Effect of Suction Vapour Superheat:

This is a usual practice to admit slightly superheated vapor before the starting of compression to ignore the risk of wet compression. Wet compression is unwanted as there might be accumulation of liquid inside the cylinder, that in turn shall wash away the lubricant resulting in sever mechanical problems. Therefore, to ignore this, a 5 to 20 K superheat of the refrigerant is always wanted. The vapor superheat contains the following influence on the refrigeration cycle:

 (1) It increases the refrigeration effect per unit mass of the refrigerant from h₁ - h₄ to (h₁' - h₄').

 (2) The specific volume enhance from v₁ to v₁'. It implies the decrease in mass flow rate for the similar displacement volume of the compressor.

 (3) The energy for compression of refrigerant vapor shall increase because of the diverging nature of the isentropic lines.

The above discussed effects of superheating of the vapor are illustrated in the Figure 7.

Vapour Superheating Before Suction