----- Original Message -----
From: "Ryan Etwell" > Q = h x A x (Tb - Tf)
>
> Where,
> Q - Heat Dissipated
> A - Area of body
> Tb - Temp. of body
> Tf - Temp of surrounding fluid (air in this case)
> h - Convection Heat Transfer Coefficient
>
> In this case Q is the heat generated by your device (in Watts), Tb would
> be its operation temperature (units don't really matter here since the
> equation just uses the difference of two temps)

Sorry Ryan, but this doesn't pass the "common sense" test. If the units
don't matter then I should get the same results with any units. Let's just
pick a couple numbers out of the air- boiling and freezing water seem good
as any. In celsius units thats 100 and 0 degrees respectivly and the
(Tb-Tf) term in your equation would be 100. However in Farenhieght units,
the same temps would be 212 and 32, the (Tb-Tf) term in your equation would
be 180, resulting in a very different answer.

> The magical number in
> this case is h, which is not a thermodynamic property, but an empirical
> parameter.  For free convection (no fan being used) h is listed as being
> between 10 - 100 W/m^2 K (Watts per square meter Kelvin).

Ok, now we're referencing the Kelvin scale, without a conversion in the
equation you should be using kelvin for the rest of the terms too.

-Denny

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