Mixtures

A Mixture holds a multi-component fluid and exposes the same thermodynamic and transport accessors as a Species. There are two ways to build one:

1. Flat construction, where you name the leaf components and give their composition directly.
2. Combining, where you assemble a mixture from existing Species, other Mixtures, or chemical names, given as constituent => amount pairs.

The state variables T and P follow the same conventions as Species. They default to STP and accept either bare K/Pa numbers or Unitful quantities, unless an adiabatic mix solves for the temperature instead.

Flat construction

List the component names and supply the composition through one of thermo's composition keywords: mole fractions zs, mass fractions ws, or liquid and gas volume fractions Vfls and Vfgs.

using PyThermo, Unitful

Mixture(["N2", "O2", "Ar"]; zs = [0.78, 0.21, 0.01])
Mixture(["water", "ethanol"]; ws = [0.6, 0.4], T = 60u"°C")

As a shorthand for the mole-fraction case, pass a vector of "name" => mole_fraction pairs:

julia> air = Mixture(["N2" => 0.79, "O2" => 0.21])
Mixture(79% N2, 21% O2, 298.1 K, 1.013e+05 Pa)

Fractions need not sum to one, since they are normalized.

Combining species and mixtures

A Mixture can also be assembled from a list of constituent => amount pairs, where each constituent is a Species, another Mixture, or a chemical-name String, and amount is a relative quantity (the amounts need not sum to one). Every constituent is flattened to its components, and like species are merged by CAS number, so a component appearing in more than one constituent is combined into a single entry rather than duplicated:

julia> air = Mixture(["N2" => 0.79, "O2" => 0.21]);

julia> Mixture([air => 0.8, Species("acetone") => 0.2])
Mixture(63.2% N2, 16.8% O2, 20% acetone, 298.1 K, 1.013e+05 Pa)

julia> # air already contains N2; adding more merges instead of duplicating

julia> Mixture([air => 0.5, Species("N2") => 0.5])
Mixture(89.5% N2, 10.5% O2, 298.1 K, 1.013e+05 Pa)

A bare string is treated as Species(name), so constituents can be mixed and matched freely, and a string-only list reproduces the flat "name" => mole_fraction behaviour:

Mixture([air => 0.8, "acetone" => 0.2])   # string is Species("acetone")

By default the combined mixture is built at STP (override with the usual T= and P= keywords). Only the constituents' composition is used; their individual states are ignored unless you opt into adiabatic mixing.

Mole vs mass basis

The basis keyword sets how each constituent's amount is interpreted. :mole, the default, treats amounts as relative moles, while :mass treats them as relative masses. The composition is always displayed as mole fractions, so the two bases give different results for the same numbers:

julia> Mixture([air => 0.8, Species("acetone") => 0.2])
Mixture(63.2% N2, 16.8% O2, 20% acetone, 298.1 K, 1.013e+05 Pa)

julia> Mixture([air => 0.8, Species("acetone") => 0.2]; basis = :mass)
Mixture(70.3% N2, 18.7% O2, 11% acetone, 298.1 K, 1.013e+05 Pa)

This is distinct from the flat constructor's zs and ws keywords. Those give the final leaf-component fractions directly, whereas basis governs how the per-constituent amounts are split, and each constituent may expand into several components. Use whichever matches how the quantity is known: :mole for a fluid metered by molar flow, :mass for one weighed out.

Adiabatic mixing

Passing adiabatic = true performs a constant-pressure, enthalpy-conserving mix. Instead of placing the result at a chosen temperature, the constituents' temperatures, phases, heat capacities and latent heats are accounted for and the equilibrium temperature is solved for, so T may not be given.

The headline case is evaporative cooling. Mixing room-temperature liquid acetone into air lets the acetone evaporate, drawing its heat of vaporization from the gas and dropping the temperature well below 298 K, leaving a two-phase state:

julia> air = Mixture(["N2" => 0.79, "O2" => 0.21]);

julia> mix = Mixture([air => 0.85, Species("acetone") => 0.15]; adiabatic = true)
Mixture(67.2% N2, 17.8% O2, 15% acetone, 263.0 K, 1.013e+05 Pa)

julia> phase(mix)
:two_phase

When no phase change occurs the result is a plain sensible-heat balance. For example, equal moles of argon at 300 K and nitrogen at 500 K equilibrate near 417 K, weighted toward the higher heat capacity of the diatomic:

julia> Ar = Species("Ar", T = 300u"K"); N2 = Species("N2", T = 500u"K");

julia> Mixture([Ar => 0.5, N2 => 0.5]; adiabatic = true)
Mixture(50% Ar, 50% N2, 417.2 K, 1.013e+05 Pa)

The basis keyword applies here too. :mass conserves mass-specific enthalpy through thermo's H flash rather than molar Hm. Because both bases describe the same physical system, equivalent amounts reach the same equilibrium temperature.

Pressure and convergence

If P is omitted, it is inherited from the constituents when they all agree, and otherwise defaults to 1 atm; pass P= explicitly to pin it. The equilibrium is found by thermo's enthalpy flash, which lacks usable data for some systems, notably strongly supercritical species such as helium. When the flash fails to converge the constructor raises an informative ArgumentError rather than returning a malformed mixture. Build the mixture at an explicit T in that case.

Reference

Mixture(chemnames::Vector{String}; kwargs...)
Mixture(parts::Vector{<:Pair}; adiabatic=false, kwargs...)

julia> air = Mixture(["N2" => 0.79, "O2" => 0.21]);

julia> Mixture([air => 0.8, Species("acetone") => 0.2])
Mixture(63.2% N2, 16.8% O2, 20% acetone, 298.1 K, 1.013e+05 Pa)

julia> Mixture([air => 0.8, Species("acetone") => 0.2]; basis = :mass)
Mixture(70.3% N2, 18.7% O2, 11% acetone, 298.1 K, 1.013e+05 Pa)

julia> mix = Mixture([air => 0.85, Species("acetone") => 0.15]; adiabatic=true)
Mixture(67.2% N2, 17.8% O2, 15% acetone, 263.0 K, 1.013e+05 Pa)

julia> phase(mix)
:two_phase

julia> air = Mixture(["N2" => 0.78, "O2" => 0.21, "Ar" => 0.01])
Mixture(78% N2, 21% O2, 1% Ar, 298.1 K, 1.013e+05 Pa)

julia> soundspeed(air)
346.1345044609487 m s^-1