Thermal FEA for diffusion

[Johan44256]

I would like to use FEA to study transient moisture gain in nylon, 2d axisymmteric model


I know

diffusion constant of the material (in^2/sec)
% moisture content on nylon surface (~7%)
% initial moisture content of the nylon piece (0.5%)


I want to find mass gain (weight gain by water) per hour for the model.



Here is what I did- using marc transient heat transfer, I set material properties such that



Heat conductivity value = used diffusion constant

Set density=1, and specific heat =1



I applied BC’s such that the temperature BC on the surface = % moisture content. I applied 0.5% moisture content as an initial temperature condition.

Anybody ever try this?

 

[btrueblood]

No, but it sounds like you have the right set of coefficients, and the d^2 (heat transfer) equation is the correct one for mass diffusion. Except, I'm not sure about the specific heat term...this is what "slows" the heat absorption (it takes a certain amount of heat to raise the solid temperature). I think you need to have the Cp term equate to how much water flux will cause a certain % change in moisture content of the solid. Maybe "1" is the right amount, but you should check the math?