Fan Cooling Capacity 2

[Adrian2]

Dear Folks;

I am a Mechanical Designer and I have been asked to replace the cooling fan on an industrial power supply with a model with a smaller footprint. Hopefully to reduce cost without sacrificing performance.

How do I calculate the cooling capacity of the proposed fan if I know its cfm and the its diameter ?

Any help would be much appreciated

Regards Adrian

 

[ChasBean1]

Yo, Adrian! (sorry, couldn't help that, I'm of the Rocky generation) - Cooling has nothing to do with the fan's diameter. You know the flow. Back to english units, for sensible heat, use:

Q = 1.08 * cfm * DT

Q = heat transfer in BTU/hr
cfm = volume flow, cubic feet per minute
DT = temperature difference, in °F
1.08 = a conversion factor to give non-engineers a warm fuzzy feeling

If you want to incorporate sensible and latent heat, use

Q = 19 * cfm * Dh

Dh = the difference in enthalpy, in BTU/lbm
19 = again, a warm, fuzzy conversion factor

So in essence, it's not simply the flow and diameter, but what cooling is being performed at the unit. Flow certainly plays a part in this. Feel free to re-post if you have any added questions/concerns. -CB

 

[km1997]

Since you have to reduce the footprint, the flow rate will go down with it unless you increase the RPM, which means you replace it with a smaller fan, but higher RPM (~more powerful). Essentially flow rate is proportional to Diameter^3 * RPM. You would also need to consider the pressure you need, pressure ~ diamter^2 * RPM^2.