Deck 11: Refrigeration Cycles

Question 1

Consider a heat pump that operates on the reversed Carnot cycle with R-134a as the working fluid executed under the saturation dome between the pressure limits of 140 kPa and 800 kPa. The refrigerant changes from saturated vapor to saturated liquid during the heat rejection process. The net work input for this cycle is

A)28 kJ/kg
B)143 kJ/kg
C)34 kJ/kg
D)273 kJ/kg
E)56 kJ/kg

Answer 1

28 kJ/kg

Question 2

A refrigerator removes heat from a refrigerated space at -10°C at a rate of 420 J/s and rejects it to an environment at 25°C. The minimum required power input is

A)420 W
B)56 W
C)588 W
D)124 W
E)371 W

Answer 2

56 W

Question 3

A refrigerator operates on the ideal vapor compression refrigeration cycle with R-134a as the working fluid between the pressure limits of 120 kPa and 800 kPa. If the rate of heat removal from the refrigerated space is 38 kJ/s, the mass flow rate of the refrigerant is

A)0.18 kg/s
B)0.97 kg/s
C)0.27 kg/s
D)0.22 kg/s
E)1.4 kg/s

Answer 3

0.27 kg/s

Question 4

A heat pump operates on the ideal vapor compression refrigeration cycle with R-134a as the working fluid between the pressure limits of 0.32 MPa and 1.4 MPa. If the mass flow rate of the refrigerant is 0.25 kg/s, the rate of heat supply by the heat pump to the heated space is

A)7.6 kW
B)31 kW
C)26 kW
D)39 kW
E)49 kW

Question 5

An ideal vapor compression refrigeration cycle with R-134a as the working fluid operates between the pressure limits of 120 kPa and 1000 kPa. The mass fraction of the refrigerant that is in the liquid phase at the inlet of the evaporator is

A)0.65
B)0.61
C)0.38
D)0.50
E)0

Question 6

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 0.32 MPa and 1.4 MPa. The coefficient of performance of this heat pump is

A)0.80
B)1.2
C)6.2
D)4.1
E)5.1

Question 7

An ideal gas refrigeration cycle using air as the working fluid operates between the pressure limits of 80 kPa and 240 kPa. Air is cooled to 40°C before entering the turbine. The lowest temperature of this cycle is

A)-44°C
B)29°C
C)40°C
D)-205°C
E)-71°C

Question 8

Consider an ideal gas refrigeration cycle using helium as the working fluid. Helium enters the compressor at 100 kPa and -20°C and is compressed to 220 kPa. Helium is then cooled to 20°C before it enters the turbine. For a mass flow rate of 0.22 kg/s, the net power input required is

A)1.1 kW
B)16.6 kW
C)37.8 kW
D)164 kW
E)107 kW

Question 9

An absorption air-conditioning system is to remove heat from the conditioned space at 20°C at a rate of 85 kJ/s while operating in an environment at 35°C. Heat is to be supplied from a geothermal source at 140°C. The minimum rate of heat supply required is

A)12 kJ/s
B)35 kJ/s
C)17 kJ/s
D)58 kJ/s
E)85 kJ/s

Question 10

Consider a refrigerator that operates on the vapor compression refrigeration cycle with R-134a as the working fluid. The refrigerant enters the compressor as saturated vapor at 140 kPa, and exits at 900 kPa and 70°C, and leaves the condenser as saturated liquid at 900 kPa. The coefficient of performance of this refrigerator is

A)0.67
B)1.0
C)3.6
D)2.1
E)3.1