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heat flow through Dirichlet boundary conditions

Posted Dec 4, 2011, 6:28 a.m. EST Heat Transfer & Phase Change Version 4.2a 3 Replies

George Rosala
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Hello folks,

Having solved a transient heat transfer problem in which there is a Dirichlet (esential) boundary condition, how would one get the total amount of energy input/output through that BC, from results?

Many thanks,
George
3 Replies Last Post Dec 9, 2011, 1:11 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 5, 2011, 11:10 a.m. EST
Hi

if you are using the weak form integrate the Lagrangian "lm", or use the reaction force operator, or better, most flux are predefined in COMSOL, check the variables, integrate the pertinent one

--
Good luck
Ivar
Hi if you are using the weak form integrate the Lagrangian "lm", or use the reaction force operator, or better, most flux are predefined in COMSOL, check the variables, integrate the pertinent one -- Good luck Ivar
George Rosala
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Posted: 1 decade ago Dec 7, 2011, 5:16 a.m. EST
Hi Ivar,

Thanks for your reply and hints.

Actually, my question did relate to the time integral of the reaction flux at a Dirichlet boundary, which I've managed to solve now in 3 different ways: using weak contributions, global ODE and weak constraints on the Temperature node.

With weak constraints it appears to be a problem with units, as one gets m^2 when integrating the T_lm variable over a surface(?)

Never managed to use reacf(T) though, and don't know why.

George
Hi Ivar, Thanks for your reply and hints. Actually, my question did relate to the time integral of the reaction flux at a Dirichlet boundary, which I've managed to solve now in 3 different ways: using weak contributions, global ODE and weak constraints on the Temperature node. With weak constraints it appears to be a problem with units, as one gets m^2 when integrating the T_lm variable over a surface(?) Never managed to use reacf(T) though, and don't know why. George
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 9, 2011, 1:11 a.m. EST
Hi

the Lagrangian (in fact all "...lm") are not using units, so you must apply the units yourself as "T_lm*1[W/m^2]".
They are all fluxes, the units are summarised somewhere in the doc in a table (could have been in the help, but haven't found out where)

--
Good luck
Ivar
Hi the Lagrangian (in fact all "...lm") are not using units, so you must apply the units yourself as "T_lm*1[W/m^2]". They are all fluxes, the units are summarised somewhere in the doc in a table (could have been in the help, but haven't found out where) -- Good luck Ivar

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