Dew-point calculations locate a phase-appearance boundary for a defined gas composition and pressure. They are sensitive to sampling, water or heavy-end content, model selection, binary-interaction parameters, and the specified pressure. Treat NeqSim results as calculation evidence, not as proof that a sample, measurement procedure, or delivery point complies with a standard or contract.

Choose the maintained calculation path

Engineering question Current class Current boundary
Water dew point at one pressure Standard_ISO18453 Converts a non-GERG-water input composition to an internal SystemGERGwaterEos and runs waterDewPointTemperatureFlash()
Legacy database-backed water-dew-point rows Draft_ISO18453 Retained for compatibility in BaseContract; new direct calculations should use Standard_ISO18453
Hydrocarbon dew point at the class’s fixed pressure BestPracticeHydrocarbonDewPoint Copies non-water components into an internal SRK system, applies mixing rule 2, and calculates at 50 bara
Dew-point curve, cricondentherm, or cricondenbar Phase-envelope or saturation operations The fixed-pressure standards classes do not calculate these envelope extrema

A dew point at 50 bara is not the cricondentherm. The cricondentherm is the maximum temperature on the complete phase envelope and generally occurs at a pressure determined by the envelope calculation.

Water dew point with Standard_ISO18453

The current class is documented in source as superseding Draft_ISO18453. It accepts any SystemInterface; when the input is not already a GERG-water system, the constructor copies the phase-0 component names and mole amounts into a new SystemGERGwaterEos.

The calculation pressure is absolute pressure in bara. Use setPressure(double) or setReferencePressure(double) before calculate(). The primary result key is dewPointTemperature; the no-unit getter returns degrees Celsius, while the two-argument getter recognizes "K" and "F" conversions.

Executable Java 8 example

import neqsim.standards.gasquality.Standard_ISO18453;
import neqsim.thermo.system.SystemGERGwaterEos;
import neqsim.thermo.system.SystemInterface;

SystemInterface wetGas = new SystemGERGwaterEos(268.15, 20.0);
wetGas.addComponent("methane", 0.9);
wetGas.addComponent("water", 0.0000051);
wetGas.createDatabase(true);
wetGas.setMixingRule(8);
wetGas.init(0);

Standard_ISO18453 waterDewPoint = new Standard_ISO18453(wetGas);
waterDewPoint.setPressure(70.0);
waterDewPoint.calculate();

double waterDewPointC =
    waterDewPoint.getValue("dewPointTemperature", "C");
double calculationPressureBara = waterDewPoint.getValue("pressure");

For the repository fixture, the result is approximately -21.776 °C at 70 bara. That number validates the documented API and bundled model behavior; it is not a generic natural-gas expectation.

Water-dew-point contract decisions

Apply the governing limit explicitly in the project layer:

double maximumWaterDewPointC = -8.0;
boolean withinWaterDewPointLimit =
    Double.isFinite(waterDewPointC)
        && waterDewPointC <= maximumWaterDewPointC;

isOnSpec() compares the calculated value with getSalesContract().getWaterDewPointTemperature(). The default embedded BaseContract limit is not evidence for a particular delivery point. setDewPointTemperatureSpec(double) stores a separate class field that the current isOnSpec() implementation does not read. Prefer the explicit comparison above unless a verified ContractInterface has been attached.

A failed flash is logged by the current class rather than rethrown. Callers should therefore reject non-finite or physically implausible output and retain the input composition, model, pressure, NeqSim version, and calculation diagnostics.

Hydrocarbon dew point with BestPracticeHydrocarbonDewPoint

The constructor copies every phase-0 component except exact component name water into a new SystemSrkEos, applies mixing rule 2, and initializes an internal calculation system. It does not reuse the input fluid’s EOS or fitted binary-interaction parameters.

The current implementation has a fixed specPressure of 50.0 bara. calculate() resets the internal system to that pressure. The inherited setReferencePressure(double) method does not change specPressure, and changing the pressure of the input fluid after construction does not change the calculation pressure.

Executable Java 8 example

import neqsim.standards.gasquality.BestPracticeHydrocarbonDewPoint;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

SystemInterface richGas = new SystemSrkEos(293.15, 70.0);
richGas.addComponent("methane", 0.85);
richGas.addComponent("ethane", 0.05);
richGas.addComponent("propane", 0.03);
richGas.addComponent("i-butane", 0.01);
richGas.addComponent("n-butane", 0.015);
richGas.addComponent("i-pentane", 0.005);
richGas.addComponent("n-pentane", 0.005);
richGas.addComponent("n-hexane", 0.003);
richGas.addComponent("nitrogen", 0.02);
richGas.addComponent("CO2", 0.012);
richGas.setMixingRule("classic");

BestPracticeHydrocarbonDewPoint hydrocarbonDewPoint =
    new BestPracticeHydrocarbonDewPoint(richGas);
hydrocarbonDewPoint.calculate();

double hydrocarbonDewPointC =
    hydrocarbonDewPoint.getValue(
        "hydrocarbondewpointTemperature", "C");
double calculationPressureBara =
    hydrocarbonDewPoint.getValue("pressure");

The result should be finite and the reported calculation pressure is 50 bara. The two-argument getter does not currently convert hydrocarbon-dew-point units; use "C" and report degrees Celsius.

Do not use BestPracticeHydrocarbonDewPoint.isOnSpec() for a hydrocarbon limit. The current method compares the hydrocarbon result with the attached contract’s water-dew-point temperature. Apply the verified hydrocarbon limit explicitly:

double maximumHydrocarbonDewPointC = -2.0;
boolean withinHydrocarbonDewPointLimit =
    Double.isFinite(hydrocarbonDewPointC)
        && hydrocarbonDewPointC <= maximumHydrocarbonDewPointC;

The value above only illustrates caller-owned comparison logic. Replace it with the controlled limit, pressure range, uncertainty, and rounding rules from the governing agreement.

Curves and envelope extrema

Do not build a pressure curve by changing the source fluid pressure and repeatedly constructing BestPracticeHydrocarbonDewPoint; every instance still calculates at 50 bara. For a curve or envelope extremum, use a thermodynamic phase-envelope or saturation workflow that exposes pressure as a calculation input, then validate the selected EOS and characterization against measured dew-point data.

For hydrocarbon-dew-point work, preserve and qualify:

For water-dew-point work, also qualify water-content measurement, acid gases, glycols or inhibitors, salinity where relevant, and the applicability range of the chosen water model.

Reporting and engineering boundary

Every reported result should include:

  1. sample or case identity and composition basis;
  2. NeqSim version and class name;
  3. EOS, mixing rule, characterization, and parameter provenance;
  4. absolute calculation pressure in bara;
  5. dew-point temperature and unit;
  6. convergence or failure diagnostics;
  7. governing standard or contract edition from a controlled source;
  8. project limit, uncertainty, rounding rule, and accountable reviewer.

Class names such as Standard_ISO18453 do not establish that sampling, instrumentation, calibration, data reduction, or the complete requirements of a licensed standard have been satisfied.