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Adding a material after heating

Posted 28 juil. 2015, 10:01 UTC−4 Heat Transfer & Phase Change 5 Replies

Jeff Williams
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Hi all,

I have a 2D hemisphere that I want to heat up in air. The flat edge is heated with a constant power of 100W. After 60 seconds I would like to introduce a curved piece of copper on the curved edge. The heater still runs, but the copper starts at room temperature and so cools the hemisphere down, before heating up again. I am struggling with this, because I can't figure out how to introduce the copper at room temperature, because the initial expression starts t=0, and I need t=60. Does anyone know how to do this?

Thanks
5 Replies Last Post 30 juil. 2015, 05:14 UTC−4
CHEN
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Posted: 9 years ago 28 juil. 2015, 10:30 UTC−4
Hi Jeff,

If I understand you correctly, what you need is two differenct boundary conditions at different times. I think you can do this with the build-in funciton "if" by using time as argument. Hope this is helpful for you.
Hi Jeff, If I understand you correctly, what you need is two differenct boundary conditions at different times. I think you can do this with the build-in funciton "if" by using time as argument. Hope this is helpful for you.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 9 years ago 28 juil. 2015, 11:10 UTC−4
Hi

I would run two time solver cases under the same study, one for t=0 to 60 and one for t>60 (resetting from new_t=0, but by using the last time sequence results as the new initial conditions for the second time solver case, also you must add in the new material for this new study.

You assume that you have perfect thermal contact between the new material plate and the old part and that the any thermal stress that will make the curved surfaces to disjoint is ignored

--
Good luck
Ivar
Hi I would run two time solver cases under the same study, one for t=0 to 60 and one for t>60 (resetting from new_t=0, but by using the last time sequence results as the new initial conditions for the second time solver case, also you must add in the new material for this new study. You assume that you have perfect thermal contact between the new material plate and the old part and that the any thermal stress that will make the curved surfaces to disjoint is ignored -- Good luck Ivar
Jeff Williams
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Posted: 9 years ago 29 juil. 2015, 10:15 UTC−4
Thanks for the hints but unfortunately this doesn't work. When I add the copper it is not at room temperature but it is at the temperature of the air it's displacing. How do I use the If boundary condition?

Thanks
Thanks for the hints but unfortunately this doesn't work. When I add the copper it is not at room temperature but it is at the temperature of the air it's displacing. How do I use the If boundary condition? Thanks
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 9 years ago 29 juil. 2015, 15:10 UTC−4
Hi

I expect I do not fully understand your model, from your word descriptions, but there is no reason why not to set the initial Cu plate temperature to a T value from the previous study, this can be done by a mapping operator, or that you define the copper plate as a domain for the first study, but give it "air" material properties, and then set the material to Cu for the second study, then the mapping is 1:1.

I have not used the new "if then else" features yet so there I cannot help, probably it does the job too

--
Good luck
Ivar
Hi I expect I do not fully understand your model, from your word descriptions, but there is no reason why not to set the initial Cu plate temperature to a T value from the previous study, this can be done by a mapping operator, or that you define the copper plate as a domain for the first study, but give it "air" material properties, and then set the material to Cu for the second study, then the mapping is 1:1. I have not used the new "if then else" features yet so there I cannot help, probably it does the job too -- Good luck Ivar
Jeff Williams
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Posted: 9 years ago 30 juil. 2015, 05:14 UTC−4
Hello Ivar,

Thanks for all your help so far. I'll try and be more specific. I want to heat up the aluminium in air by its self. Later on I want to put lead ontop of the aluminium. If I have 2 study steps, and add the copper to the second one, its initial temperature is not room temperature. Rather, its initial temperature is the same as everything surrounding it.

If that is not clear then let me try another way. I want to heat the aluminium to 475K. When it gets there I want to add the lead, and then find the time for the aluminium to get to 475K again.

Thanks
Hello Ivar, Thanks for all your help so far. I'll try and be more specific. I want to heat up the aluminium in air by its self. Later on I want to put lead ontop of the aluminium. If I have 2 study steps, and add the copper to the second one, its initial temperature is not room temperature. Rather, its initial temperature is the same as everything surrounding it. If that is not clear then let me try another way. I want to heat the aluminium to 475K. When it gets there I want to add the lead, and then find the time for the aluminium to get to 475K again. Thanks

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