LNG Cryogenic Multi-Stream Heat Exchanger

Overview

The LNGHeatExchanger class provides a production-grade model for brazed aluminium heat exchangers (BAHX) used in LNG liquefaction and natural gas processing. It extends NeqSim’s MultiStreamHeatExchanger2 with ten advanced capabilities (P1–P10) covering thermodynamic analysis, mechanical integrity, and project economics.

Package: neqsim.process.equipment.heatexchanger

Extends: MultiStreamHeatExchanger2

When to Use

LNG main cryogenic heat exchanger (MCHE) design and rating
Mixed refrigerant (MR) process simulation (C3MR, DMR, SMR)
Cryogenic gas processing (NGL recovery, nitrogen rejection)
Any multi-stream plate-fin heat exchanger application

Key Capabilities

Feature	ID	Description
Rigorous H-T curves	P1	TP-flash at every zone boundary captures phase transitions
Per-stream pressure drop	P2	Linear ΔP interpolation shifts saturation temperatures
Exergy analysis	P3	Zone-by-zone entropy generation and second-law efficiency
Adaptive zone refinement	P4	Auto-subdivides zones near phase boundaries
Manglik-Bergles correlations	P5	Offset-strip fin j-factor and f-factor
Two-phase pressure drop	P6	Lockhart-Martinelli separated flow model
Dynamic cool-down transient	P7	Lumped thermal mass model for start-up
Core sizing	P8	BAHX L × W × H from duty and fin geometry
Freeze-out detection	P9	CO₂ and heavy hydrocarbon solid risk per zone
Flow maldistribution	P10	MITA correction factor for non-uniform distribution
Thermal stress assessment	—	Gradient-based fatigue warning per API 662 Part II
Mercury risk assessment	—	LME risk check for aluminium BAHX
Mechanical design	—	ASME VIII Div.1 wall thickness, fatigue life (BAHXMechanicalDesign)
Cost estimation	—	Weight-based CAPEX with installation factor (BAHXCostEstimator)
Design feasibility report	—	Verdict + supplier matching + issues + JSON report

Architecture

LNGHeatExchanger (process equipment)
├── extends MultiStreamHeatExchanger2
│   └── NR solver for outlet temperatures
├── computeRigorousZoneData()
│   ├── P1: TP-flash at each zone boundary
│   ├── P2: Per-stream pressure interpolation
│   ├── P3: Exergy destruction per zone
│   ├── P4: Adaptive zone refinement
│   ├── P5: Manglik-Bergles j/f correlations
│   ├── P6: Lockhart-Martinelli two-phase ΔP
│   ├── P9: Freeze-out detection
│   └── P10: Maldistribution correction
├── sizeCore()                    → P8: Core L × W × H
├── runCooldownTransient()        → P7: Dynamic transient
├── assessMercuryRisk()           → Mercury LME check
└── generateFeasibilityReport()   → Combined report
    ├── BAHXMechanicalDesign      → ASME VIII wall thickness + fatigue
    ├── BAHXCostEstimator         → CAPEX / OPEX / lifecycle
    └── HeatExchangerDesignFeasibilityReport
        ├── Supplier matching     → HeatExchangerSuppliers.csv
        ├── Feasibility checks    → BLOCKER / WARNING / INFO
        └── Verdict               → FEASIBLE / WITH_WARNINGS / NOT_FEASIBLE

Quick Start

Java

import neqsim.process.equipment.heatexchanger.LNGHeatExchanger;
import neqsim.process.equipment.stream.Stream;
import neqsim.process.processmodel.ProcessSystem;
import neqsim.thermo.system.SystemSrkEos;

// 1. Create fluids
SystemInterface hotFluid = new SystemSrkEos(273.15 + 30.0, 50.0);
hotFluid.addComponent("methane", 0.90);
hotFluid.addComponent("ethane", 0.05);
hotFluid.addComponent("propane", 0.03);
hotFluid.addComponent("nitrogen", 0.02);
hotFluid.setMixingRule("classic");

SystemInterface coldFluid = new SystemSrkEos(273.15 - 33.0, 3.0);
coldFluid.addComponent("methane", 0.40);
coldFluid.addComponent("ethane", 0.30);
coldFluid.addComponent("propane", 0.30);
coldFluid.setMixingRule("classic");

// 2. Create streams
Stream hotStream = new Stream("NG Feed", hotFluid);
hotStream.setFlowRate(100000.0, "kg/hr");

Stream coldStream = new Stream("MR Return", coldFluid);
coldStream.setFlowRate(150000.0, "kg/hr");

// 3. Configure BAHX
LNGHeatExchanger mche = new LNGHeatExchanger("MCHE");
mche.addInStream(hotStream);
mche.addInStream(coldStream);
mche.setNumberOfZones(15);
mche.setStreamPressureDrop(0, 1.5);  // 1.5 bar on hot side
mche.setStreamPressureDrop(1, 0.3);  // 0.3 bar on cold side

// 4. Run in process system
ProcessSystem process = new ProcessSystem();
process.add(hotStream);
process.add(coldStream);
process.add(mche);
process.run();

// 5. Read results
System.out.println("MITA: " + mche.getMITA() + " °C");
System.out.println("η_II: " + mche.getSecondLawEfficiency() * 100 + " %");

Python (Jupyter)

from neqsim import jneqsim

SystemSrkEos = jneqsim.thermo.system.SystemSrkEos
Stream = jneqsim.process.equipment.stream.Stream
LNGHeatExchanger = jneqsim.process.equipment.heatexchanger.LNGHeatExchanger
ProcessSystem = jneqsim.process.processmodel.ProcessSystem

# Create fluid, stream, and exchanger as above
# (see the example notebook for full Python walkthrough)

Inner Classes

FinGeometry

Describes the offset-strip fin geometry for Manglik-Bergles correlations and core sizing.

Parameter	Default	Unit	Description
`finHeight`	0.006	m	Fin height (passage height)
`finThickness`	0.0003	m	Fin metal thickness
`finPitch`	0.0016	m	Centre-to-centre fin spacing
`stripLength`	0.003	m	Offset strip length
`plateThickness`	0.0016	m	Parting sheet thickness
`finConductivity`	170.0	W/(m·K)	Fin thermal conductivity (aluminium)

Derived properties:

getHydraulicDiameter() — hydraulic diameter (m)
getSigma() — free-flow area ratio (dimensionless)
getBeta() — surface area density (m²/m³)

CoreGeometry

Holds the core dimensions from sizing or manual input.

Parameter	Unit	Description
`length`	m	Flow direction
`width`	m	Header direction
`height`	m	Stack-up direction
`numberOfLayers`	—	Layers per stream
`weight`	kg	Core metal weight

Derived: getVolume() returns L × W × H in m³.

TransientPoint

Immutable snapshot from cool-down transient analysis.

Field	Unit	Description
`timeHours`	hr	Elapsed time
`metalTempC`	°C	Average metal temperature
`fluidOutTempC`	°C	Fluid outlet temperature
`dutyKW`	kW	Instantaneous duty

Configuration Reference

Zone and Type Settings

Method	Default	Description
`setNumberOfZones(int)`	20	Axial discretisation count
`setExchangerType(String)`	`"BAHX"`	Type: `"BAHX"`, `"PCHE"`, `"CWHE"`

Pressure Drop (P2)

Method	Description
`setStreamPressureDrop(int idx, double bar)`	Set total ΔP for stream `idx`
`getStreamPressureDrop(int idx)`	Get ΔP in bar

Pressure is linearly interpolated from inlet to outlet during the zone analysis. This shifts saturation temperatures and affects pinch location, typically by 1–3 °C for LNG exchangers.

Exergy Settings (P3)

Method	Default	Description
`setReferenceTemperature(double °C)`	15.0	Dead-state temperature for exergy

Method	Default	Description
`setAdaptiveRefinement(boolean)`	false	Enable auto-refinement
`setMaxAdaptiveZones(int)`	100	Maximum zones after refinement
`setAdaptiveThresholdFactor(double)`	2.0	Gradient multiplier for refinement trigger

When enabled, zones where enthalpy gradient exceeds thresholdFactor × average are bisected. This improves resolution near phase boundaries (e.g., MR evaporation onset).

Fin Geometry (P5)

Method	Description
`setStreamFinGeometry(int idx, FinGeometry)`	Set fin geometry for stream
`getStreamFinGeometry(int idx)`	Get fin geometry (null if not set)

When fin geometry is set, Manglik-Bergles (1995) correlations compute:

j-factor (Colburn analogy heat transfer coefficient)
f-factor (Fanning friction factor)
Detailed ΔP (single-phase + Lockhart-Martinelli two-phase correction)

Maldistribution (P10)

Method	Default	Description
`setFlowMaldistributionFactor(double)`	1.0	Penalty factor (0.85–0.95 typical)

Reduces effective UA and MITA. A factor of 0.90 means 10% performance loss due to flow maldistribution.

Core Geometry (P8)

Method	Description
`setCoreGeometry(CoreGeometry)`	Set core dimensions manually
`getCoreGeometry()`	Get core geometry (populated by `sizeCore()`)
`sizeCore()`	Auto-size from UA requirement and fin geometry

Transient (P7)

Method	Description
`setCoreThermalMass(double kJ/K)`	Set metal thermal mass
`runCooldownTransient(targetC, ambientC, steps, hours)`	Run transient

Thermal Stress

Method	Default	Description
`setMaxAllowableThermalGradient(double °C/m)`	5.0	API 662 Part II limit

Result Getters

Temperature Approach

Method	Returns	Unit
`getMITA()`	Minimum internal temperature approach	°C
`getMITAZoneIndex()`	Zone index where MITA occurs	—
`getMITAPerZone()`	Per-zone approaches	°C[]

Composite Curves

Method	Returns	Description
`getHotCompositeCurve()`	`double[nPoints][2]`	Col 0: cumulative duty (kW), Col 1: temperature (°C)
`getColdCompositeCurve()`	`double[nPoints][2]`	Same format

Exergy

Method	Returns	Unit
`getExergyDestructionPerZone()`	Per-zone exergy destruction	kW[]
`getTotalExergyDestruction()`	Total destruction	kW
`getSecondLawEfficiency()`	η_II	dimensionless (0–1)

UA

Method	Returns	Unit
`getUAPerZone()`	Per-zone UA values	W/K[]

Pressure Drop Correlations

Method	Returns	Unit
`getComputedStreamDP()`	Computed ΔP per stream	bar[]
`getStreamJFactor()`	Average j-factor per stream	—[]
`getStreamFFactor()`	Average f-factor per stream	—[]

Freeze-Out (P9)

Method	Returns	Description
`getFreezeOutRiskPerZone()`	`boolean[]`	True if zone below CO₂ triple point (-56.6 °C)
`hasFreezeOutRisk()`	`boolean`	True if any zone has risk

Temperature Profiles

Method	Returns	Unit
`getZoneTempProfileHotC()`	Hot-side temperatures	°C[]
`getZoneTempProfileColdC()`	Cold-side temperatures	°C[]

Thermal Stress

Method	Returns	Description
`getThermalGradientPerZone()`	`double[]`	Gradient in °C/m
`hasThermalStressWarning()`	`boolean`	True if any zone exceeds limit

Mercury Risk

Method	Returns	Description
`isMercuryRiskPresent()`	`boolean`	True if Hg exceeds 10 ppb
`getMercuryRiskMessage()`	`String`	Detailed warning message

Cool-Down Transient

Method	Returns	Description
`getTransientResults()`	`List<TransientPoint>`	Time-series data

Mechanical Design (BAHXMechanicalDesign)

Package: neqsim.process.mechanicaldesign.heatexchanger

BAHX-specific mechanical design calculations per ASME VIII Div.1 and ALPEMA standards.

Materials

Component	Alloy	Allowable Stress (MPa)	Density (kg/m³)
Core (fins, plates)	Al 3003-H14	62	2730
Headers, nozzles	Al 5083	117	2730

Brazed joint efficiency: 0.80 per ASME VIII.

Wall Thickness Calculations

Parting sheet (ASME UG-27 cylindrical shell formula):

\[t = \frac{P \cdot R}{S \cdot E - 0.6 \cdot P}\]

Where $P$ = design pressure (MPa), $R$ = half fin height (mm), $S$ = allowable stress (MPa), $E$ = joint efficiency.

Header plate (flat plate formula):

\[t = d \sqrt{\frac{C \cdot P}{S}}\]

Where $d$ = header port width, $C$ = 0.33 (simply supported).

Nozzle (cylindrical shell, same as parting sheet with nozzle radius).

Thermal Fatigue Assessment

Per API 662 Part II guidelines:

Computes thermal stress: $\sigma = E \cdot \alpha \cdot \Delta T$
Uses Al S-N curve (endurance limit 35 MPa at 10⁷ cycles, slope m=4)
Reports fatigue utilisation ratio: design cycles / allowable cycles

Usage

BAHXMechanicalDesign mech = new BAHXMechanicalDesign(lngHX);
mech.setMaxOperationPressure(50.0);  // bara
mech.setMaxOperationTemperature(273.15 + 30.0);  // K
mech.calcDesign();

double partingSheet = mech.getRequiredPartingSheetThicknessMm();
double coreWeight = mech.getCoreWeightKg();
String json = mech.toJson();

Cost Estimation (BAHXCostEstimator)

Package: neqsim.process.costestimation.heatexchanger

Weight-based and area-based cost model for BAHX.

Cost Model

Component	Rate	Basis
Core material (Al)	$8/kg	Raw aluminium
Manufacturing	$25/kg	Forming, assembly
Header/nozzle surcharge	$15/kg	Additional to material
Brazing	$120/m²	Vacuum brazing
Testing & inspection	12%	Of material + manufacturing
Engineering overhead	1.15×	Applied to PEC
LNG installation factor	3.5×	Installed cost
Contingency	1.10×	Applied to installed cost
Annual maintenance	2%	Of equipment cost

Usage

BAHXCostEstimator cost = new BAHXCostEstimator(mechDesign);
double equipment = cost.getEquipmentCostUSD();
double installed = cost.getInstalledCostUSD();
double specific = cost.getSpecificCostPerM2();
Map<String, Object> breakdown = cost.getCostBreakdown();

Design Feasibility Report

Package: neqsim.process.mechanicaldesign.heatexchanger

Combines mechanical design, cost estimation, supplier matching, and feasibility checks into a single report.

Verdict Categories

Verdict	Meaning
`FEASIBLE`	All checks pass, no blockers or warnings
`FEASIBLE_WITH_WARNINGS`	No blockers, but warnings present
`NOT_FEASIBLE`	At least one BLOCKER issue

Feasibility Checks

General checks:

Temperature range (operating vs. supplier capability)
Pressure range
Heat transfer area range
Cost reasonableness (< $50M equipment cost)
Supplier availability

BAHX-specific checks:

Mercury risk (aluminium LME)
Freeze-out risk (CO₂ solidification)
Thermal stress (gradient limit)
MITA adequacy (> 1.0 °C)
Thermal fatigue utilisation (< 1.0)
Exergy efficiency (> 50%)

Supplier Database

The report matches against HeatExchangerSuppliers.csv containing 18 vendors. Key BAHX suppliers:

Chart Industries — plate-fin BAHX, -269 °C to +65 °C, 100–300,000 kW, 5–30,000 m²
Other vendors matched on type, duty, area, pressure, and temperature ranges

Usage

// Direct construction
HeatExchangerDesignFeasibilityReport report =
    new HeatExchangerDesignFeasibilityReport(lngHX);
report.setDesignStandard("ALPEMA / ASME VIII Div.1");
report.setAnnualOperatingHours(8400);
report.generateReport();

String verdict = report.getVerdict();
double pec = report.getPurchasedEquipmentCostUSD();
String json = report.toJson();

// Or use the convenience method
HeatExchangerDesignFeasibilityReport report = lngHX.generateFeasibilityReport();

JSON Report Structure

{
  "verdict": "FEASIBLE_WITH_WARNINGS",
  "operatingPoint": {
    "dutyKW": 45000.0,
    "hotInletTempC": 30.0,
    "coldInletTempC": -33.0,
    "maxPressureBara": 50.0,
    "estimatedAreaM2": 8500.0
  },
  "mechanicalDesign": {
    "partingSheetMm": 1.2,
    "headerThicknessMm": 15.4,
    "coreWeightKg": 4200,
    "totalWeightKg": 5100
  },
  "costEstimation": {
    "purchasedEquipmentCostUSD": 295000,
    "installedCostUSD": 1135000,
    "specificCostPerM2USD": 34.7,
    "annualMaintenanceCostUSD": 5900
  },
  "matchingSuppliers": [...],
  "bahxDiagnostics": {
    "mita_C": 3.2,
    "secondLawEfficiency": 0.91,
    "hasFreezeOutRisk": false,
    "hasThermalStressWarning": false,
    "mercuryRiskPresent": false
  },
  "issues": [
    {"severity": "WARNING", "category": "thermal_stress", "message": "..."}
  ]
}

Physical Background

Composite Curves and MITA

In a multi-stream heat exchanger, composite curves represent the aggregated temperature-duty relationship of all hot streams (being cooled) and all cold streams (being heated). The minimum internal temperature approach (MITA) is the closest point between these curves and represents the thermodynamic bottleneck.

For LNG exchangers, the MITA typically occurs at:

MR evaporation onset (where the cold curve flattens due to latent heat)
Methane condensation (where the hot curve flattens)

Typical MITA values: 1.5–3.0 °C for large MCHE, 3.0–5.0 °C for smaller exchangers.

Exergy Analysis

Exergy destruction quantifies thermodynamic irreversibility:

\[\dot{E}_{dest,zone} = T_0 \cdot \dot{S}_{gen,zone}\]

Where $T_0$ is the dead-state temperature and $\dot{S}_{gen}$ is the entropy generation rate. The second-law efficiency is:

\[\eta_{II} = \frac{\dot{E}_{gained,cold}}{\dot{E}_{released,hot}}\]

Typical η_II for LNG MCHE: 85–95%.

Manglik-Bergles Correlations

For offset-strip fins (OSF), valid for $120 < Re < 10{,}000$:

\[j = 0.6522 \cdot Re^{-0.5403} \cdot \alpha^{-0.1541} \cdot \delta^{0.1499} \cdot \gamma^{-0.0678} \cdot F_j\] \[f = 9.6243 \cdot Re^{-0.7422} \cdot \alpha^{-0.1856} \cdot \delta^{0.3053} \cdot \gamma^{-0.2659} \cdot F_f\]

Where $\alpha = s/h$, $\delta = t/l_s$, $\gamma = t/s$ are dimensionless fin geometry ratios.

Mercury Risk in BAHX

Mercury attacks aluminium through liquid metal embrittlement (LME), forming an Hg-Al amalgam that destroys brazed joints. Industry specification for feed gas to aluminium BAHX: < 10 ppb Hg (some operators specify < 0.01 µg/Nm³). Mitigation: activated carbon or metal sulfide bed upstream.

Applicable Standards

Standard	Application
ASME VIII Div.1, UG-27	Pressure vessel wall thickness
ALPEMA	BAHX design and manufacturing
API 662 Part II	Plate-type heat exchanger thermal fatigue
ISO 14692	GRP piping systems (if applicable)

Class	Package	Description
`MultiStreamHeatExchanger2`	`process.equipment.heatexchanger`	Parent class with NR solver
`BAHXMechanicalDesign`	`process.mechanicaldesign.heatexchanger`	ASME VIII wall thickness + fatigue
`BAHXCostEstimator`	`process.costestimation.heatexchanger`	BAHX CAPEX/OPEX model
`HeatExchangerDesignFeasibilityReport`	`process.mechanicaldesign.heatexchanger`	Combined feasibility report
`HeatExchangerType.PLATE_FIN`	`process.mechanicaldesign.heatexchanger`	BAHX geometry model enum

References

Manglik, R.M. and Bergles, A.E. (1995). “Heat transfer and pressure drop correlations for the rectangular offset-strip fin compact heat exchanger.” Experimental Thermal and Fluid Science, 10(2), pp.171-180.
Lockhart, R.W. and Martinelli, R.C. (1949). “Proposed correlation of data for isothermal two-phase, two-component flow in pipes.” Chemical Engineering Progress, 45(1), pp.39-48.
ALPEMA Standards (2010). The Standards of the Brazed Aluminium Plate-Fin Heat Exchanger Manufacturers’ Association, 3rd Edition.
ASME Boiler & Pressure Vessel Code, Section VIII Division 1 (2021).
API Standard 662, Part II (2016). Plate Heat Exchangers for General Refinery Services.

LNG Cryogenic Multi-Stream Heat Exchanger

Overview

When to Use

Key Capabilities

Architecture

Quick Start

Java

Python (Jupyter)

Inner Classes

FinGeometry

CoreGeometry

TransientPoint

Configuration Reference

Zone and Type Settings

Pressure Drop (P2)

Exergy Settings (P3)

Adaptive Refinement (P4)

Fin Geometry (P5)

Maldistribution (P10)

Core Geometry (P8)

Transient (P7)

Thermal Stress

Result Getters

Temperature Approach

Composite Curves

Exergy

UA

Pressure Drop Correlations

Freeze-Out (P9)

Temperature Profiles

Thermal Stress

Mercury Risk

Cool-Down Transient

Mechanical Design (BAHXMechanicalDesign)

Materials

Wall Thickness Calculations

Thermal Fatigue Assessment

Usage

Cost Estimation (BAHXCostEstimator)

Cost Model

Usage

Design Feasibility Report

Verdict Categories

Feasibility Checks

Supplier Database

Usage

JSON Report Structure

Physical Background

Composite Curves and MITA

Exergy Analysis

Manglik-Bergles Correlations

Mercury Risk in BAHX

Applicable Standards

Related Classes

References