Multistage Refrigeration system

What is the purpose of using intercooler?

• a) To increase the cost of the compressor

• b) To cool the superheated refrigerant

• c) To re-heat superheated refrigerant

• d) To reduce the volumetric efficiency

For a two-stage cascade system working on Carnot cycle and between low and high temperatures of -90oC and 50oC, the optimum cascade temperature at which the COP will be maximum is given by -67oC.

• a) -20oC

• b) -30oC

• c) -67oC

• d) 0oC

Which of the following is not the difference between theoretical and actual VCR cycle?

• a) Pressure drops in the evaporator

• b) Pressure drops in the condenser

• c) Compression of refrigerant is never polytropic

• d) Compression of refrigerant is always isentropic

Multi-evaporator systems with a single compressor and a pressure reducing valve yield very high COPs compared to multi-evaporator, single stage systems.

• a) Yield very high COPs compared to multi-evaporator, single stage systems

• b) Yield lower compressor discharge temperature compared to single stage systems

• c) Yield slightly higher refrigeration effect in the low temperature evaporator compared to single stage systems

• d) Yield slightly higher refrigeration effect in the high temperature evaporator compared to single stage systems

Cascade systems are widely used for applications requiring very high efficiencies.

• a) Large refrigeration capacity systems

• b) Applications requiring large temperature lifts

• c) Applications requiring very high efficiencies

• d) All of the above

Which of the following system is used for maintaining at the same temperatures when food products kept in different compartments?

• a) Evaporator at the same temperature with a single compressor

• b) Evaporator at the same temperature with multiple compressors

• c) Evaporator at different temperature with a single compressor

• d) Evaporator at different temperature with multiple compressors

Compared to multi-evaporator and single compressor systems, multi-evaporator systems with multiple compressors yield higher COP. (Choose any two)

• a) Yield higher COP

• b) Decrease maximum cycle temperature

• c) Yield higher refrigeration effect

• d) All of the above

In cascade systems:

• a) Different refrigerants are used in individual cascade cycles

• b) There is no mixing of refrigerants and no migration of lubricating oil

• c) Higher COPs compared to multi-stage systems can be obtained

• d) Operating pressures need not be too high or too low

Why is multi-stage or compound VCR with water intercooler, liquid sub-cooler, and flash intercooler used?

• a) To improve C.O.P.

• b) To decrease refrigeration effect

• c) To increase work

• d) To increase leakage loss

Choose the wrong statement for multi-stage systems.

• a) The refrigerant used should have high critical temperature and high freezing point

• b) The refrigerant used should have high critical temperature and low freezing point

• c) There is a possibility of migration of lubricating oil from one compressor to other

• d) Operating pressures can be too high or too low