41 posts
TimePosted 15/11/2010 15:49:44
babli says

Fan law

Can anybody clarify about fan law which says

that Volumetric flow rate changes with change in fan speed but not with change in density. Now My question is when ever temperature is increased , density changes and as a result voulmetric flow rate  also changes. But according to fan's law volumetric flow rate does not change with change in density. Please explain.

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138 posts
TimePosted 16/11/2010 09:20:18
lalbatros says

Re: Fan law

The volumetric flow rate is determined by the geometry of the fan and its rotation speed.

When temperature increases, the density decreases indeed, but the volumetric flow rate doesn't change since the rotation speed and the geometry of the fan remain the same. As a consequence, the massic flow rate will change: les tons/hour for the same m³(actual)/hours.

17 posts
TimePosted 16/11/2010 13:04:54
B.P.Jain says

Re: Fan law

With change of speed volume does change but with change of density volume does not change as long as motor does not get over loaded and its speed gets reduced.                     B P Jain

41 posts
TimePosted 18/11/2010 05:55:29

Re: Fan law

Hello Michal,

My understanding and experiance contradicts with the explanation given by you and Mr.Jain

lalbatros:
The volumetric flow rate is determined by the geometry of the fan and its rotation speed.When temperature increases, the density decreases indeed

Yes I absolutely agree with this...

lalbatros:
but the volumetric flow rate doesn't change since the rotation speed and the geometry of the fan remain the same.

Here comes the contradiction.. When density decreases with increase in temperature volume of the gas increases (Charles's Law), By virtue of lower density and Same RPM (Same power) Fan draws more voume of gases though geometry or RPM isn't changed. More M3/hr Ain't it? This is the Reason FLSmidth experts accounts for change in density during the PG Tests.....

More explanation is awaited....

Hussaini