for the same level of comfort. If each 8F reduction in thermostat setting reduces the heating cost of a house by 4 percent at a particular location, determine how much the heating costs of a house can be reduced by wearing heavy sweaters if the annual heating cost of the house is $600.

A typical winter day in Moscow has a temperature of 08C and a relative humidity of 40 percent. What is the relative humidity inside a dacha that has air that has been heated to 188C?

The relative humidity inside dacha of Prob. 14-120 is to be brought to 50 percent by evaporating water at 208C. How much heat, in kJ, is required for this purpose per m3 of air in the dacha?

During a summer day in Phoenix, Arizona, the air is at 1 atm, 1108F, and 15 percent relative humidity. Water at 708F is evaporated into this air to produce air at 758F and 80 percent relative humidity. How much water, in lbm/lbm dry air, is required and how much cooling, in Btu/lbm dry air, has been produced?

If the system of Prob. 14-122E is operated as an adiabatic system and the air produced by this system has a relative humidity of 70 percent, what is the temperature of the air produced?

A 1.8-m3 tank contains saturated air at 208C and 90 kPa. Determine (a) the mass of the dry air, (b) the specific humidity, and (c) the enthalpy of the air per unit mass of the dry air.

Reconsider Prob. 14124. Using EES (or other) software, determine the properties of the air at the initial state. Study the effect of heating the air at constant volume until the pressure is 110 kPa. Plot the required heat transfer, in kJ, as a function of pressure.

Air at 15 psia, 608F, and 70 percent relative humidity flows in an 6-in diameter duct at a velocity of 35 ft/s. Determine (a) the dew-point temperature, (b) the volume flow rate of air, and (c) the mass flow rate of dry air.

Air flows steadily through an isentropic nozzle. The air enters the nozzle at 358C, 200 kPa and 50 percent relative humidity. If no condensation is to occur during the expansion process, determine the pressure, temperature, and velocity of the air at the nozzle exit.

Air enters a cooling section at 97 kPa, 358C, and 30 percent relative humidity at a rate of 6 m3 /min, where it is cooled until the moisture in the air starts condensing. Determine (a) the temperature of the air at the exit and (b) the rate of heat transfer in the cooling section.

Outdoor air enters an air-conditioning system at 108C and 70 percent relative humidity at a steady rate of 26 m3 /min, and it leaves at 258C and 55 percent relative humidity. The outdoor air is first heated to 188C in the heating section and then humidified by the injection of hot steam in the humidifying section. Assuming the entire process takes place at a pressure of 1 atm, determine (a) the rate of heat supply in the heating section and (b) the mass flow rate of steam required in the humidifying section.

Humid air at 101.3 kPa, 368C dry bulb and 65 percent relative humidity is cooled at constant pressure to a temperature 108C below its dew-point temperature. Sketch the psychrometric diagram for the process and determine the heat transfer from the air, in kJ/kg dry air.

Air enters an air-conditioning system that uses refrigerant-134a at 308C and 70 percent relative humidity at a rate of 4 m3 /min. The refrigerant enters the cooling section at 700 kPa with a quality of 20 percent and leaves as saturated vapor. The air is cooled to 208C at a pressure of 1 atm. Determine (a) the rate of dehumidification, (b) the rate of heat transfer, and (c) the mass flow rate of the refrigerant.

Repeat Prob. 14131 for a total pressure of 90 kPa for air

An air-conditioning system operates at a total pressure of 1 atm and consists of a heating section and an evaporative cooler. Air enters the heating section at 158C and 55 percent relative humidity at a rate of 30 m3 /min, and it leaves the evaporative cooler at 258C and 45 percent relatively humidity. Determine (a) the temperature and relative humidity of the air when it leaves the heating section, (b) the rate of heat transfer in the heating section, and (c) the rate of water added to air in the evaporative cooler.

Reconsider Prob. 14133. Using EES (or other) software, study the effect of total pressure in the range 94 to 100 kPa on the results required in the problem. Plot the results as functions of total pressure.

Repeat Prob. 14133 for a total pressure of 96 kPa.

Conditioned air at 138C and 90 percent relative humidity is to be mixed with outside air at 348C and 40 percent relative humidity at 1 atm. If it is desired that the mixture have a relative humidity of 60 percent, determine (a) the ratio of the dry air mass flow rates of the conditioned air to the outside air and (b) the temperature of the mixture.

Reconsider Prob. 14136. Determine the desired quantities using EES (or other) software instead of the psychrometric chart. What would the answers be at a location at an atmospheric pressure of 80 kPa?

A natural-draft cooling tower is to remove 70 MW of waste heat from the cooling water that enters the tower at 428C and leaves at 308C. Atmospheric air enters the tower at 1 atm with dry- and wet-bulb temperatures of 23 and 168C, respectively, and leaves saturated at 328C. Determine (a) the mass flow rate of the cooling water, (b) the volume flow rate of air into the cooling tower, and (c) the mass flow rate of the required makeup water.

Reconsider Prob. 14138. Using EES (or other) software, investigate the effect of air inlet wet-bulb temperature on the required air volume flow rate and the makeup water flow rate when the other input data are the stated values. Plot the results as functions of wetbulb temperature.

A room is filled with saturated moist air at 258C and a total pressure of 100 kPa. If the mass of dry air in the room is 100 kg, the mass of water vapor is (a) 0.52 kg (b) 1.97 kg (c) 2.96 kg (d) 2.04 kg (e) 3.17 kg

A room contains 65 kg of dry air and 0.6 kg of water vapor at 258C and 90 kPa total pressure. The relative humidity of air in the room is (a) 3.5% (b) 41.5% (c) 55.2% (d) 60.9% (e) 73.0%

A 40-m3 room contains air at 308C and a total pressure of 90 kPa with a relative humidity of 75 percent. The mass of dry air in the room is (a) 24.7 kg (b) 29.9 kg (c) 39.9 kg (d) 41.4 kg (e) 52.3 kg

A room contains air at 308C and a total pressure of 96.0 kPa with a relative humidity of 75 percent. The partial pressure of dry air is (a) 82.0 kPa (b) 85.8 kPa (c) 92.8 kPa (d) 90.6 kPa (e) 72.0 kPa

The air in a house is at 258C and 65 percent relative humidity. Now the air is cooled at constant pressure. The temperature at which the moisture in the air will start condensing is (a) 7.48C (b) 16.38C (c) 18.08C (d) 11.38C (e) 20.28C

On the psychrometric chart, a cooling and dehumidification process appears as a line that is (a) horizontal to the left (b) vertical downward (c) diagonal upwards to the right (NE direction) (d) diagonal upwards to the left (NW direction) (e) diagonal downwards to the left (SW direction)

On the psychrometric chart, a heating and humidification process appears as a line that is (a) horizontal to the right (b) vertical upward (c) diagonal upwards to the right (NE direction) (d) diagonal upwards to the left (NW direction) (e) diagonal downwards to the right (SE direction)

An air stream at a specified temperature and relative humidity undergoes evaporative cooling by spraying water into it at about the same temperature. The lowest temperature the air stream can be cooled to is (a) the dry bulb temperature at the given state (b) the wet bulb temperature at the given state (c) the dew point temperature at the given state (d) the saturation temperature corresponding to the humidity ratio at the given state (e) the triple point temperature of water

Air is cooled and dehumidified as it flows over the coils of a refrigeration system at 85 kPa from 358C and a humidity ratio of 0.023 kg/kg dry air to 158C and a humidity ratio of 0.015 kg/kg dry air. If the mass flow rate of dry air is 0.4 kg/s, the rate of heat removal from the air is (a) 4 kJ/s (b) 8 kJ/s (c) 12 kJ/s (d) 16 kJ/s (e) 20 kJ/s

Air at a total pressure of 90 kPa, 158C, and 75 percent relative humidity is heated and humidified to 258C and 75 percent relative humidity by introducing water vapor. If the mass flow rate of dry air is 4 kg/s, the rate at which steam is added to the air is (a) 0.032 kg/s (b) 0.013 kg/s (c) 0.019 kg/s (d) 0.0079 kg/s (e) 0 kg/s

Write an essay on different humidity measurement devices, including electronic ones, and discuss the advantages and disadvantages of each device.

The air-conditioning needs of a large building can be met by a single central system or by several individual window units. Considering that both approaches are commonly used in practice, the right choice depends on the situation on hand. Identify the important factors that need to be considered in decision making, and discuss the conditions under which an air-conditioning system that consists of several window units is preferable over a large single central system, and vice versa.

Design an inexpensive evaporative cooling system suitable for use in your house. Show how you would obtain a water spray, how you would provide airflow, and how you would prevent water droplets from drifting into the living space.

The daily change in the temperature of the atmosphere tends to be smaller in locations where the relative humidity is high. Demonstrate why this occurs by calculating the change in the temperature of a fixed quantity of air when a fixed quantity of heat is removed from the air. Plot this temperature change as a function of the initial relative humidity and be sure that the air temperature reaches or exceeds the dew-point temperature. Do the same when a fixed amount of heat is added to the air.

The condensation and even freezing of moisture in building walls without effective vapor retarders are of real concern in cold climates as they undermine the effectiveness of the insulation. Investigate how the builders in your area are coping with this problem, whether they are using vapor retarders or vapor barriers in the walls, and where they are located in the walls. Prepare a report on your findings, and explain the reasoning for the current practice.