Blower Isentropic Efficiency Explained

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Learn more about isentropic efficiency and specific performance as they relate to blowers. 

Isentropic efficiency is the ratio between theoretical power and real power. To calculate it you need to know ambient conditions (ambient pressure, ambient temperature), the flow rate of the machine in question, and its operating pressure. Using those parameters you calculate the isentropic power. The higher the number the better the efficiency. 

The isentropic efficiency for the multi-stage centrifugal blower in this video is 40%. On a rotary lobe blower it is 40-55%. For the Kaeser rotary screw blower it is 70%. 

Another metric you can use is specific performance, which is input power compared to air output (kW/100 cfm). So lower numbers mean better efficiency. 

For the plant in the video it is 5 kw/100 cfm with the centrifugal blower and 3 kw/100 cfm for the rotary screw blower. A lobe blower would be about 4 kw/100 cfm. In this example (600 cfm unit, using $0.10/kW hr) annual operating costs for the centrifugal blower are $30,000 compared to $16,000 with the rotary screw blower. 

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