# How to set 2 phases in Fluent

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 October 29, 2011, 10:09 How to set 2 phases in Fluent #1 Member   CR-7 Join Date: Jun 2011 Location: Malaysia Posts: 65 Rep Power: 8 Hi every one my case as following : I posted more than 5 threads but no body answered : - The geometry is Heat pipe. - Phase 1 is ( vapor ). - phase 2 is ( water ). there is no interation between the two fluids at all ( separated in two domains ) but there r evaporation and condensation to get vapor at evaporator as well as get water at condenser !!! also there r 2 different RADIAL velocities !! How to set up this case !!!!

 October 30, 2011, 13:05 #2 Member   CR-7 Join Date: Jun 2011 Location: Malaysia Posts: 65 Rep Power: 8 this is 6th threads with no answer??

 October 31, 2011, 16:18 #3 New Member   Tom M Join Date: Oct 2011 Posts: 7 Rep Power: 8 This is a very difficult problem. There are no direct methods in fluent to solve for the evaporation and condensation from the wick, nor is the porous media module set up directly to handle capillary flows. UDF's have to be written to describe the mass and energy transfer from one phase to another. you need to use the multiphase module, and write a DEFINE_MASS_TRANSFER UDF to determine the mass flux from phase 1 to phase 2 at each cell (or vice versa for condensation) then then include an energy source term to cover the latent heat transfer. See Unnikrishnan Vadakkan's 2004 paper "Transport in Flat Heat Pipes at High Heat Fluxes From Multiple Discrete Sources" in J. Heat Transfer for a description of the equations.

 November 1, 2011, 02:04 #4 Member   CR-7 Join Date: Jun 2011 Location: Malaysia Posts: 65 Rep Power: 8 First of all thanks for this paper I got it from ASME today, Secondly, there r two ways to solve this issue the first one by using VOF model two phases ! and following the details which r inclusive in ur reply there is another way by using one phase approach by two stages: vapor in core as a discrete domain and then water in porous media to ignore the phase change inside hp!! but when I used one phase approach I faced two radial velocities how two set up them together ??? !!!!! Arjun Jayakumar likes this.

 November 1, 2011, 02:08 #5 Member   CR-7 Join Date: Jun 2011 Location: Malaysia Posts: 65 Rep Power: 8 tmulcahey3 So I have to write 2 UDFs, one for mass-heat transfer and heat flux why writing UDF for heat flux if I had the values of heat flux on the outer wall and also the heat latent of vaporization ??? Indeed I'm new with UDF ,, can u help me ??

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