12-1
SOLUTIONS MANUAL
For Thermodynamics: An Engineering Approach
10th Edition
Yunus A. Çengel, Michael A. Boles, Mehmet Kanoğlu
Mcgraw-Hill latest Update.
, 12-2
CYU 12-1 ■ Check Your Understanding
CYU 12-1.1 Select the incorrect statement below about refrigerators and heat pumps:
(a) The COP of a refrigerator is less than that of a heat pump for fixed values of and .
(b) The minimum COP value of a heat pump is one.
(c) The COP of a refrigerator cannot be less than one.
(d) for fixed values of and .
Answer: (c) The COP of a refrigerator cannot be less than one.
CYU 12-1.2 A vapor-compression refrigeration cycle absorbs heat from a cool space at a rate of 4 kW and transfers 6 kW
of heat to a warm space. What are the COP values corresponding to the mode of operation as a refrigerator and as a heat
pump?
(a)
(b)
(c)
(d)
(e)
Answer: (c) (c)
CYU 12-1.3 A heat pump absorbs heat from the cold outdoors at a rate of 2 kW and transfers 4 kW of heat to the warm
indoors. What are the COP and the power input values for this heat pump?
(a)
(b)
(c)
(d)
(e)
Answer: (e)
, 12-3
CYU 12-3 ■ Check Your Understanding
cyu 12-3.1 the state of the refrigerant at the inlet or exit of the components of a refrigerator operating on the ideal vapor-
compression refrigeration cycle are specified below. select the item with the incorrect specification.
(a) saturated vapor at the compressor inlet
(b) saturated vapor at the expansion valve inlet
(c) saturated vapor evaporator exit
(d) superheated vapor at the condenser inlet
(e) superheated vapor at the compressor exit
answer: (b) expansion valve inlet - saturated vapor
cyu 12-3.1 select the correct statement below regarding the ideal vapor-compression refrigeration cycle.
(a) it is an internally reversible cycle.
(b) replacing the expansion valve by a turbine increases the net work input to the cycle.
(c) the cop of the cycle increases when the condensing temperature is raised.
(d) the cop of the cycle increases when the evaporating temperature is raised.
answer: (c) the cop of the cycle increases when the condensing temperature is raised.
cyu 12-3.3 which equations can be used to determine the cops of a household refrigerator, an air conditioner and a heat pump
in the analysis of the ideal vapor-compression refrigeration cycle? 1: compressor inlet, 2: compressor exit, 3: expansion
valve inlet, 4: expansion valve exit
i
ii
iii
(a) only iii
(b) i and ii
(c) i and iii
(d) ii and iii
(e) i, ii, and iii
answer: (e) i, ii, and iii
cyu 12-3.4 consider a household refrigerator, an air-source air conditioner and air-source heat pump. which system is most
likely to have the highest cop value?
(a) a household refrigerator operating in a kitchen at 30 c.
(b) a heat pump keeping a room at 22 c when the outdoors is at 2 c
(c) a heat pump keeping a room at 22 c when the outdoors is at 10 c
(d) an air-conditioner keeping a room at 22 c when the outdoors is at 45 c
(e) an air-conditioner keeping a room at 22 c when the outdoors is at 36 c
, 12-4
answer: (c) a heat pump keeping a room at 22 c when the outdoors is at 10 c
SOLUTIONS MANUAL
For Thermodynamics: An Engineering Approach
10th Edition
Yunus A. Çengel, Michael A. Boles, Mehmet Kanoğlu
Mcgraw-Hill latest Update.
, 12-2
CYU 12-1 ■ Check Your Understanding
CYU 12-1.1 Select the incorrect statement below about refrigerators and heat pumps:
(a) The COP of a refrigerator is less than that of a heat pump for fixed values of and .
(b) The minimum COP value of a heat pump is one.
(c) The COP of a refrigerator cannot be less than one.
(d) for fixed values of and .
Answer: (c) The COP of a refrigerator cannot be less than one.
CYU 12-1.2 A vapor-compression refrigeration cycle absorbs heat from a cool space at a rate of 4 kW and transfers 6 kW
of heat to a warm space. What are the COP values corresponding to the mode of operation as a refrigerator and as a heat
pump?
(a)
(b)
(c)
(d)
(e)
Answer: (c) (c)
CYU 12-1.3 A heat pump absorbs heat from the cold outdoors at a rate of 2 kW and transfers 4 kW of heat to the warm
indoors. What are the COP and the power input values for this heat pump?
(a)
(b)
(c)
(d)
(e)
Answer: (e)
, 12-3
CYU 12-3 ■ Check Your Understanding
cyu 12-3.1 the state of the refrigerant at the inlet or exit of the components of a refrigerator operating on the ideal vapor-
compression refrigeration cycle are specified below. select the item with the incorrect specification.
(a) saturated vapor at the compressor inlet
(b) saturated vapor at the expansion valve inlet
(c) saturated vapor evaporator exit
(d) superheated vapor at the condenser inlet
(e) superheated vapor at the compressor exit
answer: (b) expansion valve inlet - saturated vapor
cyu 12-3.1 select the correct statement below regarding the ideal vapor-compression refrigeration cycle.
(a) it is an internally reversible cycle.
(b) replacing the expansion valve by a turbine increases the net work input to the cycle.
(c) the cop of the cycle increases when the condensing temperature is raised.
(d) the cop of the cycle increases when the evaporating temperature is raised.
answer: (c) the cop of the cycle increases when the condensing temperature is raised.
cyu 12-3.3 which equations can be used to determine the cops of a household refrigerator, an air conditioner and a heat pump
in the analysis of the ideal vapor-compression refrigeration cycle? 1: compressor inlet, 2: compressor exit, 3: expansion
valve inlet, 4: expansion valve exit
i
ii
iii
(a) only iii
(b) i and ii
(c) i and iii
(d) ii and iii
(e) i, ii, and iii
answer: (e) i, ii, and iii
cyu 12-3.4 consider a household refrigerator, an air-source air conditioner and air-source heat pump. which system is most
likely to have the highest cop value?
(a) a household refrigerator operating in a kitchen at 30 c.
(b) a heat pump keeping a room at 22 c when the outdoors is at 2 c
(c) a heat pump keeping a room at 22 c when the outdoors is at 10 c
(d) an air-conditioner keeping a room at 22 c when the outdoors is at 45 c
(e) an air-conditioner keeping a room at 22 c when the outdoors is at 36 c
, 12-4
answer: (c) a heat pump keeping a room at 22 c when the outdoors is at 10 c
