I am a research associate at Teesside University who is studying the mechanics of moisture ingression in encapsulant materials used of solar cell encapsulation. Currently, I am engaged in a study on modelling moisture ingress using ANSYS FLUENT software. However, I've encountered a significant challenge. Many research papers I've come across have used COMSOL Multiphysics to accurately capture this effect. Conversely, my challenge arises when using ANSYS FLUENT to model permeable encapsulant materials. I have discovered that in ANSYS FLUENT, one must define the material as porous, with the porosity value ranging from 0 to 1 (0 representing solid and impermeable, 1 signifying full permeability).

However, during the simulation, ANSYS FLUENT seems to employ the porosity of the material to determine its moisture concentration at saturation. For example, with a material porosity of 0.5, the moisture concentration is consistently 0.277 kg/m^3. Even with varying materials and permeabilities, this value remains unchanged. It appears that the permeability only influences the rate at which the material saturates, resulting in higher concentrations over time, but the same moisture concentration at saturation.

I am utilizing a multiphase approach for this analysis, employing water vapor and air as the fluids and monitoring plots of water vapor concentration over time. To provide further clarity, I have attached images of the plots illustrating this behaviour.

I am keen to understand the reasoning behind this behaviour and whether there are any techniques or insights you can offer to enhance the accuracy of my moisture ingress modelling in ANSYS FLUENT.