Refrigeration and Air Conditioning Questions and Answers Part-2

1. What is the term C.O.P. referred in terms of refrigeration?
a) Capacity of Performance
b) Co-efficient of Plant
c) Co-efficient of Performance
d) Cooling for Performance

Answer: c
Explanation: Co-efficient of Performance is generally referred as C.O.P. for Refrigeration, which is used to measure the capacity or level up to which the refrigeration will occur.

2. C.O.P. can be expressed by which equation?
a) \(\frac{Work \,Done}{Refrigeration \,effect}\)
b) \(\frac{Refrigeration \,effect}{Work \,Done}\)
c) \(\frac{Work\, Done}{Heat \,Transfer}\)
d) \(\frac{Heat \,Transfer}{Work \,Done}\)

Answer: b
Explanation: Co-efficient of Performance is the ratio of the Refrigeration effect produced to the work done or work supplied to produce the effect.
Whereas the ratio- Work done to Heat transfer is called the efficiency.

3. What is the term relative C.O.P. referred in terms of refrigeration?
a) \(\frac{Actual \,C.O.P.}{Theoretical \,C.O.P.}\)
b) \(\frac{Theoretical \,C.O.P.}{Actual \,C.O.P.}\)
c) \(\frac{Actual \,C.O.P.}{Average \,C.O.P.}\)
d) \(\frac{Average \,C.O.P.}{Theoretical \,C.O.P.}\)

Answer: a
Explanation: Relative Co-efficient of Performance is generally referred as the ratio of Actual C.O.P. measured to the Theoretical C.O.P. assumed before calculations. It is in relation with the theoretical C.O.P. and generally expressed in “%” value.

4. Find the C.O.P. of a refrigeration system if the work input is 40 KJ/kg and refrigeration effect produced is 130 KJ/kg of refrigerant flowing.
a) 3.00
b) 2.25
c) 3.75
d) 3.25

Answer: d
Explanation: Here, refrigeration effect = 130 KJ/kg, work input = 40 KJ/kg
C.O.P. = \(\frac{Refrigeration \,effect}{Work \,Done}\)
= \(\frac{130}{40}\)
= 3.25 (unit less).

5. Find the Relative C.O.P. of a refrigeration system if the work input is 60 KJ/kg and refrigeration effect produced is 130 KJ/kg of refrigerant flowing. Also Theoretical C.O.P. is 3.
a) 0.65
b) 0.75
c) 0.72
d) 0.89

Answer: c
Explanation: Given, work input = 60 KJ/kg, refrigeration effect = 130 KJ/kg and Theoretical C.O.P. = 3
Actual C.O.P. = \(\frac{Refrigeration \,effect}{Work \,Done}\)
= \(\frac{130}{60}\)
= 2.167 (unit less)
Relative C.O.P. = \(\frac{Actual \,C.O.P.}{Theoretical \,C.O.P.}\)
= 2.167/3 = 0.722 i.e. = 72.2 %

6. Find the C.O.P. of a refrigeration system if the work input is 30 KJ/kg and refrigeration effect produced is 120 KJ/kg of refrigerant flowing
a) 3.00
b) 4.00
c) 0.75
d) 0.25

Answer: b
Explanation: Given, work input = 30 KJ/kg and refrigeration effect = 120 KJ/kg
C.O.P. = \(\frac{Refrigeration \,effect}{Work \,Done}\)
= \(\frac{120}{30}\)
= 4 (unit less).

7. Which equation represents efficiency in general?
a) \(\frac{Work \,Done}{Refrigeration \,effect}\)
b) \(\frac{Heat \,Trasfer}{Work \,Done}\)
c) \(\frac{Work\, Done}{Heat \,Transfer}\)
d) \(\frac{Refrigeration \,effect}{Work \,Done}\)

Answer: c
Explanation: Work done to Heat transfer is called the efficiency in general sense, which can be applicable to Pumps, Refrigerators, and Turbines etc.
Whereas Co-efficient of Performance is the ratio of Refrigeration effect produced to the work done or work supplied to produce the effect.

8. The Co-efficient of Performance is always ________
a) greater than 1
b) less than 1
c) equal to 1
d) zero

Answer: a
Explanation: C.O.P. is always greater than 1, because in the ratio of C.O.P. the Refrigeration effect is always greater than the work done.

9. In a refrigerating machine, if the lower temperature is fixed, then the C.O.P. of machine can be increased by?
a) Increasing the higher temperature
b) Decreasing the higher temperature
c) Operating the machine at lower speed
d) Operating the machine at higher speed

Answer: b
Explanation: By decreasing the higher temperature, the change in temperatures can be reduced. This directly reduces the word done i.e. the denominator in C.O.P. Hence the C.O.P increases.

10. The reverse Carnot cycle C.O.P. can be expressed as _________ (Where t1 is the lower temperature and t2 is the higher temperature).
a) \(\frac{t1-t2}{t2}\)
b) \(\frac{t2-t1}{t2}\)
c) \(\frac{t2-t1}{t1-t2}\)
d) \(\frac{t2-t1}{t1}\)

Answer: d
Explanation: Reverse Carnot C.O.P is the ratio of change in temperature i.e. t2-t1 to the lower temperature i.e. t1 here.