Neqsim on java for enthalpy calculation

[myrtp]

Hi I am trying to develop a code in order to calculate a mix enthalpy in java. This is my enthalpy calculation code:

import neqsim.thermo.phase.PhaseInterface;
import neqsim.thermo.system.SystemInterface;

public class EnthalpyCalculation {

    public double enthalpyMix(String base, double P2, double T2, double P1, double T1, double[] y, SystemInterface[] subs) throws Exception {
        double h_molar = 939932;
        double mw = 20;
        double h1 = 0;
        double h2 = 0;

            subs[0].setPressure(P1, "bar");
            subs[0].setTemperature(T1, "K");
            h1 = subs[0].getEnthalpy("J/kg")
            subs[0].setPressure(P2, "bar");
            subs[0].setTemperature(T2, "K");
            h2 = subs[0].getEnthalpy("J/kg");


            double h_i = h2 - h1;

            double mw_i = (subs[0].getMolarMass("kg/mol")) * 1000;

            h_molar += y[0] * h_i;
            mw += y[0] * mw_i;

        double h_mass = h_molar / (mw * 1e-3);


        double h_mix;
        if (base.equals("mass") || base.equals("molar")) {
            h_mix = (base.equals("molar")) ? h_molar : h_mass;
        } else
            throw new Exception(" First parameter must be the specified base that enthalpy is calculated (must be string). The enthalpy must be calculated either in mass or molar based.");


        return h_mix;
    }

}

Then when I execute it on main file:

import model.EnthalpyCalculation;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;
public class Main {
    public static void main(String[] args) throws Exception {
// 1: reference state
        double P1 = 1.01325;
        double T1 = 298.15;
        double P2 = 3;
        double T2 = 350.0;

        SystemInterface[] subs = new SystemInterface[1];
        subs[0] = new SystemSrkEos(T1, P1);
        subs[0].addComponent("methane", 1.0, "kg/sec");
        subs[0].setPressure(P1, "bar");
        subs[0].setMixingRule(1);
//        subs[1] = new SystemSrkEos(350, P2);
//        subs[1].addComponent("ethane", 0.10, "kg/sec");
//        subs[1].setPressure(P1, "bar");

        double[] y = {1};
        String base = "mass";

        EnthalpyCalculation enthalpyCalculation = new EnthalpyCalculation();
        double enthalpyMix = enthalpyCalculation.enthalpyMix(base, P2, T2, P1, T1, y, subs);
        System.out.println("Enthalpy Mix: " + enthalpyMix);
    }
}

However the enthalpy returned in NaN and if I print the values of h2 or h1 they are infinite. What could be the problem?

[EvenSol]

Hi.

Try modifying the code a bit:

The first modification is setting that your fluid will only be single phase gas:

    SystemInterface[] subs = new SystemInterface[1];
    subs[0] = new SystemSrkEos(T1, P1);
    subs[0].addComponent("methane", 1.0, "kg/sec");
    subs[0].setPressure(P1, "bar");
    subs[0].setMixingRule(1);

    subs[0].init(0);
    subs[0].setNumberOfPhases(1);
    subs[0].setMaxNumberOfPhases(1);
    subs[0].setForcePhaseTypes(true);
    subs[0].setPhaseType(0, "gas");

and after setting temperature and pressure you need to call the initThermoProperties method to calculate the entahlpies at this condition:

    subs[0].setPressure(P1, "bar");
    subs[0].setTemperature(T1, "K");
    subs[0].initThermoProperties();
    h1 = subs[0].getEnthalpy("J/kg");
    subs[0].setPressure(P2, "bar");
    subs[0].setTemperature(T2, "K");
    subs[0].initThermoProperties();
    h2 = subs[0].getEnthalpy("J/kg");

[EvenSol]

In the more general case where your fluid could split in to more phases (eg. a mixture of methane and n-heptane) the code could be something like this:

import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

public class Main {
  public static void main(String[] args) throws Exception {
    // 1: reference state
    double P1 = 1.01325;
    double T1 = 298.15;
    double P2 = 3;
    double T2 = 350.0;

    SystemInterface[] subs = new SystemInterface[1];
    subs[0] = new SystemSrkEos(T1, P1);
    subs[0].addComponent("methane", 1.0, "kg/sec");
    subs[0].addComponent("n-heptane", 1.0, "kg/sec");
    subs[0].setMixingRule("classic");

    double[] y = {1};
    String base = "mass";

    EnthalpyCalculation enthalpyCalculation = new EnthalpyCalculation();
    double enthalpyMix = enthalpyCalculation.enthalpyMix(base, P2, T2, P1, T1, y, subs);
    System.out.println("Enthalpy Mix: " + enthalpyMix);
  }
}

and

import neqsim.thermo.system.SystemInterface;
import neqsim.thermodynamicOperations.ThermodynamicOperations;

public class EnthalpyCalculation {

  public double enthalpyMix(String base, double P2, double T2, double P1, double T1, double[] y,
      SystemInterface[] subs) throws Exception {
    double h_molar = 939932;
    double mw = 20;
    double h1 = 0;
    double h2 = 0;

    ThermodynamicOperations flashOps = new ThermodynamicOperations(subs[0]);

    subs[0].setPressure(P1, "bar");
    subs[0].setTemperature(T1, "K");
    flashOps.TPflash();
    subs[0].initThermoProperties();
    h1 = subs[0].getEnthalpy("J/kg");
    subs[0].setPressure(P2, "bar");
    subs[0].setTemperature(T2, "K");
    flashOps.TPflash();
    subs[0].initThermoProperties();
    h2 = subs[0].getEnthalpy("J/kg");


    double h_i = h2 - h1;

    double mw_i = (subs[0].getMolarMass("kg/mol")) * 1000;

    h_molar += y[0] * h_i;
    mw += y[0] * mw_i;

    double h_mass = h_molar / (mw * 1e-3);


    double h_mix;
    if (base.equals("mass") || base.equals("molar")) {
      h_mix = (base.equals("molar")) ? h_molar : h_mass;
    } else
      throw new Exception(
          " First parameter must be the specified base that enthalpy is calculated (must be string). The enthalpy must be calculated either in mass or molar based.");


    return h_mix;
  }

}

[EvenSol]

Also this python example might be useful:

https://colab.research.google.com/github/EvenSol/NeqSim-Colab/blob/master/notebooks/howtouseneqsim.ipynb#scrollTo=rT10YNDjfJXL