Volumetric Efficiency

The volumetric efficiency of a compressor is the ratio of actual free air delivered to the displacement of the compressor.

Substituting the value of V₄ in Eq. (10.1), we get

Where ∈ is clearance ratio  and r is pressure ratio 

Example 10.1: A single cylinder, single acting air compressor has a cylinder diameter of 150 mm and stroke of 300 mm. It draws air into the cylinder at a pressure of 1 bar and temperature 27°C. This air is then compressed adiabatically to a pressure of 8 bar if the compressor runs at a speed of 120 rpm. Find

1. Mass of air compressed per cycle.
2. Work required per cycle.
3. Power required to drive the compressor.

Neglect the clearance volume and take R = 0.287 kJ/kg K.

Solution:

1. Mass of air compressed  
2. Work required per cycle, 
3. Power required to run the compressor = Work required per cycle × cycle per sec 

Example 10.2: A single-stage reciprocating compressor is required to compress 1 kg of air from 1 to 5 bar. Initial temperature of air is 27°C. Calculate work for isothermal, isentropic, and polytropic compression for n = 1.25.

Solution: