Thermosyphon simulation using evaporative condensation model will lose mass|Lee model

nacncnacnc Member Posts: 2
edited September 9 in Fluids

I am simulating two-phase thermosyphon heat pipe with VOF model,Lee model, k-o sst, primary phase r134 vapor, secondary phase is r134 liquid, Others are initial settings 

I have tried both SIMPLE and PISO solution methods.  

Three sections - Evaporator, condenser and adiabatic, 

These are the result graphs 

Everything is fine, but quality and pressure are Abnormal. 

1)When I use VOF model, I don't observe condensation. How to solve it? This question is not important, but the following two questions are important. 

2) The pressure is the same as what I give as the operating pressure. As the temperature is increasing inside the thermosyphon, there should be a rise in pressure also. But it is not rising, Please can anyone help? 

3) The total mass in the enclosed space should be conserved, and there should be only phase change in the enclosed space. But if I use Lee model. when my heat transfer is not conserved, the total mass will decrease. What is the reason? How can I solve this problem? 

I have seen this problem in other discussions, but no one explains why mass is not conserved, and no one explains why pressure does not change. 

I hope someone can discuss the detailed causes and feasible solution steps of heat pipe evaporation and condensation here. I also hope to solve my problem. If I complete the model, I will also link the model to this problem. If you have a feasible model and udf, you can also put your download link.


  • nacncnacnc Posts: 3Member

    If I need more information, I will add it in the discussion

  • sdebsdeb Posts: 327Forum Coordinator

    1.) For condensation, check the Saturation properties. Also keep in mind that the condensation model is not wall condensation but bulk condensation.

    2.) Are you using built-in Real gas EOS or RGP files?

    3.) Are you solving it in transient? If not, then try to solve it as transient as it is totally enclosed.



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