Discussion Forum

Hi,

well COMSOL should of course consider that. Why not just try it. Make a little transient model and give your isolated domain a time dependent heat capacity. You should observe a temperture change anf you can compare it to theory.

Regards
Edgar

Thanks, but I have created little model with simle geometry (block (active element) in block (air)). Heat capacity of active element have time dependence (linear). This system is isolated. However temperature is constant and not changing. But Internal energy of body is changing.
May be I'm doing something wrong or not determine some specific value or parameter. I solve "Heat Transfer in Solids" problem with "Time Dependence" solver.
What do you mean under the " transient model "?

Thanks.

Edgar, what you think about it?
Maybe someone else can help?

Hi,

your specific adiabatic physics are not implemented in the heat transfer equation.

The heat transfer equation of the heat transfer module module has an heat source term, which takes adiabatic heats for fluids into account. With it you can easily model a temperature change for (adiabatic) air compression. See the attached file (V3.5a).

This could be a starting point for your time depending specific heat capacity. Maybe you can translate it to an time depending density. Then you need to connect your density change to a pressure change. This could be your desired solution.

best regards

Kai Herbrig, thanks for the answer and sample model, but we have solid body and can't set density depending (but we don't know it :) ).
We solve magnetocaloric problem, but approaches to it solution do not find.
Thanks again, we will be think about.

I see. But in literature there should be some heat transfer equations especially for magnetrocaloric effect?!?

I guess, this equation only differs at one term (right side of Comsol's heat transfer equation). Then it should be possible to add a new (appropriate) PDE (with the depending variable e.g. q_mc) and link it to the original equation by inserting q_em in the edit field for q.

Best regards

Hi.

I couldn't resit to do some quick checks on my own ... :)

When I insert the following expression in the edit field for "Q", I get a constant integral energy wich is of course related to a temperature change. That's what you wanted?

-rho_htgh*d(C_htgh,t)*T

Since you are using 4.0 the indices/notation should be different.


regards

Kai Herbrig, hello!
I tried your suggestion.
The model is a «cube in a cube» - a material (with a nonlinear characteristic of the heat capacity on temperature) placed in the air. On the one side of the material supplied temperature T = 300 K and on the other side T = 1 K. Duration of modelling process (solver time dependent) 10 seconds. Thus, I have a changing time-temperature for the material and, consequently, changing heat capacity. But adding the option “Heat source” in the General source
“-ht.rho*d(ht.Cp, t)*T” decision is not reached (solver don't calculate model, but no warnings displaied). Moreover, not even an error or a lack of explanation or solution. Just stop solution. If there is interest, I can upload the model. Thanks in advance!

Kai Herbrig, what you think about it?
Maybe someone else can help me?

Thanks in advance!