Questions and Answers of Fundamentals Of Thermodynamics

The natural refrigerant carbon dioxide has a fairly low critical temperature. Find the high temperature, the condensing temperature, and the COP if it is used in a standard cycle with high and low
A refrigerator receives 500Wof electrical power to the compressor driving the cycle flow of R-134a. The refrigerator operates with a condensing temperature of 40◦C and a low temperature of
A new air conditioner using R-410a is used in heat pump mode. The high pressure is 2000 kPa and the low pressure is 400 kPa. It warms a house at 20◦C, driven by an electric power input of 2 kW in
A heat pump for heat upgrade uses ammonia with a low temperature of 25◦C and a high pressure of 5000 kPa. If it receives 1 MW of shaft work, what is the rate of heat transfer at the high
Reconsider the heat pump in the previous problem. Assume the compressor is split into two. First, compress to 2000 kPa. Then take heat transfer out at constant P to reach saturated vapor and then
A car air conditioner operating with R-134a as the working fluid has a minimum temperature of −10◦C and a maximum pressure of 1 MPa. The actual adiabatic compressor exit temperature is 50◦C.
An air conditioner in the airport of Timbuktu runs a cooling system using R-410a with a high pressure of 1800 kPa and a low pressure of 200 kPa. It should cool the desert air at 45◦C down to
A heat pump uses R410a with a high pressure of 3000 kPa and an evaporator operating at−10◦C, so it can absorb energy from underground water layers at 4◦C. Find the COP and the temperature at
Consider an ideal heat pump that has a condenser temperature of 50◦C and an evaporator temperature of 0◦C. Determine the COP of this heat pump for the working fluids R-134a and ammonia.
A refrigerator using R-134a is located in a 20◦C room. Consider the cycle to be ideal, except that the compressor is neither adiabatic nor reversible. Saturated vapor at −20◦C enters the
A cascade system with one refrigeration cycle operating with R-410a has an evaporator at −40◦C and a high pressure of 1200 kPa. The high-temperature cycle uses R-134a with an evaporator at 0◦C
A cascade system is composed of two ideal refrigeration cycles, as shown in Fig. 9.28. The high temperature cycle uses R-410a. Saturated liquid leaves the condenser at 40◦C, and saturated vapor
A split evaporator is used to provide cooling of the refrigerator section and separate cooling of the freezer section, as shown in Fig. P9.109. Assume constant pressure in the two evaporators. How
A refrigerator using R-410a is powered by a small natural gas-fired heat engine with a thermal efficiency of 25%, as shown in Fig. P9.110. The R-410a condenses at 40◦C and evaporates at −20◦C,
As explained in the previous problem, the ammonia absorption cycle is very similar to the setup sketched in Problem 9.110. Assume the heat engine has an efficiency of 30% and the COP of the
Give an estimate for the overall COP' of an ammonia absorption cycle used as a chiller to cool water to 5◦Cina25◦Cambientwhen the small pump work is neglected. A heat source is available at
If we neglect the external irreversibility due to the heat transfers over finite temperature differences in a power plant, how would you define its second-law efficiency?
A condenser is maintained at 60◦C by cooling it with atmospheric air coming in at 20◦C and leaving at 35◦C. The condenser must reject 25 MW from the water to the air. Find the flow rate of air
Find the flows and fluxes of exergy in the condenser of Problem 9.29. Use them to determine the second law efficiency, T0 = 15◦C.Data from Problem 9.29.A coal-fired power plant produces 25 kg/s
A new air conditioner using R-410a is used in heat pump mode. The high pressure is 2000 kPa and the low pressure is 400 kPa. It warms a house at 20◦C driven by an electric power input of 2 kW in an
For a cryogenic experiment, heat should be removed from a space at 75 K to a reservoir at180 K. A heat pump is designed to use nitrogen and methane in a cascade arrangement (see Fig. 9.28), where the
A supercritical power plant has a high pressure of 30 MPa, and the boiler heats the water to 500◦C with 45◦C in the condenser. To avoid a quality in the turbine of less than 92%, determine the
A dairy farmer needs to heat a 0.1-kg/s flow of milk from room temperature, 20◦C, to 60◦C in order to pasteurize it and then send the flow through a cooler, bringing it to 10◦C for storage. He
Consider a solar-energy-powered ideal Rankine cycle that uses water as the working fluid. Saturated vapor leaves the solar collector at 150 psia, and the condenser pressure is 0.95 psia. Determine
A Rankine cycle with R-410a has the boiler at 600 psia superheating to 340 F, and the condenser operates at 100 psia. Find all four energy transfers and the cycle efficiency.
A low-temperature power plant operates with R-410a maintaining 60 psia in the condenser, a high pressure of 400 psia with superheat. Find the temperature out of the boiler/super heater so that the
A smaller power plant produces 50 lbm/s steam at 400 psia, 1100 F in the boiler. It cools the condenser with ocean water coming in at 60 F and returned at 65 F so that the condenser exit is at110 F.
Consider a simple ideal Rankine cycle using water at a supercritical pressure. Such a cycle has the potential advantage of minimizing local temperature differences between the fluids in the steam
A Rankine cycle uses ammonia as the working substance and is powered by solar energy. It heats the ammonia to 320 F at 800 psia in the boiler/super heater. The condenser is water cooled, and the exit
Assume that the power plant in Problem 9.156E should deliver 1000 Btu/s. What is the mass flow rate of ammonia?Data from Problem 9.156EA Rankine cycle uses ammonia as the working substance and is
An open FWH receives steam at 150 psia, 400 F from the turbine and 1150 psia, 200 F water from the feedwater line. Find the required fraction of the extraction flow in the turbine.
A Rankine cycle feeds 10 lbm/s ammonia at 300 psia, 280 F to the turbine, which has an extraction point at 125 psia. The condenser is at 0 F, and a closed FWH has an exit state (3) at the temperature
Find the flows and fluxes of exergy in the condenser of Problem 9.154E. Use those values to determine the second-law efficiency.Data from Problem 9.154E.A smaller power plant produces 50 lbm/s steam
For Problem 9.162E, consider the boiler/ superheater. Find the exergy destruction and the second-law efficiency for the boiler-source setup.Data from Problem 9.162E,A Rankine cycle feeds 10 lbm/s
Find the two heat transfer rates, the total cycle exergy destruction, and the second-law efficiency for the refrigerator in Problem 9.171E.Data from Problem 9.171E.A refrigerator receives 500Wof
A power plant is built to provide district heating of buildings that requires 90◦C liquid water at 150 kPa. The district heating water is returned at 50◦C, 100 kPa in a closed loop in an amount
The condenser in Problem 4.118 uses cooling water from a lake at 20◦C and it should not be heated more than 5◦C, as it goes back to the lake. Assume the heat transfer rate inside the condenser is
Use the computer software to solve the following problems with R-12 as the working substance:(a) 9.84, (b) 9.87, (c) 9.98,(d) 9.105,(e) 9.172E.
Use the computer software to solve the following problems with R-22 as the working substance:(a) 9.21, (b) 9.65,(c) 9.87, and(d) 9.151E.
Is a Brayton cycle the same as a Carnot cycle? Name the four processes.
For a given Brayton cycle, the cold air approximation gave a formula for the efficiency. If we use the specific heats at the average temperature for each change in enthalpy, will that give a higher
Does the efficiency of a jet engine change with altitude since the density varies?
Why is an air refrigeration cycle not common for a household refrigerator?
For a given compression ratio, does an Otto cycle have a higher or lower efficiency than a diesel cycle?
How many parameters do you need to know to completely describe the Atkinson cycle? How about the Miller cycle?
In an Otto cycle, the cranking mechanism dictates the volume given the crank position. Can you say something similar for the Brayton cycle?
For all the gas cycles, it is assumed that the ideal compression and expansions are isentropic. This is approximated with a poly tropic process having n = k. The expansion after combustion will have
For all the gas cycles, it is assumed that the ideal compression and expansions are isentropic. This is approximated with a poly tropic process having n = k. The compression in a diesel engine leads
If we compute the efficiency of an Otto or diesel cycle, we get something like 60% for a compression ratio of 10:1. Is a real engine efficiency close to this?
A hybrid power train couples a battery/motor with an internal combustion engine. Mention a few factors that make this combination a little more efficient.
A Brayton cycle has a compression ratio of 15:1 with a high temperature of 1600 K and the inlet at 290 K, 100 kPa. Use cold air properties and find the specific heat addition and specific net work
Consider an ideal air-standard Brayton cycle in which the air into the compressor is at 100 kPa, 20◦C, and the pressure ratio across the compressor is 12:1. The maximum temperature in the cycle is
A Brayton cycle has air into the compressor at 95 kPa, 290 K, and has an efficiency of 50%. The exhaust temperature is 675 K. Find the pressure ratio and the specific heat addition by the combustion
A Brayton cycle has inlet at 290 K, 90 kPa, and the combustion adds 1000 kJ/kg. How high can the compression ratio be so that the highest temperature is below 1700 K? Use cold air properties to
Assume a state of 1400 kPa, 2100K, into the turbine section of a Brayton cycle with an adiabatic expansion to 100 kPa and a compressor inlet temperature of 300 K. Find the missing temperatures in the
A Brayton cycle produces 14 MW with an inlet state of 17◦C, 100 kPa, and a compression ratio of 16:1. The heat added in the combustion is 1160 kJ/kg. What are the highest temperature and the mass
A Brayton cycle with an ideal regenerator has inlet at 290 K, 90 kPa with the highest P, T as 1170 kPa, 1700 K. Find the specific heat transfer and the cycle efficiency using cold air properties.
An ideal air-standard Brayton cycle includes an ideal regenerator. The state into the compressor is 100 kPa, 20◦C, and the pressure ratio across the compressor is 12:1. The highest cycle
Consider an ideal gas-turbine cycle with a pressure ratio across the compressor of 12:1. The compressor inlet is at 300 K, 100 kPa, and the cycle has a maximum temperature of 1600 K. An ideal
A two-stage air compressor has an intercooler between the two stages, as shown in Fig. P10.35.The inlet state is 100 kPa, 290 K, and the final exit pressure is 1.6 MPa. Assume that the constant
An air compressor has inlet at 100 kPa, 290 K, and brings it to 500 kPa, after which the air is cooled in an intercooler to 340Kby heat transfer to the ambient 290 K. Assume this first
A two-stage compressor in a gas turbine brings atmospheric air at 100 kPa, 17◦C to 500 kPa, then cools it in an intercooler to 27◦C at constant P. The second stage brings the air to 2500 kPa.
A gas turbine with air as the working fluid has two ideal turbine sections, as shown in Fig. P10.42, the first of which drives the ideal compressor, with the second producing the power output. The
Consider an ideal air-standard Ericsson cycle that has an ideal regenerator, as shown in Fig. P10.44. The high pressure is 1.5 MPa and the cycle efficiency is 60%. Heat is rejected in the cycle at a
An air-standard Ericsson cycle has an ideal regenerator. Heat is supplied at 1000◦C and heat is rejected at 80◦C. Pressure at the beginning of the isothermal compression process is 70 kPa. The
Consider an ideal air-standard cycle for a gas turbine, jet propulsion unit, such as that shown in Fig. 10.11. The pressure and temperature entering the compressor are 90 kPa, 290 K. The pressure
The turbine section in a jet engine (Fig. P10.48) receives gas (assume air) at 1200 K, 800 kPa with an ambient atmosphere at 80 kPa. The turbine is followed by a nozzle open to the atmosphere, and
Given the conditions in the previous problem, what pressure could an ideal compressor generate (not the 800 kPa but higher)?
An afterburner in a jet engine adds fuel after the turbine, thus raising the pressure and temperature due to the energy of combustion. Assume a standard condition of 800 K, 250 kPa, after the turbine
An air standard refrigeration cycle has air into the compressor at 100 kPa, 270 K, with a compression ratio of 3:1. The temperature after heat rejection is 300 K. Find the COP and the highest cycle
A standard air refrigeration cycle has −10◦C, 100 kPa into the compressor, and the ambient cools the air down to 35◦C at 400 kPa. Find the lowest temperature in the cycle, the low-T specific
The mean effective pressure scales with the net work and thus with the efficiency. Assume the heat transfer per unit mass is a given (it depends on the fuel–air mixture). How does the total power
A four-stroke gasoline engine runs at 1800 RPM with a total displacement of 3 L and a compression ratio of 10:1. The intake is at 290 K, 75 kPa, with a mean effective pressure of 600 kPa. Find the
A four-stroke gasoline 4.2-L engine running at 2000 RPM has an inlet state of 85 kPa, 280 K. After combustion it is 2000 K, and the highest pressure is 5 MPa. Find the compression ratio, the cycle
A four-stroke 2.4-L gasoline engine runs at 2500 RPM and has an efficiency of 60%. The state before compression is 40 kPa, 280 K and after combustion it is at 2400 K. Find the highest T and P in the
Suppose we reconsider the previous problem and, instead of the standard ideal cycle, we assume the expansion is a poly tropic process with n = 1.5. What are the exhaust temperature and the expansion
To approximate an actual spark-ignition engine, consider an air-standard Otto cycle that has a heat addition of 1800 kJ/kg of air, a compression ratioof 7, and a pressure and temperature at the
A 3.3-L minivan engine runs at 2000 RPM with a compression ratio of 10:1. The intake is at 50 kPa, 280 K and after expansion it is at 750 K. Find the highest T in the cycle, the specific heat
A four-stroke gasoline engine has a compression ratio of 10:1 with four cylinders of total displacement at 2.3 L. The inlet state is 280 K, 70 kPa and the engine is running at 2100 RPM, with the fuel
Assume a state of 5000 kPa, 2100 K after combustion in an Otto cycle with a compression ratio of 10:1; the intake temperature is 300 K. Find the missing temperatures in the cycle using Table A.7 and
A turbocharged engine (Fig. P10.82) runs in an Otto cycle with the lowest T at 290 K and the lowest P at 150 kPa. The highest T is 2400 K, and combustion adds 1200 kJ/kg as heat transfer. Find the
A diesel engine has an inlet at 95 kPa, 300 K and a compression ratio of 20:1. The combustion releases 1300 kJ/kg. Find the temperature after combustion using cold air properties.
A diesel engine has a compression ratio of 20:1 with an inlet of 95 kPa, 290 K, state 1, with volume 0.5 L. The maximum cycle temperature is 1800 K. Find the maximum pressure, the net specific work,
A diesel engine has a bore of 0.1 m, a strike of 0.11 m, and a compression ratio of 19:1 running at 2000 RPM. Each cycle takes two revolutions and has a mean effective pressure of 1400 kPa. With a
A supercharger is used for a two-stroke, 10-L diesel engine, so intake is 200 kPa, 320 K, and the cycle has a compression ratio of 18:1 and a mean effective pressure of 830 kPa. The engine is 10 L
The world’s largest diesel engine has displacement of 25 m3 running at 200 RPM in a two-stroke cycle producing 100 000 hp. Assume an inlet state of 200 kPa, 300 K and a compression ratio of 20:1.
Consider an ideal air-standard diesel cycle in which the state before the compression process is 95 kPa, 290 K and the compression ratio is 20. Find the thermal efficiency for a maximum temperature
Air in a piston/cylinder goes through a Carnot cycle in which TL = 26.8◦C 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 150 kPa, 300 K, a compression ratio of 9, and a heat release of 1000 kJ/kg. Find the needed expansion ratio.
An Atkinson cycle has state 1 as 150 kPa, 300 K, 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 150 kPa, 300 K, a compression ratio of 9, and an expansion ratio of 14. Find the mean effective pressure.
A Miller cycle has state 1 as 150 kPa, 300 K, a compression ratio of 9, and an expansion ratio of 14. If P4 is 250 kPa, find the heat release in the combustion.
A Miller cycle has state 1 as 150 kPa, 300 K, a compression ratio of 9, and a heat release of 1000 kJ/kg. Find the needed expansion ratio so that P4 is 250 kPa.
In a Miller cycle, assume we know state 1 (intake state) compression ratios CR1 and CR. Find an expression for the minimum allowable heat release so that P4 = P5, that is, it becomes an Atkinson
A Brayton cycle has a compression ratio of 15:1 with a high temperature of 1600 K and an inlet state of 290 K, 100 kPa. Use cold air properties to find the specific net work output and the second law
Determine the second-law efficiency of an ideal regenerator in the Brayton cycle.
Assume a regenerator in a Brayton cycle has an efficiency of 75%. Find an expression for the second-law efficiency.
Consider an ideal air-standard diesel cycle in which the state before the compression process is 95 kPa, 290 K, and the compression ratio is 20. Find the maximum temperature (by iteration) in the
In a Brayton cycle the inlet is at 540 R, 14 psia and the combustion adds 350 Btu/lbm. The maximum temperature is 2500 R due to material considerations. Find the maximum permissible compression ratio
A Brayton cycle has a compression ratio of 15:1 with a high temperature of 2900 R and the inlet at 520 R, 14 psia. Use cold air properties and find the specific heat transfer and specific net work

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