Time to clarify a bit of heat transfer theory for you non-engineers.
While it is certainly true that a "black" surface is a better emitter than
any other "color," at the temperatures that we are working with in cooling
an engine there is negligible heat transfer by radiation in this system.
Calling the thing a radiator is a misnomer. The engineering term for such a
device is "heat exchanger" or "air-to-liquid heat exchanger."
Heat transfer in this system is dependent (among other things which we
should consider unchanged) on the heat transfer coefficients, one on the
liquid side and the other on the air side. The liquid side gets less
efficient as scale builds on the interior - this scale can be from deposits
left by the liquid but it is mostly from corrosion of the "radiator"
material (whether that be copper or aluminum). The air side usually gets
less efficient because of things like bugs and other debris.
Paint on the heat transfer surfaces will definitely impair efficiency by
reducing the amount of air flowing through the "radiator" (the thickness of
the paint decreases the cross section available for air flow), and also by
adding thickness through which heat transfers by conduction from the liquid
side to the air side.
Ergo, it is not a good idea to paint the fins.
Best regards,
Rob Housman
A070
Airframe complete
Irvine, CA
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of Duncan McFadyean
Subject: Re: Europa-List: black body radioation
<ami@mcfadyean.freeserve.co.uk>
I beg to differ.
Black is far more absorptive than white. But the emissivity is little
different between the two colours; in other words, if heat is being LOST by
radiation, then black is only marginally more efficient than white. Of
course "radiators" transfer heat mostly by conduction, which is not affected
by colour.
Duncan McF.
----- Original Message -----
From: "Fred Fillinger" <n3eu@comcast.net>
Subject: Re: Europa-List: black body radioation
>
>> I was wondering whether white paint would massively affect
> the ability of
>> the radiators to dissipate heat. My gut feeling tells me
> that the bypassing
>> air molecule does not mind the color of the hot metal bit
> it gets heated up
>> by. But then again ... there was something in science
> class many years ago
>> about dark body radiation.
>> ....
>> Please advise.
>>
>> <Thomas, N81EU>
>>
>
> You want black, not white. Quantum theory, Kichoff's laws,
> good absorbers (black) are good radiators (shedding heat of
> the hot fluid). But with tradeoff as your radiators will be
> absorbs the sun's heat in a given flight condition.
>
> But as a practical matter, you'd have to dip them in paint,
> I don't think we want to do that. So anything shot on just
> the front shouldn't matter. Black will disguise the fact of
> radiators there viewed from a distance. White would look
> odd to me on such a device. Gold might look like it was
> anodized the way a popular aircraft part comes. Silver
> metallic phony; we homebuilders use too much of that.
> Office beige? Whorehouse lavender? :-)
>
> Reg,
> Fred F.
>
>
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