Understanding Vapour Compression in Refrigeration

In refrigeration cycles, the compression process is crucial. It involves increasing the pressure and temperature of the refrigerant vapour. Depending on the state of the refrigerant entering and leaving the compressor, the compression process is classified differently. The question asks about the scenario where the vapour is NOT superheated after compression.

Types of Compression

There are typically three main ways compression is described in vapour compression refrigeration systems:

• Wet Compression: In this case, the refrigerant enters the compressor as a mixture of liquid and vapour (wet vapour). This type of compression is generally avoided in practice because the liquid droplets can damage the compressor valves and cylinders. After compression in wet compression, the refrigerant might be in a saturated state or even still slightly wet. Crucially, it is NOT superheated.
• Dry Compression: Here, the refrigerant enters the compressor as saturated vapour. After compression, its temperature increases above the saturation temperature at the discharge pressure, meaning it leaves the compressor as superheated vapour.
• Superheated Compression: The refrigerant enters the compressor already in a superheated state and leaves at an even higher superheated temperature and pressure.

Analysing the Condition: Not Superheated After Compression

The question specifies that the vapour is NOT superheated after compression. Let's consider what state 'not superheated' means:

• It could be saturated vapour.
• It could be a mixture of liquid and vapour (wet vapour).

Looking at the types of compression defined above, wet compression is the one where the refrigerant enters wet and is likely to be saturated or wet after compression, definitely NOT superheated. While technically, leaving as saturated vapour from a dry compression starting point also fits "not superheated", the term specifically describing the process where superheating after compression is avoided (often starting from a wet state) is known as wet compression.

Therefore, if the vapour is NOT superheated after compression, it is referred to as wet compression.