Question

In a vapour compression system, the lowest temperature during the cycle occurs after...............

• A. Condensation
• B. Expansion
• C. Evaporation
• D. Compression

Hint:

Remember the pressure-temperature relationships in refrigeration:
- Condenser = High Pressure, High Temperature.
- Evaporator = Low Pressure, Low Temperature.
The transition from high to low pressure occurs during the expansion stage, creating the lowest temperature in the cycle.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
A vapor compression refrigeration system consists of four primary components: a compressor, a condenser, an expansion device (throttling valve or capillary tube), and an evaporator.

Step 2: Detailed Explation:
Let's trace the thermodymic states of the refrigerant throughout the cycle:
1. Compression: Low-pressure, low-temperature vapor is compressed to high-pressure, high-temperature vapor.
2. Condensation: High-pressure, high-temperature vapor releases heat to the surroundings and condenses into a high-pressure liquid.
3. Expansion: The high-pressure liquid refrigerant passes through an expansion valve or capillary tube.
This throttling process is an isenthalpic expansion that causes a sudden drop in pressure.
This pressure drop induces partial flash evaporation, which rapidly lowers the temperature of the liquid-vapor refrigerant mixture.
4. Evaporation: The low-pressure, low-temperature mixture enters the evaporator, where it absorbs heat from the cold storage space.
Because the refrigerant absorbs heat in the evaporator, its temperature remains low but rises slightly or remains at saturation.
The absolute lowest temperature in the entire refrigeration cycle occurs immediately after this expansion process, right before the refrigerant enters the evaporator.

Step 3: Fil Answer
Thus, the lowest temperature in a vapor compression cycle occurs after the expansion stage.