.Modelica.Fluid.Dissipation.Utilities.Functions.PressureLoss.TwoPhase.TwoPhaseDensity

Information

The gaseous and the liquid part of a fluid in a two phase flow are often discontinuously distributed. This complex behaviour is simplified for engineering calculations. The two phase flow of different fluid flow situations (e.g., bubble or stratified flow) is modelled as if the gaseous and the liquid phase are continuously distributed.

A mean density assuming a continuous distribution out of a discontinuous two phase fluid flow situation can be calculated with a homogeneous or a heterogeneous approach (see dp_twoPhaseOverall_DP).

The following modelling approaches can be used to calculate the mean density of two phase flow:

• homogeneous density (homogeneous approach)
• momentum flux density (heterogeneous approach)
• kinetic energy flow density (heterogeneous approach)

The heterogeneous approaches are analytically derived by minimising the momentum flux or the kinetic energy flow assuming implicitly that the two-phase flow will tend towards the minimum of this quantity.

References

VDI:

VDI - Wärmeatlas: Berechnungsblätter für den Wärmeübergang. Springer Verlag, 10th edition, 2006.

Interface

function TwoPhaseDensity
  extends Modelica.Icons.Function;
  input Modelica.Fluid.Dissipation.Utilities.Types.VoidFractionApproach voidFractionApproach = Modelica.Fluid.Dissipation.Utilities.Types.VoidFractionApproach.Homogeneous "Choice of void fraction approach" annotation(
    Dialog(group = "Choices"));
  input Boolean massFlowRateCorrection = false "Consider heterogeneous mass flow rate correction" annotation(
    Dialog(group = "Choices"));
  input SI.Density rho_g(min = Modelica.Constants.eps) "Density of gaseous phase" annotation(
    Dialog);
  input SI.Density rho_l(min = Modelica.Constants.eps) "Density of liquid phase" annotation(
    Dialog);
  input Real epsilon_A(min = 0, max = 1) "Void fraction (cross sectional averaged)" annotation(
    Dialog(enable = not twoPhaseDensityApproach == Modelica.Fluid.Dissipation.Utilities.Types.TwoPhaseDensityApproach.Homogeneous));
  input Real x_flow(min = 0, max = 1) "Mass flow rate quality" annotation(
    Dialog);
  output SI.Density rho_2ph "Mean density of two phase flow";
end TwoPhaseDensity;

Revisions

• 2 May 2011 by Stefan Wischhusen:
  Corrected a logical error in use of input massFlowRateCorrection.