Fluids

Fluids

Negative Cp in Peng_robinson Model

    • Marco Alborghetti
      Subscriber

      Good morning,

      I'm trying to implement the Peng-Robinson model in a multiphase problem, in order to see the evaporation during a transient simulation. I've found all the parameters of the model inside the "MATERIAL-pengrob.ccl" file, when i go to set the data of cp by using a piecewiese polynomial, and than I initialize it, the software tell me that the cp is invalid (negative) for that temperature, anyone is able to help me?

      Kind regards,

    • Rob
      Ansys Employee

      With polynomials it's easy for an overshoot in the curve to return a negative number. Plot the exact equation you plugged into the materials panel in Excel (or another package) and see what you get. 

    • Marco Alborghetti
      Subscriber

      Fluent provide me directly a plot of the resulting curve and it goes under 0

    • Rob
      Ansys Employee

      I keep forgetting they added the graphs into the materials panel. So, you need another curve or expression/UDF to clip the values to be positive. 

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