Fluids

Fluids

Why phase is not changing in pool boiling after applying heat flux at saturation state?

    • Anadi_Mondal
      Subscriber

      Hello,

      I am trying to simulate heat transfer in pool boiling in 2D. Heat will transfer from a heated copper surface to saturated stagnant refrigerant. To follow same experimental setup ,copper surface is placed inside a teflon block. So, heat will be transferred to the refrigerant from the top surface of copper block only. I created 3 surfaces ( one liquid, two solids ). Liquid surface is refrigerant and one of solid surface is copper and another one is teflon.

      I am using Eulerian multiphase model. As refrigerant in the pool is already at saturation temperature, liquid refrigerant should turn into vapor if heat flux is applied at the bottom surface of copper block. However, I am not getting any temperature distribution in copper block and liquid volume fraction is not also changing in the pool even after applying 50kW/m2 at the bottom of copper surface.

      In the cell zone condition , I see that the solid surfaces include liquid and vapor phase .But the solid surface should be copper or teflon only.

      Would anyone tell me if I am doing any mistake with creating surface/materials/cell zone conditions ? Or, suggest me any probable other mistakes.

      I am expecting a temperature distribution(temperature at top surface) in copper block and bubble should grow from the top surface of copper block into liquid. Teflon has very low thermal conductivity . So, heat will not propagate into the teflon block.

      Regards,

      Anadi

    • DrAmine
      Ansys Employee
      Which Models are included? Forget about phase specification in the solid cell zones: they are not used. Show temperature distribution on all cell zones: select phase liquid and show its temperature in all zones.
    • Anadi_Mondal
      Subscriber

      Thank you for the quick reply .Here is the model info- [2d,dp,pbns,eulerian,rke,transient]
      Please see the below image for water temperature. Actually I set the initial temperature 299.85K and it's not changing. Applied heat flux at the bottom of copper surface has no effect on liquid . Heat is not transferring from copper surface to liquid .What might be the reasons ?
      Regards Anadi


    • Rob
      Ansys Employee
      What is the boundary type between the solid and fluid zones? Did you do ShareTopology (or create a Multibody part) in the geometry tool?
    • Anadi_Mondal
      Subscriber

      I created 3 planes and 3 surfaces (each case operation is add frozen) and used boolean tool to substract surface 2 from 1,and surface 3 from 1.To apply heat flux I hid surfaces 1 and 2, and applied heat flux at the bottom edge(wall) of surface 3.After 2.389s of simulation the volume fraction of water in the pool is like right side image. However , water in the pool is at saturated state( temp 26.7┬░C and operating pressure 33048Pa) and I am applying heat flux of 120000W/m2 at the bottom of surface 3(copper). From my experimental experience ,the surface should be covered by bubbles/vapor and there should be many bubbles in the system. Do you think water fraction at right side image is still logical? Or, any mistake in process.
      Moreover, what might be the process to determine top edge temperature of surface 3? If I know this then I can calculate wall superheat.
      During initialization, I selected compute from 'wall_heat flux(the bottom edge of surface_3).
      My residual is like below:
      iter continuity u-water u-vapor v-water v-vapor energy-p1 energy-p2 k epsilon iac vf-vapor time/iter
      47729 1.0868e-06 1.4956e-05 8.6502e-07 1.9258e-05 1.1558e-06 2.0921e-10 3.6352e-19 2.7958e-05 3.6626e-05 6.1474e-07 8.1657e-07 0:00:19 20

      Regards Anadi


    • Rob
      Ansys Employee
      That's showing vapour (ie not liquid) above the region of the tank. With Eulerian the vapour could behave like that if gravity wasn't on. Check gravity and the temperature field on all phases in Fluent.
    • Anadi_Mondal
      Subscriber

      I turned on gravity and see vapor and liquid temperature unchanged. Actually , I am expecting these ,the vapor and liquid should be at saturation(299.85K) temperature even after applying heat flux. This is the result after 7s.
      I am expecting to plot a graph like below(LEFT SIDE) . Tw is the top edge temperature of surface_3(copper surface). The contour only gives phase temperature .However, how can I get copper surface(solid body) temperature?
      I am suspecting an error at 'Named Selections'[RIGHT SIDE].What is the right way for naming A,B and C boundary? Here , both D and E domain are solid.
      I need to apply heat flux at the bottom wall of domain D(copper surface).
      Regards Anadi
    • DrAmine
      Ansys Employee
      1/Provide a Operating Density. Just set to zero or to the density of vapor
      2/When you visualize temperatures please use Static Temperature with node values off. Do that in Fluent.
      3/It looks like you are using the Eulerian Model. Which Phase change model are you using?

    • Anadi_Mondal
      Subscriber

      Here is the info for static temperature and multiphase model. In the phase interactions , I am using 'boiling' mass transfer mechanism. If you need more info, please let me know.
      Will you or comment on 'Named selections' for boundary A,B,C of above image(RIGHT SIDE) and plotting Tw vs t (LEFT SIDE)
      Regards Anadi


    • Rob
      Ansys Employee
      A, B & C will be wall, wall:shadow pairs, interior or if you didn't do share topology interface. The former is the best option. Labelling will depend on whether you named them in another part of the project, otherwise it'll be a function of the adjacent cell zone labels. Older versions of the code insisted on walls between solids, and whilst having an interior is acceptable you may get a solver warning.
      Re the contour above, can you replot with global values off, and see if there is a difference when you turn off node values too.

    • Anadi_Mondal
      Subscriber

      Here is the temperature distribution with global values and node values off. Now I see little temperature changes. Will you give me an idea to plot flow time vs top edge temperature of copper block(Tw, bottom image)?
      Regards Anadi


    • Rob
      Ansys Employee
      Have a look at Reports and Monitors, they'll be covered in the tutorials (click on Help to find them). You can then plot area average temperature with time, and also save that data to a file.
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