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Thermal losses from RF Electromagnetic Waves

Posted Mar 19, 2012, 4:52 a.m. EDT RF & Microwave Engineering, Heat Transfer & Phase Change Version 4.2a 3 Replies

Michele Comunian
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Dear all,
my problem is the coupling between an RF probelm and a thermal problem, do to the test I made 2 "attached" Blocks
and I solve before an RF problem on block1 with the calculation of the Eigenfrequency modes as "study1" and after I solve as "study2" in the near Block 2 the problem of Heat Transfer in Solid, what I get is 2 independ solutions without
any connections. If I try to include the Heat Flux from the study1 to the study2 I get the following error:
Failed to evaluate variable.
- Variable: freq
- Geometry: 1
- Boundary: 6
Failed to evaluate variable.
- Variable: mod1.emw.freq
- Defined as: freq
Failed to evaluate variable.
- Variable: mod1.emw.omega
- Defined as: (mod1.emw.freq*(pi*2))
Failed to evaluate variable.
- Variable: mod1.emw.iomega
- Defined as: (mod1.emw.omega*i)
Failed to evaluate variable.
- Variable: mod1.emw.Jsz
- Defined as: ((sqrt((epsilon0_const/mu0_const))*mod1.tEz)*sqrt((((mod1.emw.sigmabnd/(epsilon0_const*mod1.emw.iomega))+mod1.emw.epsilonrbnd)/mod1.emw.murbnd)))
Failed to evaluate expression.
- Expression: realdot(mod1.emw.Jsz,mod1.tEz)
Failed to evaluate expression.
- Expression: realdot(mod1.emw.Jsz,mod1.tEz)
Failed to evaluate variable.
- Variable: mod1.emw.Qsrh
- Defined as: (0.5*(realdot(mod1.emw.Jsz,mod1.tEz)+(realdot(mod1.emw.Jsy,mod1.tEy)+realdot(mod1.emw.Jsx,mod1.tEx))))
Failed to evaluate variable.
- Variable: mod1.ht.q0_hf1
- Defined as: mod1.emw.Qsrh
Failed to evaluate expression.
- Expression: d((mod1.ht.q0_hf1*test(mod1.T))*(dvol),{test@4})

What can be the way to connect the two problems?
Thank you very much,
Michele Comunian
3 Replies Last Post Sep 19, 2012, 8:47 a.m. EDT
COMSOL Moderator

Hello Michele Comunian

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KH
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Posted: 1 decade ago Sep 16, 2012, 5:52 p.m. EDT
Dear Michele,

Have you done any progress in this model?

In fact I'm starting the same kind of simulation (use emw as heating source) and I have many option to do that but I can't find the right way to do it.

I want to model the heat induced by a laser beam at a fixed wavelength on a thin metallic surface. Most of the models that i found doesn't account for the wavelength, it just represent the exchange of power which is far away from what I aim to:

www.comsol.com/showroom/gallery/12317/
www.comsol.com/papers/2685/ (Many papers from this group)

I tried to use the microwave heating module in the visible, it's very hard to make any calculation converge.

I also tried the emw + Heat transfer, the calculation converged but without any heat.

I open to any suggestion.

Best regards,

Karim


Dear Michele, Have you done any progress in this model? In fact I'm starting the same kind of simulation (use emw as heating source) and I have many option to do that but I can't find the right way to do it. I want to model the heat induced by a laser beam at a fixed wavelength on a thin metallic surface. Most of the models that i found doesn't account for the wavelength, it just represent the exchange of power which is far away from what I aim to: http://www.comsol.com/showroom/gallery/12317/ http://www.comsol.com/papers/2685/ (Many papers from this group) I tried to use the microwave heating module in the visible, it's very hard to make any calculation converge. I also tried the emw + Heat transfer, the calculation converged but without any heat. I open to any suggestion. Best regards, Karim
Kevin Anglin
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Posted: 1 decade ago Sep 18, 2012, 11:03 a.m. EDT
Hi Michele and Karim,

I am trying a very similar approach as both of you, maybe we can figure this out. I want to use a mode analysis to solve for the fundamental mode of my waveguide structure, then use the power loss density as the heat source. I'm having the same problems.

Michele, I was having similar errors with the frequency. Mine was saying couldn't solve the Jacobian for variable 'freq' i think. I added a frequency domain solve with basically the same frequency that I mode solved for, and this seemed to get it past that.

On to the heat solving in study 2. I typically get 0 solution here using the emw + heat transfer, with a stationary or time-dependent study. What's more confusing is that if you plot the "heat source" from solution 2, you would expect it to plot the "power loss density" from study 1, but it gives that exact error you posted. So I believe the problem is with the heat source. It's not clear to me how it comes up with a power loss density for mode-solving, since I can't specify a power to begin with.

I'm actively working on correcting these issues, and will keep you updated. Any suggestions would be welcome!

-Kevin
Hi Michele and Karim, I am trying a very similar approach as both of you, maybe we can figure this out. I want to use a mode analysis to solve for the fundamental mode of my waveguide structure, then use the power loss density as the heat source. I'm having the same problems. Michele, I was having similar errors with the frequency. Mine was saying couldn't solve the Jacobian for variable 'freq' i think. I added a frequency domain solve with basically the same frequency that I mode solved for, and this seemed to get it past that. On to the heat solving in study 2. I typically get 0 solution here using the emw + heat transfer, with a stationary or time-dependent study. What's more confusing is that if you plot the "heat source" from solution 2, you would expect it to plot the "power loss density" from study 1, but it gives that exact error you posted. So I believe the problem is with the heat source. It's not clear to me how it comes up with a power loss density for mode-solving, since I can't specify a power to begin with. I'm actively working on correcting these issues, and will keep you updated. Any suggestions would be welcome! -Kevin
KH
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Posted: 1 decade ago Sep 19, 2012, 8:47 a.m. EDT
My first suggestion would be to use a PORT excitation in which you can specify an input power.

In any case, I'm not really sure that it's possible to make this kind of simulation with comsol, or I still don't know where to specify a spectral emissivity!

I will let you know if I progress in this direction.

Karim
My first suggestion would be to use a PORT excitation in which you can specify an input power. In any case, I'm not really sure that it's possible to make this kind of simulation with comsol, or I still don't know where to specify a spectral emissivity! I will let you know if I progress in this direction. Karim

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