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heat transfer in solids - sine wave excitation

Posted Jul 16, 2015, 7:37 a.m. EDT Heat Transfer & Phase Change Version 4.2 3 Replies

Ferran Reverter
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Dear,
I was wondering if someone with more experience than me with the heat transfer module in solids can help with the following.
I have a heat source that dissipates power following a sine waveform. Then, I am checking the temperature at some distances from the heater and it turns out that the temperature changes like a triangular waveform; I expected a sine waveform. Although I’ve changed the number of steps of the time-dependent analysis, the thermal signal is always triangular.
Does anybody know which could be the problem with my simulations?
Thanks in advance!
F.
3 Replies Last Post Jul 17, 2015, 10:48 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 9 years ago Jul 16, 2015, 8:13 a.m. EDT
Hi

I see two possibilities:

a) either you have a very special geometrical shape and material properties
but far more likely
b) your time stepper is in "free" mode and the internal solver algorithm is aliasing your time dependent sinus waveform

Use the Time stepping "Intermediate" settings and ensure you have mat least 5 time step per sinus period

--
Good luck
Ivar
Hi I see two possibilities: a) either you have a very special geometrical shape and material properties but far more likely b) your time stepper is in "free" mode and the internal solver algorithm is aliasing your time dependent sinus waveform Use the Time stepping "Intermediate" settings and ensure you have mat least 5 time step per sinus period -- Good luck Ivar

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Ferran Reverter
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Posted: 9 years ago Jul 16, 2015, 8:59 a.m. EDT
Thanks Ivar!
It works, I got the sine wave thermal signal by changing the time stepper!!
Thanks Ivar! It works, I got the sine wave thermal signal by changing the time stepper!!
Ferran Reverter
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Posted: 9 years ago Jul 17, 2015, 10:48 a.m. EDT
Dear Ivar,

After solving the problem with the sine wave signal, I got another one. Maybe you can help me.
The power is dissipated inside silicon (which corresponds to an integrated circuit) and the frequency of that power is changed
Theoretically I can estimate the thermal penetration depth for different exciting frequencies, however the simulation results do not agree.
I mean: if I change the freq. (e.g. from 1 kHz to 10 kHz), the penetration depth of the thermal signal is almost the same according to simulations, but theoretically it should be three times smaller.
The geometry under test is very simple, just a heater dissipating power inside a block of silicon. Further, I have the feeling that the bigger the block of silicon (to have a more ideal scenario), the less the effects of frequency on the penetration depth.

Is that coherent? Any clue of the reason of that??

I hope that you can help me,

F.
Dear Ivar, After solving the problem with the sine wave signal, I got another one. Maybe you can help me. The power is dissipated inside silicon (which corresponds to an integrated circuit) and the frequency of that power is changed Theoretically I can estimate the thermal penetration depth for different exciting frequencies, however the simulation results do not agree. I mean: if I change the freq. (e.g. from 1 kHz to 10 kHz), the penetration depth of the thermal signal is almost the same according to simulations, but theoretically it should be three times smaller. The geometry under test is very simple, just a heater dissipating power inside a block of silicon. Further, I have the feeling that the bigger the block of silicon (to have a more ideal scenario), the less the effects of frequency on the penetration depth. Is that coherent? Any clue of the reason of that?? I hope that you can help me, F.

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