At 07:43 AM 2/15/02 -0800, you wrote:

>Well, it is true that if you only consider true *conduction*,
>air is very poor at transporting heat (this is why a down
>sleeping-bag is so warm: those little feathers keep the air
>from moving, so it can only conduct heat away). But if there
>is room for the air to move, then *convection* can be a very
>efficient heat transport mode. This is, after all, how a
>conventional heat sink ultimately sheds its heat in most cases:
>it presents a large surface area to the air, which convects
>the heat away.

So the fiberglass conducts the heat to a wider area, and
natural convection (and, to some extent, radiation) reduce the
temperature by transferring the heat to the air, the air
transports the heat to the enclosure walls, where it is
conducted out and transferred to the ambient air, mostly
by convection.

I know well that PC board material has significant thermal
conductivity- sometimes I have slots routed into the board to
thermally isolate patches of the board and make them isothermal
to themselves (eliminate gradients across the material)- same
concept as cutting a ground plane, if you think about it.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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