Slip factor

A simple explanation for the fluid slip can be given as: Consider an impeller with z number of blades rotating at angular velocity ω.

High pressure and low velocity are observed at the leading face of the impeller's blade as compared to lower pressure with high velocity at the trailing face of the blade.

This results in circulation in the direction of ω around the impeller blade which prevents the air from acquiring the whirl velocity equivalent to impeller speed with non-uniform velocity distribution at any radius.

Mathematically, the Slip factor denoted by 'σ' is defined as the ratio of the actual & ideal values of the whirl velocity components at the exit of the impeller.

The Slip Velocity is given as: VS = Vw2 - V'w2 = Vw2(1-σ) The Whirl Velocity is given as: V'w2 = σ Vw2 The above explained models clearly states that the Slip factor is solely a function of geometry of Impeller.