Learning Forum

[omar ennaya]

hello friends

I'm confused about the properties of my phase change material, how to fix it in fluent in a right way. 

Below is a photo of my PCM thermophysical properties which indicates that the solid and liquid phase has different thermophysical values.

So how i should input these values correctly.

I tried the polynomial option but the results diverges.

Any insight will give much help.

thanks in advance.

[omar ennaya]

[Rob]

Assuming you're using the solidification-melting model you need to set properties such that a single temperature can't have two values, ie density moves from solid to liquid over a very small, non zero, temperature change. Tha may require some care and piecewise linear over polynomial. 

[omar ennaya]

Hello sir

This is the point cuz the material density value is different between the solid and the liquid state as indicated in the table above.

In fluent i cant use piecewise linear and boussinesq in the same time.

I'm so confused what to do when i use boussinesq option what value of the density should i input.

Thank you for your feedback.

I have another question or problem as well if you don't mind.

My MCP melt inside an annular cylindre and when the process of melting finnished the the temperature increase instantly which is desagree whith the experimental work.

N.B here is the the cp i used:

and this is my plot:

 

[Rob]

Bousinesq won't account for the phase change (melting).  

Re the experimental comparison, what are you comparing? Ie how/what measurement are you using?

[omar ennaya]

Hello sir

Why the bousinesq won't account for the melting?

I'm comparing the temperature at a specific position of the the experimental work against the simulation.

I'm doing the simulation so i'm calculating the temperature using the vertex maximum option in ansys, is it your question about this?

[Rob]

Where is density change due to solidification/melting covered in the Bousinesq maths? 

If you're comparing a specific location, are you seeing instant melting at that point or are conduction/convection effects in either Fluent or the experiment likely to create differences in the result.  I tend not to assume either experiment or CFD results are wrong, however I regularly see that there are differences in what is modelled that explain why the results don't match. 

[omar ennaya]

The changes in density appeares in the evolution of the temperature at the beginning and at the end of the melting process.

As you see in the picture below that i've shared the results of the experiment and the simulation are very good at the process of fusion but when it finished the curve of the simulation don't match with the experimental one.

concerning the effects of convection yes there's and approved in the experimental research.

In my model i utilised the green dashed line of the Cp property as you can see in the picture below.And you can remarque in this picture that after 36°C the Cp values decrease fastly so i supposed maybe this is the problem. So what should i do cuz i can't take another values of the Cp just like this.Is there a solution in fluent maybe i can do.

thank you sir for your interaction.This toke me a lot of time and i feel like exausted.