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How to define an area where heat is generated

Posted Mar 7, 2012, 6:21 a.m. EST Heat Transfer & Phase Change Version 4.1 5 Replies

James Grant
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Hello,

My problem, to me, appears trivial. I'd like to define an area in my geometry where EM radiation is absorbed and there is subsequent heating i.e. define a domain or a bounday where say, 2500 W/cm2 is absorbed. Then I'd like to see how the heat is transferred to my sensor and the transient characteristics.

There doesn't seem an option to do this in COMSOL.

Any suggestions?

Many thanks!
5 Replies Last Post Mar 9, 2012, 9:40 a.m. EST
Edgar Kaiser
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Posted: 1 decade ago Mar 7, 2012, 7:14 a.m. EST

Of course you can define a heat source in domains and heat flux on boundaries. Just add the respective nodes under the Heat Transfer study node.

Cheers
Edgar
Of course you can define a heat source in domains and heat flux on boundaries. Just add the respective nodes under the Heat Transfer study node. Cheers Edgar
EH Ooi
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Posted: 1 decade ago Mar 7, 2012, 7:15 a.m. EST
Hi,
Under Heat Transfer in Solids, right click and choose Heat Source. That will allow you to specify the heat absorbed by the EM radiation.


EH
Hi, Under Heat Transfer in Solids, right click and choose Heat Source. That will allow you to specify the heat absorbed by the EM radiation. EH
James Grant
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Posted: 1 decade ago Mar 8, 2012, 9:51 a.m. EST
Thank you for the responses so far.

I have used both the heat source and boundary heat source options however the temperature of my structure just continually increases with time.

I am copying a simple structure, published in a paper (www.eee.metu.edu.tr/~tayfuna/papers/akin_c15_trans99.pdf), where 2500 W/cm2 is dumped in a square silicon area of 50 x 50 microns and the connecting tracks are Al. I should get a temp increase of 0.7 K, and the thermal time constant is stated as 0.6 msec i.e. the temperature should be in equilibrium by ~ 5 msec.

When I simulate it using a boundary heat source on the square silicon region the temperature increases with time (to over 700 K after 1s) and does not reach equilibrium. I do not consider convection by air or loss by thermal radiation since the dominant heat loss mechanism of micro-bolometers (the structure I am trying to simulate) is thermal conduction by air or thermal conduction through the metal legs (if operated in vacuum).

What am I doing wrong?

P.S. I am unable to attach the COMSOL file as it is too large.
Thank you for the responses so far. I have used both the heat source and boundary heat source options however the temperature of my structure just continually increases with time. I am copying a simple structure, published in a paper (http://www.eee.metu.edu.tr/~tayfuna/papers/akin_c15_trans99.pdf), where 2500 W/cm2 is dumped in a square silicon area of 50 x 50 microns and the connecting tracks are Al. I should get a temp increase of 0.7 K, and the thermal time constant is stated as 0.6 msec i.e. the temperature should be in equilibrium by ~ 5 msec. When I simulate it using a boundary heat source on the square silicon region the temperature increases with time (to over 700 K after 1s) and does not reach equilibrium. I do not consider convection by air or loss by thermal radiation since the dominant heat loss mechanism of micro-bolometers (the structure I am trying to simulate) is thermal conduction by air or thermal conduction through the metal legs (if operated in vacuum). What am I doing wrong? P.S. I am unable to attach the COMSOL file as it is too large.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Mar 8, 2012, 2:13 p.m. EST
Does that mean you did not account for any form of heat loss? If there is a heat source and no route for heat loss then the temperature will increase indefinitely. To reduce the model size (in order to post it on the Forum) clear all solutions and all meshes.

Nagi Elabbasi
Veryst Engineering
Does that mean you did not account for any form of heat loss? If there is a heat source and no route for heat loss then the temperature will increase indefinitely. To reduce the model size (in order to post it on the Forum) clear all solutions and all meshes. Nagi Elabbasi Veryst Engineering
James Grant
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Posted: 1 decade ago Mar 9, 2012, 9:40 a.m. EST
Hi,

Thanks for your input.

All micro-bolometers (the device which I am trying to simulate) are operated in vacuum so there is little loss by convection or conduction through air while heat loss via radiation is also typically not an issue. Thus the only heat loss is via conductuion through the connecting tracks.

I have attached the .mph file to this post.

I would also be interested in simulation the effect of thermal conduction by air. I am not 100% sure how to do this - I think I may need to draw an air box around my structure and define the material as air.
Hi, Thanks for your input. All micro-bolometers (the device which I am trying to simulate) are operated in vacuum so there is little loss by convection or conduction through air while heat loss via radiation is also typically not an issue. Thus the only heat loss is via conductuion through the connecting tracks. I have attached the .mph file to this post. I would also be interested in simulation the effect of thermal conduction by air. I am not 100% sure how to do this - I think I may need to draw an air box around my structure and define the material as air.

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