Example 13.1

Free air of 25 m³/min is compressed from 1 bar to 2.5 bar. Calculate the indicated power required if the compression is carried out in (a) roots blower and (b) vanes blower. Assume that there is 20% reduction in volume before the backflow occurs. Also, calculate the isentropic efficiency in each case.

Solution

The p−V diagrams for roots blower and vanes blower are shown in Fig. 13.5(a) and (b), respectively.

Figure 13.5 p−V diagrams: (a) Roots blower, (b) Vanes blower

1. Roots blower, 
2. Vanes blower,  I.P. if whole compression is carried out isentropically,Isentropic efficiency of roots blower Isentropic efficiency of vanes blower