Discussion Forum

Hi,
I have been computing a similar problem and found the same issue. I managed to improve the results slightly by refining the cooling parameters. If these aren't correct then energy just keeps being inputted and cannot go anywhere other than heat the object.

I have defined cooling measures. The model consists of a box with three batteries in it. For a first simple analysis, I defined the outer boudaries of the box to be constant at ambient temperature, and you can see the temperature distribution. I have also made models were air flows past the box to provide cooling.

My question is more related to how I should define the heat source. How did you do this with your problem?

I looked at the heat sink tutorial within comsol before modelling my problem, here they define a heat source with a total power, my model has this too. If you have the cooling measures I am unsure of why it isn't producing expected results.
The only other difference with your model that I can think of are the material properties. With batteries being composed of multiple materials, the heat capacities etc may differ from actual?
Sorry I cannot be of more help

Hi

COMSOL indeed simulates 2D as 3D with generally (if not always) 1 [m] depth, hence all fluxes are per m, and all heat densities are per meters.

This is OK if you respect the units in densities, some care if you use absolute values.

Try it out on a simple example: make a 2D 1m^2 square block add 1[MW/m^2] heat flux on the top, cte T temperature on the bottom, solve, this corresponds to an integrated value of 1MW input power for 1m depth and 1m aside, but only 1kW integrated power for a 1mm thin block

Then add anotherseparate square block of 1 m aside, add 1kW "total power" on top surface/edge and cte T on bottom, if you integrate now you have only 1kW/m^2 average top power density that is the value COMSOl averages out evenly, so a 1mm thick block would, with this intensity only consider 1W through the top edge

Basically if you think Flux it's OK, when passing on full total power you must each time remind yourself what is the true depth considered

Then do not mix up boundary sources and Volume sources, here it applies too, appart that your source is distributed evenly (if you use a scalar) over the full domain

Hope I'm clar

--
Good luck
Ivar

Hi,
I am a beginner with COMSOL heat transfer module. I have a hollow cylinder which is being cooled by water on the inside and on the outside by air. I am supposed to model it as a steady state problem. Now the cylinder is supposed to be generating heat due to some reactions which I have to neglect. The amount of heat is 3.5 MW/m3. My problem is that my heat source is not being recognised. The temperature profiles look as though there is no heat generation. Any suggestions

Hi,

I have the same problem as above, setting temp on boundary or overall heat transfer rate works, but not general heat source.
Thanks.