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Associate

Join Date: Sep 2005
Posts: 27

Fan Air Loss

01/27/2009 10:44 AM

We have to move a cooling fan on an engine, we have to fit the engine in a confined space and the fan diameter is too large.

We have a 23" Fan and we need to cut 1" off for a total diameter of 21"

turning at 2200 rpm, how mush air loss can we expect? approximate?

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Power-User

Join Date: Jan 2008
Location: since 20 Jan 09, the USSA
Posts: 375
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#1

Re: Fan Air Loss

01/27/2009 11:26 AM

Other things equal, the amount of air you lose will go as the square of the change in fan diameter. Now if the fan speeds up because there is a smaller load on the fan motor, then that will partially compensate for the smaller diameter. If that happens or not depends on the type of motor used. You could also change fan blade pitch to compensate for the reduced diameter to maintain constant airflow.

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Guru
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Join Date: Jun 2006
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#2

Re: Fan Air Loss

01/27/2009 4:27 PM

Or remount smaller fan on smaller pulley if belt driven.

Or go to electric fan and pick your own.

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Guru

Join Date: May 2007
Location: Geelong, Australia
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#3

Re: Fan Air Loss

01/28/2009 1:43 AM

As emcc says use the ratio of swept area.

ie ∏(23/2)² : ∏(21/2)² Canceling the common things on both sides gives you 23² : 21²

So the flow will be about 83% of the original amount

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Guru
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Join Date: Sep 2006
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#4

Re: Fan Air Loss

01/28/2009 10:57 AM

As long as you are not in an area of extreme temperatures, you should not notice any differences, they are designed to work in extremes of temperature, so at lesser temps, its sometimes "over done!"...

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