The comparison of rotary and reciprocating compressors is given in Table 13.1.
Table 13.1 Comparison of rotary and reciprocating compressors
Example 13.3
Free air of 30 m3/min is compressed from 101.3 kPa to 2.23 bar in roots blower. Determine the power required and the isentropic efficiency.
Solution
The p − V diagrams for roots blower is shown in Fig. 13.7.

Figure 13.7 p − V diagrams
V1 = 30 m3/min, p1 = 101.3 kPa
p2 = 2.23 bar
Refer Fig. 13.8.
Indicated power, I.P. = ![]()

Isentropic indicated power, (I.P.)isen = 

Isentropic efficiency, ηisen = ![]()

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