fluids.air
Humid air (IEC 61094-2:2009, Annex F).
Annex F carries the CIPM-2007 formulation for the density of moist air together with fits for the speed of sound, the ratio of specific heats, the viscosity and the thermal diffusivity. It is the only model of air in this library that is computed rather than quoted: every other air in the tree is a value some standard printed for its own procedure, and those stay where their clause prints them.
Table F.1 (printed folio 40) prints five quantities at two condition sets, and every one of them reproduces here from the Table F.2 coefficients (printed folio 41) to better than 1,5e-7 relative, which is inside the rounding of the last printed figure. Thermal conductivity and specific heat capacity come from the two expressions of Clause F.6 (printed folio 39); the annex prints their formulae and units but tabulates only the diffusivity they form, so those two are anchored in closed form rather than against a printed number.
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air( *, temperature_c: float, static_pressure_pa: float | None = None, relative_humidity_percent: float | None = None, co2_mole_fraction: float | None = None,) -> FluidHumid air at one state (IEC 61094-2:2009, Annex F).
Returns the density, speed of sound, ratio of specific heats, viscosity and thermal diffusivity Table F.1 tabulates, and the thermal conductivity and specific heat capacity Clause F.6 gives expressions for.
Parameters
| Name | Description |
|---|---|
temperature_c | Air temperature t, in degrees Celsius. Required: there is no defensible default for the one condition the caller actually measured. |
static_pressure_pa | Absolute static pressure p_s, in pascals. None assumes DEFAULT_STATIC_PRESSURE_PA and warns. |
relative_humidity_percent | Relative humidity H, in per cent. None assumes DEFAULT_RELATIVE_HUMIDITY_PERCENT and warns. |
co2_mole_fraction | Carbon dioxide mole fraction x_c. None takes DEFAULT_CO2_MOLE_FRACTION, the value Clause F.2 recommends for laboratory conditions, and does not warn: unlike the other two it is a value the annex names, and it reaches the fifth figure of the density at most. |
Returns: The Fluid at that state.
Raises
| Exception | When |
|---|---|
| ValueError | if the temperature is at or below -273,15 degC, the pressure is not positive, the humidity is outside 0 % to 100 %, the carbon dioxide mole fraction is outside 0 to 1, any of the four is not finite, or the pressure and humidity cannot hold together at that temperature. That last one is a combination rather than an argument: at 20 degC and 1 kPa, 50 % relative humidity asks for a water vapour mole fraction of 1,17, and a mole fraction cannot reach 1. |
Nothing else is refused. Annex F states a domain for its equations and this warns outside it, because a fit past its range is still arithmetic; what it refuses is a state that cannot exist.
DEFAULT_CO2_MOLE_FRACTION
Section titled “DEFAULT_CO2_MOLE_FRACTION”Constant (float).
DEFAULT_CO2_MOLE_FRACTION = 0.0004DEFAULT_RELATIVE_HUMIDITY_PERCENT
Section titled “DEFAULT_RELATIVE_HUMIDITY_PERCENT”Constant (float).
DEFAULT_RELATIVE_HUMIDITY_PERCENT = 50.0DEFAULT_STATIC_PRESSURE_PA
Section titled “DEFAULT_STATIC_PRESSURE_PA”Constant (float).
DEFAULT_STATIC_PRESSURE_PA = 101325.0