Casting aside all pretense of diplomacy, I think many of these
assumptions are hopelessly wrong.

On Nov 13, 2007 2:54 PM, Ron Springer <ron2369@sbcglobal.net> wrote:
> Assume you have two radiators:
>
> 1) Radiator 1 is twice the frontal area of Radiator 2
> 2) Same wetted fin area and fin spacing, so Radiator 2
> is twice as thick as Radiator 1.

> 3) Same air inlet with same mass flow rate

This is where it starts to go badly wrong and/or misses the whole
point.  The main object of using a thick rad is to use fewer CFM
(lower mass flow rate).   If you want to assume same mass flow, there
is no advantage (and probably a disadvantage) for a thick rad.

> 4) Different diffusers, but both have no flow
> separation and perfectly uniform flow arrives at the
> radiator face.

As pointed out earlier, one of the benefits to thicker rads is that it
is easier to achieve better diffuser performance.  If you just assume
it up front, well phooey, let's just assume the darn thing works and
go fly!.

> 5) Both radiators have the same average skin friction
> coefficient and average heat transfer coefficient in
> the boundary layers that develop across the fins (this
> is a small stretch and could be refined, but it is not
> going to change the trends in this example).
>

So far there are no trends in this example :>)

> Then, because heat transfer and drag scale with
> velocity squared, and velocity is twice as high for
> the thick radiator, and the thick radiator would have
> four times the heat transfer, but also four times the
> drag. There is always a tradeoff between heat transfer
> and drag.
>

 Here's the thing, 'Drag' through the radiator has very little to do
with cooling drag of an aircraft.  (see Monty's diatribe on Ed's
devious plot for why I shall not attempt to explain here)  We are
attempting to design efficient airplanes, not efficient water coolers.
 If we were, I would be on the thin radiator side of the argument.

> That is my take on the situation.
>
> Ron

Good take anyway Ron, it gets the gray matter churning.
I'm still waiting for someone to poke holes in my ultra simplification
/ ROT.  (fewer CFMs = less cooling drag).

And BTW Al,  2 3/4"  * IS *  a thick radiator.  2 5/8" is the very
thickest rad I could buy without going to the expense of a custom job.
 That's what I put on my 20B  RV-8.

Tracy



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