Learning Forum

[snr1]

I am modelling a refrigerant vapour absorption process in a weak solution which happens in a vapour absorption refrigeration system. The problem which I am facing is to incorporate the shape change of the refrigerant vapour bubble due to mass transfer from vapour to a weak solution.  Kindly, do the help to develop a UDF to account the mass transfer effect in this absorption process.

[DrAmine]

We do only provide guidance. Can you please add more details? How many phases are included? Are phases rather stratified? Which models do you think to use?

[snr1]

There are two phases involved in this simulation. They are liquid, and vapour and these two phases are miscible with each other. I am using VOF multiphase model with Species transport equation. But the problem I am facing is modelling interface mass transfer. How to include interfacial mass transfer in this case?

[DrAmine]

You would probably require an UDF to incorporate mass transfer between phases: you require calculating the interfacial area and the mass flux through that area to get the volume specific mass transfer.

You can however try using the species mass transfer built-in there which is available for mixture and Eulerian models.

[snr1]

Here both phases are miscible. Still, can i use VOF formulation for this problem?

 

[DrAmine]

Actually for miscible fluids you do not require using multiphase models at all. But you have two fluids at different states of aggregation, so I am sure we have immiscible fluids, even if its is looking diffuse the fluids are not mixed at molecular level!

[snr1]

Dear sir, as you have stated above, can you suggest any UDF example to develop the interfacial mass transfer?

In the mixture model, to use species mass transfer model, we have to mention the saturation pressure, which I don't know exactly. How to proceed further

[DrAmine]

1/Check material databases to get saturation curve: that is the user input. The pressure would corresponding to vapor pressure at the reference temperature. So you need the saturation line of the pure solute which get absorbed and released

2/I cannot provide any example on how to deal with that within an UDF. 

 

 

[snr1]

Dear sir, i have the correlation for the saturation pressure in terms of temperature. Apart from that, i want to use VOF method to capture the interface. So, kindly suggest me to sort out this problem

[DrAmine]

Writing UDF. I cannot write that for you. So you need to think thoroughly about that and check if you can find examples. As ANSYS Staff (not stuff) I cannot provide you with any snippets there. Perhaps other members might step in here and give some other advice.

[shitizsehgal]

HI snr1, nWere you able to solve this problem? I am working on the same problem as part of validation study and I am using oxygen and water-liquid as my fluids. I want to understand the diffusion of oxygen into water flowing past a flat plate. I have been able to get physically meaningful results for hydrodynamics but I am still trying to understand the correct way to simulate the mass transfer process. nI have used VOF model w/ Energy and Species transport. It is my understanding that I will have to define multi-component mixtures when using Species Transport model. My doubts are as follows-nHow to define the mixture templates(No. of species to be included) and what mass fraction to specify at the inlets?nWill each phase need to have a mixture or just a simple fluid like liquid or gas?nWIl I need to define a source term in species transport to account for mass transfer mechanism or use a UDF like DEFINE_MASS-Transfer or its Linearized Version?nBased on the my understanding, the convective diffusion and Fick's Diffusion is accounted for by Species Transport model but in the literature some people have used source term to account for mass transfer and some have used Mass Transfer UDF. What is the correct approach?nCan someone please help?nRegards,nshitiz sehgaln