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Subject: RE: [FlyRotary] Cooling Model Enhancement
Date: Mon, 20 Oct 2003 23:10:02 -0400
Message-ID: <0B27ED95697C4D4CBC82D79E790FE567086FAA@exchange.rfgonline.com>
Thread-Topic: [FlyRotary] Cooling Model Enhancement
Thread-Index: AcOXfXgwVL3+hn9vQP+HPVft8vbWMwAAI96A
From: "Robinson, Chad" <crobinson@rfgonline.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>

Ed, are these calculated or measured numbers? If calculated, what's the =
formula being used?

This should normally be a tricky business. Cooling/heating formulae =
normally involve the specific heat and mass of the substance being =
cooled, the amount of heat transferred, etc. One common formula is:

  heat transferred =3D mass * deltaT * specific heat (1 for water)

So yeah, this seems odd. The bigger the deltaT (in this case, difference =
between air and radiator temperature) the more heat you can transfer.

There are a bunch of these at:
http://www.fordhamprep.com/gcurran/sho/sho/lessons/lesson210.htm

But a complete formula is complex because it depends on radiator =
configuration, efficiency, etc. I found a bunch of auto =
radiator-specific formulae at:

http://www.unb.ca/che/Undergrad/proposed/auto.pdf

but then you're on your own. Or you could ask one of the ACRE guys. =3D)

> -----Original Message-----
> From: Ed Anderson [mailto:eanderson@carolina.rr.com]
> Sent: Monday, October 20, 2003 10:46 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Cooling Model Enhancement
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> I finally found a math model that provides the rise in=20
> temperature as it
> goes through a radiator.  The model indicates that for the=20
> two evaporator
> cores that the air temp should rise between 35F and 38F for=20
> 161 HP at 120
> MPH burning 15 GPH.  Less of a rise if less BTU are being generated.
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> Here is what the temp rise model gives (all temps in farenheit):
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> OAT  Delta T   Exit Radiator
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> 0            34.9        34.9
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> 30            35.59    65.59
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> 60        36.15        96.15
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> 90        36.02        126.02
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> 120        37.48        157.48
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> I guess I am surprised to find that the delta T is decreasing with
> decreasing OAT. The only way I can rationalize the lower=20
> delta T at the
> lower temps  still removing the same amount of heat is that=20
> the cold air is
> denser and therefore  the mass flow is greater and that=20
> accounts for carring
> away the same amount of heat with a lower Delta T.  Would any of your
> thermodynamic folks comment on this?
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> In any case, it appears that some of Todd's delta T figures=20
> fall in this
> ball park, so this model may not be too far off.
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> Ed Anderson
> RV-6A N494BW Rotary Powered
> Matthews, NC
> eanderson@carolina.rr.com
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> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
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