Hydrocarbon Homogeneous Equilibrium Critical Mass Flux Calculator

Calculation sequence

1. Enter an equilibrium stagnation PT feed and a lower search pressure below 0.8 times the stagnation pressure. This lower value defines the numerical search interval; it is not automatically the actual backpressure or an assurance that the throat is bracketed.
2. At each trial pressure solve a fully checked equal-entropy PR state. Convert molar enthalpy to J/kg before calculating available kinetic energy, velocity and mass flux. Phase change is homogeneous and instantaneously equilibrated. This is distinct from locating the EOS critical point, which is not the nozzle choking condition.
3. Locate the largest of 31 sampled fluxes, require an interior bracket and refine the local maximum with a proven bounded optimizer. Test both neighboring pressures before returning the throat. An endpoint maximum or a failed entropy/phase query rejects the result; the tool never labels an unsearched low-pressure endpoint as choked.
4. At every returned state independently re-evaluate classical PR pressure, log fugacity and residual enthalpy/entropy. Require component balance <=2e-7, log-fugacity mismatch <=2e-5 and relative pressure residual <=2e-6. Reject vanishing phase fractions below 1e-6 and density separation below 1.1 for ordinary splits. These are numerical checks, not measured-PVT validation.
5. Calculations run locally in a dedicated WebAssembly worker. The advanced Python/scientific engine is a roughly 33 MB first download, separate from ordinary calculators; it is self-hosted and version pinned. No composition or measurements are sent to a calculation server. Save and file backups retain canonical inputs, while CSV/PDF include returned tables and source notes. The worker is released after idle time and failures never return partial results.

Worked check

The synthetic default 5 MPa, 400 K C1-C6 stagnation state has a bounded PR equilibrium maximum around 2.952383 MPa, 370.116736 K and 10799.618 kg/(m2.s), with throat speed about 293.202929 m/s. This ideal flux excludes discharge losses and is not an installed relief-device capacity.

Synthetic examples for reproducibility, not measured field results.

Assumptions and limitations

• Six components C1-C6, normal C4-C6, classical PR and all kij=0. No water, isomers, sour gas, heavy fractions, reactions, solids or volume translation. Use the expanded-mixture tools for their explicitly supported alternatives, not by inserting a new species in these fixed feed slots.
• Every flash trial must remain at 180-450 K and 0.1-10 MPa absolute, with consistent mole fractions summing to one. Near-critical, vanishing-phase or failed closure states are rejected. Single-phase states are not given an invented vapor quality. Independent engine agreement is not experimental validation.
• Instantaneous equilibrium and the documented steady balance only. No machinery efficiency, transient behavior, separator sizing, phase residence time, mechanical safety approval or claimed field calibration. A rejected or unbracketed root is not extrapolated into an unsupported range.
• Ideal homogeneous equilibrium nozzle, negligible inlet speed, equal phase velocities, reversible adiabatic flow and no friction, discharge coefficient or relaxation time. Not a relief-valve, short-orifice, erosion or multiphase choke design model. Nonequilibrium and metastability can materially change actual discharge.
• The whole pressure search and all entropy trial states must remain in the EOS envelope. Only one resolved interior maximum is reported; no global assurance outside the specified interval. No nozzle geometry, backpressure flow curve, sound-speed validation or equipment capacity certification is supplied.

Sources and maintenance

Published by PetroCalcHub Team. Implementation and source checks: 2026-10-22. This does not claim independent expert review.

• Thermo: FlashVL/FlashVLN stability and phase splitting (runtime pinned to 0.6.0)
• CoolProp v8.0.0: pinned cubic pure-component parameters
• Travis et al., ICHS 2011: isentropic direct-evaluation mass flux, equations 12-17 (not the paper's nonequilibrium extension)

Related tools and references