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engineering
mechanical engineering

Thermodynamics An Engineering Approach 8th edition Yunus A. Cengel, Michael A. Boles - Solutions

Repeat Prob. 14-131 for a total pressure of 90 kPa for air. Prob. 14-131 Air enters an air-conditioning system that uses refrigerant-134a at 30oC and 70 percent relative humidity at a rate of 4m3/min. The refrigerant enters the cooling section at 700 kPa with a quality of 20 percent and leaves as
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 15oC and 55 percent relative humidity at a rate of 30 m3/min, and it leaves the evaporative cooler at 25oC and 45 percent relatively
Reconsider Prob. 14-133. 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. Prob. 14-133 An air-conditioning system operates at a total pressure of 1 atm and consists
Repeat Prob. 14-133 for a total pressure of 96 kPa. Prob. 14-133 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 15oC and 55 percent relative humidity at a rate of 30 m3/min, and it
Conditioned air at 13oC and 90 percent relative humidity is to be mixed with outside air at 34oC 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
Reconsider Prob. 14-136. 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 42oC and leaves at 30oC. Atmospheric air enters the tower at 1 atm with dry- and wet-bulb temperatures of 23 and 16oC, respectively, and leaves saturated at 32oC. Determine (a) The mass
Reconsider Prob. 14-138. 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. Prob. 14-138 A
Repeat Prob. 14-13 for a pressure of 85 kPa. Prob. 14-13 A room contains air at 20oC 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. (c) The enthalpy per unit mass of dry air.
A room is filled with saturated moist air at 25oC 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 25oC 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 30oC 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 30oC 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 25oC 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
Air is cooled and dehumidified as it flows over the coils of a refrigeration system at 85 kPa from 35oC and a humidity ratio of 0.023 kg/kg dry air to 15oC 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)
Air at a total pressure of 90 kPa, 15oC, and 75 percent relative humidity is heated and humidified to 25oC 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
A room contains air at 858F and 13.5 psia at a relative humidity of 60 percent. Determine (a) The partial pressure of dry air. (b) The specific humidity. (c) The enthalpy per unit mass of dry air.
An 8 m3-tank contains saturated air at 30oC, 105 kPa. Determine (a) The mass of dry air. (b) The specific humidity. (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 90-m3 room at 93 kPa, 26oC, and 50 percent relative humidity.
Humid air at 100 kPa, 20oC, 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?
What is the difference between the specific humidity and the relative humidity?
After a long walk in the 12oC outdoors, a person wearing glasses enters a room at 25oC and 55 percent relative humidity. Determine whether the glasses will become fogged.
Repeat Prob. 14-25 for a relative humidity of 30 percent. Prob. 14-25 After a long walk in the 12oC outdoors, a person wearing glasses enters a room at 25oC and 55 percent relative humidity. Determine whether the glasses will become fogged.
A thirsty woman opens the refrigerator and picks up a cool canned drink at 40oF. Do you think the can will "sweat" as she enjoys the drink in a room at 70oF and 38 percent relative humidity?
The dry- and wet-bulb temperatures of atmospheric air at 95 kPa are 25 and 17oC, respectively. Determine (a) The specific humidity. (b) The relative humidity. (c) The enthalpy of the air, in kJ/kg dry air.
The air in a room has a dry-bulb temperature of 26oC and a wet-bulb temperature of 21oC. Assuming a pressure of 100 kPa, determine (a) The specific humidity. (b) The relative humidity. (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? Prob. 14-29 The air in a room has a dry-bulb temperature of 26oC and a wet-bulb temperature of 21oC. Assuming a pressure of 100 kPa, determine (a) The
The air in a room has a dry-bulb temperature of 75oF and a wet-bulb temperature of 65oF. Assuming a pressure of 14.3 psia, determine (a) The specific humidity. (b) The relative humidity. (c) The dew-point temperature.
Atmospheric air at 35oC flows steadily into an adiabatic saturation device and leaves as a saturated mixture at 25oC. Makeup water is supplied to the device at 25oC. Atmospheric pressure is 98 kPa. Determine the relative humidity and specific humidity of the air.
A room contains air at 1 atm, 82oF, 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. (e) The specific volume of the air (in ft3/lbm dry air).
Reconsider Prob. 14-37E. 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? Prob. 14-37E A room contains air at 1 atm, 82oF, and 70 percent relative humidity. Using the
The air in a room has a pressure of 1 atm, a dry-bulb temperature of 24oC, and a wet-bulb temperature of 17oC. 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. (e) The specific volume of
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? Prob. 14-39 The air in a room has a pressure of 1 atm, a dry-bulb temperature of 24oC, and a wet-bulb
Atmospheric air at a pressure of 1 atm and drybulb temperature of 28oC has a wet-bulb temperature of 20oC. Using the psychrometric chart, determine(a) The relative humidity.(b) The humidity ratio.(c) The enthalpy.(d) The dew-point temperature.(e) The water vapor pressure.
Determine the adiabatic saturation temperature of the humid air in Prob. 14-41.Prob. 14-41.Atmospheric air at a pressure of 1 atm and drybulb temperature of 28oC has a wet-bulb temperature of 20oC. Using the psychrometric chart.
Atmospheric air at a pressure of 1 atm and drybulb temperature of 90oF has a dew-point temperature of 75oF. Using the psychrometric chart, determine (a) The relative humidity. (b) The humidity ratio. (c) The enthalpy. (d) The wet-bulb temperature (e) The water vapor pressure.
Determine the adiabatic saturation temperature of the humid air in Prob. 14-43E.Prob. 14-43EAtmospheric air at a pressure of 1 atm and drybulb temperature of 90oF has a dew-point temperature of 75oF. Using the psychrometric chart.
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. (c) Air motion?
What is latent heat? How is the latent heat loss from the human body affected by the (a) Skin wittedness 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 32oC and 35 percent relative humidity. The building is maintained at 24oC
Repeat Prob. 14-58 for an infiltration rate of 1.8 ACH. Prob. 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 32oC
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
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
Air enters a heating section at 95 kPa, 12oC, and 30 percent relative humidity at a rate of 6m3/min, and it leaves at 25oC. Determine (a) The rate of heat transfer in the heating section. (b) The relative humidity of the air at the exit.
Humid air at 1 atm, 35oC, 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, 50oF, and 90 percent relative humidity is heated in a pipe at constant pressure to 120oF. 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, 35oC, and 45 percent relative humidity at 18 m/s. Heat is removed from the air at a rate of 750kJ/min. Determine(a) The exit temperature(b) The exit relative humidity of the air(c) The exit velocity.
Repeat Prob. 14-67 for a heat removal rate of 950kJ/min.Prob. 14-67Air enters a 30-cm-diameter cooling section at 1 atm, 35oC, and 45 percent relative humidity at 18 m/s. Heat is removed from the air at a rate of 750kJ/min. Determine(a) The exit temperature(b) The exit relative humidity of the
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, 50oF, 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. (c) The
Air at 1 atm, 15oC, and 60 percent relative humidity is first heated to 20oC in a heating section and then humidified by introducing water vapor. The air leaves the humidifying section at 25oC and 65 percent relative humidity. Determine (a) The amount of steam added to the air (b) The amount of
Air at 14.7 psia, 35oF, and 50 percent relative humidity is first heated to 65oF in a heating section and then humidified by introducing water vapor. The air leaves the humidifying section at 75oF and 55 percent relative humidity. Determine (a) The amount of steam added to the air, in lbm H2O/lbm
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 100oC. Air enters the heating section at 10oC and 70 percent relative humidity at a rate of 35m3/min, and it leaves the humidifying
Reconsider Prob. 14 - 81E. 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. 14-81E for a total pressure of 14.4 psia for air.
Air from a workspace enters an air conditioner unit at 30oC dry bulb and 20oC wet bulb. The air leaves the air conditioner and returns to the space at 20oC dry-bulb and 6.5oC dew-point temperature. If there is any, the condensate leaves the air conditioner at the temperature of the air leaving the
Atmospheric air from the inside of an automobile enters the evaporator section of the air conditioner at 1 atm, 27oC and 50 percent relative humidity. The air returns to the automobile at 10oC and 90 percent relative humidity. The passenger compartment has a volume of 2 m3 and 5 air changes per
Atmospheric air at 1 atm, 32oC, and 95 percent relative humidity is cooled to 24oC 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 4oC and its
Humid air is to be conditioned in a constant pressure process at 1 atm from 39oC dry bulb and 50 percent relative humidity to 17oC dry bulb and 10.8oC 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
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?
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.
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, 40oC, and 25 percent relative humidity and exits saturated. Determine the exit temperature of air.
Air enters an evaporative cooler at 14.5 psia, 93oF, and 30 percent relative humidity and exits saturated. Determine the exit temperature of air.
Air enters an evaporative cooler at 1 atm, 40oC, and 20 percent relative humidity at a rate of 7m3/min, and it leaves with a relative humidity of 90 percent. Determine(a) The exit temperature of the air.(b) The required rate of water supply to the evaporative cooler.
Air enters an evaporative cooler at 1 atm, 32oC, and 30 percent relative humidity at a rate of 5m3/min and leaves at 22oC. Determine (a) The final relative humidity. (b) The amount of water added to air.
Air at 1 atm, 20oC, and 50 percent relative humidity is first heated to 35oC in a heating section and then passed through an evaporative cooler where its temperature drops to 25oC. Determine (a) The exit relative humidity. (b) The amount of water added to air, in kg H2O/kg dry air.
During an air-conditioning process, 900ft3/min of conditioned air at 65oF and 30 percent relative humidity is mixed adiabatically with 300ft3/min of outside air at 80oF and 90 percent relative humidity at a pressure of 1 atm. Determine (a) The temperature (b) The specific humidity (c) The relative
Reconsider Prob. 14 - 98E. 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.
How does the presence of N2 in air affect the outcome of a combustion process?
A steady-flow combustion chamber is supplied with CO gas at 37oC and 110 kPa at a rate of 0.4 m3/min and air at 25oC 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
A 6-m3 rigid tank initially contains a mixture of 1 kmol of hydrogen (H2) gas and the stoichiometric amount of air at 25oC. The contents of the tank are ignited, and all the hydrogen in the fuel burns to H2O. If the combustion products are cooled to 25oC, determine(a) The fraction of the H2O that
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
Propane gas (C3H8) enters a steady-flow combustion chamber at 1 atm and 25oC 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
Determine the highest possible temperature that can be obtained when liquid gasoline (assumed C8H18) at 25oC is burned steadily with air at 25oC and 1 atm. What would your answer be if pure oxygen at 25oC were used to burn the fuel instead of air?
Liquid propane (C3H8()) enters a combustion chamber at 25oC 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 25oC. The heat transfer from the combustion process is 53 kW. Write the balanced combustion equation and
Determine the work potential of 1 lbmol of diesel fuel (C12H26) at 77oF 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 25oC and 1 atm.
A steam boiler heats liquid water at 200oC to superheated steam at 4 MPa and 400oC. Methane fuel (CH4) is burned at atmospheric pressure with 50 percent excess air. The fuel and air enter the boiler at 25oC and the products of combustion leave at 227oC. Calculate (a) The amount of steam generated
Repeat Prob. 15-108 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 25oC 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
Develop an expression for the higher heating value of a gaseous alkane CnH2n + 2 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
Consider the combustion of hydrocarbon fuel, CnHm, with excess theoretical air and incomplete combustion according to the chemical reaction as follows:CnHm + (1 + B)Ath(O2 + 3.76 N2) → D CO2 + E CO + F H2O + G O2 + J N2where Ath is the theoretical O2 required for this fuel and B is the excess
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 + y2CwHz + (1 + B)Ath(O2 + 3.76 N2)ï‚¾ï‚® D CO2 + E CO + F H2O + G O2 + J N2where y1 and y2
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 25oC.
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 25oC. Determine the adiabatic flame temperature for 75, 90, 100, 120, 150, 200, 300, 500, and 800 percent
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 25oC 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,
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
Using EES (or other) software, repeat Prob. 15-119 for (a) 50, (b) 100, and (c) 200 percent excess air. Prob. 15-119 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
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 air-fuel 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 air-fuel 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 60oC 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 60oC. The entropy change of carbon dioxide in the dehumidifying section is (a)
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 25oC 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
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 25oC, 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

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