Questions and Answers of Thermodynamics An Engineering Approach

Based on data from the refrigerant-134a tables, the Joule-Thompson coefficient of refrigerant-134a at 0.8 MPa and 60°C is approximately(a) 0(b) 5°C/MPa(c) 11°C/MPa(d) 16°C/MPa(e) 25°C/MPa
Methane is contained in a piston–cylinder device and is heated at constant pressure of 5 MPa from 100 to 250°C. Determine the heat transfer, work, and entropy change per unit mass of the methane
Propane at 500 kPa and 100°C is compressed in a steady-flow device to 4000 kPa and 500°C. Calculate the change in the specific entropy of the propane and the specific work required for this
Estimate the cp of nitrogen at 300 kPa and 400 K, using(a) The relation in Prob. 12–91,Data From Q#91:Consider an infinitesimal reversible adiabatic compression or expansion process. By taking s =
For ideal gases, the development of the constant-volume specific heat yieldsProve this by using the definitions of pressure and temperature, T = (∂u/∂s)v and P = −(∂u/∂v)s. ди = 0 du.
Develop expressions for h, u, s°, Pr, and vr for an ideal gas whose cop is given bywhere ai, a0, n, and β are empirical constants. c = Ea,T- BIT eNT - 1
Reconsider Prob. 12–79. Determine the exergy destruction associated with the process. Assume T0 = 30°C.Data From Reconsider Prob. 12–79:Propane is compressed isothermally by a piston–cylinder
Oxygen is adiabatically and reversibly expanded in a nozzle from 200 psia and 600°F to 70 psia. Determine the velocity at which the oxygen leaves the nozzle, assuming that it enters with negligible
Determine the enthalpy change and the entropy change of oxygen per unit mole as it undergoes a change of state from 220 K and 5 MPa to 300 K and 10 MPa(a) By assuming ideal-gas behavior(b) By
Saturated water vapor at 300°C is expanded while its pressure is kept constant until its temperature is 700°C. Calculate the change in the specific enthalpy and entropy using(a) The departure
Why is the generalized enthalpy departure chart prepared by using PR and TR as the parameters instead of P and T?
What is the enthalpy departure?
The equation of state of a gas is given bywhere a and b are constants. Use this equation of state to derive an equation for the Joule-Thomson coefficient inversion line. RT U = a + b T %3D
What is the most general equation of state for which the Joule-Thomson coefficient is always zero?
Estimate the Joule-Thomson coefficient of refrigerant-134a at 30 psia and 20°F.
Estimate the Joule-Thomson coefficient of refrigerant-134a at 200 kPa and 20°C.
The pressure of a fluid always decreases during an adiabatic throttling process. Is this also the case for the temperature?
Does the Joule-Thomson coefficient of a substance change with temperature at a fixed pressure?
What does the Joule-Thomson coefficient represent?
Demonstrate that Va k = Cu (dulaP),
Determine the change in the enthalpy of air, in kJ/kg, as it undergoes a change of state from 100 kPa and 20°C to 600 kPa and 300°C using the equation of state P(v – a) = RT where a = 0.10 m3/kg,
Estimate the specific heat difference cp – cv for liquid water at 1000 psia and 300°F.
The saturation table for refrigerant-134a lists the following at −40°C: P = 51.25 kPa, hfg = 225.86 kJ/kg, and vfg = 0.35993 m3/kg. Estimate the saturation pressure of refrigerant-134a at −50°C
Estimate sfg of the substance in Prob. 12–29 at 80°C.Data From Q#29:Two grams of a saturated liquid are converted to a saturated vapor by being heated in a weighted piston–cylinder device
Two grams of a saturated liquid are converted to a saturated vapor by being heated in a weighted piston–cylinder device arranged to maintain the pressure at 200 kPa. During the phase conversion,
What approximations are involved in the Clapeyron-Clausius equation?
Prove that ƏP k k – 1\aT
Show how you would evaluate T, v, u, a, and g from the thermodynamic function h = h(s, P).
Repeat Prob. 12–8 for helium.Data From Q#8:Consider air at 350 K and 0.75 m3/kg. Using Eq. 12–3, determine the change in pressure corresponding to an increase of(a) 1 percent in temperature at
Consider air at 350 K and 0.75 m3/kg. Using Eq. 12–3, determine the change in pressure corresponding to an increase of(a) 1 percent in temperature at constant specific volume(b) 1 percent in
Consider a function f(x) and its derivative df/dx. Can this derivative be determined by evaluating dx/df and taking its inverse?
Consider a function z(x, y) and its partial derivative (∂z/∂y)x. Can this partial derivative still be a function of x?
Consider a function z(x, y) and its partial derivative (∂z/∂y)x. If this partial derivative is equal to zero for all values of x, what does it indicate?
Consider a function z(x, y) and its partial derivative (∂z/∂y)x. Under what conditions is this partial derivative equal to the total derivative dz/dy?
In the 1800s, before the development of modern air conditioning, it was proposed to cool air for buildings with the following procedure using a large piston–cylinder device [“ John Gorrie:
Consider a solar pond power plant operating on closed Rankine cycle. Using refrigerant-134a as the working fluid, specify the operating temperatures and pressures in the cycle, and estimate the
It is proposed to use a solar-powered thermoelectric system installed on the roof to cool residential buildings. The system consists of a thermoelectric refrigerator that is powered by a
The temperature in a car parked in the sun can approach 100°C when the outside air temperature is just 25°C, and it is desirable to ventilate the parked car to avoid such high temperatures.
Solar or photovoltaic (PV) cells convert sunlight to electricity and are commonly used to power calculators, satellites, remote communication systems, and even pumps. The conversion of light to
Design a thermoelectric refrigerator that is capable of cooling a canned drink in a car. The refrigerator is to be powered by the cigarette lighter of the car. Draw a sketch of your design.
The heat supplied by a heat pump used to maintain a building’s temperature is often supplemented by another source of direct heat. The fraction of the total heat required that is supplied by
Develop and discuss techniques that apply the principle of regeneration to improve the performance of vapor compression refrigeration systems.
An absorption air-conditioning system is to remove heat from the conditioned space at 20°C at a rate of 90 kJ/s while operating in an environment at 35°C. Heat is to be supplied from a geothermal
Consider a heat pump that operates on the ideal vapor-compression refrigeration cycle with R-134a as the working fluid between the pressure limits of 0.24 and 1.2 MPa. The coefficient of performance
A refrigerator removes heat from a refrigerated space at 0°C at a rate of 1.5 kJ/s and rejects it to an environment at 20°C. The minimum required power input is(a) 102 W(b) 110 W(c) 140 W(d) 150
An absorption refrigeration system is to remove heat from the refrigerated space at 2°C at a rate of 28 kW while operating in an environment at 25°C. Heat is to be supplied from a solar pond at
Repeat Prob. 11–122 if the heat exchanger provides 9.51°C of subcooling.Data From Q#122:The refrigeration system of Fig. P11–122 is another variation of the basic vapor-compression refrigeration
Reconsider Prob. 11–120E. The refrigeration system of that problem cools one reservoir at −15°F and one at 40°F while rejecting heat to a reservoir at 80°F. Which process has the highest
Rework Prob. 11–116 with a 2.7°C sub cooling at the exit of the condenser.Data From Rework Prob. 11–116:A refrigerator using refrigerant-134a as the working fluid operates the condenser at 700
A refrigerator using refrigerant-134a as the working fluid operates the condenser at 700 kPa and the evaporator at −10°C. This refrigerator freezes water while rejecting heat to the ambient air at
Consider an ice-producing plant that operates on the ideal vapor-compression refrigeration cycle and uses refrigerant-134a as the working fluid. The refrigeration cycle operating conditions require
A copper wire and a constantan wire are formed into a closed circuit by connecting the ends. Now one junction is heated by a burning candle while the other is maintained at room temperature. Do you
An iron wire and a constantan wire are formed into a closed circuit by connecting the ends. Now both junctions are heated and are maintained at the same temperature. Do you expect any electric
Consider a circular copper wire formed by connecting the two ends of a copper wire. The connection point is now heated by a burning candle. Do you expect any current to flow through the wire?
What is a thermoelectric circuit?
Reconsider Prob. 11–80. How will the answers change when the isentropic efficiency of each compressor is 85 percent and the isentropic efficiency of the turbine is 95 percent?Data From Reconsider
An ideal gas refrigeration cycle uses air as the working fluid. The air is at 5 psia and −10°F as it enters the compressor with a compression ratio of 4. The temperature at the turbine entrance is
An ideal gas refrigeration system operates with air as the working fluid. Air is at 100 kPa and 20°C before compression and 500 kPa and 30°C before expansion. The system is to provide 15 kW of
Repeat Prob. 10–3 for a heat rejection pressure of 10 kPa.Data From Repeat Prob. 10–3: A steady-flow Carnot cycle uses water as the working fluid. Water changes from saturated liquid to
Water enters the boiler of a steady-flow Carnot engine as a saturated liquid at 300 psia and leaves with a quality of 0.95. Steam leaves the turbine at a pressure of 20 psia. Show the cycle on a T-s
Simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of 3 MPa in the boiler and 30 kPa in the condenser. If the quality at the exit of the turbine cannot be
Reconsider Prob. 10–25. Using appropriate software, determine how much the thermal efficiency of the cycle would change if there were a 50 kPa pressure drop across the boiler.Data From Reconsider
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. The
Reconsider Prob. 10–21. Irreversibilities in the turbine cause the steam quality at the outlet of the turbine to be 70 percent. Determine the isentropic efficiency of the turbine and the thermal
Is there an optimal pressure for reheating the steam of a Rankine cycle? Explain.
Consider a steam power plant that operates on the ideal reheat Rankine cycle. The plant maintains the boiler at 17.5 MPa, the reheater at 2 MPa, and the condenser at 50 kPa. The temperature is 550°C
Reconsider Prob. 10–34. How much does the thermal efficiency of the cycle change when the temperature at the entrance to the low-pressure turbine is increased to 550°C?Data From Q#34:Consider a
Consider a simple ideal Rankine cycle and an ideal regenerative Rankine cycle with one open feedwater heater. The two cycles are very much alike, except the feedwater in the regenerative cycle is
Cold feedwater enters a 200-kPa open feedwater heater of a regenerative Rankine cycle at 70°C with a flow rate of 10 kg/s. Bleed steam is available from the turbine at 200 kPa and 160°C. At what
In a regenerative Rankine cycle. the closed feedwater heater with a pump as shown in the figure is arranged so that the water at state 5 is mixed with the water at state 2 to form a feedwater which
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 combined gas–steam power cycle uses a simple gas turbine for the topping cycle and simple Rankine cycle for the bottoming cycle. Atmospheric air enters the gas turbine at 101 kPa and 20°C, and
Reconsider Prob. 10–83. An ideal regenerator is added to the gas cycle portion of the combined cycle. How much does this change the efficiency of this combined cycle?Data From Reconsider Prob.
Reconsider Prob. 10–83. Determine which components of the combined cycle are the most wasteful of work potential.Data From Reconsider Prob. 10–83:A combined gas–steam power cycle uses a simple
Feedwater at 4000 kPa is heated at a rate of 6 kg/s from 200°C to 245°C in a closed feedwater heater of a regenerative Rankine cycle. Bleed steam enters this unit at 3000 kPa with a quality of 90
Repeat Prob. 10–98 assuming both the pump and the turbine are isentropic.Data From Q#98:Consider a steam power plant that operates on a regenerative Rankine cycle and has a net power output
Stack gases exhausting from electrical power plants are at approximately 150°C. Design a basic Rankine cycle that uses water, refrigerant-134a, or ammonia as the working fluid and that produces the
A natural gas–fired furnace in a textile plant is used to provide steam at 130°C. At times of high demand, the furnace supplies heat to the steam at a rate of 30 MJ/s. The plant also uses up to 6
A 10-MW geothermal power plant is being considered at a site where geothermal water at 230°C is available. Geothermal water is to be flashed into a chamber to a lower pressure where part of the
A steady-flow Carnot refrigeration cycle uses refrigerant-134a as the working fluid. The refrigerant changes from saturated vapor to saturated liquid at 60°C in the condenser as it rejects heat. The
Does the ideal vapor-compression refrigeration cycle involve any internal Irreversibilities?
A 10-kW cooling load is to be served by operating an ideal vapor compression refrigeration cycle with its evaporator at 400 kPa and its condenser at 800 kPa. Calculate the refrigerant mass flow rate
An air conditioner using refrigerant-134a as the working fluid and operating on the ideal vapor-compression refrigeration cycle is to maintain a space at 22°C while operating its condenser at 1000
An ideal vapor-compression refrigeration cycle using refrigerant-134a as the working fluid is used to cool a brine solution to −5°C. This solution is pumped to various buildings for the purpose of
A refrigerator uses refrigerant-134a as the working fluid and operates on the ideal vapor-compression refrigeration cycle except for the compression process. The refrigerant enters the evaporator at
An ideal vapor-compression refrigeration cycle that uses refrigerant-134a as its working fluid maintains a condenser at 800 kPa and the evaporator at −20°C. Determine this system’s COP and the
A refrigerator uses refrigerant-134a as its working fluid and operates on the ideal vapor-compression refrigeration cycle. The refrigerant evaporates at 5°F and condenses at 180 psia. This unit
Repeat Prob. 11–19E using appropriate software if ammonia is used in place of refrigerant-134a.Data From Q#19:A refrigerator uses refrigerant-134a as its working fluid and operates on the ideal
A refrigerator uses refrigerant-134a as the working fluid and operates on the vapor-compression refrigeration cycle. The evaporator and condenser pressures are 200 kPa and 1400 kPa, respectively. The
A heat pump that operates on the ideal vapor-compression cycle with refrigerant-134a is used to heat a house and maintain it at 26°C by using underground water at 14°C as the heat source. Select
A heat pump operates on the ideal vapor-compression refrigeration cycle and uses refrigerant-134a as the working fluid. The condenser operates at 1000 kPa and the evaporator at 200 kPa. Determine
The liquid leaving the condenser of a 100,000 Btu/h heat pump using refrigerant-134a as the working fluid is subcooled by 9.5°F. The condenser operates at 160 psia and the evaporator at 50 psia. How
Reconsider Prob. 11–44E. What is the effect on the compressor power requirement when the vapor entering the compressor is superheated by 10°F and the condenser operates ideally?Data From
Reconsider Prob. 11–48. What is the effect on the COP when the vapor entering the compressor is superheated by 2°C and the compressor has no Irreversibilities?Data From Q#48:A heat pump using
Can a vapor-compression refrigeration system with a single compressor handle several evaporators operating at different pressures? How?
A two-stage compression refrigeration system with an adiabatic liquid-vapor separation unit as shown in Fig. P11–60 uses refrigerant-134a as the working fluid. The system operates the evaporator at
A two-stage compression refrigeration system with an adiabatic liquid-vapor separation unit like that in Fig. P11– 60 uses refrigerant-134a as the working fluid. The system operates the evaporator
Repeat Prob. 11–63E if the 30 psia evaporator is to be replaced with a 60 psia evaporator to serve a 15,000 Btu/h cooling load.Data From Q#63:A two-evaporator compression refrigeration system like
In gas refrigeration cycles, can we replace the turbine with an expansion valve as we did in vapor-compression refrigeration cycles? Why?
How do we achieve very low temperatures with gas refrigeration cycles?

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