This information is part of the Modelica Standard Library maintained by the Modelica Association.

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.

rho_2ph = TwoPhaseDensity(voidFractionApproach, massFlowRateCorrection, rho_g, rho_l, epsilon_A, x_flow)

voidFractionApproach	Default Value: Modelica.Fluid.Dissipation.Utilities.Types.VoidFractionApproach.Homogeneous Type: VoidFractionApproach Description: Choice of void fraction approach
massFlowRateCorrection	Default Value: false Type: Boolean Description: Consider heterogeneous mass flow rate correction
rho_g	Type: Density (kg/m³) Description: Density of gaseous phase
rho_l	Type: Density (kg/m³) Description: Density of liquid phase
epsilon_A	Type: Real Description: Void fraction (cross sectional averaged)
x_flow	Type: Real Description: Mass flow rate quality

rho_2ph	Type: Density (kg/m³) Description: Mean density of two phase flow