Two-fluid solver

The Solvers.TwoFluid module in OpenSTREAM provides classes and tools for simulating two-phase flows using a two-fluid approach. In this method, each phase (liquid and vapor) is modeled as an interpenetrating continuum with its own set of conservation equations for mass, momentum, and energy. This framework enables explicit representation of phase interactions, slip velocities, and non-equilibrium effects, making it well-suited for applications where phase separation, interfacial dynamics, and transient boiling phenomena are significant.

This module includes:

Solvers.TwoFluid.TwoFluidSolver.solve(twfSolver)

SOLVE Executes the two-fluid solver for steady-state and transient simulations.

Runs the full solution process for the Solvers.TwoFluid.TwoFluidSolver object. It manages initialization, time stepping, axial sweeps, inner iterations, convergence checks, and logging.

Workflow:

  • Enables logging and opens persistent log file

  • Validates solver state before execution

  • Runs steady-state initialization (solveINIT = true)

  • If initial step converges, proceeds with transient simulation

  • Handles exceptions and ensures proper log closure

Notes:

  • Uses internal solver function to handle both steady-state and transient modes

  • Applies relaxation factors for phase flows, velocities, and enthalpies

  • Supports thermal non-equilibrium modeling

  • Logs progress and outputs to session directory

class Solvers.TwoFluid.TwoFluidSolver.TwoFluidSolver(inputSet, mixSolver)

Bases: Solvers.AbstractSolver

TWOFLUIDSOLVER Solver for initializing, solving, and visualizing two-fluid flow.

The TwoFluidSolver class handles the setup, execution, and visualization of thermal-hydraulic simulations using a two-phase two-fluid approach.

Responsibilities:

Key Components:

  • Phase construction (liquid/vapor)

  • Phase mass/momentum/energy transport modeling

  • Pressure drop gradient obtained from mixture solver

  • Support for relaxation models

  • Visualization of results across time and axial domains

Constructor Summary
TwoFluidSolver(inputSet, mixSolver)

TWOFLUIDSOLVER Constructor for the TwoFluidSolver class.

Creates a new instance of the TwoFluidSolver class using the provided Inputs.InputSet. This constructor initializes the solver by calling the abstract Solvers.AbstractSolver superclass constructor and then sets up all necessary solver parameters and internal data structures via Solvers.TwoFluid.TwoFluidSolver.initializeSolver

Input:

  • inputSet — An Inputs.InputSet object containing model configuration, geometry, boundary conditions, and solver options.

Notes:

  • This constructor assumes Inputs.InputSet is fully validated.

  • Solver initialization includes liquid and vapor objects setup.

  • Time/space discretization and boundary condition interpolation initialized by Solvers.Mixture.MixtureSolver are used

Property Summary
DT = 0

Time step size [s] from Inputs.Options.TSTEP

DZ = 0

Axial step size [m]

NTIME = 0

Number of time steps [-]

NZ = 0

Number of axial steps [-] from Inputs.Model.NNODES

TIME = 0

Time series [s]

Z = 1.

Elevation [m]

boundaryConditions

Boundary conditions object Inputs.BoundaryConditions

fluid

Fluid object Inputs.FluidProperties

inputSet

Input set object Inputs.InputSet

liquid

Liquid object

liquidInit

Null transient liquid object

mixSolver

Mixture object Solvers.Mixture.Mixture

vapor

Vapor object

vaporInit

Null transient vapor object

Method Summary
initializeSolver(twfSolver)

INITIALIZESOLVER Initializes solver parameters and constructs liquid/vapor objects.

Sets up the solver’s internal state using the provided Inputs.InputSet and Solvers.TwoFluid.TwoFluidSolver, This includes initialization of data structures for transient and steady-state simulations based on the mixture solver solutions.

Operations performed:

  • Initializes liquid and vapor arrays for each time step

  • Initializes fluid property objects

  • Sets up mixture object

  • Assigns initial conditions for phase mass flow rates, velocities, enthalpies

Notes:

  • The function assumes uniform axial discretization.

  • Wall heat flux is computed from interpolated boundary conditions.

plott(twfSolver, zIdx, opt)

PLOTT Plots temporal distributions of two-fluid parameters at a given axial location.

Generates time-series plots of selected two-fluid parameters at a specified axial index. The method supports multiple display modes, wall selections, and plot arrangements.

Inputs:

  • twfSolver — Solvers.TwoFluid.TwoFluidSolver object containing simulation data

  • zIdx — Axial index (scalar, positive integer)

  • opt.display — Parameters to display (e.g., ‘HFLUX’, ‘W’, ‘U’, etc.)

  • opt.solveMode — Solve mode: ‘REAL’ or ‘NULL’

  • opt.wall — Wall index(es) to plot

  • opt.tIdx — Time indices to include in the plot

  • opt.reverseTime — Logical flag to reverse time axis

  • opt.unitTemp — Temperature unit: ‘K’ or ‘C’

  • opt.arrangement — Plot arrangement: ‘flow’, ‘vertical’, or ‘horizontal’

  • opt.resize — Resize factor for plot scaling

Notes:

  • If opt.display is set to ‘ALL’, all supported parameters are plotted.

  • The function validates that at least two time indices are provided.

  • Temperature unit conversion is applied if ‘C’ is selected.

  • Each wall is plotted in a separate tile with appropriate legends and axis scaling.

plotz(twfSolver, tIdx, opts)

PLOTZ Plots spatial (axial) distributions of two-fluid parameters.

Generates axial plots of selected two-fluid parameters at specified time indices. The function supports multiple display modes, wall selections, and optional animation over time.

Inputs:

  • twfSolver — Solvers.TwoFluid.TwoFluidSolver object containing simulation data

  • tIdx — Time index or indices (vector of positive integers)

  • opts.display — Parameters to display (e.g., ‘HFLUX’, ‘W’, ‘U’, etc.)

  • opts.solveMode — Solve mode: ‘REAL’ or ‘NULL’

  • opts.wall — Wall index(es) to plot

  • opts.zIdx — Axial indices to include in the plot

  • opts.obstructions — Logical flag to display obstruction locations

  • opts.unitTemp — Temperature unit: ‘K’ or ‘C’

  • opts.arrangement — Plot arrangement: ‘flow’, ‘vertical’, or ‘horizontal’

  • opts.resize — Resize factor for plot scaling

Notes:

  • If multiple time indices are provided, the function creates an animated plot.

  • At least two axial indices must be specified to enable spatial plotting.

  • Temperature unit conversion is applied if ‘C’ is selected.

  • Obstruction locations are plotted if opts.obstructions is true.

  • Each wall is plotted in a separate tile with appropriate legends and axis scaling.

plotzt(twfSolver, opt)

PLOTZT Plots 2D time/elevation distributions of two-fluid parameters.

Generates surface plots of selected two-fluid related parameters over time and axial (elevation) positions. It supports plotting for liquid and vapor fields, and can handle both real and null (initial) transient data.

Inputs:

  • twfSolver — Solvers.TwoFluid.TwoFluidSolver object containing simulation data

  • opt.display — Parameter(s) to display (e.g., ‘HFLUX’, ‘U’, etc.)

  • opt.label — Corresponding labels for display parameters

  • opt.unit — Units for each parameter

  • opt.field — Field to plot: ‘liquid’ or ‘vapor’

  • opt.solveMode — Solve mode: ‘REAL’ or ‘NULL’

  • opt.wall — Wall index(es) to plot

  • opt.zIdx — Axial indices (must include at least 2)

  • opt.tIdx — Time indices (must include at least 2)

  • opt.reverseTime — Logical flag to reverse time axis

  • opt.shading — Surface shading style: ‘faceted’, ‘flat’, or ‘interp’

  • opt.view — View angle for 3D plot [azimuth elevation]

Notes:

  • If ‘ALL’ is passed to opt.display, all supported parameters are plotted.

  • The function validates that at least two axial and time indices are provided to enable meaningful 2D plotting.

  • Each wall is plotted in a separate figure window with appropriate titles and subplot grouping.

class Solvers.TwoFluid.Liquid(inputSet, fluid)

Bases: Solvers.AbstractField

LIQUID Class for modeling liquid field in two-fluid solver

This class encapsulates the physical and numerical properties of the liquid phase, including flow variables, phase interactions, heat transfer,and relaxation models. It supports multiple solver models and provides methods for computing derived quantities and handling flow regime transitions.

Constructor Summary
Liquid(inputSet, fluid)

LIQUID Constructor for Liquid class

Initializes the liquid field object with input configuration and fluid properties.

Inputs:

Property Summary
DT = 0

Time step size [s] from Inputs.Options.TSTEP

H = 1E6

Enthalpy [J/kg]

ITR

Iteration tracking

NTIME = 0

Number of time steps [-]

NZ = 0

Number of axial steps [-] from Inputs.Model.NNODES

TIDX = 1

Time step index [-]

TIME = 0

Time series [s]

U = 1.

Velocity [m/s]

W = 1.

Mass flow rate [kg/s]

Z = 1.

Elevation [m]

mix = NaN

Solvers.TwoFluid.Mixture object

Method Summary
AREA(liquid, vapor, zIdx)

AREA Liquid cross-section area [m^2]

Computes the effective cross-sectional area occupied by the liquid phase.

Inputs:

CD(liquid, vapor, zIdx)

CD Drag coefficient for dispersed liquid [-]

Computes the drag coefficient for dispersed liquid based on Inputs.Model.DROPDRAG model.

Inputs:

Notes:

  • Values are clamped to a maximum of 1

FBUOY(liquid, vapor, zIdx)

FBUOY Liquid buoyancy force [N/m]

Computes the buoyancy force acting on the liquid phase due to pressure gradient.

Inputs:

Notes:

  • The pressure gradient from the mixture solver is used

FDRAG(liquid, vapor, zIdx)

FDRAG Interfacial drag force [N/m]

Computes the interfacial drag force acting on the liquid phase.

Inputs:

Notes:

  • Uses smooth transition between dispersed gas and liquid drag based on Inputs.Model.DISPGAS2DISPLIQ model.

FGRAV(liquid, vapor, zIdx)

FGRAV Liquid gravity force [N/m]

Computes the gravitational force acting on the liquid phase.

Inputs:

FINTCOND(liquid, vapor, zIdx)

FINTCOND Momentum exchange through interfacial condensation [N/m]

Computes the momentum exchange due to interfacial condensation.

Inputs:

FLOWID(liquid, zIdx)

FLOWID Two-phase flow regime ID

Returns the integer ID corresponding to the flow regime classification.

Inputs:

FLOWREGIME(liquid, zIdx)

FLOWREGIME Categorical two-phase flow regimes

Classifies flow regime based on equilibrium quality and boiling transition flags.

Inputs:

Returns:

FTOT(liquid, vapor, zIdx)

FTOT Total force [N/m]

Computes the total force acting on the liquid phase, including gravity, buoyancy, wall shear, drag, and interfacial condensation.

Inputs:

FWALL(liquid, vapor, zIdx)

FWALL Liquid wall shear force [N/m]

Computes the wall shear force acting on the liquid phase, weighted by void fraction.

Inputs:

HFLUX(liquid, zIdx)

HFLUX Wall heat flux to liquid phase [W/m^2]

Computes the net wall heat flux transferred to the liquid phase, combining direct wall heating and boiling contributions.

Inputs:

Notes:

HFLUXWALEVAP(liquid, zIdx)

HFLUXWALEVAP Wall evaporation (boiling) heat flux [W/m^2]

Computes the portion of wall heat flux attributed to evaporation (e.g., boiling), based on the wall evaporation mass ratio.

Inputs:

HINT(liquid, vapor, zIdx)

HINT Linear interfacial heat transfer rate [W/m]

Computes the interfacial heat transfer rate using mass transfer and enthalpy difference (based on Inputs.Model.INTTRANSH model).

Inputs:

Returns:

  • Hcond — Condensation heat transfer rate [W/m]

  • Hevap — Evaporation heat transfer rate [W/m]

HINTCOND(liquid, vapor, zIdx)

HINTCOND Linear interfacial heat condensation rate [W/m]

Extracts the condensation component from Solvers.TwoFluid.Liquid.HINT.

Inputs:

HINTEVAP(liquid, vapor, zIdx)

HINTEVAP Linear interfacial heat evaporation rate [W/m]

Extracts the evaporation component from Solvers.TwoFluid.Liquid.HINT.

Inputs:

HTOT(liquid, vapor, zIdx)

HTOT Total linear vapor heat rate [W/m]

Computes the total heat transfer to the vapor phase, including interfacial and wall contributions.

Inputs:

HWALEVAP(liquid, vapor, zIdx)

HWALEVAP Linear wall heat evaporation (boiling) rate [W/m]

Computes the wall boiling heat transfer rate using latent heat (based on Inputs.Model.INTTRANSH model) and wall mass evaporation.

Inputs:

HWALHEAT(liquid, zIdx)

HWALHEAT Linear wall heat to liquid rate [W/m]

Returns the wall heat generation rate transferred to the liquid phase.

Inputs:

Notes:

  • Set to zero beyond CBT

INTAREA(liquid, vapor, zIdx)

INTAREA Volumetric interfacial area [m^-1]

Computes the interfacial area concentration based on flow regime and phase topology.

Inputs:

Notes:

  • Uses a smooth transition between dispersed gas and dispersed liquid models

INTHFLUX(liquid, vapor, zIdx)

INTHFLUX Interfacial heat flux [W/m^2]

Computes the interfacial heat flux due to evaporation and condensation based on Inputs.Model.INTAREA interfacial area model.

Inputs:

Returns:

  • inthflux_evap — Evaporation heat flux [W/m^2]

  • inthflux_cond — Condensation heat flux [W/m^2]

Notes:

  • Uses interfacial Nusselt number and length scale

  • Driven by deviation from saturated temperature

INTNU(liquid, vapor, zIdx)

INTNU Interfacial Nusselt number for dispersed liquid [-]

Computes the interfacial Nusselt number based on Inputs.Model.INTNU model.

Inputs:

J(liquid, zIdx)

J Liquid superficial velocity [m/s]

Computes the superficial velocity of the liquid phase.

Inputs:

L(liquid, zIdx)

L Dispersed liquid interfacial length scale [m]

Returns the characteristic length scale for dispersed liquid (e.g., drop Sauter mean diameter).

Inputs:

Notes:

  • Currently uses a constant model

MINT(liquid, vapor, zIdx)

MINT Linear interfacial mass transfer rates [kg/s/m]

Computes condensation and evaporation mass transfer rates using either heat flux-based or relaxation-based models.

Inputs:

Returns:

  • Mcond — Condensation mass transfer rate [kg/s/m]

  • Mevap — Evaporation mass transfer rate [kg/s/m]

Notes:

  • Supports ‘CONSTANT’, ‘RANZMARSHALL’, and ‘RELAXATION’ models based on Inputs.Model.INTNU model

  • Applies wall-wise distribution

MINTCOND(liquid, vapor, zIdx)

MINTEVAP Linear interfacial condensation mass transfer [kg/s/m]

Extracts the evaporation component from Solvers.TwoFluid.Liquid.MINT.

Inputs:

MINTEVAP(liquid, vapor, zIdx)

MINTEVAP Linear interfacial evaporation mass transfer [kg/s/m]

Extracts the evaporation component from Solvers.TwoFluid.Liquid.MINT.

Inputs:

MTOT(liquid, vapor, zIdx)

MTOT Total linear mass transfer [kg/s/m]

Computes the total vapor mass transfer rate by summing interfacial condensation, evaporation, and wall boiling contributions.

Inputs:

MWALEVAP(liquid, vapor, zIdx)

MWALEVAP Linear wall mass evaporation rate [kg/s/m]

Computes the wall boiling mass transfer rate using latent heat (based on Inputs.Model.INTTRANSH model) and wall heat flux.

Inputs:

RE(liquid, zIdx)

RE Liquid Reynolds number [-]

Computes the liquid-phase Reynolds number based on flow rate and viscosity.

Inputs:

REV(liquid, vapor, zIdx)

REV Dispersed liquid Reynolds number [-]

Computes the Reynolds number for dispersed liquid using vapor properties and relative velocity.

Inputs:

S(liquid, vapor, zIdx)

S Phase vapor/liquid slip ratio [-]

Computes the slip ratio between vapor and liquid velocities.

Inputs:

T(liquid, zIdx)

T Liquid temperature [K]

Computes the temperature of the liquid phase from enthalpy.

Inputs:

TAUW(liquid, zIdx)

TAUW Liquid wall shear stress [N/m^2]

Returns the wall shear stress acting on the liquid phase.

Inputs:

USLIP(liquid, vapor, zIdx)

USLIP Liquid velocity based on input phase slip [m/s]

Computes the liquid velocity using a slip-based void fraction model.

Inputs:

VF(liquid, vapor, zIdx)

VF Liquid volumetric fraction [-]

Computes the liquid volumetric fraction as the complement of vapor VF.

Inputs:

VISC(liquid, vapor, zIdx)

VISC Viscosity number for dispersed liquid [-]

Computes the dimensionless viscosity number using vapor properties and interfacial tension.

Inputs:

VR(liquid, vapor, zIdx)

VR Local relative velocity [m/s]

Computes the relative velocity between vapor and liquid phases using various models (AREAMEAN, SCALED, DRIFT, FLOWREGIME) based on Inputs.Model.LOCRELVEL model.

Inputs:

WALEVAPRATIO(liquid, zIdx)

WALEVAPRATIO Wall evaporation mass ratio [-]

Returns the fraction of liquid mass undergoing wall boiling.

Inputs:

X(liquid, zIdx)

X Liquid mass fraction [-]

Computes the liquid mass fraction relative to the mixture flow.

Inputs:

XTR_ANN(liquid)

XTR_ANN Quality at onset of annular flow region [-]

Returns the equilibrium quality threshold for the onset of annular flow.

Inputs:

Notes:

  • Uses minimum value from mix.OAFX

XTR_ITM(liquid)

XTR_ITM Quality at onset of intermediate region [-]

Returns the equilibrium quality threshold for the onset of the intermediate flow regime.

Inputs:

XTR_SAT(liquid)

XTR_SAT Quality at saturated boiling transition [-]

Returns the equilibrium quality threshold for the onset of saturated boiling.

Inputs:

XTR_SUB(liquid)

XTR_SUB Quality at subcooled boiling transition [-]

Returns the equilibrium quality threshold for the onset of subcooled boiling.

Inputs:

class Solvers.TwoFluid.REGIMES

Bases: double

REGIMES Enumeration of two-phase flow regimes

This class defines the available two-phase flow regimes for constitutive model selection, used by the two-fluid solver.

The flow regimes are defined as an enum class to increase computational efficiency while increasing readability of code, particularly when different calculations are carried out for different flow regimes.

Flow regimes:

  • LIQUID — Single-phase liquid

  • BUBBLY_SUBCOOLED — Bubbly flow in subcooled region

  • BUBBLY_SATURATED — Bubble flow in saturated region

  • INTERMEDIATE — Intermediate flow region

  • ANNULAR — Annular flow

  • DFFB — Dispersed Flow Film Boiling

class Solvers.TwoFluid.Vapor(inputSet, fluid)

Bases: Solvers.AbstractField

VAPOR Class for modeling vapor field in two-fluid solver

This class encapsulates the physical and numerical properties of the vapor phase, including flow variables, phase interactions, heat transfer,and relaxation models. It supports multiple solver models and provides methods for computing derived quantities and handling flow regime transitions.

Constructor Summary
Vapor(inputSet, fluid)

VAPOR Constructor for Vapor class

Initializes the vapor field object with input configuration and fluid properties.

Inputs:

Property Summary
DT = 0

Time step size [s] from Inputs.Options.TSTEP

H = 1E6

Enthalpy [J/kg]

ITR

Iteration properties

NTIME = 0

Number of time steps [-]

NZ = 0

Number of axial steps [-] from Inputs.Model.NNODES

TIDX = 1

Time step index [-]

TIME = 0

Time series [s]

U = 1.

Velocity [m/s]

W = 1.

Mass flow rate [kg/s]

Z = 1.

Elevation [m]

mix = NaN

Solvers.TwoFluid.Mixture object

Method Summary
AREA(vapor, liquid, zIdx)

AREA Vapor cross-section area [m^2]

Computes the effective cross-sectional area occupied by the vapor phase.

Inputs:

CD(vapor, liquid, zIdx)

CD Drag coefficient for dispersed gas [-]

Computes the drag coefficient for dispersed vapor based on Inputs.Model.DROPDRAG model.

Inputs:

Notes:

  • Values are clamped to a maximum of 1

FBUOY(vapor, liquid, zIdx)

FBUOY Vapor buoyancy force [N/m]

Computes the buoyancy force acting on the vapor phase due to pressure gradient.

Inputs:

Notes:

  • The pressure gradient from the mixture solver is used

FDRAG(vapor, liquid, zIdx)

FDRAG Interfacial drag force [N/m]

Computes the interfacial drag force acting on the vapor phase by reversing the sign of the liquid-phase drag (Solvers.TwoFluid.Liquid.FDRAG()).

Inputs:

FGRAV(vapor, liquid, zIdx)

FGRAV Vapor gravity force [N/m]

Computes the gravitational force acting on the vapor phase.

Inputs:

FINTEVAP(vapor, liquid, zIdx)

FINTEVAP Momentum exchange through interfacial evaporation [N/m]

Computes the momentum exchange due to interfacial evaporation.

Inputs:

FLOWREGIME(vapor, liquid, zIdx)

FLOWREGIME Categorical two-phase flow regimes

Returns the flow regime classification based on liquid-phase criteria (Solvers.TwoFluid.Liquid.FLOWREGIME)().

Inputs:

Returns:

FTOT(vapor, liquid, zIdx)

FTOT Total force [N/m]

Computes the total force acting on the vapor phase, including gravity, buoyancy, wall shear, drag, and interfacial momentum exchanges.

Inputs:

FWALEVAP(vapor, liquid, zIdx)

FWALEVAP Momentum exchange through wall evaporation [N/m]

Computes the momentum exchange due to wall boiling evaporation.

Inputs:

FWALL(vapor, liquid, zIdx)

FWALL Wall shear force [N/m]

Computes the wall shear force acting on the vapor phase, weighted by void fraction.

Inputs:

HFLUX(vapor, zIdx)

HFLUX Wall heat flux to vapor phase [W/m^2]

Computes the net wall heat flux transferred to the vapor phase.

Inputs:

Notes:

HFLUXWALEVAP(vapor, liquid, zIdx)

HFLUXWALEVAP Wall boiling heat flux [W/m^2]

Computes the portion of wall heat flux attributed to boiling (evaporation) for the vapor phase, based on liquid-phase calculations (Solvers.TwoFluid.Liquid.HFLUXWALEVAP()).

Inputs:

HINT(vapor, liquid, zIdx)

HINT Linear interfacial heat transfer rate [W/m]

Computes the interfacial heat transfer rate for the vapor phase based on mass transfer and enthalpy difference (based on Inputs.Model.INTTRANSH model).

Inputs:

Returns:

  • Hcond — Condensation heat transfer rate [W/m]

  • Hevap — Evaporation heat transfer rate [W/m]

HINTCOND(vapor, liquid, zIdx)

HINTCOND Linear interfacial heat condensation rate [W/m]

Extracts the condensation component from Solvers.TwoFluid.Vapor.HINT.

Inputs:

HINTEVAP(vapor, liquid, zIdx)

HINTEVAP Linear interfacial heat evaporation rate [W/m]

Extracts the evaporation component from Solvers.TwoFluid.Vapor.HINT.

Inputs:

HTOT(vapor, liquid, zIdx)

HTOT Total linear vapor heat rate [W/m]

Computes the total heat transfer to the vapor phase, including interfacial and wall contributions.

Inputs:

HWALEVAP(vapor, liquid, zIdx)

HWALEVAP Linear wall heat evaporation (boiling) rate [W/m]

Computes the wall boiling heat transfer rate using latent heat (based on Inputs.Model.INTTRANSH model) and wall mass evaporation.

Inputs:

HWALHEAT(vapor, zIdx)

HWALHEAT Linear wall heat to vapor rate [W/m]

Returns the wall heat generation rate transferred to the vapor phase.

Inputs:

Notes:

  • Set to zero before CBT

INTAREA(vapor, liquid, zIdx)

INTAREA Volumetric interfacial area [m^-1]

Computes the interfacial area concentration using liquid-phase logic (from Solvers.TwoFluid.Liquid.INTAREA)().

Inputs:

INTHFLUX(vapor, liquid, zIdx)

INTHFLUX Interfacial heat flux [W/m^2]

Computes the interfacial heat flux due to evaporation and condensation (delegated to liquid-phase calculation in Solvers.TwoFluid.Liquid.INTHFLUX()).

Inputs:

Returns:

  • inthflux_evap — Evaporation heat flux [W/m^2]

  • inthflux_cond — Condensation heat flux [W/m^2]

Notes:

  • Positive toward liquid phase

INTNU(vapor, liquid, zIdx)

INTNU Interfacial Nusselt number for dispersed vapor [-]

Computes the interfacial Nusselt number based on Inputs.Model.INTNU model.

Inputs:

J(vapor, zIdx)

J Vapor superficial velocity [m/s]

Computes the superficial velocity of the vapor phase.

Inputs:

L(vapor, zIdx)

L Dispersed vapor interfacial length scale [m]

Returns the characteristic length scale for dispersed vapor (e.g., bubble diameter).

Inputs:

Notes:

  • Currently uses a constant model

MINT(vapor, liquid, zIdx)

MINT Linear interfacial mass transfer rates [kg/s/m]

Computes condensation and evaporation mass transfer rates for the vapor phase by reversing the sign of liquid-phase values (attr:Solvers.TwoFluid.Liquid.MINT).

Inputs:

Returns:

  • Mcond — Condensation mass transfer rate [kg/s/m]

  • Mevap — Evaporation mass transfer rate [kg/s/m]

MINTCOND(vapor, liquid, zIdx)

MINTCOND Linear interfacial condensation mass transfer [kg/s/m]

Extracts the condensation component from Solvers.TwoFluid.Vapor.MINT.

Inputs:

MINTEVAP(vapor, liquid, zIdx)

MINTEVAP Linear interfacial evaporation mass transfer [kg/s/m]

Extracts the evaporation component from Solvers.TwoFluid.Vapor.MINT.

Inputs:

MTOT(vapor, liquid, zIdx)

MTOT Total linear mass transfer [kg/s/m]

Computes the total vapor mass transfer rate by reversing the sign of the liquid-phase total (Solvers.TwoFluid.Liquid.MTOT()).

Inputs:

MWALEVAP(vapor, liquid, zIdx)

MWALEVAP Linear wall mass evaporation rate [kg/s/m]

Computes the wall boiling mass transfer rate for vapor by reversing the sign of the liquid-phase value (meth:Solvers.TwoFluid.Liquid.MWALEVAP).

Inputs:

RE(vapor, zIdx)

RE Vapor Reynolds number [-]

Computes the vapor-phase Reynolds number based on flow rate and viscosity.

Inputs:

REL(vapor, liquid, zIdx)

REL Dispersed vapor Reynolds number [-]

Computes the Reynolds number for dispersed vapor using liquid properties and relative velocity.

Inputs:

S(vapor, liquid, zIdx)

S Phase slip ratio [-]

Returns the slip ratio between vapor and liquid phases.

Inputs:

T(vapor, zIdx)

T Vapor temperature [K]

Computes the vapor temperature from enthalpy.

Inputs:

TAUW(vapor, zIdx)

TAUW Wall shear stress [N/m^2]

Returns the wall shear stress acting on the vapor phase.

Inputs:

Notes:

  • Uses mixture-level shear stress for consistency

USLIP(vapor, liquid, zIdx)

USLIP Vapor velocity based on input phase slip [m/s]

Computes the vapor velocity using slip ratio and liquid velocity.

Inputs:

VF(vapor, liquid, zIdx)

VF Vapor volumetric fraction [-]

Computes the vapor volumetric (i.e., void) fraction using slip ratio and densities.

Inputs:

VISC(vapor, liquid, zIdx)

VISC Viscosity number for dispersed gas [-]

Computes the dimensionless viscosity number using liquid and vapor properties.

Inputs:

WALEVAPRATIO(vapor, liquid, zIdx)

WALEVAPRATIO Wall evaporation mass ratio [-]

Returns the fraction of liquid mass undergoing wall boiling.

Inputs:

Returns:

  • walevapratio — Wall boiling mass ratio [-]

X(vapor, zIdx)

X Vapor mass fraction [-]

Computes the vapor mass fraction relative to the mixture flow.

Inputs:

XTR_ANN(vapor, liquid)

XTR_ANN Quality at onset of annular flow region

XTR_CBT(vapor, liquid)

XTR_CBT Quality at Critical Boiling Transition [-]

Returns the equilibrium quality threshold for the onset of critical boiling transition.

Inputs:

XTR_ITM(vapor, liquid)

XTR_ITM Quality at onset of intermediate region [-]

Returns the equilibrium quality threshold for the onset of the intermediate flow regime.

Inputs:

XTR_SAT(vapor, liquid)

XTR_SAT Quality at end of subcooled boiling transition [-]

Returns the equilibrium quality threshold for the onset of saturated boiling.

Inputs:

XTR_SUB(vapor, liquid)

XTR_SUB Quality at onset of subcooled boiling transition [-]

Returns the equilibrium quality threshold for the onset of subcooled boiling.

Inputs:

class Solvers.TwoFluid.Mixture(mixture, liquid, vapor)

Bases: Solvers.AbstractPhase

MIXTURE Class for two-fluid mixture properties in thermal-hydraulic solver

Represents combined properties of liquid and vapor phases in a two-fluid solver. Provides methods to compute mixture-level quantities such as mass flow, density, velocity, heat flux, and thermodynamic quality.

Responsibilities:

  • Aggregate liquid and vapor properties into mixture-level results

  • Compute derived quantities (void fraction, equilibrium quality, CHF)

  • Provide access to geometry and fluid properties for calculations

Key features:

  • Supports axial indexing for spatially resolved calculations

  • Interfaces with liquid and vapor sub-objects for phase-specific data

Constructor Summary
Mixture(mixture, liquid, vapor)

MIXTURE Constructor for Mixture class

Initializes the mixture object by linking liquid and vapor phase objects and copying solver configuration and fluid properties.

Inputs:

mixture — Solvers.Mixture.Mixture object liquid — Solvers.TwoFluid.Liquid object vapor — Solvers.TwoFluid.Vapor object

Method Summary
AFDISTR(mix, param1, param2, zIdx)

AFDISTR Annular flow distribution function [-]

Computes the annular flow distribution function for given parameters.

Inputs:

mix — Solvers.TwoFluid.Mixture object param1 — First parameter for distribution function param2 — Second parameter for distribution function zIdx — Axial indices to evaluate (optional)

CBT(mix, zIdx)

CBT Critical Boiling Transition flag [-]

Returns the CBT flag for each axial location.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

CHF(mix, zIdx)

CHF Critical Heat Flux [W/m^2]

Returns the CHF value for each axial location.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

DPDZ(mix, zIdx)

DPDZ Pressure gradient [Pa/m]

Computes the axial pressure gradient from mixture pressure drop.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

H(mix, zIdx)

H Mixture enthalpy [J/kg]

Calculates the mixture enthalpy as a mass-weighted average of phase enthalpies.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

HFLUX(mix, zIdx)

HFLUX Wall heat flux [W/m^2]

Returns the wall heat flux distribution along the axial domain.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

LHGR(mix, zIdx)

LHGR Linear heat generation rate [W/m]

Computes the linear heat generation rate from wall heat flux and perimeter.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

MFLUX(mix, zIdx)

MFLUX Mixture mass flux [kg/m^2/s]

Calculates the mixture mass flux using total flow and channel area.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

OAFX(mix, zIdx)

OAFX Onset of annular flow equilibrium quality [-]

Returns the OAF quality from the mixture object.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

RELAXTCOND(mix, zIdx)

RELAXTCOND Time relaxation for interfacial evaporation [s]

Returns the relaxation time applied to interfacial evaporation processes in the two-fluid mixture model.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

RELAXTEVAP(mix, zIdx)

RELAXTEVAP Time relaxation for interfacial condensation [s]

Returns the relaxation time applied to interfacial condensation processes in the two-fluid mixture model.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

RHO(mix, zIdx)

RHO Mixture density [kg/m^3]

Computes the mixture density based on void fraction and phase densities.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

TAUW(mix, zIdx)

TAUW Wall shear stress [N/m^2]

Returns the wall shear stress from the mixture object.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

TIME(mix)

TIME Time series [s]

Returns the time array from the mixture object.

Inputs:

mix — Solvers.TwoFluid.Mixture object

U(mix, zIdx)

U Mixture velocity [m/s]

Calculates the mixture velocity as a mass-weighted average of phase velocities.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

VF(mix, zIdx)

VF Void fraction [-]

Computes the vapor volume fraction in the mixture.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

W(mix, zIdx)

W Mixture mass flow rate [kg/s]

Computes the total mass flow rate as the sum of liquid and vapor flows.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

WALEVAPRATIO(mix, zIdx)

WALEVAPRATIO Wall mass evaporation ratio [-]

Returns the ratio of wall heat flux converted to evaporation.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

XEQ(mix, zIdx)

XEQ Equilibrium thermodynamic quality [-]

Returns the equilibrium quality from the mixture object.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)

Z(mix, zIdx)

Z Axial nodes [m]

Returns the axial positions for the mixture domain.

Inputs:

mix — Solvers.TwoFluid.Mixture object zIdx — Axial indices to evaluate (optional)