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Two vertical plates cooling by a fan. Doubts about the use of Comsol.
Posted 14.06.2012, 06:34 GMT-4 Fluid & Heat Version 4.2a 1 Reply
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Hi,
I am a new user in Comsol Multiphysics and I need to use the program for my thesis. The item to study consists of two plastic vertical-parallel plates. The left one generates 100 W and also there are radiation and convection due to the difference of temperatures. The right one is only a plastic plate which is used like a wall. Between both sides there is a fan which cooling the left side. First, I did an analytical calculation and I calculated the convective heat transfer (due to natural convection and forced convection because of the fan), h=13 W/m2*K, and the velocity needed by the fan, v=2 m/s
After this, I tried to build the model using Comsol but I have numerous doubts:
1. I don’t know if is better to used “Conjugate heat Transfer” or “Heat transfer in solids” taking into account that I have convection and radiation. I used “Heat transfer in solids”
2. I don’t know if I defined the contribution of the air that produces the fan in good way (I used another physic: laminar flow) and I introduce the data calculated before (h=13 W/m2*K, v=2m/s)
3. To introduce the convection I used “heat flux”. Also, I don´t know how to show that the air is at 323 K but the wall in left side is at 343K, because in heat flux, q=h (Text-T), I need to introduce the temperature Text=343 K and the heat flux contributes with: Temperature WALL 1, and in Temperature WALL 1 I need to introduce the temperature T. But, the temperature of WALL 1 is 343 K again, isn’t it???So, I don´t know how to show this effect.
4. In model inputs, I don’t understand the difference between “contribution of temperature (ht/ht)” or “user defined”. In my case, what would I have to use??
If anyone can help me I will be really grateful to you.
I didn't introduce the radiation because I wanted to see first the result of convection.
I add the simulation by Comsol.
Thanks.
I am a new user in Comsol Multiphysics and I need to use the program for my thesis. The item to study consists of two plastic vertical-parallel plates. The left one generates 100 W and also there are radiation and convection due to the difference of temperatures. The right one is only a plastic plate which is used like a wall. Between both sides there is a fan which cooling the left side. First, I did an analytical calculation and I calculated the convective heat transfer (due to natural convection and forced convection because of the fan), h=13 W/m2*K, and the velocity needed by the fan, v=2 m/s
After this, I tried to build the model using Comsol but I have numerous doubts:
1. I don’t know if is better to used “Conjugate heat Transfer” or “Heat transfer in solids” taking into account that I have convection and radiation. I used “Heat transfer in solids”
2. I don’t know if I defined the contribution of the air that produces the fan in good way (I used another physic: laminar flow) and I introduce the data calculated before (h=13 W/m2*K, v=2m/s)
3. To introduce the convection I used “heat flux”. Also, I don´t know how to show that the air is at 323 K but the wall in left side is at 343K, because in heat flux, q=h (Text-T), I need to introduce the temperature Text=343 K and the heat flux contributes with: Temperature WALL 1, and in Temperature WALL 1 I need to introduce the temperature T. But, the temperature of WALL 1 is 343 K again, isn’t it???So, I don´t know how to show this effect.
4. In model inputs, I don’t understand the difference between “contribution of temperature (ht/ht)” or “user defined”. In my case, what would I have to use??
If anyone can help me I will be really grateful to you.
I didn't introduce the radiation because I wanted to see first the result of convection.
I add the simulation by Comsol.
Thanks.
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1 Reply Last Post 14.06.2012, 07:31 GMT-4
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Posted:
1 decade ago
Hi
you have many questions there, here are some replies of what I quickly understand:
1) conjugated heat flow is the combination of fluid and solid flow and heat exchange, so if you have a fluid that you explicitely model its better to use this "physics" in my sens than only HT heat transfer in solid (which does notmtake the flow/transport into account), but its a complex multi-physics case and it might give you some convergence issues, depending on your model complexity. Doing the same manually allows you, perhaps easier, not sure, to decouple some physics to better get the system to converge, if that is an issue.
If you use HT for solids, you can add "convecting cooling boundaries" but this does not simulate the fluid flow, it only applies known heat exchange formulas to the boundary, while NITF really solves fluid flow + heat and solid heat transer + their coupling. On the other side NITF is not fully symmetric, you have either heat sources in the solid side , or from the fluid side, so there is some "master and slave" link to consider
2) COMSOL has internal "perfect" fan elements as "thin" boundaries, usefull for the fluid flow part
3) both heat Flux and Convective cooling applie the same formula, apart that the two do not really use the same sign convention in the wording, and only Convective cooling adds the heat exchange to the internal convective heat flux summer variable, not the heat flux BC.
4) the model inputs are the default variables (if applicable and often temperature) to say which to use, the one from another physics (in your case HT) or some variable you have defined
--
Good luck
Ivar
you have many questions there, here are some replies of what I quickly understand:
1) conjugated heat flow is the combination of fluid and solid flow and heat exchange, so if you have a fluid that you explicitely model its better to use this "physics" in my sens than only HT heat transfer in solid (which does notmtake the flow/transport into account), but its a complex multi-physics case and it might give you some convergence issues, depending on your model complexity. Doing the same manually allows you, perhaps easier, not sure, to decouple some physics to better get the system to converge, if that is an issue.
If you use HT for solids, you can add "convecting cooling boundaries" but this does not simulate the fluid flow, it only applies known heat exchange formulas to the boundary, while NITF really solves fluid flow + heat and solid heat transer + their coupling. On the other side NITF is not fully symmetric, you have either heat sources in the solid side , or from the fluid side, so there is some "master and slave" link to consider
2) COMSOL has internal "perfect" fan elements as "thin" boundaries, usefull for the fluid flow part
3) both heat Flux and Convective cooling applie the same formula, apart that the two do not really use the same sign convention in the wording, and only Convective cooling adds the heat exchange to the internal convective heat flux summer variable, not the heat flux BC.
4) the model inputs are the default variables (if applicable and often temperature) to say which to use, the one from another physics (in your case HT) or some variable you have defined
--
Good luck
Ivar