[pritam.gole]

I have a query regarding choosing mass transfer mechanism. If my domain has evaporation as well as condensation, then do I have to give just 1 mass transfer mechanism or two(one for each)?
Also, I read that the lee model is updated in the latest versions to consider these two effects together so that UDF is not required. Is it right or UDF is a must?

[vinerm]

E-C model in Fluent, either as a UDF or as a in-built function, has always been two-way, i.e., it models both evaporation and condensation. So, you need to hook only one mass-transfer mechanism. And it does not require any UDF, until and unless you want to apply saturation temperature as a function of saturation pressure.

[pritam.gole]

Thank you clearing my doubt. I also want to know about selecting the primary phase and secondary phases in thermosyphon. I read many thread but those are confusing. Few people says, the water should be the secondary phase because calculations are performed on secondary phases. The other says, it doesn't matter.

[vinerm]

It doesn't really matter if you are using VOF; the only thing it affects is calculation time. Since, conservation PDE is solved only for the secondary phase(s), time can be saved if less abundant phase is defined as secondary phase; that way solver needs to go through lesser number of cells for solving PDE (solver doesn't really go through cells to solve PDE, its just a way of explaining; mathematically, its just that the matrix is much more sparse).

[arunraj]

Hello sir, could you explain bit more about Lee model and its application in heat pipe. It would be helpful for many of us. I am new to this field. I tried to solve a sample problem of heat pipe with wick and wall. I have attached the domain. I have attached the details of paper. As you can see from the pic, it is a phase change heat transfer problem. I would like to know bit more about solving the problem. Can Lee model of evaporation-condensation with VOF solve the problem without any UDFs in latest version of ANSYS Fluent? How to treat the interfacial velocities and temperature at the condenser-wick and evaporator-wick. I have seen a thesis on this problem and they have used several UDFs and one UDS citing that ANSYS Fluent doesnt follow the interfacial temperature boundary condition. However, he has used ANSYS Fluent v16. I have attached the link of thesis. Kindly explain if lee model can solve this problem without any UDFs.

Poplaski, L.M., Benn, S.P. and Faghri, A., 2017. Thermal performance of heat pipes using nanofluids. International Journal of Heat and Mass Transfer, 107, pp.358-371.

https://scholarcommons.sc.edu/etd/4026/

[arslan waheed]

Originally Posted by vinerm

E-C model in Fluent, either as a UDF or as a in-built function, has always been two-way, i.e., it models both evaporation and condensation. So, you need to hook only one mass-transfer mechanism. And it does not require any UDF, until and unless you want to apply saturation temperature as a function of saturation pressure.

Hello sir, could you explain bit more about Lee model and its application in heat pipe. It would be helpful for many of us. I am new to this field. I tried to solve a sample problem of heat pipe with wick and wall. I have attached the domain. I have attached the details of paper. As you can see from the pic, it is a phase change heat transfer problem. I would like to know bit more about solving the problem. Can Lee model of evaporation-condensation with VOF solve the problem without any UDFs in latest version of ANSYS Fluent? How to treat the interfacial velocities and temperature at the condenser-wick and evaporator-wick. I have seen a thesis on this problem and they have used several UDFs and one UDS citing that ANSYS Fluent does not follow the interfacial temperature boundary condition. However, he has used ANSYS Fluent v16. I have attached the link of thesis. Kindly explain if lee model can solve this problem without any UDFs.

Poplaski, L.M., Benn, S.P. and Faghri, A., 2017. Thermal performance of heat pipes using nanofluids. International Journal of Heat and Mass Transfer, 107, pp.358-371.

https://scholarcommons.sc.edu/etd/4026/

Thanks in Advance