Received-SPF: pass
 receiver=logan.com; client-ip=24.25.9.102; envelope-from=eanderson@carolina.rr.com
Message-ID: <000401c538c7$83f472d0$2402a8c0@edward2>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-853858@logan.com>
Subject: Re: [FlyRotary] Re: Cooling -Learned a lot
Date: Sun, 3 Apr 2005 23:36:40 -0400
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit


-----  >
> So, we're back to that Bernoulli guy.  Increasing the speed decreases
> the pressure, because all the little molecules are running together in
> one direction instead of banging into things on either side.  But this
> time we're working it in reverse.  We're lowering the speed (by slowly
> increasing the duct's cross sectional area), giving them a chance to
> knock up against things they wouldn't otherwise (like the radiator
> core's fins).
>
> This leads me to believe that with the proper duct, you could decrease
> the fin density and allow the air to flow through without the need to
> generate all that turbulance.  You create the turbulance to keep the air
> mixed (so the cooler air gets a chance to grab some heat).  But if the
> molecules are already picking up the heat there's no need to waste enery
> making tiny little vortexes all over the place.  Am I dreaming again?
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."
>
>
Earnest, It starts to get a bit complicated at this point. But, I don't
think it would work like that.

 There are several theories about how heat gets transferred among air
molecules during flow and I don't pretend to understand them all.  However,
at any point in time the molecules nearest the fin walls have the greatest
chance of hitting the fin and picking up heat. As I understand it if the
flow is laminar then only that relative thin layer of air molecules are
effectively transporting the heat and the rest of the molecules (in the
center of the non-turbulent flow) are loafing and not carrying their fair
share of heat.  The reason for this lack of heat transfer from the outer
layer of molecules to the inner is laminar flow - no turbulence!  More
pressure in laminar flow would simply have the molecule in that thin layer
hitting the fins more often - but they would quickly reach the point of
being heat saturated.

So you would like higher pressure (more contacts per unit time for those
molecules close enough to the fin walls) AND turbulence so that those outer
hotter molecules can mix into the inner flow area and transfer heat to those
molecules.  Therefore for cooling both higher pressure and more turbulence
(within limits) would appear to give better cooling..

At least that is the way it appears to me.

Ed A