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# COMSOL Multiphysics - Electromagnetic Heating, formulae connection2

## COMSOL Multiphysics - Electromagnetic Heating, formulae connection

(OP)
Hi,

I am currently working on a simulation where I am using the multiphysics "Electromagnetic Heating".
I aim to discuss the equational connection between the two physics present; "Electric Currents (ec)" and "Heat Transfer in Solids (ht)".

I find my self in question as to how they are both accounted for. By looking at the equations provided by COMSOL, I can quite easily identify the equations used by all three physics but I can't seem to grasp the connection.

The "Electric Current" equations:

The "Heat Transfer in Solids" equations:

Multiphysics equation:

As far as I can see, there is not much difference between the Heat transfer equation and the multiphysics equation. The difference however, is not clear to me how it should be coming from the electric current equations. The Qe term, does not appear among the electric current equations, even though I would assume this is main contribution.

Best regards,
Gustav Leth-Larsen

### RE: COMSOL Multiphysics - Electromagnetic Heating, formulae connection

The equation view provided by COMSOL is nice but I would focus more on the documentation if you want to dig deeper into the theory behind these analyses. Search for Joule heating since that's the term used for this type of electromagnetic heating multiphysics simulations. But by looking at the equations displayed in COMSOL we can already see that Q_e is resistive heating calculated as current density times electric field strength (this equation should be visible below the one you show in the last screenshot). Then Q_e is used as a source term for the heat transfer equation.

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