Gas Properties Table
Molar mass, specific gas constant, specific-heat ratio, specific gravity, density at normal (0 °C) and standard (15 °C) conditions, viscosity, and speed of sound for 23 gases — plus the critical constants behind real-gas (Peng-Robinson) calculations. The same data SimuPipe's compressible solvers use.
Densities are ideal-gas values ρ = PM/RᵤT at 101.325 kPa absolute — "normal" (Nm³ basis) at 0 °C, "standard" (Sm³ basis) at 15 °C. Real-gas deviation is under ~1% at these conditions except near condensation. * Steam is quoted at 100 °C (it condenses at ambient temperature, so the 0/15 °C columns do not apply). Natural gas is a fixed pipeline-quality pseudo-composition (SG 0.60), not a variable mixture. Derived columns (R, SG, ρ, a) are computed from unrounded values, so recomputing them from the rounded M or γ shown may differ in the last digit. 1 µPa·s = 10⁻⁶ Pa·s.
Above its critical temperature a gas cannot be liquefied by pressure alone. These constants feed the Peng-Robinson equation of state, from which SimuPipe computes the compressibility factor Z for non-ideal gases. Near-ideal gases (air, N₂, O₂, H₂, He, Ar, Ne, CO) are treated with Z = 1 and are not listed.
Gas density follows from the ideal-gas law in mass terms:
- — density (kg/m³), — absolute pressure (Pa)
- — molar mass (kg/kmol = g/mol), — absolute temperature (K)
- J/(kmol·K) — universal gas constant; — specific gas constant (J/kg·K)
Specific gravity relative to air and the speed of sound:
- g/mol, — specific-heat ratio
- — sonic velocity (m/s), the choked-flow limit for gas in a pipe or valve throat
For a real gas, density becomes with the compressibility factor Z from an equation of state. SimuPipe's compressible solvers carry Z (Peng-Robinson) through the flow equations, warn as flow approaches Mach 1, and cap it at the choke limit — see the isothermal vs adiabatic gas flow guide.
- Molar mass and specific-heat ratio are from CoolProp 7.2.0 (Helmholtz-energy equations of state); γ is evaluated at 20 °C and 1 atm. Natural gas is a pipeline-quality pseudo-gas (SG 0.60); steam uses IAPWS-IF97.
- Viscosities are evaluated from the same temperature correlations the solver uses — CoolProp-fitted polynomial fits for 18 gases, Sutherland-form handbook correlations for CO, SO₂, C₂H₄ and Ne.
- Densities are ideal-gas values at the stated reference conditions, computed from M — not measured values — so they are exactly consistent with the Nm³/Sm³ flow-conversion bases. R, SG, and sonic velocity are derived via the relations above.
- Critical constants (Tc, Pc, ω) are the Peng-Robinson inputs the simulator uses for real-gas density; refrigerant blends (R-410A class) carry ASHRAE pseudo-critical values in the application, and the four pure refrigerants listed here use CoolProp values.
- This table is a view of the application's fluid data — the same 23 gas presets the editor offers — not a separate transcription, so published values and simulated values cannot drift apart.
Frequently Asked Questions
What is the difference between normal (Nm³) and standard (Sm³) conditions?
What is the specific gas constant R?
What is the specific-heat ratio γ used for?
What is the specific gravity of a gas?
When does the ideal-gas assumption break down?
Why is gas viscosity so much lower than liquid viscosity?
Model compressible gas flow
Pick a gas, set pressure and temperature, and SimuPipe solves the network with real-gas density, temperature-dependent viscosity, and sonic-choking checks.