Rise of temperature in a thin film by electric potential
 

Hello everyone,

I'm having some problems solving a heat trasfer problem.

I have some experimental data about temperature rise in a thin film due to electic power, i need to simulate them in fluent.
I have a glass, thickness around 4mm, over this glass there is a thin film of a material that conduct elecricity. At the edge of the glass and the film i have two clips that are connected to a generator that has a 12V voltage, I wanted to find out how the temperature rise in the upper surface of the thin film (the surface in contact with air).
I simulate this problem first of all by adding to fluent both energy equation and electric potential (I add the Joule equation too), but the temperauture rise was way too small compared to the actual temperature rise that i had in the experimental data. So i tried to add on my own the electric power that was generated in the film by adding a source terms, the heat generated per unit volume was calculated by the formula P=V^2/R and then i divide everything by the volume of the thin film by assuming that all the heat generated was in the thin film and not in the glass, approximation that i think was good becuase the electric conducticity of the film was 10^4 grater then the one of the glass. Of course when i added the source term i took out the electic potential in models.
By this system i got some more realistic data, but I wonder why?
By adding the source term wasnt the system the same as the one in which i had the electric potential?
In both case dont i just add a heat generation in the energy equation?

I'm sorry form my english but it's not my first language i did my best, i hope it's undestandable by someone:)

Thank you so much