Multiphase simulation test for a cryogenic shell and tube heat exchanger

    • keans0018

      I have a problem with the 2D simulation test of shell and tube heat exchanger using the software Ansys Fluent, which is used to turn nitrogen gas into liquid. The results showed from the Fluent was completely wrong compared to my theoretical calculation. There is no phase interaction between nitrogen-gas, and nitrogen liquid as well as the result of temperature are not correct. The temperature is not distributed throughout the whole heat exchanger. The model I am using is a multiphase-volume of fluid model, the formulation is explicit, and selected implicit body force. The surface tension value is between nitrogen gas and nitrogen liquid is 0.00174. K-Epsilon model was using in my simulation test and selected two phase, which are the nitrogen gas as primary phase and second phase will be nitrogen liquid.

      Also, within the phase interaction setting i have added a mass transfer mechanism from phase nitrogen gas to nitrogen liquid, using an evaporation-condensation model, and i have set the my saturation temperature at 121 K, since my operating pressure value is 3Mpa, using temperature-entropy diagram of nitrogen. I have found the saturation temperature to be approximately 121 K at the pressure value.

      The inlet velocity boundary condition for the shell side as 4.2m/s, the volume fraction for nitrogen liquid at inlet is set to 0, temperature = 0 K, and volume fraction for nitrogen liquid is equal 1, at the shell side.

      For the surface body wall boundary condition, i have selected a heat flux value of -10,000. For solution methods, I am using PISO, pressure velocity coupling. Then i initialize my results and compute from the inlet making sure the volume fraction of nitrogen liquid at inlet is 0, so that the whole heat exchanger is filled with nitrogen gas. Then after i mark a region using adapt feature at specified location where i think it will turn to nitrogen liquid, i patch the region with a volume fraction of nitrogen liquid of 1.The time step value is setup as 1E-08 to avoid any diverge number and the iteration is 25, and number of iteration per time step is 20. 

      But now is the problem, there is no change with the phases , no flow distribution at all, just stay exactly the same the way i had set it, i've been doing this for many times but the phases still not interact with each other. I am seeking someone to give me some guidance here please.  

    • keans0018

      Inlet properties

      The top of the image shows the inlet properties


      Multiphase model setup


      Phases setup


      The Contour plot from my simulation result.

    • Raef.Kobeissi


      did you use phase interaction, evaporation-condensation model with the right saturation temperature?

      can you please attach the case file.


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