## COMPRESSOR CAPACITY

The capacity of a compressor is the volume of gas that it handles in a given period of time. For example, CFM indicates the volume of the gas handled by the compressor in 1 minute. The flow rate of a gas in CFM in a pipe line depends on the velocity of the gas and the diameter of the flow path. For the same velocity, the rate in CFM is higher for a larger diameter passage.

Example:

Air passes through two pipe lines, one with 6 in. diameter and another with

8 in. diameter. The velocity of air in both the pipes is 500 ft/min. What is

the flow rate of air through these two pipe lines?

Denote the diameter of the 6 in. pipe as d1 and that of the 8 in. pipe

by d2.

a.b.c.d.Area of cross-section of the 6 in. pipe = ? × d12/4 = (22/7) × (6/12)2/4

= 0.19643 ft2

Volume of air flow =

velocity × cross-section area = 500 × 19643

= 98.2 cfm

Area of cross-section of the 8 in. pipe = ? × d22/4 = (22/7) × (8/12)2/4

= 0.34921 ft2

Volume of air flow =

velocity × cross-section area = 500 × 0.34921

= 174.6 cfm

Result: Air flow rate in 6 in. and 8 in. diameter pipes for the velocity

of 500 ft/min are 98.2 and 174.6 cfm, respectively.

If the gas velocity is greater, then the pressure at the discharge section

is lower.

During compression, the volume of gas entering the compressor is

greater than the gas leaving the discharge. The ACFM is measured at the

suction of the compressor.