Source: https://jmrplens.github.io/phonometry/reference/api/fluids/gas/ An ideal gas from the two numbers a gas table prints. A table of gases prints a ratio of specific heats and a molar mass, and those two close the ideal-gas state completely: $$ c = \sqrt{\frac{\gamma R T}{M}} \qquad \rho = \frac{p\,M}{R\,T} $$ so a caller who has a gas that is not air or water can still have a [`Fluid`](/phonometry/reference/api/fluids/fluids/#fluid) for it, computed rather than typed. How far the closure goes ------------------------ Hopkins (2007) Table A1, PDF page 634 (printed p. 607), prints both columns for six gases at 20 degC and 1,013 x 10^5 Pa, as its own footnote states. Against it, the speeds land within 0,5 m/s for all six and the densities within 0,002 kg/m3 for the four light ones. Carbon dioxide comes out 0,7 % light and sulphur hexafluoride 2 % light. That shortfall is not an error in the arithmetic, it is the compressibility factor: a real gas has `rho = p M / (Z R T)`, so the ideal density is `Z` times the real one and the fraction missing is `1 - Z`. It grows with the molecule, and SF6, a heavy one whose attraction is not negligible at room conditions, is exactly the gas a demonstration reaches for. The model says so in [`IDEAL_GAS_VALIDITY`](/phonometry/reference/api/fluids/gas/#ideal_gas_validity) rather than pretending otherwise. What it does not give --------------------- Viscosity, thermal conductivity and the Prandtl number are transport properties. Nothing in the ideal-gas closure determines them, so the returned fluid does not carry them and reading one raises [`FluidPropertyUnavailable`](/phonometry/reference/api/fluids/fluids/#fluidpropertyunavailable) naming the model, which is what every other fluid here does with a quantity its model did not fix. > Auto-generated from the source docstrings by `scripts/generate_api_docs.py` (`make api-docs`). Do not edit by hand. ## ideal_gas ```python ideal_gas( *, temperature_c: float, heat_capacity_ratio: float, molar_mass_kg_mol: float, static_pressure_pa: float | None = None, ) -> Fluid ``` A gas at one state, from its ratio of specific heats and molar mass. $c = \sqrt{\gamma R T / M}$ and $\rho = p M / (R T)$, the two ideal-gas relations, which is all a table that prints `gamma` and `M` supports. See the module docstring for how far that goes and what it leaves out. **Parameters** | Name | Description | | :--- | :--- | | `temperature_c` | Temperature `t`, in degrees Celsius (above absolute zero). | | `heat_capacity_ratio` | Ratio of specific heats `gamma` (> 1). It is 1,67 for a monatomic gas, about 1,4 for a diatomic one and lower for a polyatomic one, and it is above 1 for every gas, because `gamma` is `c_p/c_v` and `c_p - c_v` is the gas constant. | | `molar_mass_kg_mol` | Molar mass `M`, in kg/mol (> 0). The tables print kg/mol, so 0,028 95 for dry air and not 28,95. | | `static_pressure_pa` | Static pressure `p`, in pascals (> 0). When omitted, one standard atmosphere is assumed and a [`FluidAssumptionWarning`](/phonometry/reference/api/fluids/fluids/#fluidassumptionwarning) says so, because the density is proportional to it. | **Returns:** The [`Fluid`](/phonometry/reference/api/fluids/fluids/#fluid) at that state, carrying a density, a speed of sound and the ratio of specific heats it was given. **Raises** | Exception | When | | :--- | :--- | | ValueError | for a non-positive input or a temperature at or below absolute zero. | ## IDEAL_GAS_VALIDITY *Constant* (`str`). ```python IDEAL_GAS_VALIDITY = "ideal gas: exact for a dilute gas and within about 1 % of a printed table for the light gases at room conditions. The density comes out light by 1 - Z, the compressibility factor's distance from unity, and that grows with the molecule: carbon dioxide is 0,7 % light and sulphur hexafluoride 2 % against Hopkins Table A1, where the speeds still land within 0,5 m/s." ``` ## MOLAR_GAS_CONSTANT *Constant* (`float`). ```python MOLAR_GAS_CONSTANT = 8.31446261815324 ```