Fluid Mechanics Package

The fluidmechanics package provides models for pipeline flow, pressure drop calculations, and transient flow simulation with rigorous non-equilibrium thermodynamic calculations for mass and heat transfer.

Overview
Compatibility
Theoretical Foundation
Package Structure
Flow Systems
Flow Nodes
Non-Equilibrium Modeling
Mass Transfer Models
Heat Transfer Models
Two-Phase Mass Transfer
Two-Phase Heat Transfer
Reactive Mass Transfer
Usage Examples

Document	Description
MassTransferAPI.md	Complete API documentation for mass transfer with methods, parameters, and examples
EvaporationDissolutionTutorial.md	Practical tutorial for liquid evaporation and gas dissolution with worked examples
PipelineLiquidEvaporation.md	Finite-rate droplet/film evaporation distance with Maxwell-Stefan mass transfer and coupled heat transfer
MASS_TRANSFER_MODEL_IMPROVEMENTS.md	Technical review of mass transfer model with improvement recommendations
InterphaseHeatMassTransfer.md	Complete theory for interphase mass and heat transfer
droplet_flow_correlations.md	Ranz-Marshall, Kronig-Brink, Abramzon-Sirignano for droplet/bubble flow
mass_transfer.md	Diffusivity models, correlations, and reactive mass transfer
heat_transfer.md	Heat transfer correlations and wall boundary conditions
TwoPhasePipeFlowModel.md	Two-phase flow governing equations and numerical methods
flow_pattern_detection.md	Flow regime identification algorithms

Overview

Location: neqsim.fluidmechanics

Purpose:

Single-phase and two-phase pipe flow modeling
Pressure drop calculations
Transient flow simulation
Flow regime identification
Non-equilibrium heat and mass transfer
Multicomponent diffusion modeling
Reactive absorption (e.g., CO₂ into amine solutions)

Compatibility

Java Version: Java 8 and above
Build System: Maven
All code is Java 8 compatible (no use of Java 9+ features like var, String.repeat(), etc.)

Theoretical Foundation

The fluid mechanics module in NeqSim is based on the work presented in:

Solbraa, E. (2002). Equilibrium and Non-Equilibrium Thermodynamics of Natural Gas Processing. Dr.ing. thesis, Norwegian University of Science and Technology (NTNU). ISBN: 978-82-471-5541-7. Available at NVA

The key contributions from this work include:

Two-fluid model for gas-liquid pipe flow with interphase mass and heat transfer
Multicomponent mass transfer based on the Maxwell-Stefan equations
Film theory with thermodynamic and finite flux corrections
Reactive mass transfer with enhancement factors for chemical absorption
High-pressure effects on mass transfer coefficients and equilibrium

Governing Equations

The two-phase flow is modeled using separate conservation equations for each phase:

Mass Conservation (per component i): $\frac{\partial (\alpha_k \rho_k x_{i,k})}{\partial t} + \frac{\partial (\alpha_k \rho_k x_{i,k} v_k)}{\partial z} = \dot{m}_{i,k}$

Momentum Conservation: $\frac{\partial (\alpha_k \rho_k v_k)}{\partial t} + \frac{\partial (\alpha_k \rho_k v_k^2)}{\partial z} = -\alpha_k \frac{\partial P}{\partial z} - F_{w,k} - F_{i,k} + \alpha_k \rho_k g \sin\theta$

Energy Conservation: $\frac{\partial (\alpha_k \rho_k h_k)}{\partial t} + \frac{\partial (\alpha_k \rho_k h_k v_k)}{\partial z} = \dot{Q}_{w,k} + \dot{Q}_{i,k}$

Where:

$\alpha_k$ = volume fraction of phase k
$\rho_k$ = density
$v_k$ = velocity
$\dot{m}_{i,k}$ = interphase mass transfer rate of component i
$F_{w,k}$, $F_{i,k}$ = wall and interphase friction
$\dot{Q}{w,k}$, $\dot{Q}{i,k}$ = wall and interphase heat transfer

Package Structure

Package under `neqsim.fluidmechanics`	Current entry points
`flowsystem.onephaseflowsystem.pipeflowsystem`	`PipeFlowSystem`
`flowsystem.twophaseflowsystem.twophasepipeflowsystem`	`TwoPhasePipeFlowSystem`, builder and `PipeFlowResult`
`flownode.onephasenode.onephasepipeflownode`	`onePhasePipeFlowNode`
`flownode.twophasenode.twophasepipeflownode`	`StratifiedFlowNode`, `AnnularFlow`, `DropletFlowNode`
`geometrydefinitions.pipe`	`PipeData`
`flownode.fluidboundary.heatmasstransfercalc`	`FluidBoundary`, `FluidBoundaryInterface`
`flowsolver.onephaseflowsolver.onephasepipeflowsolver`	`OnePhaseFixedStaggeredGrid`
`flowsolver.twophaseflowsolver.twophasepipeflowsolver`	`TwoPhaseFixedStaggeredGridSolver`, `MassTransferConfig`

Flow Systems

Single-Phase Pipe Flow

The low-level class is PipeFlowSystem; its geometry uses PipeData. Flow rate and inlet thermodynamics belong to the fluid, while length/elevation/thermal boundary arrays belong to the flow system. Arrays below describe the two ends of one leg. This complete steady, isothermal gas example is compiled and run by PipelineGuideDocumentationTest.

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import neqsim.fluidmechanics.flowsystem.onephaseflowsystem.pipeflowsystem.PipeFlowSystem;
import neqsim.fluidmechanics.geometrydefinitions.GeometryDefinitionInterface;
import neqsim.fluidmechanics.geometrydefinitions.pipe.PipeData;
import neqsim.thermo.system.SystemSrkEos;

Logger logger = LogManager.getLogger("SinglePhaseFlowExample");
SystemSrkEos gas = new SystemSrkEos(288.15, 70.0); // K, bara
gas.addComponent("methane", 0.95);
gas.addComponent("nitrogen", 0.05);
gas.setMixingRule("classic");
gas.setTotalFlowRate(50.0, "kg/sec");
gas.init(0);
gas.initProperties();

PipeFlowSystem flow = new PipeFlowSystem();
flow.setInletThermoSystem(gas);
flow.setNumberOfLegs(1);
flow.setNumberOfNodesInLeg(12);
GeometryDefinitionInterface[] geometry = {
    new PipeData(0.5, 1.0e-5), new PipeData(0.5, 1.0e-5)
}; // Inner diameter and roughness, m
flow.setEquipmentGeometry(geometry);
flow.setLegHeights(new double[] {0.0, 0.0});
flow.setLegPositions(new double[] {0.0, 15000.0}); // m
flow.setLegOuterTemperatures(new double[] {288.15, 288.15}); // K
flow.setLegWallHeatTransferCoefficients(new double[] {0.0, 0.0});
flow.setLegOuterHeatTransferCoefficients(new double[] {0.0, 0.0});
flow.createSystem();
flow.init();
flow.setFailOnNonConvergence(true);
flow.solveSteadyState(1); // Isothermal hydraulic solve

int outletIndex = flow.getTotalNumberOfNodes() - 1;
double outletPressure = flow.getNode(outletIndex).getBulkSystem().getPressure();
logger.info("Outlet: {} bara; pressure drop: {} bar", outletPressure,
    gas.getPressure() - outletPressure);
logger.info("Outlet velocity: {} m/s", flow.getNode(outletIndex).getVelocity());

// Solver type 1 uses face velocities and the upstream cell's EOS density.
double inletMassFlux = flow.getNode(1).getVelocityIn().doubleValue()
    * flow.getNode(0).getGeometry().getArea()
    * flow.getNode(0).getBulkSystem().getPhase(0).getDensity();
double outletMassFlux = flow.getNode(outletIndex).getVelocityIn().doubleValue()
    * flow.getNode(outletIndex - 1).getGeometry().getArea()
    * flow.getNode(outletIndex - 1).getBulkSystem().getPhase(0).getDensity();
logger.info("Finite-volume boundary flows: inlet={} kg/s; outlet={} kg/s",
    inletMassFlux, outletMassFlux);
logger.info("Reported outlet node flow: {} kg/s",
    flow.getNode(outletIndex).getBulkSystem().getFlowRate("kg/sec"));
logger.info("Convergence: {}", flow.getConvergenceReport().getMessage());

Expect positive outlet pressure below 70 bara and a converged hydraulic solve. This example assumes a single gas phase throughout. Solver type 1 does not solve a cooling-pipeline energy balance. Inventory-residual diagnostics in the convergence report are only defined for transient calculations.

Flow reporting limitation: for this 12-cell case, the current outlet node reports approximately 49.893754 kg/s, a 0.21249% difference from the specified 50 kg/s feed. The finite-volume inlet and outlet boundary fluxes are both approximately 49.885716 kg/s and agree to about 2 × 10⁻¹² relative. Thus the node-reported difference is not evidence of global finite-volume mass loss. The distinction arises from the staggered face/cell layout and the solver’s EOS density (getPhase(0).getDensity()), versus the physical-property density used when initializing/reporting node flow. The boundary flux also differs from the specified feed; account for that consistency limitation when connecting this low-level model to other equipment.

The regression independently reconstructs and compares the two boundary fluxes using the solver’s equation tolerance. It does not require the current node-flow discrepancy to remain present.

Two-Phase Pipe Flow

Simplified API (Recommended)

This complete short-pipe example uses the factory and structured result API. The component amounts are in mol/s (0.1 mol/s methane and 0.05 mol/s water) and supply an explicit inlet flow. The phase indices seed the initial condition; the model determines the subsequent phase state. The short length keeps this an API demonstration, not a long-pipeline qualification.

import java.util.Map;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import neqsim.fluidmechanics.flowsystem.twophaseflowsystem.twophasepipeflowsystem.TwoPhasePipeFlowSystem;
import neqsim.fluidmechanics.flowsystem.twophaseflowsystem.twophasepipeflowsystem.PipeFlowResult;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

Logger logger = LogManager.getLogger("TwoPhaseFlowExample");
SystemInterface fluid = new SystemSrkEos(295.3, 5.0); // K, bara
fluid.addComponent("methane", 0.1, 0); // mol/s, initial gas phase
fluid.addComponent("water", 0.05, 1); // mol/s, initial liquid phase
fluid.setMixingRule("classic");
TwoPhasePipeFlowSystem pipe = TwoPhasePipeFlowSystem.horizontalPipe(fluid, 0.025, 3.0, 10);
PipeFlowResult result = pipe.solveWithMassTransfer();
logger.info("Pressure drop: {} bar; outlet temperature: {} K",
    result.getTotalPressureDrop(), result.getOutletTemperature());
Map<String, double[]> data = result.toMap();
logger.info("Returned profile fields: {}", data.keySet());

Factory Methods

Method	Description
`horizontalPipe(fluid, diam, len, nodes)`	Horizontal pipe
`verticalPipe(fluid, diam, len, nodes, upward)`	Vertical pipe
`inclinedPipe(fluid, diam, len, nodes, angleDeg)`	Inclined pipe
`subseaPipe(fluid, diam, len, nodes, seawaterTempC)`	Subsea pipeline
`buriedPipe(fluid, diam, len, nodes, groundTempC)`	Buried pipeline

Builder Pattern (Full Control)

This is an alternative configuration using the fluid defined above.

import neqsim.fluidmechanics.flownode.FlowPattern;
// For advanced configurations, use the builder
TwoPhasePipeFlowSystem pipe = TwoPhasePipeFlowSystem.builder()
    .withFluid(fluid)
    .withDiameter(0.15, "m")
    .withLength(1000, "m")
    .withNodes(50)
    .withFlowPattern(FlowPattern.STRATIFIED)
    .withConvectiveBoundary(278.15, "K", 10.0)
    .enableNonEquilibriumMassTransfer()
    .build();

PipeFlowResult result = pipe.solve();

Flow Nodes

Flow nodes discretize the pipe and calculate local conditions.

Node Properties

Property	Description
Pressure	Local pressure
Temperature	Local temperature
Velocity	Phase velocities
Holdup	Liquid holdup
Reynolds number	Flow regime indicator
Friction factor	Wall friction

Flow Regimes (Two-Phase)

Regime	Class	Description
Stratified	`StratifiedFlowNode`	Separated gas-liquid layers
Annular	`AnnularFlow`	Liquid film on wall, gas core
Droplet/Mist	`DropletFlowNode`	Liquid droplets in gas
Slug	`SlugFlowNode`	Intermittent gas-liquid slugs
Bubble	`BubbleFlowNode`	Gas bubbles in liquid

Non-Equilibrium Modeling

NeqSim distinguishes between equilibrium and non-equilibrium calculations at the gas-liquid interface. In equilibrium calculations, the phases are assumed to be at thermodynamic equilibrium at the interface. In non-equilibrium calculations, finite mass and heat transfer rates are considered.

Architecture

FluidBoundary (abstract)
├── EquilibriumFluidBoundary       # Interface at equilibrium
└── NonEquilibriumFluidBoundary    # Finite transfer rates
    └── KrishnaStandartFilmModel   # Film theory implementation
        └── ReactiveKrishnaStandartFilmModel  # With chemical reactions

Equilibrium vs Non-Equilibrium

Aspect	Equilibrium	Non-Equilibrium
Interface conditions	Thermodynamic equilibrium	Finite driving forces
Mass transfer	Instantaneous	Rate-limited
Heat transfer	Instantaneous	Rate-limited
Computation	Simpler	More rigorous
Applications	Long residence times	Short contact times, absorption

Enabling Non-Equilibrium Calculations

// Get the flow node
FlowNodeInterface node = flowSystem.getNode(i);

// Enable mass and heat transfer calculations
node.getFluidBoundary().setMassTransferCalc(true);
node.getFluidBoundary().setHeatTransferCalc(true);

// Enable thermodynamic corrections (activity coefficients)
node.getFluidBoundary().useThermodynamicCorrections(true, 0);  // Gas phase
node.getFluidBoundary().useThermodynamicCorrections(true, 1);  // Liquid phase

// Enable finite flux corrections (Stefan flow)
node.getFluidBoundary().useFiniteFluxCorrection(true, 0);
node.getFluidBoundary().useFiniteFluxCorrection(true, 1);

Mass Transfer Models

Film Theory

The mass transfer in NeqSim is based on the film theory with multicomponent extensions. The key classes are:

Class	Description
`FluidBoundary`	Abstract base for interphase calculations
`NonEquilibriumFluidBoundary`	Non-equilibrium mass/heat transfer
`KrishnaStandartFilmModel`	Krishna-Standart multicomponent model
`ReactiveKrishnaStandartFilmModel`	With chemical reaction enhancement

Single-Phase (Wall) Mass Transfer

For mass transfer from a flowing fluid to a wall (e.g., pipe wall, packing surface):

\[Sh = \frac{k_c \cdot d}{D_{AB}} = f(Re, Sc)\]

Where:

$Sh$ = Sherwood number
$k_c$ = mass transfer coefficient (m/s)
$d$ = characteristic length (m)
$D_{AB}$ = binary diffusion coefficient (m²/s)
$Sc = \nu / D_{AB}$ = Schmidt number

Correlations implemented:

Flow Regime	Correlation	Range
Laminar	$Sh = 3.66$	$Re < 2300$
Turbulent	$Sh = 0.023 \cdot Re^{0.83} \cdot Sc^{0.33}$	$Re > 10000$
Transition	Interpolation	$2300 < Re < 10000$

Heat Transfer Models

Single-Phase Heat Transfer

Heat transfer to/from pipe walls follows analogous correlations to mass transfer:

\[Nu = \frac{h \cdot d}{k} = f(Re, Pr)\]

Where:

$Nu$ = Nusselt number
$h$ = heat transfer coefficient (W/m²·K)
$k$ = thermal conductivity (W/m·K)
$Pr = \mu \cdot c_p / k$ = Prandtl number

Correlations implemented:

Flow Regime	Correlation
Laminar	$Nu = 3.66$ (constant wall temp)
Turbulent	Dittus-Boelter: $Nu = 0.023 \cdot Re^{0.8} \cdot Pr^{n}$
Transition	Gnielinski correlation

Where $n = 0.4$ for heating and $n = 0.3$ for cooling.

Heat Transfer with Phase Change

When mass transfer occurs, the heat transfer is coupled:

\[\dot{Q}_i = h_{eff} \cdot A \cdot (T_{bulk} - T_i) + \sum_j \dot{n}_j \cdot \Delta H_{vap,j}\]

The effective heat transfer coefficient accounts for the latent heat of evaporation/condensation.

Two-Phase Mass Transfer

Multicomponent Maxwell-Stefan Model

For multicomponent systems, the mass transfer is described by the Maxwell-Stefan equations rather than Fick’s law. The molar flux of component $i$ relative to the molar average velocity is:

\[-c_t \nabla x_i = \sum_{j=1, j \neq i}^{n} \frac{x_i N_j - x_j N_i}{c_t D_{ij}}\]

In NeqSim, this is solved using the Krishna-Standart film model:

Binary Mass Transfer Coefficients

The binary mass transfer coefficients are calculated from:

\[k_{ij} = \frac{Sh \cdot D_{ij}}{d}\]

Where $D_{ij}$ is the binary diffusion coefficient calculated from:

Gas phase: Chapman-Enskog theory
Liquid phase: Wilke-Chang correlation

Mass Transfer Coefficient Matrix

For multicomponent systems, the mass transfer coefficients form a matrix $[k]$:

The following is schematic matrix assembly, not a callable public method.

// In KrishnaStandartFilmModel
public double calcMassTransferCoefficients(int phaseNum) {
    int n = getNumberOfComponents() - 1;

    for (int i = 0; i < n; i++) {
        double tempVar = 0;
        for (int j = 0; j < getNumberOfComponents(); j++) {
            if (i != j) {
                tempVar += x[j] / k_binary[i][j];
            }
            if (j < n) {
                K[i][j] = -x[i] * (1.0/k_binary[i][j] - 1.0/k_binary[i][n]);
            }
        }
        K[i][i] = tempVar + x[i] / k_binary[i][n];
    }
    return K.inverse();  // [k] matrix
}

Interphase Mass Transfer

The total molar flux vector is:

\[\mathbf{N} = c_t [\mathbf{k}] (\mathbf{x}_{bulk} - \mathbf{x}_{interface})\]

With corrections for:

Thermodynamic non-ideality: Activity coefficient gradients
Finite flux (Stefan flow): High mass transfer rates
Film thickness variations: Due to flow regime

Schmidt Number

The Schmidt number characterizes the ratio of momentum to mass diffusivity:

\[Sc_{ij} = \frac{\nu}{D_{ij}}\]

// Calculation in KrishnaStandartFilmModel
for (int i = 0; i < nComponents; i++) {
    for (int j = 0; j < nComponents; j++) {
        binarySchmidtNumber[phase][i][j] =
            kinematicViscosity / diffusionCoefficient[i][j];
    }
}

Interphase Transport Coefficients

The interphase transport coefficients depend on the flow regime:

Flow Regime	Gas-side $k_G$	Liquid-side $k_L$
Stratified	Smooth interface correlation	Penetration theory
Annular	Film correlation	Film flow correlation
Droplet	Droplet correlations	Internal circulation
Bubble	External mass transfer	Higbie penetration

Two-Phase Heat Transfer

Interphase Heat Transfer

Heat transfer between gas and liquid phases occurs at the interface:

\[\dot{Q}_{GL} = h_{GL} \cdot A_i \cdot (T_G - T_L)\]

Where $A_i$ is the interfacial area per unit volume.

Heat Transfer Coefficient Correlations

The interphase heat transfer coefficient is related to mass transfer through the Chilton-Colburn analogy:

\[\frac{h}{k_c \cdot \rho \cdot c_p} = \left(\frac{Sc}{Pr}\right)^{2/3}\]

Implemented correlations by flow regime:

Flow Regime	Correlation Type
Stratified	Flat interface model
Annular	Film evaporation/condensation
Dispersed	Droplet/bubble heat transfer

Coupling of Heat and Mass Transfer

In non-equilibrium calculations, heat and mass transfer are coupled through:

Latent heat effects: Evaporation/condensation carries enthalpy
Sensible heat: Temperature gradients drive conduction
Dufour effect: Mass flux induces heat flux (usually negligible)
Soret effect: Temperature gradient induces mass flux (usually negligible)

The interphase heat flux includes both contributions:

\[\dot{Q}_i = h \cdot (T_{bulk} - T_i) + \sum_j N_j \cdot \bar{H}_j\]

Where $\bar{H}_j$ is the partial molar enthalpy of component $j$.

Wall Heat Transfer in Two-Phase Flow

For PipeBeggsAndBrills, use setHeatTransferCoefficient(double) for an effective U-value and setConstantSurfaceTemperature(double, String) for the thermal boundary. See the heat-transfer examples for full setup and the resistance equations with a consistent reference area.

Reactive Mass Transfer

Enhancement Factors

For absorption with chemical reaction (e.g., CO₂ into amine solutions), the mass transfer is enhanced:

\[N_{CO2} = E \cdot k_L \cdot (C_{CO2,i} - C_{CO2,bulk})\]

Where $E$ is the enhancement factor.

Enhancement Factor Models

Model	Description	Application
Film theory	$E = \sqrt{1 + Ha^2}$	Fast reactions
Penetration theory	Numerical solution	Moderate reactions
Danckwerts	Pseudo-first order	Industrial absorbers

The Hatta number characterizes the reaction regime:

\[Ha = \frac{\sqrt{k_{rxn} \cdot D_A}}{k_L}\]

Reactive Film Model

The following describes enhancement-factor application schematically.

// ReactiveKrishnaStandartFilmModel extends KrishnaStandartFilmModel

// Enhancement factor calculation
EnhancementFactor enhancement = new EnhancementFactor();
double E = enhancement.calculate(hattaNumber, reactionOrder);

// Apply to mass transfer
double N_CO2 = E * k_L * (C_interface - C_bulk);

CO₂-Amine Systems

NeqSim includes specific models for CO₂ absorption into:

MDEA (methyldiethanolamine)
MEA (monoethanolamine)
DEA (diethanolamine)
Activated MDEA (with piperazine)

Reaction kinetics: $r_{CO2} = k_2 \cdot [CO2] \cdot [Amine]$

With temperature-dependent rate constants from experimental data.

Pressure Drop Correlations

Single-Phase

// Darcy-Weisbach equation
// ΔP = f * (L/D) * (ρ * v²/2)

// Friction factor correlations:
// - Moody (explicit)
// - Colebrook-White (implicit)
// - Chen (explicit approximation)

Two-Phase

Correlation	Application
Beggs-Brill	General two-phase
Lockhart-Martinelli	Separated flow
Duns-Ros	Vertical wells
Hagedorn-Brown	Vertical wells
Gray	Gas-condensate wells

Transient Flow Simulation

For PipeFlowSystem, initialize and solve the steady flow first. Supply the boundary time series through getTimeSeries().setTimes(double[]), setInletThermoSystems(SystemInterface[]), and setNumberOfTimeStepsInInterval(int) before solveTransient(1). The argument 1 selects the solver equations; it is not a one-second timestep. Repeated calls without a time series do not define a transient boundary event.

See compositional tracking for complete time-series examples, conservation diagnostics, and supported boundary conditions.

Heat Transfer

For a process-level cooling calculation, use the self-contained heat-transfer example. It selects PipeBeggsAndBrills, explicitly defines mass flow and surrounding temperature, and uses the model’s actual thermal API.

For the low-level flow system, set per-leg temperatures with setLegOuterTemperatures(double[]) and wall/external coefficients with setLegWallHeatTransferCoefficients(double[]) and setLegOuterHeatTransferCoefficients(double[]) before creating the system. An energy-enabled solver is required for temperature evolution; the isothermal example above deliberately sets both coefficients to zero.

Geometry Definitions

Pipe Geometry

PipeData describes inner diameter, roughness, and wall/environment properties. It does not contain the whole route; use the flow system’s setLegPositions and setLegHeights for that. The single-phase example above shows the complete route/geometry setup.

Internal Geometry

Use PipeData.setCarbonSteelWall(thicknessM) and PipeData.addMineralWoolInsulation(thicknessM) for material layers. The heat-transfer guide demonstrates the distinction between wall resistance and the fluid-side coefficient. A deposit also changes the hydraulic flow area; assigning an insulation material is not a model of wax deposition kinetics.

Flow Solver Options

flow.getSolver() returns the active FlowSolverInterface after solving. Solver-specific controls and convergence reports are documented by the actual solver class. For the single-phase example, setFailOnNonConvergence(true) and getConvergenceReport() expose whether the hydraulic solve succeeded. Do not assume generic setMaxIterations, setConvergenceCriteria, or setRelaxationFactor methods exist on that interface.

Integration with Process Equipment

Use OnePhasePipeLine, MultiphasePipe, or a correlation model such as PipeBeggsAndBrills for a ProcessSystem. Pipeline is their base class and should not be used as a substitute for selecting a physical model. See the complete pipeline examples for inlet streams, real geometric setters, and outlet results.

Visualization

Read node values from flow.getNode(i).getBulkSystem() and iterate through flow.getTotalNumberOfNodes() in a low-level model. Process models such as PipeBeggsAndBrills provide pressure, temperature, and length profiles for plotting with the caller’s charting tool. See the profile example for units and array lengths.

Example: Gas Pipeline

The single-phase example is a complete 15 km gas pipeline calculation using the low-level API. For a 100 km process-equipment example, use the gas export pipeline. Both explicitly define the fluid, mixing rule, flow rate, inner diameter, roughness, calculation mode, and result units.

Best Practices

Use appropriate number of nodes - more nodes for accuracy, fewer for speed
Check flow regime in two-phase calculations
Validate against correlations for your specific application
Consider elevation profile for long pipelines
Include heat transfer for hot fluids or cold environments
Enable non-equilibrium for absorption and short-contact processes
Use thermodynamic corrections for non-ideal liquid phases

Test Suite

The fluid mechanics package includes comprehensive unit tests:

Test File	Coverage
`TwoPhasePipeFlowSystemTest.java`	System setup, steady-state solving, mass/heat transfer, model comparisons
`NonEquilibriumPipeFlowTest.java`	Non-equilibrium mass transfer, evaporation, dissolution, bidirectional transfer
`FlowPatternDetectorTest.java`	Flow pattern detection models (Taitel-Dukler, Baker, Barnea, Beggs-Brill)
`InterfacialAreaCalculatorTest.java`	Interfacial area calculations for all flow patterns
`MassTransferCoefficientCalculatorTest.java`	Mass transfer coefficient correlations
`TwoPhasePipeFlowSystemBuilderTest.java`	Builder API tests

Known Test Limitations

Some advanced test scenarios are disabled pending solver optimization:

Complete phase evaporation/dissolution tests (solver timeout)
Transient water drying simulations (solver timeout)
Subsea pipeline with large temperature gradients (temperature calculation issues)

See TwoPhasePipeFlowSystem_Development_Plan.md for details.

References

Solbraa, E. (2002). Equilibrium and Non-Equilibrium Thermodynamics of Natural Gas Processing. Dr.ing. thesis, NTNU. ISBN: 978-82-471-5541-7. Available at NVA
Krishna, R., Standart, G.L. (1976). Mass and energy transfer in multicomponent systems. Chemical Engineering Communications, 3(4-5), 201-275.
Taylor, R., Krishna, R. (1993). Multicomponent Mass Transfer. Wiley.
Bird, R.B., Stewart, W.E., Lightfoot, E.N. (2002). Transport Phenomena. 2nd ed. Wiley.
Danckwerts, P.V. (1970). Gas-Liquid Reactions. McGraw-Hill.

Mass Transfer Modeling - Detailed multicomponent mass transfer models
Heat Transfer Modeling - Detailed heat transfer correlations and models
Process Pipeline Equipment - Pipeline in process simulation
Physical Properties - Viscosity, diffusivity, and density models
Thermodynamics - Equations of state and phase equilibria
Transient Pipeline Simulation - Dynamic pipeline modeling

Table of Contents

Related Documentation

Overview

Compatibility

Theoretical Foundation

Governing Equations

Package Structure

Flow Systems

Single-Phase Pipe Flow

Two-Phase Pipe Flow

Simplified API (Recommended)

Factory Methods

Builder Pattern (Full Control)

Flow Nodes

Node Properties

Flow Regimes (Two-Phase)

Non-Equilibrium Modeling

Architecture

Equilibrium vs Non-Equilibrium

Enabling Non-Equilibrium Calculations

Mass Transfer Models

Film Theory

Single-Phase (Wall) Mass Transfer

Heat Transfer Models

Single-Phase Heat Transfer

Heat Transfer with Phase Change

Two-Phase Mass Transfer

Multicomponent Maxwell-Stefan Model

Binary Mass Transfer Coefficients

Mass Transfer Coefficient Matrix

Interphase Mass Transfer

Schmidt Number

Interphase Transport Coefficients

Two-Phase Heat Transfer

Interphase Heat Transfer

Heat Transfer Coefficient Correlations

Coupling of Heat and Mass Transfer

Wall Heat Transfer in Two-Phase Flow

Reactive Mass Transfer

Enhancement Factors

Enhancement Factor Models

Reactive Film Model

CO₂-Amine Systems

Pressure Drop Correlations

Single-Phase

Two-Phase

Transient Flow Simulation

Heat Transfer

Geometry Definitions

Pipe Geometry

Internal Geometry

Flow Solver Options

Integration with Process Equipment

Visualization

Example: Gas Pipeline

Best Practices

Test Suite

Known Test Limitations

References

Related Documentation