Learning Forum

[cnemecek05]

I am trying to predict the heat transfer coefficient to an avionics box with a known power dissipation (ie, watts). There is an impinging jet on the box providing cooling. The simulation domain consists of the fluid volume only. The avionics box is not modeled as a solid, but just as a void in the fluid volume. Is it appropriate to specify the heat generation rate of the box as the known power dissipation divided by the volume of the box?

[Rob]

Possibly, the problem with that is working out how much heat would be lost to each surface. Ie is the box cooled more on one side than the other, and what does that do to the heat loss & temperature distribution?

[cnemecek05]

For the purpose of this problem, we would assume the power dissipation is evenly distributed across all surfaces of the box (ie, an area-weighted average for the dissipation) such that integrating the heat flux across all surfaces yields the known power dissipation. The box will be cooled more so on one side, but we'd still assume the power dissipation is an area-weighted average across all surfaces.

[Rob]

In which case I'd use a heat flux, ie W/m2 The heat generation is more for heated layers in systems, eg a thin heating element between a steel & insulation solid on a pipeline.

[DrAmine]

Energy source when soving temperature equation for the wall as a layer.