November 6, 2020 at 11:19 amzaqureshiSubscriber
I am trying to perform a 2D solid-liquid phase change simulation using two distinct PCMs. They are separated by a vertical wall of some thickness and there is a PCM on its left and one on its right (like shown in the image attached).November 6, 2020 at 12:54 pmDrAmineAnsys EmployeeYou can create UDF or Fluent Expression to mimic Boussinesq. Boussinesq is just assuming constant density but with source term for momentum based on temperature dependent density. Just do that.Alternative is just to provide temperature dependent density for each PCM material and allow gravity and provide zero operating density.nNovember 6, 2020 at 4:23 pmzaqureshiSubscriberthanks for providing a response. I understand that the boussinesq model assumes constant density but still mimics buoyancy through a rho*g*beta*delta_T source term in momentum equation. I have actually never used UDFs in FLUENT and i dont know exactly how to include a source term to momentum equation. Could you please specific insight into it?nRegarding the alternate method that you mentioned, i can define temperature dependent density for both PCMs. Should i subsitute a zero operating density in 'Cell zone conditions'? Also, does providing temp-dependent densities for PCMs take into account volume expansion (in which case i may have to use VOF model by allowing some space for PCM volume expansion)?nFinally, going back to the original query, is there a way to describe two boussinesq temperature for two distinct PCMs?nRegards,nZahid nNovember 6, 2020 at 5:21 pmDrAmineAnsys EmployeeIf you enable gravity you account for buoyancy. Zero as r?f?rence will be ok first. What do you mean with expansion?nNovember 6, 2020 at 5:59 pmzaqureshiSubscriberi will try re-phrase myself again, perhaps i was not clear. Since you asked to put temperature-dependent density, it means that the density will vary as the temperature is changed, so the PCM will either contract or expand depending upon the density variation defined for it. So when you recommended adding temperature dependent densities for both PCMs, i thought that this will be a problem as i will have to provide room in the geometry to account for volume expansion. Is it true, the way i see it. What if i specify temperature dependent density and not provide extra room for PCM to expand, will its pressure increase?nI was looking for the simplest solution to use boussinesq model with two PCMs and defining different boussinesq temperature for both PCMs. The way i handle this for a single PCM problem is like this: I enable gravity in general tab, provide a boussinesq density in materials tab, and finally add boussinesq temp in cell zone conditions. This same method i followed with two PCMs, all worked fine, until i faced the problem of only being able to put one boussinesq temperature. I wanted to add two different boussinesq temperatures for the two PCMs.nNovember 6, 2020 at 6:14 pmDrAmineAnsys EmployeeYes. Either you model it via source terms or deal with temperature dependent densities. For the latter case I recommend using transient solver for mass conservation and pressure build up.nNovember 7, 2020 at 1:23 pmzaqureshiSubscriberI will try to model it using source terms. nViewing 6 reply threads
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