NeqSim provides experimental fundamental Helmholtz equations for pure solid argon and phase-I para-hydrogen. Use these models when you need a reproducible solid-state property calculation or a pure para-hydrogen freezing point. They are not general mixture solid solutions, precipitation models, kinetic nucleation models, or design-certification tools.

The two supported workflows have different owners:

Validity and units

Model Temperature Absolute pressure Intended use
Solid argon Above 0 K through 300 K Above 0 through 160,000 bara (16 GPa) Pure solid-state properties
Solid para-hydrogen Above 0 K through 200 K Above 0 through 100,000 bara (10 GPa) Pure solid state and para-hydrogen freezing equilibrium

Constructor and equation pressures use bara. SolidHelmholtzState returns molar volume in m3/mol, energies in J/mol, entropy and molar heat capacities in J/(mol K), and the natural logarithm of the fugacity coefficient. Phase-level extensive getters multiply these molar properties by the phase mole inventory.

Both equations solve for a mechanically stable volume root and reject invalid or out-of-range states. Treat a thrown exception or a non-converged freezing result as a failed calculation; do not extrapolate silently.

Pure solid-argon state

Use the calibrated system-owned equation when absolute Gibbs energy or entropy matters. A raw ArgonSolidHelmholtzEquation does not contain the reference shifts recovered for the published sample state.

import neqsim.thermo.phase.PhaseSolidHelmholtzEos;
import neqsim.thermo.system.SystemArgonSolidHelmholtzEos;
import neqsim.thermo.util.solid.SolidHelmholtzState;

SystemArgonSolidHelmholtzEos solid =
    new SystemArgonSolidHelmholtzEos(70.0, 10.0);
solid.init(3);

PhaseSolidHelmholtzEos phase =
    (PhaseSolidHelmholtzEos) solid.getPhase(0);
SolidHelmholtzState state = phase.getSolidState();

double molarVolume = state.getMolarVolume();
double heatCapacityCp = state.getHeatCapacityCp();

At 70 K and 10 bara (1 MPa), the current regression obtains approximately 2.39546e-5 m3/mol and 30.2861 J/(mol K). These values reproduce the rounded Table 8 state used by the solid-argon implementation; they do not validate another substance or a mixed phase.

Para-hydrogen freezing point

Construct the Leachman system for the explicit "para-hydrogen" component with solid checking enabled. freezingPointTemperatureFlashResult() returns convergence, temperature, iteration count, residual, controlling component, and a failure reason. The call declares IsNaNException; catch it or declare it in the surrounding method.

import neqsim.thermo.system.SystemLeachmanEos;
import neqsim.thermodynamicoperations.ThermodynamicOperations;
import neqsim.thermodynamicoperations.flashops.saturationops.FreezingPointResult;

SystemLeachmanEos hydrogen =
    new SystemLeachmanEos(13.6, 0.07042, "para-hydrogen", true);
hydrogen.setSolidPhaseCheck("para-hydrogen");

ThermodynamicOperations operations =
    new ThermodynamicOperations(hydrogen);
FreezingPointResult result =
    operations.freezingPointTemperatureFlashResult();

if (!result.isConverged()) {
  throw new IllegalStateException(result.getFailureReason());
}
double freezingTemperatureK = result.getTemperature("K");
double equilibriumResidual = result.getResidual();

At the calibrated triple-point pressure, the regression converges to 13.8033 K with an absolute dimensionless Gibbs-equilibrium residual below 1e-10. The operation updates the system temperature to the converged result.

Do not substitute "hydrogen" or "ortho-hydrogen" when the Helmholtz solid model is required. Those spin-isomer choices retain the established empirical pure-solid phase. For an unsuccessful result, getTemperature(...) throws; inspect getFailureReason() instead.

API ownership

API Contract
SystemArgonSolidHelmholtzEos(double, double) Calibrated one-phase solid-argon system; K and bara
PhaseSolidHelmholtzEos.getSolidState() Last initialized immutable molar state
SolidHelmholtzState getters SI molar properties and ln(phi)
SystemLeachmanEos(double, double, String, boolean) Pure hydrogen spin-isomer fluid system; true configures a solid phase
ThermodynamicOperations.freezingPointTemperatureFlashResult() Structured solid-fluid equilibrium outcome
FreezingPointResult.getTemperature(String) Converged temperature in a supported unit; throws after failure
SystemSolidHelmholtzEos Single-component extension point for a supplied solid equation

Model and engineering boundaries