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2D Power Density

Posted 30.11.2012, 12:49 GMT-5 Fluid & Heat, Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD) Version 4.3 3 Replies

Lucas Kyriazidis
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Good Afternoon,
I am having some trouble calculating what my power density should be in my 2-D model. I am modeling a cross sectional cut of a heated aluminum plate in air. In my experimental runs, the plate has a power of approximately 60 Watts. If I did a 3-D model, the power density would just be 60W divided by the total volume of the plate. But What should I input in a 2-D model. How should this be scaled. I have looked at the previous posts describing this but still am having trouble visualizing it. The total volume of the aluminum plate is 8.8 in^3.
In my current 2D model, I just input 60W/8.8in^3. The simulated model and experimental results are off in temperature (almost by a factor of 2).
Any suggestions would be great.
Thanks,
Lucas
3 Replies Last Post 05.12.2012, 01:42 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 30.11.2012, 14:55 GMT-5
Hi

COMSOl solves always in 3D, 2D representation is for 1[m] by default Z depth (into the paper) and 1D is for 1[m^2] area normal to the 1D line. So you should always enter densities, based on the true volume, and then extract values by integrating over the boundary and multipying by 1[] (no unit) for 3D, by d[m] true Z depth in 2D and A[m^2] true area in 1D.

2D-axi is special as here the depth is vcarying and represents the "loop lengh 2*pi*r that you should add to surface integrals to map the 2D cut section into a true 3D reprsentation

--
Good luck
Ivar
Hi COMSOl solves always in 3D, 2D representation is for 1[m] by default Z depth (into the paper) and 1D is for 1[m^2] area normal to the 1D line. So you should always enter densities, based on the true volume, and then extract values by integrating over the boundary and multipying by 1[] (no unit) for 3D, by d[m] true Z depth in 2D and A[m^2] true area in 1D. 2D-axi is special as here the depth is vcarying and represents the "loop lengh 2*pi*r that you should add to surface integrals to map the 2D cut section into a true 3D reprsentation -- Good luck Ivar
Lucas Kyriazidis
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Posted: 1 decade ago 03.12.2012, 13:40 GMT-5
Thanks for your answer, I have tested this and it is true. I believe inputting a power density is not my error with the large temperature differences seen between COMSOL and experimental data. My next question/idea is if assuming no radiative losses is a poor assumption. Therefore, I tried to input in my model surface to ambient radiation, but COMSOL will not let me select the domain of interest. I have attached my model, in case you have some free time and can look into it.
Thanks,
Lucas
Thanks for your answer, I have tested this and it is true. I believe inputting a power density is not my error with the large temperature differences seen between COMSOL and experimental data. My next question/idea is if assuming no radiative losses is a poor assumption. Therefore, I tried to input in my model surface to ambient radiation, but COMSOL will not let me select the domain of interest. I have attached my model, in case you have some free time and can look into it. Thanks, Lucas
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 05.12.2012, 01:42 GMT-5
Hi

check your mesh, you have no boundary wall mesh, your velocity increases rapidly very locally, so even most of your model could be dropped for a symmetry condition, in my view.

Then radiative excahnge surface to ambient works on external boundaries only, for surface to surface calculations, you need to turn on the extra equations with the tick mark in the main heat physics tab

--
Good luck
Ivar
Hi check your mesh, you have no boundary wall mesh, your velocity increases rapidly very locally, so even most of your model could be dropped for a symmetry condition, in my view. Then radiative excahnge surface to ambient works on external boundaries only, for surface to surface calculations, you need to turn on the extra equations with the tick mark in the main heat physics tab -- Good luck Ivar

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