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Heat flux boundary condition
Posted Aug 6, 2015, 11:38 a.m. EDT Heat Transfer & Phase Change 2 Replies
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Hi,
I have to define a boundary condition for a 3D conduction problem, such that the total heat flux into the surface is constant (Qt) and the surface is isothermal.
To do this I was asked to use a temperature boundary condition with variable temperature Tb, and Tb is given by simultaneously solving 'global ODE and DAE',
surface integral(lagrangian multiplier of T)-Qt=0
from what I understand this is equivalent to K*surface integral(grad( T))=Qt
Is this correct?
If yes could someone please explain to me how lagrangian multiplier of T is K*grad(t)
If not how can I implement the boundary condition
Regards
Anjan
I have to define a boundary condition for a 3D conduction problem, such that the total heat flux into the surface is constant (Qt) and the surface is isothermal.
To do this I was asked to use a temperature boundary condition with variable temperature Tb, and Tb is given by simultaneously solving 'global ODE and DAE',
surface integral(lagrangian multiplier of T)-Qt=0
from what I understand this is equivalent to K*surface integral(grad( T))=Qt
Is this correct?
If yes could someone please explain to me how lagrangian multiplier of T is K*grad(t)
If not how can I implement the boundary condition
Regards
Anjan
2 Replies Last Post Aug 8, 2015, 7:03 a.m. EDT
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Posted:
9 years ago
Hi Anjan,
what is your target? An isothermal boundary condition is a Dirichlet boundary condition. You define the temperature.
But if you want to define the temperature in a way that you get a pre defined heat flux you have to set up an integral boundary probe and an additional ODE. Look inside the COMSOL blog. There is an advisable article:
www.comsol.de/blogs/overview-integration-methods-space-time/
Best regards
Michael
what is your target? An isothermal boundary condition is a Dirichlet boundary condition. You define the temperature.
But if you want to define the temperature in a way that you get a pre defined heat flux you have to set up an integral boundary probe and an additional ODE. Look inside the COMSOL blog. There is an advisable article:
www.comsol.de/blogs/overview-integration-methods-space-time/
Best regards
Michael
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Posted:
9 years ago
Hi Michael,
My target is get variation of wall temperature of a borehole heat exchanger with a fixed load.
Thanks for the help. The article was useful, I was looking for something like this. But the flux became unstable after some time and increased exponentially.
I used the Tb as the additional degree of freedom and the additional equation was intop1(ht.ntflux)-Qtot.
I got a constant flux when I used intop1(T_lm)-Qtot. but I do not know how this equations works and I might have problems debugging it.
Thanks again
Anjan
My target is get variation of wall temperature of a borehole heat exchanger with a fixed load.
Thanks for the help. The article was useful, I was looking for something like this. But the flux became unstable after some time and increased exponentially.
I used the Tb as the additional degree of freedom and the additional equation was intop1(ht.ntflux)-Qtot.
I got a constant flux when I used intop1(T_lm)-Qtot. but I do not know how this equations works and I might have problems debugging it.
Thanks again
Anjan