pifira

Pressure-based Inverse Fire-heat-flux and Radiative-Area analysis, with evidence-gated liquid-hydrogen utilities.

pifira is a research toolkit for two related process-safety workflows:

1. estimating heat input and effective flame-contact area from pressure and wall-temperature histories of pressurized LPG tanks; and
2. evaluating traceable liquid-hydrogen (LH2) ortho-para thermodynamics, state-point and pathwise composition screens, published Milenko/Petitpas kinetics, and a CoolProp HEOS nozzle closure.

No experimental or validation data are distributed in the repository, source archive, or wheel. The validation material belongs to its original publishers and depositors. VALIDATION_SOURCES.md identifies the original DOI or official download page, the evidence used, and the limits of each comparison.

Installation

python -m pip install pifira

Python 3.10 or newer is required. Plotting support is optional:

python -m pip install "pifira[plot]"

LPG inverse-analysis example

import pifira

tank = pifira.TankSpec(
    volume=0.619,
    fluid="HEOS::Propane[0.95]&n-Butane[0.05]",
    fill=0.70,
)

heat_W = pifira.heat_input(
    P1_bar=10.83,
    P2_bar=16.30,
    dt=544.5,
    tank=tank,
)

arc = pifira.effective_arc(
    angles_deg=[0, 90, 180, -90],
    T_wall_C=[271, 49, 39, 46],
    T_amb_C=35.0,
)["arc_deg"]

height = pifira.effective_height(flame_height_m=0.767, liquid_height_m=0.885)
area = pifira.effective_area(diameter_m=0.75, arc_deg=arc, height_m=height)
print(pifira.heat_flux(heat_W, area), "kW/m2")

The pressure-rise calculation uses a closed-vessel interval before relief venting. The internal energy is evaluated with CoolProp while total mass and vessel volume remain fixed. The effective circumferential width is obtained from a Gaussian fit to the radiative driving force T_wall^4 - T_ambient^4.

LH2 evidence-gated example

from pifira.lh2 import MilenkoCorrelation, RigidRotorSpinThermo

thermo = RigidRotorSpinThermo()
print(thermo.equilibrium_ortho(20.3))
print(thermo.conversion_energy_J_per_kg(20.3))

kinetics = MilenkoCorrelation()
k = kinetics.forward_rate_per_s(
    temperature_K=20.3,
    density_kg_m3=70.0,
    phase="liquid",
)
print(k, "1/s")

The LH2 functions enforce the reported temperature, density, phase and composition domains by default. They do not constitute a certified relief valve sizing method. In particular, the package does not infer a discharge coefficient, effective area, lift law or two-phase capacity for a commercial PSV from pressure cycling alone.

State-point and full-path OP criteria

The state at relief and the complete warming path are deliberately separate claims. The following data-free calculation reproduces the 50 psia landmarks used in the associated method paper:

from pifira.lh2 import (
    apply_para_composition_allowance,
    equilibrium_path_ledger,
    required_para_fraction_for_nonheating,
    required_para_fraction_for_pathwise_nonheating,
)

pressure_Pa = 50.0 * 6894.757293168
state_point = required_para_fraction_for_nonheating(pressure_Pa)
full_path = required_para_fraction_for_pathwise_nonheating(
    pressure_Pa, initial_temperature_K=20.3
)
adjusted, feasible = apply_para_composition_allowance(full_path, 0.1)
ledger = equilibrium_path_ledger(0.003, pressure_Pa)  # 99.7% para

print(100 * state_point)  # 98.9565% para at the relief state
print(100 * full_path)    # 99.7951% para over the declared path
print(100 * adjusted, feasible)
print(ledger["crossover_pressure_kPa_abs"])  # 134.6 kPa(abs)

The ledger is an equilibrium-direction accounting result. It neither predicts realized conversion heat without a kinetic path nor authorizes a reduction in standards-required or certified relief capacity. See examples/lh2_pathwise_credit.py.

Public API

Validation-data policy

Only source metadata and acquisition instructions are versioned. The project does not redistribute source PDFs, spreadsheets, presentation files, figure rasters, digitized traces, or derived validation tables. Users who reproduce a comparison must obtain the material from the original source, comply with its terms, and keep it outside version control. See VALIDATION_SOURCES.md.

Package releases are checked automatically for common third-party data and document formats before PyPI publication.

Scope and safety

pifira is research software. It is not an ISO 21013, API 520/521, ASME or KGS design implementation, and it must not replace certified sizing, manufacturer capacity data, or engineering review. A successful numerical reproduction means that the code regenerated a reported result; it does not by itself establish physical validation or fitness for safety-critical use.

Citation and release history

Use CITATION.cff and cite the archived Zenodo release. The badge above uses the concept DOI, which resolves to the newest archived version. Changes are listed in CHANGELOG.md.

License

The software is released under the MIT License. Third-party source material is not covered by that license and is not included.