[sdiy] Small form-factor PSU challenge!

[David G. Dixon]

I believe that oxidized (including anodized) metal sheet always has HIGHER
emissivity than unoxidized metal sheet.  However, in any case, the normal
(i.e., straight outward) emissivity of aluminum sheet is very low, even for
metals.  Steel, e.g., is much higher, and oxidized steel is much higher
still.  However, again, unless the sheet is very hot (several hundred
degrees), the loss of heat by radiation will be a very small component of
the overall heat loss in any case.  By far the larger component of heat loss
will be convective heat transfer from the sheet surface to the surrounding
air.  In this case, an exposed vertical sheet is best, as it induces natural
convective flow of air upwards along the face.


David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
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Tel 1-604-822-3679
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-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Andre Majorel
Sent: Tuesday, October 21, 2008 10:12 AM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Small form-factor PSU challenge!

On 2008-10-21 10:03 -0400, David Anderson wrote:

> You don't have to use a finned heatsink for your power supply.
> If you  make one side of your case from sheet aluminum, it might
> be enough  heatsink for your application. Consider that the
> Power One supplies use  sheet aluminum for their heatsinks.

Yes and you can make custom heat sinks by folding aluminium sheet.
Not being black anodised, they'll have lower thermal emissivity
but I suspect most of the heat exchange is through convection
anyway, another reason why it's best to keep the fins outside the
case.

Case manufacturers select alloys for mechanical properties
(machinability, rigidity), not for thermal conductivity. In
general, purer alloys (the 1xxx series) are easier to fold and
have better thermal conductivity.

The thermal conductivity of copper is at least 1.5 that of the
best aluminium alloys.

-- 
André Majorel <URL:http://www.teaser.fr/~amajorel/>
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