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temperature control in heat transfer

Posted 12 nov 2012, 13:50 GMT-5 RF & Microwave Engineering, Heat Transfer & Phase Change Version 4.3 2 Replies

Cong Liu
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Hello, I am modelling a heat transfer problem, and the details are: when the temperature increases to 315K, heating is stopped; however, when temperature drops belows 310K, heating restarted. If the upper and lower bound temperatures are the same, it can be easily solved by step function. i want to ask how to describe temperature increase phase in Comsol. I tried to define a step function of Tt, and with this function to differentiate the heating up and cooling down processes. however, an error message poped out: Failed to evaluate variable Jacobian. Can anyone suggest some ways to solve this? Thanks a lot.
Cong
2 Replies Last Post 12 nov 2012, 22:55 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 12 nov 2012, 14:32 GMT-5
Hi

when you use bolean or Dirac type fnctions, you have no derivatives at the transition points, this makes life complicated for the solver tht relies on the continuity of your BCs. try using a "rect" function with smoothed transition, or perhaps even a sinus function.

--
Good luck
Ivar
Hi when you use bolean or Dirac type fnctions, you have no derivatives at the transition points, this makes life complicated for the solver tht relies on the continuity of your BCs. try using a "rect" function with smoothed transition, or perhaps even a sinus function. -- Good luck Ivar
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 12 nov 2012, 22:55 GMT-5
You can also use the nojac() operator to inform COMSOL to not evaluate the Jacobian of an expression. Use it carefully however.

Nagi Elabbasi
Veryst Engineering
You can also use the nojac() operator to inform COMSOL to not evaluate the Jacobian of an expression. Use it carefully however. Nagi Elabbasi Veryst Engineering

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