Radial Vane Fan Question

[gpas]

I was wondering if someone could tell me what the 'typical' efficiency of a radial vane fan, used in a scroll case blower, would be?

Some things I have read state 50% or less, others say it is 80%.

Also, is the "discharge coeffecient" variable I've seen used in CFM formulae the efficiency of the fan, or does it refer to something entirely different?

 

[vanstoja]

From a General Electric Fluid Flow Databook I hold, centrifugal fan efficiencies are shown to be a function of blade configuration (backward-curved, forward curved, radial tip, etc. and fan specific speed, a parameter based on rotating speed, pressure rise and flow). Peaks of plotted parabolic efficiency curves show efficiencies rising from about 65% at specific speed of 8000 to about 80% at a specific speed of 40,000. Static efficiency is given by eff=0.000157*Q*delp/P where delp is static pressure rise in inches water, Q in flow in cfm and P in input horsepower. Specific speed=(nQ^0.5/delp^0.75)*(rho/0.075)^0.75 where n is speed in rpm and rho is air/gas density. I don't find anything on discharge coefficient.