Fluids

Fluids

Temperature increase in a Two-Phase simulation in FLUENT (VOF)

    • abhnv_01
      Subscriber

      hello,

      I am working with 2-D transient simulation with compressible flow, gravity assisted.

      I am using VOF- multiphase model and evaporation condensation model as the phase change model, with saturation temperature as a function of saturation pressure.

      Liquid is primary phase and Vapor is secondary phase.

      liquid properties - piece-wise polynomial function of temperature

      vapor density - Ideal gas

      vapor viscosity and thermal conductivity - piece-wise poly function of temperature.

       

       

      Operating pressure - (Floating) 0 Pa, gauge pressure - 76043 Pa

      Operating density - 0 kg/m3

       

       

      Initial temp - 75K

       

       

      CONVERGANCE criteria -

      (continuity - 1e-05), (velocity - 1e-04) and (energy - 1e-06)

       

       

      SOLUTION METHODS

      Pressure-velocity coupling - SIMPLE

      Gradient - Least squares cell based

      Pressure - PRESTO

      Density - second order upwind

      Momentum - Quick

      Volume fraction - Conpressive

      Energy - first order upwind

       

      All the URFs are default.

       

      The temperature of the evaporator section is increasing. I do not understand why..

       Any help will be highly appreciated.

    • Rob
      Ansys Employee

      What are the boundary conditions?

    • abhnv_01
      Subscriber

      So, basically I have three sections of the PHP. 

      BCs are Thermal wall boundary conditions

      Evaporator section - Constant heat flux

      Condenser section - Constant temperature 

      Adiabatic section - Zero heat flux

       

    • Rob
      Ansys Employee

      Evaporator section will increase in temperature because the wall MUST push in the defined heat flux. So, that wall will heat up to infinity if you don't extract sufficient energy from the condensor section. 

    • abhnv_01
      Subscriber

      Rightly said Rob. 

      Thanks for the reply.

      The boundary conditions are set according to experimental values. 

      Regarding the sufficient energy generated on the condensor section, I have two queries as following:

      Say, if I am not being able to get sufficient cold from the condenser section, will it be the right way to decrease the condensor temperature to get enough cold? 

      Or is there any way to check whether enough cold is generated on the condensor side or not?

    • Rob
      Ansys Employee

      That depends on what you want to adjust: I can only advise on what the solver is doing, not what boundary values you ought to pick. 

      I also assume that the mesh is sufficiently well refined to pick up the wall & free surface boiling & flow. 

    • abhnv_01
      Subscriber

      Yes, my mesh is well refined. 

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