Refrigeration and Air Conditioning Questions and Answers Part-15

1. By using flash chambers the total work done per kg of refrigerant is reduced.
a) True
b) False

Answer: a
Explanation: By using flash chambers the total work done per kg of refrigerant is reduced as the refrigerant can be expanded close to the liquid line and hence work done per kg reduces.

2. Which one of the following is not an advantage of water intercooling when used in a multi stage compression?
a) Reduces the work to be done in high pressure
b) Reduces the specific volume of the refrigerant
c) Requires a compressor of more stroke volume
d) Requires a compressor of less stroke volume

Answer: c
Explanation: When water intercooling is used in a multi stage compression the work to be done in high pressure is reduced, the specific volume of the refrigerant is reduced and a compressor of less stroke volume is required.

3. What is the value of Refrigeration effect if m2 = 2 kg/min, m3 = 0.8 kg/min and enthalpies for the refrigerant at saturated vapor and saturated liquid line are 1420 and 1260 kJ/kg?
a) 192
b) 194
c) 196
d) 129

Answer: a
Explanation: Given: m2 = 2 kg/min
m3 = 0.8 kg/min
h1 = 1420 kJ/kg and hf10 = h11 = 1260 kJ/kg
As, m1 = m2 – m3
= 2 – 0.8
= 1.2
Refrigeration effect = m1 (h1 – h11)
= 1.2 (1420 – 1260)
= 1.2 x 160
= 192 kJ/min.

4. Why is the cascade system used?
a) To attain low C.O.P.
b) To decrease the refrigeration effect
c) To produce low temperatures
d) To increase leakage loss

Answer: c
Explanation: If the vapor compression system is to be used for the production of temperatures, the common choice to stage type compression is a cascade system.

5. What is Cryogenics?
a) C.O.P. reduction
b) Low-temperature refrigeration
c) Work enhancement
d) High-temperature refrigeration

Answer: b
Explanation: Cryogenics means low-temperature refrigeration. It is applied to very low-temperature refrigeration applications. This word is derived Greek word Cryos meaning cold or frost.

6. What is the principal advantage of the cascade system?
a) Increase of work done
b) Decrease the refrigeration effect
c) Use of only one refrigerant
d) Use of multiple refrigerants

Answer: d
Explanation: Multiple refrigerants can be used in this type of system. It helps to attain lower temperatures, and the refrigeration effect can be enormously increased.

7. How is a cascade system structured?
a) VCR system in parallel combination
b) VCR system is not used
c) VCR system in a series combination
d) VAR system is used

Answer: c
Explanation: The cascade refrigeration system is structured by connecting two or more vapor compression refrigeration systems in series which use different refrigerants.

8. Low-temperature cascade system use refrigerants with ______ boiling temperature and high temperature cascade system use refrigerants with _________ boiling temperature.
a) low, high
b) high, low
c) low, low
d) high, high

Answer: a
Explanation: The high-temperature cascade system uses a refrigerant with high boiling temperatures such as R-12 or R-22. The low-temperature cascade system uses a refrigerant with low boiling temperatures such as R-13 or R-13 BI. This is used to achieve a higher coefficient of performance by increasing the refrigeration effect.

9. What does low boiling refrigerants ensure?
a) Lower C.O.P.
b) Higher C.O.P.
c) Lower pressure
d) Larger compressor displacement

Answer: b
Explanation: Low boiling temperature refrigerant has extremely high pressure. Due to this smaller compressor displacement is ensured. So, smaller displacement decreases overall work and increases the C.O.P. of the system.

10. Which intermediate refrigerants were used for the first time in the cascade system?
a) CO2 and CO
b) CO and SO2
c) NH3 and CO2
d) CO2 and SO2

Answer: d
Explanation: Firstly, the cascade system was used by Pietet in 1877. Cascade system was used for the liquefaction of oxygen using the Sulphur dioxide (SO2) and Carbon dioxide (CO2) as intermediate refrigerants.