Fluids

Fluids

Boundary conditions of temperature

    • Ric_Rin_DTU
      Subscriber

      Good afternoon everybody,

      I am simulating the performances of a chemical reactor for methanol production through CFX software. After many efforts, the model now works pretty well and the predicted performances are in very good agreement with literature results and with a previous 2D model I have developed.

      In spite of this, I am having a problem with the inlet section of the unit. I impose the temperature at the inlet, but, when I look at the results at the entrance of the reactor, the inlet temperature is not the one I imposed, but there is a thermal profile at the entrance cross section (I would expect temperature to be constant and equal to the imposed value there). I would like to preface that the outer wall of the reactor is at a constant temperature of 240°C and the reacting mixture is colder than 240°C and hence it is normal that the reacting mixture changes its temperature along the reactor because of the presence of the hotter wall. Though, this should not occur at the entrance of the unit, where the temperature boundary condition is imposed.

      How can I effectively fix the value of temperature at the entrance so that it is equal to the value I impose as boundary condition?


      Thanks a lot for your help,

      Riccardo  

    • Rob
      Ansys Employee
      Please post some images. How well resolved is the mesh?
    • Ric_Rin_DTU
      Subscriber
      Good afternoon,
      Thanks for the reply.
      Here is the comparison between the temperatures of the 2D and the CFD models. As you can see, the agreement is very good, but the inlet value is different (the second image is an enlargement of the first one, to better highlight the differences).


      The strange thing is that, when I look at the results, the correct number is reported (the yellow colour corresponds to 472.77 K), as depicted below:

      But, either when I use the "probe" function or when I calculate the average value of temperature on the inlet plane, I get other numbers, as depicted below.
      1) The probe function gives a value of 486.562 (!!!) in a point of the section of interest


      2) The average calculated value for the inlet section is 481.742 K (!!!).

      The imposed inlet temperature, though, is the same (472.777 K):

      Let me know if you need some more pieces of information!

      Thanks Riccardo
    • Rob
      Ansys Employee
      What does the mesh look like on the inlet? What is the material/mixture density?
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