Questions and Answers of Fundamentals Of Thermodynamics

Find the missing properties of P, v, u, and x and the phase of ammonia, NH3.a. T = 65◦C, P = 600 kPab. T = 20◦C, P = 100 kPac. T = 50◦C, v = 0.1185 m3/kg
Helium flows at 75 psia, 900 R, 330 ft/s into a convergent-divergent nozzle. Find the throat pressure and temperature for reversible flow and M = 1 at the throat.
What is the exit pressure that will allow a reversible subsonic exit flow in the previous problem?Data from previous problemAir flows into a convergent-divergent nozzle with an exit area 2.0 times
The high-velocity exit flow in Example 15.7 is at 183 K. Can that flow be used to cool a room? Example 15.7 A converging-diverging nozzle has an exit area to throat area ratio of 2. Air enters this
Find the equilibrium constant for CO2 ⇔ CO + 12 O2 at 3960 R using Table A.11.
Find the equilibrium constant for the reaction 2NO + O2 ⇔ 2NO2 from the elementary reaction in Table A.11 to answer these two questions: Which nitrogen oxide, NO or NO2, is more stable at 25◦C,
Calculate the equilibrium constant for the first reaction in the Zeldovich mechanism at 2600 K, 500 kPa. Notice that this is not listed in Table A.11.
Redo the previous problem but include the dissociation of oxygen and nitrogen.Data from previous problem Consider air at 2600 K, 1 MPa. Find the equilibrium concentration of NO, neglecting
Repeat the previous problem, assuming the argon constitutes 1% of a gas mixture where we neglect any reactions of other gases and find the pressure that will give a mole concentration of A r + of
Consider a gasifier that receives 4 kmol CO, 3 kmol H2, and 3.76 kmol N2 and brings the mixture to equilibrium at 900 K, 1 MPa, with the following reaction:2 CO+ 2H2 ⇔ CH4 + CO2which is the sum of
A coal gasifier produces a mixture of 1 CO and 2H2 that is fed to a catalytic converter to produce methane. This is the methanation reaction in Eq. 14.33 with an equilibrium constant at 600 K of
Assume dry air (79% N2 and 21% O2) is heated to 2000 K in a steady-flow process at 200 kPa and only the reactions listed in Table A.11 (and their linear combinations) are possible. Find the final
Consider the water–gas reaction in Example 14.4. Find the equilibrium constant at 500, 1000, 1200, and 1400 K. What can you infer from the result?
Power plants may use off-peak power to compress air into a large storage facility (see Problem 7.55). The compressed air is then used as the air supply to a gas-turbine system where it is burned with
A basic hydrogen–oxygen fuel cell operates at 600 K instead of 298 K, as in Example 13.15. For a total power of 5 kW, find the hydrogen mass flow rate and the exergy in the exhaust flow.
A reversible fuel cell operating with hydrogen and pure oxygen produces water at the reference conditions P0, T0; this is described in Example 13.15. Find the work output and any heat transfer, both
Redo the previous problem for natural gas D in Table 13.3.Data from previous problem Consider natural gas A in Table 13.2. Calculate the enthalpy of combustion at 25◦C, assuming that the
Consider natural gas A in Table 13.2. Calculate the enthalpy of combustion at 25◦C, assuming that the products include vapor water. Repeat the answer for liquid water in the products.
Solve the following problem (assign only one at a time, like Problem 12.183 c SI or E) with the CATT3 software: (a) 12.81, (b) 12.85 (12.165E), (c) 12.86 (12.166E), (d) 12.108
R-410a is a 1:1 mass ratio mixture of R-32 and R-125. Find the specific volume at 80 F, 200 psia using Kay’s rule and the generalized charts and compare to Table F.9.
Find the heat of evaporation, hfg, for R-134a at 30 F from the generalized charts and compare to the value in Table F. 10.
Use Table F.9 to find the compressibility of R-410a at 140 F and (a) Saturated liquid, (b) Saturated vapor, and (c) 400 psia.
Use the EOS in Example 12.3 and find an expression for isothermal changes in the Helmholtz function between two states.
Gases like argon and neon have constant specific heats. Develop an expression for the ideal gas contribution to the Helmholtz function in Eq. 12.92 for these cases. a* = h* – RT – Ts* (12.92)
Verify that the ideal gas part of the Helmholtz function substituted in Eq. 12.86 does lead to the ideal gas law, as in the note after Eq. 12.97. da/RT da" = p pRT ap = 8 as =1+8 a8 (12.97) T
R-410a is a 1:1 mass ratio mixture of R-32 and R-125. Find the specific volume at 20◦C, 1200 kPa, using Kay’s rule and the generalized charts, and compare it to the solution using Table B.4.
An alternative energy power plant has carbon dioxide at 6 MPa, 100◦C flowing into a turbine and exiting as saturated vapor at 1 MPa. Find the specific turbine work using generalized charts and
A new refrigerant, R-123, enters a heat exchanger as saturated liquid at 40◦C and exits at 100 kPa in a steady flow. Find the specific heat transfer using Fig. D.2.
Find the heat of evaporation, hfg, for R-134a at 0◦C from the generalized charts and compare to the value in Table B.5.
Show that the van der Waals equation can be written as a cubic equation in the compressibility factor, as in Eq. 12.53. 2 () () - 27P, +1) z+ 6472 27P? 51273 z - = 0 (12.53)
Show how to find the constants in Eq. 12.52 for the van der Waals EOS. Vc = 3b 27 R?T? a 64 P. (12.52) RT. b 8P.
Use Table B.4 to find the compressibility of R-410a at 60◦C and (a) Saturated liquid, (b) Saturated vapor, and (c) 3000 kPa.
Use Table B.3 and find the compressibility of carbon dioxide at the critical point.
Use Table B.3 to find the speed of sound for carbon dioxide at 2500 kPa near 100◦C. Approximate the partial derivative numerically.
Use Eq. 12.32 to solve for (∂T/∂P)s in terms of T, v, Cp, and αp. How large a temperature change does water at 25◦C (αp = 2.1 × 10−4 K−1) have when compressed from 100 kPa to 1000 kPa in
Use Eq. 12.34 to derive an expression for the derivative (∂T/∂v)s. What is the general shape of a constant s process curve in a T–v diagram? For an ideal gas, can you say a little more about
The triple point of carbon dioxide is −56.4◦C. Predict the saturation pressure at that point using Table B.3.
To reduce the 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 200 F to 120 F, as
In the production of ethanol from corn, the solids left after fermentation are dried in a continuous-flow oven. This process generates a flow of 35 lbm/s moist air, 200 F with 70% relative humidity,
A moist air flow of 5 kg/min at 30◦C, Φ = 60%, 100 kPa goes through a dehumidifier in the setup shown in Problem 11.107. The air is cooled down to 15◦Cand then blown over the condenser. The
Repeat the previous problem using variable specific heats.Data from previous problem 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
A commercial laundry runs a dryer that has an exit flow of 1 lbm/s moist air at 120 F, 70% relative humidity. To reduce the heating cost, a counter flow stack heat exchanger is used to heat the
A steady flow of 0.6 lbm/s of a 60% carbon dioxide and 40% water mixture by mass at 2200Rand 30 psia is used in a constant-pressure heat exchanger where 300 Btu/s is extracted from the flow. Find the
Do the previous problem for R-507a, which is a 1:1 mass ratio of R-125 and R-143a. The refrigerant R-143a has a molecular mass of 84.041 lbm/lbmol, and Cp = 0.222 Btu/lbm-R.
The cycle in the previous problem is used in a 2.4-L engine running at 1800 RPM. How much power does it produce?Data from previous problem A turbocharged engine (Fig. P10.82) runs in an Otto
A steady flow of 0.3 kg/s of 60% carbon dioxide and 40%water by mass at 1200 K, 200 kPa is used in a heat exchanger where 300 kW is extracted from the flow. Find the flow exit temperature and the
A steady flow of 0.3 kg/s of 60% carbon dioxide and 40% water mixture by mass at 1200 K, 200 kPa is used in a constant-pressure heat exchanger where 300 kW is extracted from the flow. Find the exit
Do Problem 11.24 for R-507a, which has a 1:1 mass ratio of R-125 and R-143a. The refrigerant R-143a has a molecular mass of 84.041 kg/kmol and Cp = 0.929 kJ/kg-K.Data from problem 11.24A new
The effect of adding a regenerator to the gas-turbine cycle in the previous problem is to be studied. Repeat this problem by including a regenerator with various values of the regenerator efficiency.
Can the combined cycles in the previous problem deliver more heat than what comes from the R-410a? Find any amounts, if so, by assuming some conditions.Data from previous problem A small utility
A refrigerator with R-134a as the working fluid has a minimum temperature of −10◦C and a maximum pressure of 1 MPa. Assume an ideal refrigeration cycle, as in Fig. 9.23. Find the specific heat
A refrigeration cycle, as in Fig. 9.23, can be used for cooling or for heating purposes using one of the two heat exchangers. Suppose a refrigerator should cool meat at −10◦C in a 30◦C kitchen.
Reconsider the previous problem and find the second-law efficiency if we do consider the “value” of the exhaust flow.'Data from previous problem A Brayton cycle has a compression ratio of
The conversion efficiency of the Brayton cycle in Eq. 10.1 was determined with cold air properties. Find a similar formula for the second-law efficiency, assuming the low-T heat rejection is assigned
Redo the previous problem for a large stationary Brayton cycle where the low-T heat rejection is used in a process application and thus has nonzero exergy.Data from previous problemThe conversion
A gasoline engine has a volumetric compression ratio of 9. The state before compression is 290 K, 90 kPa, and the peak cycle temperature is 1800 K. Find the pressure after expansion, the cycle net
A Rankine cycle maintains 130 F in the condenser which is cooled by a 70 F reservoir. The steam out of the boiler is at 600 psia, 700 F being heated from a 900 F source. Determine the flux of exergy
The refrigerant R-134a is used as the working fluid in a conventional heat pump cycle. Saturated vapor enters the compressor of this unit at 50 F; its exit temperature from the compressor is measured
A refrigerator receives 500Wof electrical power to the compressor driving the cycle flow of R-134a. The refrigerator operates with a condensing temperature of 100 F and a low temperature of −10 F.
Find the high temperature, the condensing temperature, and the COP if ammonia is used in a standard refrigeration cycle with high and low pressures of 800 psia and 300 psia, respectively.
An automobile air conditioner (refrigerator) in 70 F ambient uses R-134a, and I want to have cold air at 20 F produced. What is the minimum high P and the maximum low P it can use?
Write the analysis (continuity and energy equations) for the closed FWH with a drip pump, as shown in Fig. 9.13. Assume that the control volume has state 4 out, so it includes the drip pump. Find the
For the previous problem, also find the specific entropy generation in the boiler heat source setup.Data from previous problem A steam power plant operates with a high pressure of 4 MPa and has
The power plant in the previous problem has too low a quality in the low-pressure turbine section, so the plant wants to increase the superheat. What should the superheat be so that the quality of
A steam power plant, as shown in Fig. 9.3 operating in a Rankine cycle, has saturated vapor at 3.0 MPa leaving the boiler. The turbine exhausts to the condenser operating at 10 kPa. Find the specific
(Adv.) Reexamine the previous problem when the intercooler cools the substance to a temperature, T2 > T1, due to finite heat-transfer rates. What is the effect of having isentropic
A can of volume 8 ft3 is empty and is filled with R-410a from a line at 200 psia, 100 F. The process is adiabatic and stops at P = 150 psia. Use Table F.9 to find the final temperature and the
A large supply line has a steady air flow at 900 R, 2 atm. It is used in the three different adiabatic devices shown in Fig. P7.101: a throttle flow, an ideal nozzle, and an ideal turbine. All the
A large supply line has a steady flow of R-410a at 175 psia, 140 F. It is used in three different adiabatic devices shown in Fig. P7.101: a throttle flow, an ideal nozzle, and an ideal turbine. All
A 200-L insulated tank contains nitrogen gas at 200 kPa, 300 K. A line with nitrogen at 1500 K, 1000 kPa adds 40% more mass to the tank with a flow through a valve. Use Table A.8 to find the final
A flow of 2 kg/s hot exhaust air at 150◦C, 125 kPa supplies heat to a heat engine in a setup similar to that of the previous problem, with the heat engine rejecting heat to the ambient air at 290
Write a program to solve a problem similar to Problem 6.103, but instead of the ideal gas tables, use the formula for the specific heat as a function of temperature in Table A.6.Data from Problem
A cylinder/piston contains 0.1 lbm methane gas at 15 psia, 70 F. The gas is compressed reversibly to a pressure of 120 psia. Calculate the work required if the process is adiabatic.
R-410a at 60 psia is brought from 60 F to 240 F in a constant-pressure process. Evaluate the change in specific entropy using Table F.9 and using ideal gas with Cp = 0.1935 Btu/lbmR.
Water at 20 psia, 240 F, receives 40 Btu/lbm in a reversible process by heat transfer. Which process changes s the most: constant T, constant V, or constant P?
A car engine block receives 2 kW at its surface of 450 K from hot combustion gases at 1500 K. Near the cooling channel, the engine block transmits 2 kW out at its 400 K surface to the coolant flowing
Room air at 23◦C is heated by a 2000-W space heater with a surface filament temperature of 700 K, shown in Fig. P6.170. The room at steady state loses the power to the outside which is at 7◦C.
A heat pump with COP = 4 uses 1 kW of power input to heat a 25◦C room, drawing energy from the outside at 15◦C. Assume the high/low temperatures in the heat pump are 45◦C/0◦C. Find the total
A radiant heating lamp powered by electricity has a surface temperature of 1000 K emitting 500 W. The radiation is absorbed by surfaces at the ambient temperature of 18◦C. Find the total entropy
Reconsider the heat pump in the previous problem and assume it has a COP of 2.5. What are the fluxes of entropy into and out of the heat pump and the rate of entropy generation inside it?Data from
A heat pump (see Problem 5.49) should upgrade 5 MW of heat at 85◦C to heat delivered at 150◦C. For a reversible heat pump, what are the fluxes of entropy into and out of the heat pump?Data from
A cylinder/piston contains 100 L air at 110 kPa, 25◦C. The air is compressed in a reversible poly tropic process to a final state of 800 kPa, 500 K. Assume the heat transfer is with the ambient at
A room at 22◦C is heated electrically with 1500W to keep a steady temperature. The outside ambient is at 5◦C. Find the flux of S (= ˙Q/T) into the room air, into the ambient, and the rate of
Do Problem 6.103 and assume that the process is poly tropic with n = 1.15.Data from Problem 6.103A cylinder/piston contains 1 kg methane gas at 100 kPa, 300 K. The gas is compressed reversibly to a
The air in the engine cylinder of Problem 3.156 loses the heat to the engine coolant at 100◦C. Find the entropy generation (external to the air) using constant specific heat.Data from Problem
Do the previous problem but assume that the process is isothermal.Data from previous problem A cylinder/piston contains 1 kg methane gas at 100 kPa, 300 K. The gas is compressed reversibly to a
Nitrogen at 600 kPa, 127◦C is in a 0.5-m3 insulated tank connected to a pipe with a valve to a second insulated initially empty tank of volume 0.25 m3, shown in Fig. P6.158. The valve is opened,
One kilogram carbon dioxide at 100 kPa, 400 K is mixed with 2 kg carbon dioxide at 200 kPa, 2000 K, in a rigid, insulated tank. Find the final state (P, T) and the entropy generation in the process
The unrestrained expansion of the reactor water in Problem 3.101 has a final state in the two-phase region. Find the entropy generated in the process.
Air in a piston/cylinder is at 1800 K, 7 MPa and expands in a poly tropic process with n = 1.5 to a volume eight times larger. Find the specific work and specific heat transfer in the process using
Hot combustion air at 2000 K expands in a poly tropic process to a volume six times as large with n = 1.3. Find the specific boundary work and the specific heat transfer using Table A.7.
A piston/cylinder contains pure oxygen at 500 K, 600 kPa. The piston is moved to a volume such that the final temperature is 700 K in a poly tropic process with exponent n = 1.25. Use ideal gas
A cylinder/piston contains 1 kg methane gas at 100 kPa, 300 K. The gas is compressed reversibly to a pressure of 800 kPa. Calculate the work required if the process is adiabatic.
A nitrogen gas goes through a poly tropic process with n = 1.3 in a piston/cylinder arrangement. It starts out at 600 K, 600 kPa and ends at 800 K. Is the heat transfer positive, negative, or zero?
Repeat the previous problem for the gas carbon monoxide.Data from previous problem An ideal gas having constant specific heat undergoes a reversible polytropic expansion with exponent n = 1.4.
A hydrogen gas in a piston/cylinder assembly at 300 K, 100 kPa with a volume of 0.1 m3 is now slowly compressed to a volume of 0.01 m3 while cooling in a reversible isothermal process. What is the
Two rigid tanks, shown in Fig. P6.97, each contains 10 kg N2 gas at 1000 K, 500 kPa. They are now thermally connected to a reversible heat pump, which heats one tank and cools the other, with no heat
Two rigid, insulated tanks are connected with a pipe and valve. One tank has 0.5 kg air at 200 kPa, 300K and the other has 0.75 kg air at 100 kPa, 400 K. The valve is opened, and the air comes to a
Argon in a light bulb is at 90 kPa, 20◦C when it is turned on and electricity input now heats it to 60◦C. Find the entropy increase of the argon gas.
A piston/cylinder, shown in Fig. P6.92, contains air at 1380 K, 15MPa, with V1 =10 cm3, Acyl =5 cm2. The piston is released, and just before the piston exits the end of the cylinder, the pressure

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