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Date: Wed, 21 Nov 2007 13:51:25 -0800 (PST)
From: Ron Springer <ron2369@sbcglobal.net>
Subject: Re: [FlyRotary] Naca Report on Radiator Thickness
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-2499874@logan.com>
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Message-ID: <265791.23755.qm@web81302.mail.mud.yahoo.com>

Ed,

The most the rejected heat could change in this case
is 300%. You made a 300% change in thickness which
results in a 300% change in wetted surface area.

Your number will be lower for a couple reasons:

1) Decreased mass flow (5% in your case)

2) Boundary layer thickness grows as you go deeper
into the radiator. The last 1" of radiator will never
be as effective as the first 1".

I know your equations accounted for (1) but not sure
about (2). I haven't checked your reference.

The drag increase of 58% sounds way too low. You
increased surface area by 300%. Unless mass flow
decreased a lot (it didn't) or drag coefficient
dropped a lot (it shouldn't), then this can't be
right.

Ron

--- Ed Anderson <eanderson@carolina.rr.com> wrote:

> But in any case, assuming I did not screw up
> someplace, here are the results I got when I changed
> only the thickness of the radiator on drag, mass
> flow and heat removal:
> 1. The Drag (R) went from 4.28 lbf/ft2 to 6.77
> lbf/ft2 or a 58% increase presumably due to wall
> friction
> 
> 2. The Mass flow (M) decreased from 12.33
> lbm/ft^2/sec to 11.705 or a 5.13 % decrease  
> 
> 3. The Heat Rejected(Q) increased from 6.1707
> HP/100F to 23.66 HP/100F for a 283% increase