Learning Forum

[Oluwagbemiga Fabunmi]

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.

[SRP]

Hi,

You mentioned that you are using a porous media model. Verify that you have set up the porous media properties correctly. The porosity and permeability values should be defined in a way that accurately represents the material you are simulating, and make sure you have defined the material properties accurately, including moisture diffusivity and other relevant properties for the encapsulant material.

Thank you.

[Oluwagbemiga Fabunmi]

I  really appreciate your earlier response. As you suggested, I have carefully reviewed and input all the necessary information into ANSYS Fluent for modeling moisture ingress. The goal is to simulate water ingress into EVA and PVB back sheets, using an accelerated approach based on the IEC 61215 Damp heat test conditions, specifically at 85°C temperature and 85% humidity.

Here's a concise summary of the key parameters I've employed in the simulation:

Geometry:

• EVA and PVB cube with dimensions 26 x 26 x 26 mm
• Mesh size: 0.5mm

Moisture Application:

• Moisture applied to one side of the cube (single inlet, no outlet)

EVA Material Properties:

• Diffusion Coefficient (as a function of 85°C temperature): 1.30598e-9 m^2/s
  • Converted to fluid velocity: 5.023e-8 m/s
• Permeability (as a function of 85°C temperature): 3.205806e-12 m^2
  • Converted to viscous resistance: 1/Permeability = 3.11934e11 m^-2
• Porosity: 0.1

PVB (Back Sheet) Material Properties:

• Diffusion Coefficient: 7.53453e-9 m^2/s (as a function of 85°C temperature):
  • Converted to fluid velocity: 2.8979e-7 m/s
• Permeability: 2.98197e-12 m^2 (as a function of 85°C temperature):
  • Viscous resistance: 3.35349e11 m^-2
• Porosity: 0.1

I have carefully ensured the accuracy of these parameters, and with your confirmation, I would greatly appreciate your expert guidance in setting up the simulation step by step.

My work email address is o.fabunmi@tees.ac.uk

Your support in this endeavor would be of immense value to my research, and I look forward to your response.

Thank you for your time and consideration.