<VV> Mo Fan

[RoboMan91324 at aol.com]

Hello Padgett,

I beg to differ.  Your theory with the increased density is correct if you 
are pumping against a blockage AND still flowing the same volume or even mass.  
However, if you have no flow through, you are doing less work.  With zero flow 
through, think of the fan as an air/metal composite rotating component.  Both 
the air and metal are turning as a unit.  Of course, there will be some 
losses due to turbulence but there are also turbulence effects in the flow through 
model.  Here is an experiment.  If you have a shop vac, turn it on and put 
your hand over the intake and exhaust sides.  In both cases, you can hear the 
speed increase.  This would indicate to me that the load has gone down.  Of 
course, my shop vac leaks like a sieve on the pressure side so the difference is 
not that great when I cover the exit port.  I suppose that a canister vacuum 
would be better for this experiment if some Corvair guys hadn't exploded them all 
in a childish prank.

Now I imagine everyone running out to their respective garages to try the 
experiment.

Doc
~~~~~~~~~~~~
In a message dated 7/14/2005 11:56:37 AM Pacific Daylight Time, 
virtualvairs-request at corvair.org writes:

> Message: 5
> Date: Thu, 14 Jul 2005 13:47:43 -0400
> From: Padgett <pp2 at 6007.us>
> Subject: <VV>Mo Fan
> To: virtualvairs at corvair.org
> Message-ID: <5.2.0.9.2.20050714133425.0251a758 at mail.bellsouth.net>
> Content-Type: text/plain; charset="us-ascii"; format=flowed
> 
> 
> >Sorry Padgett, but this is just not correct. When you block the output 
> cooling air, the fan has much less work to do and the required horsepower goes 
> DOWN, not up.
> 
> Guys: the fan loss (hp required) has nothing to do with the amount of air 
> moved but rather the power required to turn the fan. The power required to turn 
> the fan at maximum air movement (unblocked inlet and outlet) is actually a 
> middle value. Block the inlet and the fan is turning in a partial vacuum of 
> its own creation and the power required for a constant rpm goes down (in the 
> tank vacuum example or a turbosupercharger, the rpm will increase). Block the 
> outlet and the air density in the plenum goes up, increasing the drag on the 
> impeller. This increases the power required to turn the fan and the 
> temperature of the air in the plenum goes up slightly.
> 
> Now if you want to get heat quickly and increase the heater air flow in cold 
> weather, this makes sense since the change in drag is not a whole lot for 
> the engine driven cooling fan in a Corvair but in a turbo, particularly one 
> making a lot of boost, it is a serious issue.
> 
> Padgett