Question

Purpose of a compressor in a vapour compression refrigeration system include(s)
A. To compress high pressure vapour coming from evaporator
B. Conversion of liquid refrigerant to vapour
C. To compress low pressure vapour refrigerant
D. To compress liquid refrigerant
E. Maintain pressure of liquid refrigerant
Choose the correct answer from the options given below:

• A. A only
• B. A and E only
• C. C only
• D. C and D only

Hint:

Remember the state of the refrigerant at key points in a VCRS:
- Evaporator exit Compressor inlet: Low-pressure, low-temperature vapour.
- Compressor exit Condenser inlet: High-pressure, high-temperature vapour.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
A vapour compression refrigeration system (VCRS) consists of four primary components: evaporator, compressor, condenser, and expansion valve.
The compressor acts as the heart of the system, driving the circulation of the refrigerant.

Step 2: Detailed Explanation:
Let us examine the functions and characteristics of the compressor in a VCRS:
- The refrigerant leaves the evaporator as a low-temperature, low-pressure vapour.
- Statement A: "To compress high pressure vapour coming from evaporator" is incorrect. The vapour entering the compressor is at low pressure, not high pressure.
- Statement B: "Conversion of liquid refrigerant to vapour" is incorrect. This phase change occurs in the evaporator where the refrigerant absorbs heat from the surrounding environment.
- Statement C: "To compress low pressure vapour refrigerant" is correct. The compressor draws in this low-pressure, low-temperature vapour and compresses it mechanically, increasing both its pressure and temperature before delivering it to the condenser.
- Statement D: "To compress liquid refrigerant" is incorrect. Compressors are designed to handle gaseous state refrigerants only. If liquid refrigerant enters the compressor cylinder (a condition known as liquid slugging), it can cause severe mechanical damage.
- Statement E: "Maintain pressure of liquid refrigerant" is incorrect. The expansion device (throttling valve) is responsible for regulating the pressure of the liquid refrigerant entering the evaporator.
Therefore, only Statement C is correct.

Step 3: Final Answer:
The correct option is (C).