Thermodynamic models¶

package_for turns component names into a ready property package for any of the methods in METHODS (cubic, NRTL, UNIQUAC, UNIFAC, Dortmund, PC-SAFT, or a reference fluid), with explicit parameter provenance. Every model= argument in fugacio.sim takes its result. The page also covers the lightweight modified-Raoult helpers for quick ideal-ish estimates.

Model builders¶

models ¶

Model bridge: turn component names + a method choice into a property package.

A flowsheet works in component names. package_for resolves those names to the curated constants (reusing the cached lookup in fugacio.sim.properties), assembles the activity model from the curated binary database (NRTL / UNIQUAC) or predictive group contribution (UNIFAC / modified UNIFAC), or the PC-SAFT and reference-fluid parameters, and returns a ready, differentiable fugacio.thermo.PropertyPackage (equilibrium and energy) with explicit parameter provenance. Its result is what every unit operation, the rigorous column, the phase diagrams, and the equation-oriented engine accept through their model argument, so a flowsheet switches from Peng-Robinson to NRTL by changing one method name, and stays end-to-end differentiable, including with respect to the thermodynamic parameters.

Classes:

Name	Description
`UnifacModel`	An `ActivityModel` adapter over predictive UNIFAC.

Functions:

Name	Description
`resolve_package`	Pick the property package a unit should use for `components`.
`helmholtz_package_for`	One-component reference-fluid package for a named pure fluid (water, CO2, ...).
`package_for`	Build the property package for named `components` by `method`.

UnifacModel `dataclass` ¶

UnifacModel(components: tuple[str, ...], dortmund: bool)

An ActivityModel adapter over predictive UNIFAC.

Wraps fugacio.thermo.unifac_activity (classic, Hansen VLE parameters) or fugacio.thermo.modified_unifac_activity (Dortmund, T-dependent) so that group-contribution predictions present the same ln_gamma(x, T) API as the fitted activity models. Carries no fitted leaves: it is a pure predictor keyed by the (static) component names.

Methods:

Name	Description
`ln_gamma`	Log activity coefficients predicted by (modified) UNIFAC.

ln_gamma ¶

ln_gamma(x: Array, t: ArrayLike) -> Array

Log activity coefficients predicted by (modified) UNIFAC.

resolve_package ¶

resolve_package(
    components: Sequence[str], model: Model = None
) -> PropertyPackage

Pick the property package a unit should use for components.

model wins when given; otherwise the Peng-Robinson default.

Raises:

Type	Description
`TypeError`	if `model` isn't a property package.
`ValueError`	if the package's components don't match the stream's.

helmholtz_package_for ¶

helmholtz_package_for(component: str) -> HelmholtzPackage

One-component reference-fluid package for a named pure fluid (water, CO2, ...).

The name is resolved through fugacio.thermo.reference_fluid, so any of the 26 vendored multiparameter formulations is accepted.

package_for ¶

package_for(
    components: Sequence[str],
    method: str = "pr",
    *,
    parameter_policy: str = "strict",
    measured_fit: Any = None,
    **options: Any,
) -> PropertyPackage

Build the property package for named components by method.

This is the constructor a flowsheet author reaches for; every unit operation, the rigorous column, the two-sided heat exchanger, the phase diagrams, and the equation-oriented engine take its result through their model argument.

Parameters:

Name	Type	Description	Default
`components`	`Sequence[str]`	Component names (from the curated database).	required
`method`	`str`	One of `METHODS`: `"pr"` / `"srk"` / `"rk"` / `"vdw"`: phi-phi cubic package (options: `kij`, `use_database_kij`); `"nrtl"` / `"uniquac"`: gamma-phi package with the curated binary parameters (options: `vapor`, `poynting`, `phi_saturation`, `eos`, `kij`, and `alpha_default` for NRTL); `"unifac"` / `"dortmund"`: gamma-phi package with predictive (modified) UNIFAC (same options, no fitted parameters); `"pcsaft"`: PC-SAFT package (options: `kij`, `use_database_kij`); `"iapws"`: a single reference fluid (one component only).	`'pr'`
`parameter_policy`	`str`	`"strict"` (default) raises for missing NRTL/UNIQUAC interactions; `"allow_ideal"` explicitly permits zero interactions. Cubic zero-kij assumptions remain visible in the package evidence.	`'strict'`
`measured_fit`	`Any`	A converged `fugacio.thermo.measured_regression.MeasuredFit` for binary NRTL. Its observed bounds travel with the package, and checked calculations reject extrapolation unless their acceptance policy explicitly permits it.	`None`
`**options`	`Any`	Method options as listed above.	`{}`

Returns:

Type	Description
`PropertyPackage`	A `fugacio.thermo.PropertyPackage` with explicit provenance.

Raises:

Type	Description
`ValueError`	For an unknown method, an invalid policy, or an unusable fit.
`TypeError`	For an option the method doesn't accept.
`KeyError`	For missing curated parameters under the strict policy.

Modified-Raoult helpers¶

vle ¶

Vapor-liquid equilibrium for binary mixtures (modified Raoult's law).

A deliberately small but real vertical slice that sits on top of fugacio.thermo: it combines Antoine vapor pressures with Margules activity coefficients to compute a bubble-point pressure. Everything is differentiable end-to-end with respect to composition, temperature, and the activity-model parameters.

Functions:

Name	Description
`antoine_psat`	Saturation pressure from the base-10 Antoine equation.
`bubble_pressure`	Bubble-point pressure and vapor composition for a binary at fixed `T`, `x`.

antoine_psat ¶

antoine_psat(
    temperature: ArrayLike,
    a: ArrayLike,
    b: ArrayLike,
    c: ArrayLike,
) -> Array

Saturation pressure from the base-10 Antoine equation.

log10(Psat) = a - b / (temperature + c)

Pressure and temperature units follow whatever convention the Antoine constants were fit in; Fugacio does not impose one here.

bubble_pressure ¶

bubble_pressure(
    x1: ArrayLike,
    temperature: ArrayLike,
    antoine1: Antoine,
    antoine2: Antoine,
    a12: ArrayLike = 0.0,
    a21: ArrayLike = 0.0,
) -> tuple[Array, Array]

Bubble-point pressure and vapor composition for a binary at fixed T, x.

Uses modified Raoult's law p_i = x_i * gamma_i * Psat_i with two-parameter Margules activity coefficients. Setting a12 = a21 = 0 recovers ideal (Raoult's law) behaviour.