# Ratio of actual whirl velocity to ideal whirl velocity in centrifugal compressor

Q.  The ratio of actual whirl velocity to the ideal whirl velocity in the centrifugal compressor is called as _________.
- Published on 16 Sep 15

a. velocity factor
b. slip factor
c. work factor
d. none of the above

#### Discussion

• Pankaj   -Posted on 15 Oct 15
The ideal velocity of whirl Cwo equals to blade velocity Cbo at exit. However, this condition is not satisfied in actual practice because of the inertia of gas trapped between the impeller blades lags behind compared to the movement of impeller.

This condition results into reduction in whirl velocity component from Cwo to C’wo. This phenomenon is called as slip. Thus the difference between ideal and actual velocities (Cwo – C’wo ) is called as slip.

And the ratio of actual whirl velocity (C’wo) to the ideal whirl velocity (Cwo) is called as slip factor.

Slip factor Ψs = (actual whirl velocity C’wo) / (ideal whirl velocity Cwo)

But for an impeller with radial vanes,
(Cwo) = (Cbo)

Therefore,

Slip factor Ψs = (C’wo) = (Cbo)

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