Chemical and mixture property data for safety calculations
Every consequence calculation depends on property data, and inconsistent data is one of the commonest sources of error in a safety study. This module provides a single vetted property set for the components used across the toolkit, plus Peng-Robinson flash calculations for defined mixtures.
Open the Chemical Properties moduleWhat this calculator returns
- Molar mass, critical temperature and critical pressure
- Vapour pressure and saturation temperature
- Ratio of specific heats and compressibility factor
- Flammability limits, flash point and net heating value
- Mixture bubble point, dew point and phase split
Required inputs
- Component selection or mixture composition
- Temperature and pressure of interest
Calculation method
Pure-component constants are held in a curated library and reused by every calculation module so results stay internally consistent.
Vapour pressure is evaluated from tabulated saturation data with controlled extrapolation outside the tabulated range.
Mixture phase behaviour uses the Peng-Robinson equation of state with standard mixing rules to give the flash split at the specified conditions.
Governing equations
P = R T / (v - b) - a alpha / ( v^2 + 2 b v - b^2 )Peng-Robinson equation of state used for real-gas and flash calculations.
Z = P v / ( R T )Compressibility factor used by the discharge and blowdown modules.
Nomenclature
- P, T, v
- pressure (Pa), temperature (K), molar volume (m3/mol)
- a, b
- Peng-Robinson attraction and co-volume parameters
- alpha
- temperature-dependent alpha function
- Z
- compressibility factor, dimensionless
Assumptions and limitations
- Library values are representative literature data and should be checked against the project's own basis of design.
- Vapour pressure outside the tabulated range is extrapolated and should be treated with care.
Reference practice
- Property definitions follow standard chemical engineering practice as used in DIPPR-style property compilations.
Worked example
Assembling the property set needed before running a release calculation for a hydrocarbon stream.
| Step | Value | Basis |
|---|---|---|
| Identify the component | Library component or user-defined | Critical properties and acentric factor drive the equation of state |
| Thermodynamic state | Saturation pressure at the operating temperature | Determines whether the release is gas, liquid or two-phase |
| Release-relevant data | Molar mass, ratio of specific heats, density | These feed the discharge and dispersion equations directly |
| Hazard data | LFL, UFL, toxicity endpoints, flash point | These set the criteria that consequence distances are measured against |
Almost every downstream error in a consequence study traces back to the property set, so the same component data should be used across discharge, dispersion and effect calculations.
Illustrative numbers only — rerun the module with the project basis of design before using any result.
Common questions
Which properties matter most for a gas release?
Molar mass, ratio of specific heats and compressibility for the source term, then LFL and toxicity endpoints for the hazard criterion.
How are mixtures handled?
Through Peng-Robinson flash calculations, which give the phase split and mixture properties rather than a simple mole-weighted average.
What if a component is not in the library?
It can be defined from critical temperature, critical pressure, acentric factor and molar mass; correlations without those data fall back to ideal-gas behaviour.
Related calculators
- Gas Discharge — Gas discharge rate calculator for pressurised releases
- Two-Phase Blowdown — Two-phase blowdown and depressurisation calculator