solprop.physdata.equation_of_state#

Gas number density and pressure from the equation of state.

Number densities are optmat’s real-gas equations of state (SEP 3): CoolProp’s Helmholtz-energy equations through optmat.gas.eos, adapted by OptmatGas, whose exact inverse gives the pressure. An ideal-gas expression is available for comparison; the two agree to better than 1e-3 relative below about 0.1 bar for every gas here.

Note

Pressures in this module are in bar, the one documented departure from SI at the user interface (docs/dev/conventions.md section 1), because the field works in bar. Everything else is SI: number densities are in m^-3, temperatures in K.

optmat imports CoolProp, which costs about a second, so the import happens inside the functions and import solprop stays cheap. Lookups are cached, and none is made at module load.

Functions

`density`(gas, pressure_bar[, temperature, ideal])	Return the number density of a gas.
`ideal_gas_density`(pressure_bar[, temperature])	Return the ideal-gas number density.
`pressure`(gas, number_density[, temperature, ...])	Return the pressure at which a gas reaches a given number density.

solprop.physdata.equation_of_state.density(gas, pressure_bar, temperature=293.15, *, ideal=False)[source]#

Return the number density of a gas.

Parameters:

gasGas or str: The species.
pressure_barfloat: Absolute pressure in bar (the documented non-SI user-interface unit), >= 0. Zero returns zero without consulting the equation of state, which is undefined there; a pressure gradient terminating in vacuum needs this.
temperaturefloat, optional: Temperature in K, > 0. Defaults to 293.15 K.
idealbool, optional: Use p / (k_B T) instead of the equation of state. Default False.

Returns:

float: Number density in m^-3.

Raises:

MaterialError: If the gas is unknown, the pressure is negative, the temperature is not positive, or the state lies outside the equation of state’s domain.

Notes

The equation of state is optmat’s real-gas one: at 293.15 K the deviation from ideal is about 0.14 % at 2 bar and 2.5 % at 40 bar for argon, so it matters for the high-pressure fills used in self-compression.

Examples

>>> from solprop.physdata import Gas, density
>>> f"{density(Gas.Ar, 1.0):.6e}"
'2.472418e+25'
>>> density(Gas.He, 0.0)
0.0

solprop.physdata.equation_of_state.ideal_gas_density(pressure_bar, temperature=293.15)[source]#

Return the ideal-gas number density.

rho = p / (k_B T). Independent of the species, so it takes no gas argument.

Parameters:

pressure_barfloat: Absolute pressure in bar (the documented non-SI user-interface unit), >= 0.
temperaturefloat, optional: Temperature in K, > 0. Defaults to 293.15 K.

Returns:

float: Number density in m^-3.

Raises:

MaterialError: If the pressure is negative or the temperature is not positive.

Examples

The Loschmidt constant is the ideal-gas density at 1 atm and 0 degrees Celsius.

>>> from solprop.physdata import ideal_gas_density
>>> f"{ideal_gas_density(1.01325, 273.15):.6e}"
'2.686780e+25'

solprop.physdata.equation_of_state.pressure(gas, number_density, temperature=293.15, *, ideal=False)[source]#

Return the pressure at which a gas reaches a given number density.

The inverse of density() at fixed temperature.

Parameters:

gasGas or str: The species.
number_densityfloat: Number density in m^-3, >= 0. Zero returns zero.
temperaturefloat, optional: Temperature in K, > 0. Defaults to 293.15 K.
idealbool, optional: Use p = rho k_B T instead of the equation of state. Default False.

Returns:

float: Absolute pressure in bar (the documented non-SI user-interface unit).

Raises:

MaterialError: If the gas is unknown, the density is negative, the temperature is not positive, or the state lies outside the equation of state’s domain.

Examples

>>> from solprop.physdata import Gas, density, pressure
>>> f"{pressure(Gas.Ar, density(Gas.Ar, 5.0)):.6f}"
'5.000000'