In fact, according to the table (The Normal Total Emissivity of Various
Substances) in "Chemical Engineers' Handbook" black lacquer and white
lacquer have identical emissivity in the range of 100 to 200 deg F. The
range is from 0.80 (at the lower temperature) to 0.95.
Bare aluminum at room temperature is in the range of 0.04 to 0.06 depending
on the surface condition.
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>
David,
I was taught that too.
Only it's wrong!
However, good absorbers often radiate more because, being good absorbers,
they get hotter. But at equal surface temperatures the emissivity of the
lighter colours is not much different.
Rgds.,
Duncan.
----- Original Message -----
From: "David Joyce" <davidjoyce@doctors.org.uk>
Subject: Re: Europa-List: black body radioation
> <davidjoyce@doctors.org.uk>
>
> Duncan, Fifty years ago when I was doing A level physics, absorption and
> radiation coefficients of a coloured surface were directly related. Good
> absorbers were good radiators, etc Regards, David
> ----- Original Message -----
> From: "Duncan McFadyean" <ami@mcfadyean.freeserve.co.uk>
> To: <europa-list@matronics.com>
> 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>
>> To: <europa-list@matronics.com>
>> 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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