Learning Forum

[abhaymh]

I'm trying to run a multiphase simulation in order to incorporate icing on the surface of an evaporator. Inside the pipes of the evaporator, I'm required to have a flow of propane that undergoes a phase change. On the outside, there is humid air + ice that is supposed to deposit on the surface of the evaporator fins. I seem to be making some mistake as there is no ice being deposited. I have setup the external flow to be a mixture with water vapour and air in phase one and ice crystals in phase 2 (in accordance with literature), with a 0 volume fraction.. The internal flow, currently, is just propane in phase 1, with zero volume fraction ice crystals in phase 2.nIs there anything I've missed here? And is the 0 volume fraction sensible? nThanksn

[Rob]

Did you set up a phase change model in the multiphase panel? I recommend splitting the model for this one, trying to get two distinct flow paths each with phase change to work at once is going to be tricky. We are looking at Fluid-Fluid system coupling for this type of application. n

[abhaymh]

No, I haven't set up explicit phase change. I didn't realise I had to do that separately. I thought it was automated. I'll look into it. nAlso, how do I go about splitting the model? I didn't understand.n

[YasserSelima]

Rob meant to do the inside simulation in a separate case from the outside simulation.nI am wondering how are you going to set mass transfer between vapour to solid without having condensation film !!n

[abhaymh]

http://xeric.eu/wp-content/uploads/ICMFHT_125_online.pdfnI used that paper as a reference for the boundary conditions, do I need to set up an additional model as well?n

[Rob]

As we're not permitted to open/download files I'll leave you to decide. I'd split the model in two as trying to stabilise two phase change domain in a single model is going to be really hard, getting one phase change model to work can be difficult enough. n

[abhaymh]

Understood, I'll consider that. nI tried just the external flow, simulating the internal evaporation as a negative heat flux on the inner wall of the pipes of the evaporator. However, the film thickness even after 308 seconds was in the micrometres range. I added the wall film as YasserSelima suggested, with phase change (water vapour was the film vapour material, with ice being the film material).n

[Rob]

Sounds about right. For the EWF you'll need a fairly small time step so you may find the model hasn't been run for long enough. n

[abhaymh]

Thank you Rob for your answer. This worked and I have the ice being successfully deposited on the outer fins. However, I achieved this by essentially giving a constant heat flux on the inner walls of the pipe (which is unrealistic). You had suggested splitting the simulations for the internal and external flow into two separate cases. A colleague of mine suggested 'Mapping' the values of the heat flux from the pipe-flow simulation to the icing simulation. Could you please help me as to how I can go about doing this?nThanksn

[YasserSelima]

From Fluent, in the internal flow case, use File-Write-Profile ... Then read it in the external flow case using the same procedure but Readn

[abhaymh]

Thank you very much. But with this, when I'm using the EWF model, do I need Eulerian Multiphase model to be enabled?n

[Rob]

EWF and the Eulerian Multiphase model are NOT linked. So, no need to turn on the multiphase model if you just want the wall film. n