Question

In a vapour compressor refrigeration system, function of compressor include(s)
(A) To circulate refrigerant through the refrigeration system
(B) To raise the pressure of refrigerant
(C) To raise temperature of refrigerant
(D) To reduce temperature of refrigerant
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A) and (B) only.
• C. (A), (B) and (C) only.
• D. (B) and (C) only.

Hint:

Remember that compressing a gas always increases both its pressure and temperature due to thermodynamic work input. Therefore, any option stating that a compressor reduces temperature can be immediately eliminated.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The Vapor Compression Refrigeration System (VCRS) is the most common thermodynamic cycle used for air conditioning and food refrigeration. The compressor is considered the heart of this cycle, serving several thermodynamic functions.

Step 2: Detailed Explanation:
Let us analyze each function of the compressor:

Function (A): To circulate refrigerant through the system: The compressor maintains a pressure difference between the high-pressure side (condenser) and low-pressure side (evaporator). This continuous pumping action circulates the refrigerant through the closed loop. Thus, (A) is a core function.

Function (B): To raise the pressure of the refrigerant: The compressor draws low-pressure, superheated vapor from the evaporator and compresses it, raising its pressure to the saturation pressure corresponding to the condenser temperature. This allows the refrigerant to condense at ambient temperature. Thus, (B) is a core function.

Function (C): To raise the temperature of the refrigerant: The compression process is thermodynamically modeled as an isentropic or polytropic process. Work input from the compressor increases the enthalpy and temperature of the vapor, raising it above the temperature of the surrounding cooling medium (air or water). This temperature difference is necessary for heat rejection to occur in the condenser. Thus, (C) is a core function.

Function (D): To reduce the temperature of the refrigerant: The compressor does work on the gas, which always increases its temperature. The temperature reduction in the cycle occurs elsewhere—first during heat rejection in the condenser, then via pressure drop across the expansion valve (throttling), and finally as it absorbs heat in the evaporator. Thus, (D) is not a function of the compressor.
Combining these, the compressor functions are (A), (B), and (C).

Step 3: Final Answer:
The correct option is (C), representing (A), (B), and (C) only.