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engineering
thermodynamics an engineering approach
Questions and Answers of
Thermodynamics An Engineering Approach
An ideal-gas mixture consists of 3 kmol of N2 and 6 kmol of CO2. The mass fraction of CO2 in the mixture is(a) 0.241(b) 0.333(c) 0.500(d) 0.667(e) 0.759
In the liquefaction process, why are gases compressed to very high pressures?
A heat pump using refrigerant-134a as a refrigerant operates its condenser at 800 kPa and its evaporator at −1.25°C. It operates on the ideal vapor-compression refrigeration cycle, except for the
A photographic equipment manufacturer uses a flow of 64,500 lbm/h of steam in its manufacturing process. Currently the spent steam at 3.8 psia and 224°F is exhausted to the atmosphere. Do the
Design the condenser of a steam power plant that has a thermal efficiency of 40 percent and generates 10 MW of net electric power. Steam enters the condenser as saturated vapor at 10 kPa, and it is
A steam power plant operates on the simple ideal Rankine cycle between the pressure limits of 10 kPa and 5 MPa, with a turbine inlet temperature of 600°C. The rate of heat transfer in the boiler is
A simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of 4 MPa in the boiler and 20 kPa in the condenser and a turbine inlet temperature of 700°C.
An ideal reheat Rankine cycle with water as the working fluid operates the inlet of the high-pressure turbine at 8000 kPa and 450°C, the inlet of the low-pressure turbine at 500 kPa and 500°C, and
A simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of 15 MPa in the boiler and 100 kPa in the condenser. Saturated steam enters the turbine. Determine
Atmospheric air at a pressure of 1 atm and dry-bulb temperature of 30°C has a relative humidity of 80 percent. Using the psychrometric chart, determine(a) The wet-bulb temperature(b) The humidity
What is vapor pressure?
Can the water vapor in air be treated as an ideal gas? Explain.
Is the relative humidity of saturated air necessarily 100 percent?
Moist air is passed through a cooling section where it is cooled and dehumidified. How do(a) The specific humidity(b) The relative humidity of air change during this process?
Is it possible to obtain saturated air from unsaturated air without adding any moisture? Explain.
Repeat Prob. 14–14 for a temperature of 40°C.Data From Q#14: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)
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(c) The enthalpy per unit mass of dry air.
Humid air at 100 psia and 400°F and a humidity ratio of 0.025 lbm H2O/lbm dry air is expanded to 15 psia in an isentropic nozzle. How much of the initial water vapor has been converted to liquid
What is the dew-point temperature?
When are the dry-bulb and dew-point temperatures identical?
When are the adiabatic saturation and wet-bulb temperatures equivalent for atmospheric air?
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(c) The dew-point
The air in a room has a dry-bulb temperature of 75°F and a wet-bulb temperature of 60°F. Assuming a pressure of 14.3 psia, determine(a) The specific humidity(b) The relative humidity(c) The
How do constant-enthalpy and constant-wet-bulb temperature lines compare on the psychrometric chart?
At what states on the psychrometric chart are the dry-bulb, wet-bulb, and dew-point temperatures identical?
Can the enthalpy values determined from a psychrometric chart at sea level be used at higher elevations?
Atmospheric air at a pressure of 1 atm and dry-bulb temperature of 90°F has a wet-bulb temperature of 85°F. Using the psychrometric chart, determine(a) The relative humidity(b) The humidity
Reconsider Prob. 14–39E. Determine the adiabatic saturation temperature of the humid air.Data From Prob. 14–39E:Atmospheric air at a pressure of 1 atm and dry-bulb temperature of 90°F has a
Reconsider Prob. 14–43. Determine the adiabatic saturation temperature of the humid air.Data From Prob. 14–43. Atmospheric air at a pressure of 1 atm and dry-bulb temperature of 28°C
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(c) Hot and humid weather?
What are humidification and dehumidification?
Humid air at 150 kPa, 40°C, and 70 percent relative humidity is cooled at constant pressure in a pipe to its dewpoint temperature. Calculate the heat transfer, in kJ/kg dry air, required for this
Air enters a heating section at 95 kPa, 10°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(b) The
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
Atmospheric air at 1 atm, 30°C, and 80 percent relative humidity is cooled to 20°C while the mixture pressure remains constant. Calculate the amount of water, in kg/kg dry air, removed from the air
Ten thousand cubic feet per hour of atmospheric air at 1 atm and 85°F with a dew-point temperature of 70°F are to be cooled to 60°F. Determine the rate at which condensate leaves this system and
Air enters a 40-cm-diameter cooling section at 1 atm, 32°C, 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
Repeat Prob. 14–79 for a total pressure of 88 kPa for air.Data From Repeat Prob. 14–79:Air enters a 40-cm-diameter cooling section at 1 atm, 32°C, and 70 percent relative humidity at 120 m/min.
On a summer day in New Orleans, Louisiana, the pressure is 1 atm: the temperature is 32°C; and the relative humidity is 95 percent. This air is to be conditioned to 24°C and 60 percent relative
Reconsider Prob. 14–82. How far will the temperature of the humid air have to be reduced to produce the desired dehumidification?Data From Reconsider Prob. 14–82:On a summer day in New Orleans,
Atmospheric air from the inside of an automobile enters the evaporator section of the air conditioner at 1 atm, 27°C, and 50 percent relative humidity. The air returns to the automobile at 10°C and
Humid air at 101.3 kPa, 39°C dry bulb, and 50 percent relative humidity is cooled at constant pressure to a temperature 10°C below its dew-point temperature.(a) Sketch the system hardware and the
Saturated humid air at 70 psia and 200°F is cooled to 100°F as it flows through a 3-in-diameter pipe with a velocity of 50 ft/s and at constant pressure. Calculate the rate at which liquid water is
What is evaporative cooling? Will it work in humid climates?
Desert dwellers often wrap their heads with a water soaked porous cloth. On a desert where the pressure is 1 atm, temperature is 45°C, and relative humidity is 15 percent, what is the temperature of
Air enters an evaporative (or swamp) cooler at 14.7 psi, 95°F, and 20 percent relative humidity, and it exits at 80 percent relative humidity. Determine(a) The exit temperature of the air and(b) The
Air at 1 atm, 20°C, and 70 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)
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?
Saturated humid air at 1 atm and 10°C is to be mixed with atmospheric air at 1 atm, 32°C, and 80 percent relative humidity, to form air of 70 percent relative humidity. Determine the proportions at
Reconsider Prob. 14–104E. Calculate the rate of entropy generation for this process.Data From Q#104:Two humid airstreams are adiabatically mixed at 1 atm pressure to form a third stream. The first
A wet cooling tower is to cool 60 kg/s of water from 40 to 33°C. Atmospheric air enters the tower at 1 atm with dry and wet-bulb temperatures of 22 and 16°C, respectively, and leaves at 30°C with
Water at 100°F is to be cooled in a cooling tower which it enters at a rate of 10,000 lbm/h. Humid air enters this tower at 1 atm, 60°F, and 20 percent relative humidity with a dry airflow rate of
Water at 30°C is to be cooled to 22°C in a cooling tower which it enters at a rate of 5 kg/s. Humid air enters this tower at 1 atm and 15°C with a relative humidity of 25 percent and leaves at
Reconsider Prob. 14–112. How much work potential, in kJ/kg dry air, is lost in the cooling tower? Take T0 = 15°C.Data From Q#112:Water at 30°C is to be cooled to 22°C in a cooling tower which it
The U.S. Department of Energy estimates that 190,000 barrels of oil would be saved per day if every household in the United States raised the thermostat setting in summer by 6°F (3.3°C). Assuming
A laboratory has a volume of 700 m3 and must have one complete air change per minute when being used. Outside atmospheric air at 100 kPa, 30°C dry bulb, and 60 percent relative humidity is ducted
Air at 15 psia, 60°F, and 70 percent relative humidity flows in a 6-in diameter duct at a velocity of 27 ft/s. Determine(a) The dew-point temperature(b) The volume flow rate of air(c) The mass flow
During a summer day in El Paso, Texas, outdoor air is at 1 atm, 40°C, and 20 percent relative humidity. Water at 20°C is evaporated into this air to produce air at 25°C and 80 percent relative
What is the difference between dry air and atmospheric air?
A pressurized mixture of nitrogen and argon is supplied to a directional control nozzle on a space satellite. Plot the gas velocity at the nozzle exit as a function of the argon mass fraction with
Prolonged exposure to mercury even at relatively low but toxic concentrations in the air is known to cause permanent mental disorders, insomnia, and pain and numbness in the hands and the feet, among
You have a rigid tank equipped with a pressure gauge. Describe a procedure by which you could use this tank to blend ideal gases in prescribed mole-fraction portions.
The simple additive rule may not be appropriate for the volume of binary mixtures of gases, Prove this for a pair of gases of your choice at several different temperatures and pressures using Kay’s
An ideal-gas mixture consists of 60 percent helium and 40 percent argon gases by mass. The mixture is now expanded isentropically in a turbine from 400°C and 1.2 MPa to a pressure of 200 kPa. The
A piston–cylinder device contains an ideal-gas mixture of 3 kmol of He gas and 7 kmol of Ar gas at 70°C and 400 kPa. Now the gas expands at constant pressure until its volume doubles. The amount
One compartment of an insulated rigid tank contains 2 kmol of CO2 at 20°C and 150 kPa while the other compartment contains 5 kmol of H2 gas at 35°C and 300 kPa. Now the partition between the two
A 60-L rigid tank contains an ideal-gas mixture of 5 g of N2 and 5 g of CO2 at a specified pressure and temperature. If N2 were separated from the mixture and stored at mixture temperature and
Using Dalton’s law, show thatfor a real-gas mixture of k gases, where Z is the compressibility factor. Z„ = EyZi %3D i=1
A mixture of gases consists of 1 kmol of carbon dioxide, 1 kmol of nitrogen, and 0.3 kmol of oxygen. Determine the total amount of work required to compress this mixture isothermally from 10 kPa and
A mixture of gases is assembled by first filling an evacuated 0.15-m3 tank with neon until the pressure is 35 kPa. Oxygen is added next until the pressure increases to 105 kPa. Finally, nitrogen is
Reconsider Prob. 13–79. Using appropriate software, investigate the effect of the salinity of the ocean on the maximum power generated. Let the salinity vary from 0 to 5 percent. Plot the power
A river is discharging into the ocean at a rate of 150,000 m3/s. Determine the amount of power that can be generated if the river water mixes with the ocean water reversibly. Take the salinity of the
A mixture of hydrogen and oxygen has a hydrogen mass fraction of 0.33. Determine the difference in the entropy of the mixture between a state of 750 kPa, 150°C and another state of 150 kPa, 150°C,
In a liquid-oxygen plant, it is proposed that the pressure and temperature of air that is initially at 9000 kPa and 10°C be adiabatically reduced to 50 kPa and −73°C. Using Kay’s rule and the
A mixture of gases consists of 0.1 kg of oxygen, 1 kg of carbon dioxide, and 0.5 kg of helium. This mixture is heated from 10°C to 260°C while its pressure is maintained constant at 350 kPa.
A mixture of nitrogen and carbon dioxide has a carbon dioxide mass fraction of 50 percent. This mixture is heated at constant pressure in a closed system from 120 kPa and 30°C to 200°C. Calculate
When evaluating the entropy change of the components of an ideal-gas mixture, do we have to use the partial pressure of each component or the total pressure of the mixture?
Answer Prob. 13–46C and 13–47C for entropy.Data From Q#46:Is the total internal energy of an ideal-gas mixture equal to the sum of the internal energies of each individual gas in the mixture?
Is the specific internal energy of a gas mixture equal to the sum of the specific internal energies of each individual gas in the mixture?
Is the total internal energy of an ideal-gas mixture equal to the sum of the internal energies of each individual gas in the mixture? Answer the same question for a real-gas mixture.
The dry stack gas of an electrical-generation station boiler has the following Orsat analysis: 15 percent CO2, 15 percent O2, and 1 percent CO. This gas passes through a 10-ft2- cross-section
One pound-mass of a gas whose density is 0.001 lbm/ft3 is mixed with 2 lbm of a gas whose density is 0.002 lbm/ft3 such that the pressure and temperature of the gases do not change. Determine the
One liter of a liquid whose specific volume is 0.0003 m3/kg is mixed with 2 liters of a liquid whose specific volume is 0.00023 m3/kg in a container whose total volume is 3 liters. What is the
The mass fractions of a mixture of gases are 15 percent nitrogen, 5 percent helium, 60 percent methane, and 20 percent ethane. Determine the mole fractions of each constituent, the mixture’s
Separation units often use membranes, absorbers, and other devices to reduce the mole fraction of selected constituents in gaseous mixtures. Consider a mixture of hydrocarbons that consists of 60
Is this statement correct? The pressure of an ideal gas mixture is equal to the sum of the partial pressures of each individual gas in the mixture. If not, how would you correct it?
Consider a rigid tank that contains a mixture of two ideal gases. The gas mixture is heated, and the pressure and temperature in the tank rise. Will the partial pressure of each component change? How
Consider a rigid tank that contains a mixture of two ideal gases. A valve is opened and some gas escapes. As a result, the pressure in the tank drops. Will the partial pressure of each component
In a gas mixture, which component will have the higher partial pressure—the one with the higher mole number or the one with the larger molar mass?
Repeat Prob. 13–9 by replacing N2 with O2.Data From Repeat Prob. 13–9:A gas mixture has the following composition on a mole basis: 60 percent N2 and 40 percent CO2. Determine the gravimetric
What is the apparent gas constant for a gas mixture? Can it be larger than the largest gas constant in the mixture?
What is the apparent molar mass for a gas mixture? Does the mass of every molecule in the mixture equal the apparent molar mass?
Consider a mixture of two gases. Can the apparent molar mass of this mixture be determined by simply taking the arithmetic average of the molar masses of the individual gases? When will this be the
Somebody claims that the mass and mole fractions for a mixture of CO2 and N2O gases are identical. Is this true? Why?
The sum of the mole fractions for an ideal-gas mixture is equal to 1. Is this also true for a real-gas mixture?
Consider a mixture of several gases of identical masses. Will all the mass fractions be identical? How about the mole fractions?
Consider the function z = z(x, y). Write an essay on the physical interpretation of the ordinary derivative dz/dx and the partial derivative (∂z/∂x)y. Explain how these two derivatives are
Several attempts have been made to express the partial derivatives of the most common thermodynamic properties in a compact and systematic manner in terms of measurable properties. The work of P. W.
There have been several attempts to represent the thermodynamic relations geometrically, the best known of these being Koenig’s thermodynamic square shown in the figure. There is a systematic way
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