Effect of Clearance Volume on Volumetric Efficiency of a Reciprocating Compressor

The clearance volume is the volume of the clearance space between the piston and cylinder head at the end of the compression stroke. The volumetric efficiency is the ratio of actual volume of gas delivered by the compressor to the swept volume of the compressor cylinder.

When the clearance volume of a reciprocating compressor decreases, the volumetric efficiency of the compressor increases. This can be explained as follows:

1. Reduced clearance volume leads to reduced dead space: The clearance volume is the volume of the space between the piston and the cylinder head when the piston is at the top of its stroke. This space does not contribute to the compression of the gas, and is therefore referred to as dead space. When the clearance volume is reduced, the dead space is also reduced, which means that a larger volume of gas can be compressed within the same cylinder volume. This leads to an increase in volumetric efficiency.

2. Reduced clearance volume leads to increased compression ratio: The compression ratio is the ratio of the absolute discharge pressure to the absolute suction pressure. When the clearance volume is reduced, the compression ratio increases for the same delivery pressure. This means that the compressor is able to compress a larger mass of gas into the same cylinder volume, leading to an increase in volumetric efficiency.

3. Reduced clearance volume leads to reduced leakage: The clearance volume is also responsible for gas leakage during the compression process. When the clearance volume is reduced, the leakage is reduced, leading to an increase in volumetric efficiency.

Therefore, it can be concluded that when the clearance volume of a reciprocating compressor decreases, the volumetric efficiency of the compressor increases.