A MATLAB/Octave toolbox for PVT (Pressure-Volume-Temperature) calculations using cubic equations of state. Supports vapor-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE), phase stability testing, and residual enthalpy calculations for multicomponent mixtures.

% 1. Initialise (adds all subdirectories to path)
PVTinitialize()

% 2. Load components from the built-in database
[comp, flag] = addComponents({'CH4', 'C2H6', 'C10H22'});

% 3. Create a mixture at T = 300 K, P = 5 MPa
mix = addMixture(comp, 300, 5e6);
mix.mole_fraction = [0.6 0.2 0.2];

% 4. Configure thermodynamic model (defaults: PR EOS, vdW mixing)
thermo = addThermo();

% 5. Run a stability test
[flag, SL, SV, result] = stabilityTest(mix, thermo);
disp(result.message)

% 6. Run a VLE flash
opts = FlashOptions();
[y, x, V] = vleflash(mix, thermo, opts);
fprintf('Vapor fraction: %.4f\n', V)

All classes are defined in Classes/ and are available after PVTinitialize().

The Mixture constructor creates a fully-initialised BIP object with all matrices set to zero. Set non-zero parameters by assigning individual fields:

mix = addMixture(comp, T, p);

% EOS kij parameters
mix.bip.EOScons = [0 -0.05; -0.05 0];

% NRTL parameters  (A + B*T + C*T² + D/T + E*ln(T))
mix.bip.NRTLcons    = [0 A12; A21 0];     % [J/mol]
mix.bip.NRTLtdep    = [0 B12; B21 0];
mix.bip.NRTLalfa    = [0 0.3; 0.3 0];     % non-randomness

All BIP fields: EOScons, EOStdep, NRTLcons, NRTLtdep, NRTLtdep2, NRTLtdepm1, NRTLtdeplog, NRTLalfa, Wilsoncons, Wilsontdep, UNIQUACcons, UNIQUACtdep, UNIQUACR, UNIQUACQ.

stability_flag values: 1 = stable (trivial), 2 = unstable (non-trivial), 3 = inconclusive.
result.overall: 'stable' | 'unstable' | 'inconclusive'.

Basic signature: [liquid_z, vapor_z, fugacity, HR] = EOS(mixture, thermo)
Extended signature (5th output): [..., props] = EOS(mixture, thermo) where props contains HR, SR, GR, VR, Cp_R, Cv_R.

Residual properties (from the optional props struct):

All share the signature [gErt, gama] = Model(T, x, component, bip).

All examples are in the Examples/ folder and can be run after PVTinitialize().

Run the test suite from the project root:

PVTinitialize()
cd Tests
run_all_tests

Tests cover: class construction, EOS Z-factors and residual properties, VLE flash vs experimental data, stability test stable/unstable cases, and bubble/dew point calculations.

Tested with Octave 7+. All classes use value semantics (no handle). No MATLAB-only toolboxes are required.

BSD 2-Clause — see source file headers.
Copyright © 2012–2013 Ali Akbar Eftekhari.