Learning Forum

[b.claudet]

Hello,

I am trying to conduct a coupled transient simulation with assigned physics of thermal and electrical conduction.

My geometry is in a natural convection condition. I applied an electrical current of 400A on 3 aluminum plaques representing connection cables that are screwed to a large circular aluminum rod. 

I fixed a ground voltage on three other plaques which are screwed on also at the other side of the rod, signifying that my current goes from one side through the large rod to the other. My aim is to figure out the max temperature i can obtain due to the joule heating loss from the circulation of this current. I already did a practial test inside an enclosure and i found out that after 25000 seconds, my temperature for 200A becomes steady at 70°C.

Whereas in my model, i obtain much smaller values and a stable temperature in much less time. I noticed that by changing the film coefficient h value from 10 to 0.5W/m2 C, i get my stable temperature approximately at the desired time, and by modifying the electrical contact conductance between the small plaques and the large rod from program controlled to a value of 1e09, i get similar temperature values. Is it logical to assume such small film coefficient for a natural convection simulation? Also how can i get the exact electrical contact conductance( in S/m2) between two aluminum surfaces ?

Thank you for any sort of help or response.

[Ravikrishna K V S]

electrical contact conductance ( ECC) is the input and the exact one should be obtained by experiments. By default simulation assumes high/perfect contact. But the reality is different as factors like surface roughness and enviromental effects play a significant role.

You can iterate by doing some Design of experiments / optimisation appraoch with ECC and film coefiecent & desired temperature ( thanks to experiments) as an objective. 

Coming to the value low film coeficent,it is meaning  the rate of heat generation rate slower than heat dissipation. please check the material properties and proper modeling ( cross section changes) are followed well.