Message-ID: <004b01c3bb9e$205b7f40$1702a8c0@WorkGroup>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2790442@logan.com>
Subject: Re: [FlyRotary] Re: K&M and Thick Radiators
Date: Fri, 5 Dec 2003 21:05:19 -0500
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> Ed,
>
>    It looks like you and I were coming to similar conclusions.
>
>    My present plan for my, as yet, unstarted Cozy (unless
> one counts completion of the shop facilities) is to mount
> two cores - e.g. the Frigidaire EV6709 - in tandem, with
> the water flow going first through the rear core and then
> through the front one.  The delta-T won't be *ideal* in
> either core, but it will be substantial.  I just have to
> work out a plenum that allows no air leakage between the
> cores.
>
> Still trying to keep the expenses down, without being
> "cheap".
>
> Dale R.

Sounds like a reasonable approach to me, Dale.  With the hotest coolant in
the rear core which is seeing the hotest air (after going through the first
core), you are still maintaing the greatest delta T between your metal core
wall temperatures and the air temperature.  The as the coolant has given up
some of its heat in the rear core, it flows into the front core where the
air is cooler thereby "maintaining" the maximum delta T spread.  So in
theory looks good.

As Al mentioned, however (always an however {:>)), you must have sufficient
dynamic pressure to push adequate air mass through both radiators.  In a
Cozy at cruise, I don't think you would have any problem.  Low airspeeds
like take off an extended climb will the the case that really tests the
idea.

I do not recall anyone actually having flown with this type of set up
although it has come up in discussion before.

I still going through chapter 12 of Kuchemann and Webber and am starting to
understand ( I believe) some of the sutelties in it about cooling.  Some
excellence information - just a bit heavy on the math side and
interpretating all the various "coefficients" they throw around.
It appears (If I am interpreting it correctly) that there are a few "ground
rules" that can be distilled applying to a cooling system design.

Some good information on inlet diffusers/heat exchangers AND what makes good
practices in exit ducts (the part I am trying to get into my dense head at
this time).  I am trying to understand the math well enough to put some of
it into a spreadsheet and see if the numbers that come out make any sense.

So, I would say,  that you are on a good path.  The only thing I can think
of is you may want that you give a lot of  attention to your take off and
climb regime cooling requirements.

One thing I read that is encouraging about thick radiators, is that one of
the radiator design companies claim that a 4" thick radiator only offers
about 10% more air resistance than a 2" thick radiator.  If so then I would
think a stack of two evaporator cores shouldn't offer much more than 15% of
so added resistance over one.

  Lets see - I wonder if that means since the dynamic pressure is 1/2density
*Velocity squared (and that is the delta pressure that really ends up
pushing the air mass through the radiator) would you need to go 15% faster
air speed or  perhaps only sqrt(15) = 3.87 say 4% faster to get sufficient
delta P to compensate for the thicker core stack.  Only crunching some
numbers would probably provide the answer.

Anyhow, get to work, so we can see how it works out.

Best Regards

Ed Anderson