Vapor-liquid equilibrium (flash)

Stability test

stability_2ph(eos, c, [K])

Determine if mixture is single-phase stable under conditions c.

This is done using a version of Michelsen's stability test.

Flash using Newton's method for zero solve.

Only conditionally convergent, but has better convergence rate than SSI.

Flash method that uses successive subtition.

Unconditionally convergent, does not require derivatives, but is very slow around critical regions.

SSINewtonFlash([swap_iter = 5])

Perform a number of SSI iterations, followed by Newton until convergence.

flash_2ph!(storage, K, eos, c, [V]; <keyword arguments>)

Non-allocating version of flash_2ph where storage is pre-allocated.

Useful if you are performing many flashes of the same system with varying conditions.

Arguments

storage: Should be output from flash_storage(eos, c, method = method). Preallocated storage.

Remaining arguments documented in flash_2ph.

Keyword arguments

update_forces = true: Update the p, T dependent forces in storage initially.

flash_2ph(eos, c, [K], [V]; <keyword arguments>)

Perform two-phase flash with a given EOS under a set of specific conditions. Returns vapor fraction. Modifies K in-place.

Given a mixture with pressure, temperature and mole fractions, this routine performs a vapor-liquid equilibrium calculation after a stability test.

Two outcomes are possible:

A single-phase condition prevails (returned vapor fraction is NaN) and a single phase (liquid or vapor) is stable.
A two-phase condition is possible. The routine produces K-values and vapor fraction so that the following holds:
1. Isofugacity constraint for all components ($f_{li} = f_{vi}$)
2. Molar balance for all components ($(1-V) x_i - V y_i - z_i$)
3. Unity condition ($\sum_i (x_i - y_i) = 0$)

Arguments

eos: the equation-of-state to be used for the flash
c: conditions to flash the mixture at on the form (p = 10e5, T = 303.15, z = [0.5, 0.3, 0.2])
K: optionally a buffer of length number_of_components(eos) used to hold K-values. Modified in-place.
V: optionally the initial guess for V. If this value is not NaN, the stability check will be skipped.

Keyword arguments

method = SSIFlash(): Flash method to use. Can be SSIFlash(), NewtonFlash() or SSINewtonFlash().
tolerance = 1e-8: Tolerance for the convergence criterion. Relative to $\|1-R_i\|_\infty$ where $R_i = f_{il}/f_{iv}$
maxiter = 10000: Maximum nubmer of iterations for both stability tests and the main flash.
verbose = false: Emit extra information during solve.
extra_out = false: Return (V, K, conv) where conv contains iterations and oncergence status instead of just V.

flash_storage(eos, [c]; <keyword arguments>)

Pre-allocate storage for flash_2ph!.

Arguments

eos: the equation-of-state to be used for the flash
c: conditions for the mixture. Types in conditions must match later usage (e.g. for use with ForwardDiff).

Keyword arguments

method = SSIFlash(): Flash method to use. Can be SSIFlash(), NewtonFlash() or SSINewtonFlash().
static_size = false: Use SArrays and MArrays for fast flash, but slower compile times.
inc_jac: Allocate storage for Newton/Jacobian. Required for Newton (and defaults to true for that method) or for diff_externals.
diff_externals = false: Allocate storage for matrix inversion required to produce partial derivatives of flash using set_partials.