Questions and Answers of Fundamentals Of Thermodynamics

A Brayton cycle produces 14 000 Btu/s with an inlet state of 60 F, 14.7 psia and a compression ratio of 16:1. The heat added in the combustion is 480 Btu/lbm. What are the highest temperature and the
An air-standard refrigeration cycle has air into the compressor at 14 psia, 500 R, with a compression ratio of 3:1. The temperature after heat rejection is 540 R. Find the COP and the highest cycle
A four-stroke gasoline engine runs at 1800RPM with a total displacement of 150 in.3 and a compression ratio of 10:1. The intake is at 520 R, 10 psia, with a mean effective pressure of 90 psia. Find
A four-stroke, 85 in.3 gasoline engine runs at 2500 RPM and has an efficiency of 60%. The state before compression is 6 psia, 500 R, and after combustion it is at 4400 R. Find the highest T and P in
A four-stroke gasoline engine has a compression ratio of 10:1 with four cylinders of total displacement 75 in.3. The inlet state is 500 R, 10 psia and the engine is running at 2100 RPM, with the fuel
A turbocharged Otto cycle has the lowest T as 520 R and the lowest P as 22 psia. The highest T is 4500 R, and combustion adds 500 Btu/lbm as heat transfer. Find the compression ratio and the mean
A supercharger is used for a diesel engine, so the intake is 30 psia, 580 R. The cycle has a compression ratio of 18:1, and the mean effective pressure is 120 psia. If the engine is 600 in.3 running
At the beginning of compression in a diesel cycle, T = 540 R, P = 30 lbf/in.2, and the state after combustion (heat addition) is 2600 R and 1000 lbf/in.2. Find the compression ratio, the thermal
Consider an ideal Stirling-cycle engine in which the pressure and temperature at the beginning of the isothermal compression process are 14.7 lbf/in.2, 80 F, the compression ratio is 6, and the
Air in a piston/cylinder goes through a Carnot cycle in which TL = 560 R and the total cycle efficiency is η =2/3. Find TH, the specific work, and the volume ratio in the adiabatic expansion for
An Atkinson cycle has state 1 as 20 psia, 540 R, a compression ratio of 9, and an expansion ratio of 14. Find the needed heat release in the combustion.
An Atkinson cycle has state 1 as 20 psia, 540 R, a compression ratio of 9, and an expansion ratio of 14. Find the mean effective pressure.
A Miller cycle has state 1 as 20 psia, 540 R, a compression ratio of 9, and an expansion ratio of 14. If P4 is 30 psia, find the heat release in the combustion.
A Miller cycle has state 1 as 20 psia, 540 R, a compression ratio of 9, and a heat release of 430 Btu/lbm. Find the needed expansion ratio so that P4 is 30 psia.
Consider an ideal air-standard diesel cycle where the state before the compression process is 14 lbf/in.2, 63 F and the compression ratio is 20. Find the maximum temperature (by iteration) in the
Write a program to solve the following problem. The effects of varying parameters on the performance of an air-standard Brayton cycle are to be determined. Consider a compressor inlet condition of
Write a program to simulate the Otto cycle using nitrogen as the working fluid. Use the variable specific heat given in Table A.6. The beginning of compression has a state of 100 kPa, 20◦C.
Equal masses of argon and helium are mixed. Is the molecular mass of the mixture the linear average of the two individual ones?
Constant flows of pure argon and pure helium are mixed to produce a flow of mixture mole fractions 0.25 and 0.75, respectively. Explain how to meter the inlet flows to ensure the proper ratio,
For a gas mixture in a tank, are the partial pressures important?
An ideal mixture at T, P is made from ideal gases at T, P by charging them into a steel tank. Assume heat is transferred, so T stays the same as the supply. How do the properties (P, v, and u) for
An ideal mixture at T, P is made from ideal gases at T, P by flow into a mixing chamber with no external heat transfer and an exit at P. How do the properties (P, v, and h) for each component
If a certain mixture is used in a number of different processes, is it necessary to consider partial pressures?
Why is it that a set of tables for air, which is a mixture, can be used without dealing with its composition?
Develop a formula to show how the mass fraction of water vapor is connected to the humidity ratio.
For air at 110◦C and 100 kPa, is there any limit on the amount of water it can hold?
Can moist air below the freezing point, say −5◦C, have a dew point?
Why does a car with an air conditioner running often have water dripping out?
Moist air at 35◦C, ω = 0.0175, and Φ = 50% should be brought to a state of 20◦C, ω = 0.01, and Φ = 70%. Is it necessary to add or subtract water?
A 3-L liquid mixture is one-third each of water, ammonia, and ethanol by volume. Find the mass fractions and total mass of the mixture.
A mixture of 60% N2, 30% Ar, and 10% O2 on a mass basis is in a cylinder at 250 kPa, 310 K with a volume of 0.5 m3. Find the mole and the mass fractions and the mass of argon.
A slightly oxygenated air mixture is 69% N2, 1% Ar, and 30% O2 on a mole basis. Assume a total pressure of 101 kPa and find the mass fraction of oxygen and its partial pressure.
In a car engine, gasoline (assume octane, C8H18) is evaporated and then mixed with air in a ratio of 1:15 by mass. In the cylinder the mixture is at 750 kPa, 650Kwhen the spark fires. For that time,
A 2-kg mixture of 25% N2, 50% O2, and 25% CO2 by mass is at 150 kPa and 300 K. Find the mixture gas constant and the total volume.
A diesel engine sprays fuel (assume n-dodecane, C12H26, M = 170.34 kg/kmol) into the combustion chamber already filled with 1 mol fuel per 88 mol air. Find the fuel fraction on a mass basis and the
A new refrigerant, R-410a, is a mixture of R-32 and R-125 in a 1:1 mass ratio. What are the overall molecular weight, the gas constant, and the ratio of specific heats for such a mixture?
A flow of 1 kg/s argon at 300Kand another flow of 1 kg/s carbon dioxide at 1600 K, both at 150 kPa, are mixed without any heat transfer. What is the exit T, P?
A flow of 1 kg/s argon at 300Kand another flow of 1 kg/s carbon dioxide at 1600 K, both at 150 kPa, are mixed without any heat transfer. Find the exit T, P using variable specific heats.
A pipe flows 0.1 kg/s of a mixture with mass fractions of 40% CO2 and 60% N2 at 400 kPa, 300 K. Heating tape is wrapped around a section of pipe with insulation added, and 2 kW electrical power is
A steady flow of 0.1 kg/s carbon dioxide at 1000K in one line is mixed with 0.2 kg/s nitrogen at 400Kfrom another line, both at 100 kPa. The mixing chamber is insulated and has constant pressure of
A mixture of 0.5 kg nitrogen and 0.5 kg oxygen is at 100 kPa, 300Kin a piston/cylinder maintaining constant pressure. Now 1200 kJ is added by heating. Find the final temperature and the increase in
A new refrigerant, R-410a, is a mixture of R-32 and R-125 in a 1:1 mass ratio. A process brings 0.5 kg R-410a from 270 K to 320 K at a constant pressure of 250 kPa in a piston/cylinder. Find the work
A piston/cylinder device contains 0.1 kg of a mixture of 40% methane and 60% propane gases by mass at 300 K and 100 kPa. The gas is now slowly compressed in an isothermal (T = constant) process to a
Two insulated tanks, A and B, are connected by a valve. Tank A has a volume of 1 m3 and initially contains argon at 300 kPa, 10◦C. Tank B has a volume of 2 m3 and initially contains ethane at 200
A steady flow of 0.1 k mol/s carbon dioxide at 1000 K in one line is mixed with 0.2 kmol/s nitrogen at 400 K in another line, both at 100 kPa. The exit mixture at 100 kPa is compressed by a
A piston/cylinder has a 0.1-kg mixture of 25% argon, 25% nitrogen, and 50% carbon dioxide by mass at a total pressure of 100 kPa and 290 K. Now the piston compresses the gases to volume seven times
A flow of gas A and a flow of gas B are mixed in a 1:2 mole ratio with the same T. what is the entropy generation per k mole flow out?
A saturated air–water vapor mixture at 20◦C, 100 kPa is contained in a 5-m3 closed tank in equilibrium with 1 kg liquid water. The tank is heated to 80◦C. Is there any liquid water in the final
A flow of 2 kg/s mixture of 50% carbon dioxide and 50% oxygen by mass is heated in a constant pressure heat exchanger from 400 K to 1000 K by a radiation source at 1400 K. Find the rate of heat
A flow of 1 kg/s carbon dioxide at 1600 K, 100 kPa is mixed with a flow of 2 kg/s water at 800 K, 100 kPa, and after the mixing it goes through a heat exchanger, where it is cooled to 500 K by a 400
A mixture of 60% helium and 40% nitrogen by mass enters a turbine at 1 MPa, 800 K at a rate of 2 kg/s. The adiabatic turbine has an exit pressure of 100 kPa and an isentropic efficiency of 85%. Find
A tank has two sides initially separated by a diaphragm. Side A contains 1 kg water and side B contains 1.2 kg air, both at 20◦C, 100 kPa. The diaphragm is now broken and the whole tank is heated
If I have air at 100 kPa and (a) −10◦C, (b) 45◦C,(c) 110◦C, what is the maximum absolute humidity I can have?
A new high-efficiency home heating system includes an air-to-air heat exchanger that uses energy from outgoing stale air to heat the fresh incoming air. If the outside ambient temperature is
A room with air at 40% relative humidity, 20◦C having 50 kg of dry air is made moist by boiling water to a final state of 20◦C and 80% humidity. How much water was added to the air?
A flow of 0.2 kg/s liquid water at 80◦C is sprayed into a chamber together with 16 kg/s dry air at 60◦C. All the water evaporates, and the air leaves at 40◦C. What is the exit relative humidity
A rigid container, 10m3 in volume, contains moist air at 45◦C, 100 kPa, φ = 40%. The container is now cooled to 5◦C. Neglect the volume of any liquid that might be present and find the final
In the production of ethanol from corn, the solids left after fermentation are dried in a continuous flowoven. This process generates a flow of 15 kg/s moist air, 90◦C with 70% relative humidity,
To reduce natural gas use in the previous problem, a suggestion is to take and cool the mixture and condense out some water before heating it again. So, the flow is cooled from 90◦C to 50◦C and
Use the formulas and the steam tables to find the missing property of φ, ω, and Tdry; total pressure is 100 kPa. Repeat the answers using the psychometric chart.a. φ = 50%, ω = 0.010b. Tdry =
The discharge moist air from a clothes dryer is at 40◦C, 80% relative humidity. The flow is guided through a pipe up through the roof and a vent to the atmosphere. Due to heat transfer in the pipe,
In a ventilation system, inside air at 34◦C and 70% relative humidity is blown through a channel, where it cools to 25◦C with a flow rate of 0.75 kg/s dry air. Find the dew point of the inside
To make dry coffee powder, we spray 0.2 kg/s coffee (assume liquid water) at 80°C in to a chamber, where we add 10 kg/s dry air at T. All the water should evaporate, and the air should leave at a
An insulated tank has an air inlet, ω1 = 0.0084, and an outlet, T2 = 22◦C, φ2 = 90%, both at 100 kPa. A third line sprays 0.25 kg/s water at 80◦C, 100 kPa. For steady operation, find the outlet
An air flow of 2 kg/s at 30◦C, relative humidity 80%, is conditioned by taking half of the air flow, cooling it, and mixing it with the other half. Assume the outlet flow should have a water
Moist air at 31◦C and 50% relative humidity flows over a large surface of liquid water. Find the adiabatic saturation temperature by trial and error. Hint: it is around 22.5◦C.
A flow of air at 10◦C, φ = 90% is brought into a house, where it is conditioned to 25◦C, 60% relative humidity. This is done with a combined heater-evaporator in which any liquid water is at
An air conditioner for an airport receives desert air at 45◦C, 10% relative humidity and must deliver it to the building at 20◦C, 50% relative humidity. The buildings have a cooling system with
A flow of moist air from a domestic furnace, state 1, is at 45◦C, 10% relative humidity with a flow rate of 0.05 kg/s dry air. A small electric heater adds steam at 100◦C, 100 kPa generated from
A flow out of a clothes dryer of 0.05 kg/s dry air is at 40◦Cand relative humidity 60%. It flows though a heat exchanger, where it exits at 20◦C. After exiting the heat exchanger, the flow
A commercial laundry runs a dryer that has an exit flow of 0.5 kg/s moist air at 48◦C, 70% relative humidity. To reduce the heating cost, a counter flow stack heat exchanger is used to heat the
An indoor pool evaporates 1.512 kg/h of water, which is removed by a dehumidifier to maintain 21◦C, φ = 70% in the room. The dehumidifier, shown in Fig. P11.107, is a refrigeration cycle in which
A flow of moist air at 21◦C, 60% relative humidity should be produced by mixing two different moist air flows. Flow1 is at 10◦C, relative humidity 80% and flow 2 is at 32◦C and has Twet =
Consider a mixing process as in Fig. P11.114 where flow 1 comes in as cold and moist, 10◦C, φ = 90%. It is mixed with a flow 2 at 42◦C, T = 31◦C. If the exit flow should be at 21◦C, φ = 50%
A flow of moist air at 100 kPa, 35◦C, 40% relative humidity is cooled by adiabatic evaporation of liquid 20◦C water to reach a saturated state. Find the amount of water added per kg dry air and
A flow out of a clothes dryer of 0.1 kg/s dry air is at 60◦C and relative humidity 60%. It flows through a heat exchanger, where it exits at 20◦C. After exiting the heat exchanger, the flow
To refresh air in a room, a counter flow heat exchanger (see Fig. P11.122) is mounted in the wall, drawing in outside air at 0.5◦C, 80% relative humidity and pushing out room air at 40◦C, 50%
Consider several flow processes with ideal gases: (1) Compression of a gas mixture from 100 kPa to 200 kPa; (2) Cooling a gas mixture from 50◦C to ambient 20◦C using ambient
A mixture of 75% carbon dioxide and 25% water on a mole basis is flowing at 1600 K, 100 kPa into a heat exchanger, where it is used to deliver energy to a heat engine. The mixture have leave the heat
For flows with moist air where the water content is changed either by evaporation or by condensation, what happens to the exergy? Is the water vapor in air flowing over a lake in equilibrium with the
A semipermeable membrane is used for the partial removal of oxygen from air that is blown through a grain elevator storage facility. Ambient air (79% nitrogen, 21% oxygen on a mole basis) is
The accuracy of calculations can be improved by using a better estimate for the specific heat. Reconsider the previous problem and use Cp = Δh/ΔT from Table A.8 centered at 1000 K.
A large air separation plant takes in ambient air (79% N2, 21% O2 by mole) at 100 kPa, 20◦C at a rate of 25 kg/s. It discharged a stream of pure O2 gas at 200 kPa, 100◦C and a stream of pure N2
A piston/cylinder contains helium at 110 kPa at ambient temperature 20◦C and an initial volume of 20 L, as shown in Fig. P11.136. The stops are mounted to give a maximum volume of 25 L, and the
An insulated rigid 2-m3 tank A contains carbon dioxide gas at 200◦C, 1MPa. An uninsulated rigid 1-m3 tank B contains ethane, (C2H6), gas at 200 kPa, room temperature 20◦C. The two tanks are
A 0.2-m3 insulated rigid vessel is divided into two equal parts, A and B, by an insulated partition, as shown in Fig. P11.140. The partition will support a pressure difference of 400 kPa before
An air–water vapor mixture enters a steady-flow heater humidifier unit at state 1: 10◦C, 10% relative humidity, at the rate of 1 m3/s. A second air–vapor stream enters the unit at state 2:
A gas mixture at 250 F, 18 lbf/in.2 is 50% N2, 30% H2O, and 20% O2 on a mole basis. Find the mass fractions, the mixture gas constant, and the volume for 10 lbm of mixture.
In a car engine, gasoline (assume octane, C8H18) is evaporated and then mixed with air in a ratio of 1:15 by mass. In the cylinder the mixture is at 110 psia, 1200 R when the spark fires. For that
A diesel engine sprays fuel (assume n-dodecane, C12H26, M = 170.34 Ibm/lbmol) into the combustion chamber already filled with 1 mol fuel per 88 mol air. Find the fuel fraction on a mass basis and the
A new refrigerant, R-410a, is a mixture of R-32 and R-125 in a 1:1 mass ratio. What is the overall molecular weight, the gas constant, and the ratio of specific heats for such a mixture?
A rigid container has 1 lbm carbon dioxide at 540 R and 1 lbm argon at 720 R, both at 20 psia. Now they are allowed to mix without any heat transfer. What is the final T, P?
A flow of 1 lbm/s argon at 540 R and another flow of 1 lbm/s carbon dioxide at 2800 R, both at 20 psia, are mixed without any heat transfer. What is the exit T, P?
A piston/cylinder device contains 0.3 lbm of mixture of 40% methane and 60% propane by mass at 540 R, 15 psia. The gas is now slowly compressed in an isothermal (T =constant) process to a final
Two insulated tanks, A and B, are connected by a valve. Tank A has a volume of 30 ft3 and initially contains argon at 50 lbf/in.2, 50 F. Tank B has a volume of 60 ft3 and initially contains ethane at
A rigid container has 1 lbm argon at 540 R and 1 lbm argon at 720 R, both at 20 psia. Now they are allowed to mix without any external heat transfer. What is the final T, P? Is any s generated?
A 1-lbm/s flow of saturated moist air (relative humidity 100%) at 14.7 psia and 50 F goes through a heat exchanger and comes out at 77 F. What is the exit relative humidity and how much power is
If I have air at 14.7 psia and (a) 15 F, (b) 115 F, and (c) 230 F, what is the maximum absolute humidity I can have?
Consider a 35-ft3/s flow of atmospheric air at 14.7 psia, 77 F, and 80% relative humidity. Assume this flows into a basement room, where it cools to 60 F at 14.7 psia. How much liquid will condense
The cogeneration gas-turbine cycle can be augmented with a heat pump to extract more energy from the turbine exhaust gas, as shown in Fig. P11.194. The heat pump upgrades the energy to be delivered

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