<VV> Fans and air flow

[JVHRoberts at aol.com]

Bottom line: Want more cooling? You need to reduce the resistance to air  
flow, AND increase the driving pressure for that air flow. It's really quite  
basic. 
 
In a message dated 8/1/2007 4:47:41 P.M. Eastern Daylight Time,  chsadek at comca
st.net writes:

Good  comments. Thanks.

Chuck S
----- Original Message ----- 
From:  <ScottyGrover at aol.com>
To: <virtualvairs at corvair.org>
Cc:  <fastvair at yahoogroups.com>
Sent: Wednesday, August 01, 2007 4:23  PM
Subject: <VV> Fans and air flow


>I have been reading  this line of comments and maybe I could add a little
> something.   For my credentials--I don't have a ME degree But what I do 
> have   is
> 45 years as an estimator reading HVAC plans and specs.   OK??
> An axial fan (prop) is fine mounted on a floor stand or in an  outside wall
> where there is little or no ductwork attached to it; it  can circulate 
> quite a
> lot or air.  When it is ducted  (duct-axial or vane-axial) it can move air
> against air resistance  (called static pressure) but the horsepower 
> requirements
> are  quite high; airlines have lots of horsepower to spare so that's how 
>  they
> run  those FAT jet engines on modern planes.  Now  centrifugal fans 
> (sometimes
> called squirrel-cage blowers)  need--ideally--a scroll-shaped casing and 
> send
> the  air  parallel to the outside wall of the scroll.  Centrifugal toilet
>  exhaust  fans (the kind you see in a restroom with the stamped grille  
> showing) don't
> have  a scroll but as long as they are in  a box they can put up pressure
> which will  force3 the air out of  any available opening.  Corvairs use a
> centrifugal  fan of a  rather crude design (at least the magnesium fans 
> are) which  is
> using  the shroudwork as its plenum.  They would work  better if there was 
> less
> clearance at the top of the "turkey  roaster" but the wheel design uses 
> much
> more  power to  get the job done than it should.  Maybe the early model fan
>  wheels  should be used as a mold to make a lightweight plastic fan  
> modified to make
> sure  it fits is the roaster but with a  minimun clearance.
> I have not seen photos of the prop. fan that was  used in the test but one
> report stated that the fan was blowing on a  flat plate and was observed to 
> blow
> upwards; this is a total  SNAFU.  There should never be an obstruction like 
> a
> flat  plate near a prop. fan; any ductwork downstream of the fan should be
>  carefully angled to bend the flow of air outward and direct it to the 
>  cylinder
> fins.
> Also, as several people have stated, the fins  should be cleaned up to
> minimise the obstruction to air flow; this  probably lowers the HP 
> requirements  of a
> stock fan  also.  Anyone trying to use an electric fan should take all 
>  steps
> necessary to lower the power requirements of the engine before  they mount 
> the
> electric setup; however, this was not part of  the test requirements; it
> would be interesting to mount the electric  system on a properly cleaned-up 
> engine
> and see what that  would do in the way of changes.
>
> Scotty from  Hollyweird
>


 



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