Learning Forum

[Ata Sabra]

Hello, 

I am trying to model a phase change material. In order to do this I have to model the freezing or solidification of water and check if the temprature of water remain constant during the freezing/solidification. 

I saw an example here lesson 4: phase change and enthalpy. The following link:  /courses/wp-content/uploads/sites/2/2020/05/Lesson-4-Phase-change-and-enthalpy.pdf. 

In this example they did a simulation of freezing of water with Ansys Mechanical as a thermal- transient analysis (not fluent!), however in all exmples and video tutorial I see on youtube, they use Ansys fluent to simulate a pcm- material. 

My question is: 

can I use for this model a thermal transient analysis (Ansys Mechanical) instead of using ansys fluent because it would be easier for me to work in Ansys mechanical. I tryed to do the simulation as it shown in the example (lesson 4 above) and it seems that the definition of enthalpy werent taken in considration. would you help me here please. 

 

Thank you in adavnced.

[dlooman]

Yes.  See Section 3.8 of the APDL Thermal Analysis Guide.  The Enthalpy curve can be specified in Engineering Data, so the analysis can be completely within Workbench.

[Ata Sabra]

Thank you for your reply. I defined the enthalpy curve in the engeeniering data and did exactly the same as the lady in lesson 4 did. But still I get the temprature curve as that the enthalpy has not been defined (the curve in the phase change period is not constant), which of course wrong. 

Could it be that I need to activate some solver or energy equation or is there a special command that I need to use. It would be so helpful if you explain more for me. 

I did the following steps exactly: 

1- define engineering data (all values I get from the lady in lesson 4: phase change material) 

2- Draw the geometry 

3- meshing and addition of boundray condition 

4- solve and draw the temprature regarding to time 

and as I sayed the temprature should be constand on 0°C but still I dont get this results and it seems the solver doesent recognize the definition of enthalpy in engineering data. Would you help me please and give some tips, steps or advices. 

 

[dlooman]

If you issue mplist with a commands object do you see your enthalpy input? 

[Ata Sabra]

I try to define the enthalpy through the engineering data and through an APDL command and in both cases I didnt get constant temprature by the solidification/melting point. 

to your question: when I define the enthalpy through APDL command it has not been shown in the material property. Photos 1 and 2 

when I defined it in the engineering data it has been shown in the property but has not been considerd in the solution. Photos 3 and 4

 

[Ata Sabra]

[Ata Sabra]

[Ata Sabra]

[dlooman]

Your enthalpy input is correct.  By default Mechanical uses a "fast" solver that doesn't update the material properties every iteration.  I think that's the problem

In the Details for Analysis Settings> Nonlinear Controls> set "Nonlinear Formulation" to "Full" and "Line Search" to "On."  To help convergence you might need to step the enthalpy increase over a wider temperature range, say 690 to 700.   

[Ata Sabra]

 

 

 

[Ata Sabra]

In order to do the melting of ice or solidification of water I am simulating now the solidification of Aluminum ( a example which I found in internet and then I can put the values of water/ice if the simulation works). 

I tried your 3 helpful advices but the results did not change. the temprature remain constant by solidification point but dont get down after that with time (Photo). In the boundray condition I put that the Aluminum in the middle has a temprature of 800 which start to fall down after 0,1 s.

[Ata Sabra]

[dlooman]

Maybe you need to run it longer.

[Ata Sabra]

I tried it before and now after you sayed but still unfortunatily not completly correct. here are the results, the temprature is not getting under 690 

[dlooman]

It is approaching 690 though.  Maybe you need to run it even longer.  

[Ata Sabra]

It works! thank you so much.. 

I will try now to replace the properties of Aluminum with properties of water and write here if it is gonna work or I need again a question. 

again thank you for the helpful tips. 

 

[Ata Sabra]

Hallo, 

I tried to replace the Properties of Aluminum with the properties of RT21 (a material that melt or freez on 21 °C). In the photo you see the enthalpy's curve of this material in [J/kg]. I faced 2 problems doing this: 

1- as you see I have the data of 16 points. but in the APDL command I can tip maximum 6 Tempratures (photo 2). for now it is not a problem, I can choose the most important 6 points. but can I in general tip more than six ? 

2- when I put the most important 6 points, Ansys showed me an error, that the enthalpy should always increse with higher temprature! and as you see from my diagramm the enthalpy get down at some points. In order to avoid this I have modificated the curve to get always increseing values. It seems ansys didnt take it in considiration. would you check please if I typed the command correctly and in which units should I write the enthalpy? can you give some advices where the problem could be. I will put the table and the command in the following messege. 

Thank you

[Ata Sabra]

the temprature should be constant between 20 and 21

[Ata Sabra]

[Gurpreet Singh]

Hi Everyone
I am trying to conduct a similar analysis using ANSYS mech. to calculate the time taken to freeze a PCM. I am stuck at modeling the material properties for phase change. I have the following grpah shared by the PCM manufacturer. Can you suggest the correct graphical method to input the properties.
Thanks