Refrigeration Multiple Choice Questions on “Compound VCR System – Cascade Systems – 1”.
1. 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
Clarification: 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.
2. What is Cryogenics?
a) C.O.P. reduction
b) Low-temperature refrigeration
c) Work enhancement
d) High-temperature refrigeration
Clarification: 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.
3. 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
Clarification: Multiple refrigerants can be used in this type of system. It helps to attain lower temperatures, and the refrigeration effect can be enormously increased.
4. 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
Clarification: The cascade refrigeration system is structured by connecting two or more vapor compression refrigeration systems in series which use different refrigerants.
5. 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
Clarification: 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.
6. What does low boiling refrigerants ensure?
a) Lower C.O.P.
b) Higher C.O.P.
c) Lower pressure
d) Larger compressor displacement
Clarification: 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.
7. 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
Clarification: 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.
8. The difference between low-temperature cascade condenser temperature and high-temperature cascade evaporator temperature is called temperature ______
Clarification: Temperature overlap is the difference between low-temperature cascade condenser temperature and high-temperature cascade evaporator temperature. Temperature overlap is a crucial phenomenon to attain higher C.O.P. because it shows the heat transfer in the system.
9. What is Intermediate temperature?
a) Temperature overlap is zero
b) Temperature overlap is infinity
c) The temperature of the low-temperature cascade system
d) The temperature of the high-temperature cascade system
Clarification: Intermediate temperature is achieved when the temperature overlap is zero i.e., the difference between low-temperature cascade condenser temperature and high-temperature cascade evaporator temperature is zero. Intermediate temperature indicates that both temperatures are equal. Intermediate temperature affects the heat transfer in the system.
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