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# Does "Heat Transfer Rate" take into account only convection, or conduction as well?

Question asked by 1-D8GBWG on Apr 1, 2010
Latest reply on Apr 9, 2010 by Rich Bayless

Flow Simulation 2009.

Does the Integral Surface Parameter "Heat Transfer Rate" take into account both the conduction & convection mechanism, or just convection?

I am trying to determine how much heat goes through the various surfaces of my part; e.g. for a heat source like a TO-220, I'd want to know how much of the heat produced inside is removed by radiation of the casing, how much by convection on the casing and how much is conducted through its back plate to the heatsink attached.

I know that for radiation I need to look at Net Radiation Rate (thermal), as Heat Transfer Rate will not take it into account.

But it seems to me that Heat Transfer Rate only calculates the heat transfer by convection and somehow ignores any heat conducted through the surface.

The reason I'm saying this is that the energy balance for my part does not hold when there is conduction.

Suppose radiation were turned off and and I assigned a volume source to my part, say 1W.

If my part were hanging in free air, with only convection to remove the heat produced, then when I select all outer surfaces of the part and I look at "Heat Transfer Rate", I get ~1W as expected. Energy balance holds for a steady-state case, all heat produced inside goes out.

If my part now were contacting another part, with no heat source in the 2nd part, the energy balance does not hold anymore.

Again I select all outer surfaces of my heat source, but this time "Heat Transfer Rate" is much less than the 1W produced inside; whatever is missing is most likely the heat conducted into the adjacent part.

Does anybody know how to calculate the heat transfer rate by conduction through a surface?

Am I missing anything?

Thanks for your help.

Victor Isac.