Tips Speeds and Centrifugal Compressors, Blowers and Fans

Hello Nilesh,

It is my understanding that 'tip speed' refers to the linear velocity of the impeller blade tips (as in the edge radial extremity of each blade). The speed of the impeller tip is proportional to the flow-rate at which your impeller will begin to cavitate. Cavitation will result in excessive wear on the blades. Basically, the higher maximum tip speed that a manufacturer may quote in a spec-sheet, the higher RPM you'll be able to safely operate your impeller (i.e. higher flow rate).

Hope that helps

TinTin

How it is related to Flow rate ??

Tip speed is direcly proportional to Diameter and Speed. Where flow comes in pictrure.

Could you please elaborate your view.

I agree with the suggestion of Mr. Steve and Mr. The Prof.

Hi Nilesh,

It does seem like my post was off-topic. After re-reading your initial question, I realised that you're obviously intending to move a volume of gas, not liquid - so disregard my tangential about cavitation. As I, (and even yourself!) alluded to; flow rate is propotional to tip speed : V(tip speed) = θ(blade RPM) x R (radial distance). Higher RPM gives you a higher volumetric flow rate, as does increasing the diameter (though you'll need more torque). When you're pumping gases as opposed to liquids, the tip speed becomes significant for different reasons -one of them, as 'The Prof' pointed out is that you dont want your blades to fail under their own centrifugal forces (due to the higher RPM's involved).

In summary; listen to the Prof - he knows what he's talking about

Regards,

TinTin

You need to be concerned about the centrifugal forces at these tip speeds and the limits of the materials of construction of the impeller. Maximum allowable Tip speed will therefore depend on the temperature of the gas, the corrosivity of the gas, the yield of the impeller material etc.

Also one of the important characteristic numbers for a centrifugal compressor is the Mach number. This is given by M = u₂/(kZRT)^0.5

Where u 2 is impeller tip speed, k = isentropic exponent , Z=compressibility factor, R = gas constant, T = temperature

For industrial gases this may vary between 0,2 and 1,2 approximately.