RCAIDE.Library.Attributes.Gases.Air

Air

class Air(*args, **kwarg)

Bases: Gas

A class representing air and its thermodynamic properties. Provides methods for computing various gas properties including density, speed of sound, specific heat, and transport properties.

tag

Identifier for the gas type (‘air’)

Type:

str

molecular_mass

Molecular mass of air in kg/kmol

Type:

float

gas_specific_constant

Specific gas constant in m²/s²-K

Type:

float

specific_heat_capacity

Specific heat capacity in J/kg·K

Type:

float

composition

Chemical composition of air

• O2float

  Mass fraction of oxygen (0.20946)

• Arfloat

  Mass fraction of argon (0.00934)

• CO2float

  Mass fraction of carbon dioxide (0.00036)

• N2float

  Mass fraction of nitrogen (0.78084)

• otherfloat

  Mass fraction of other components (0.00)

Type:

Data

Notes

This class implements standard atmospheric air properties and various methods for computing thermodynamic and transport properties.

compute_density(T=300.0, p=101325.0)

Computes air density using the ideal gas law.

Parameters:

• T (float) – Temperature in Kelvin

• p (float) – Pressure in Pascal

Returns:

rho – Density in kg/m³

Return type:

float

Notes

Major Assumptions

• Air behaves as an ideal gas

compute_speed_of_sound(T=300.0, p=101325.0, variable_gamma=False)

Computes speed of sound in air.

Parameters:

• T (float) – Temperature in Kelvin

• p (float) – Pressure in Pascal

• variable_gamma (bool) – If True, uses temperature-dependent specific heat ratio

Returns:

a – Speed of sound in m/s

Return type:

float

Notes

Major Assumptions

• If variable_gamma is False, assumes γ = 1.4

• Air behaves as an ideal gas

compute_cp(T=300.0, p=101325.0)

Computes specific heat capacity at constant pressure using a 3rd-order polynomial fit.

Parameters:

• T (float) – Temperature in Kelvin

• p (float) – Pressure in Pascal

Returns:

cp – Specific heat capacity in J/(kg·K)

Return type:

float

Notes

Major Assumptions

• Valid for temperature range: 123 K < T < 673 K

Theory .. math:

c_p(T) = c_1T^3 + c_2T^2 + c_3T + c_4

References

[1] Ekin, J. (2006). Experimental techniques for low-temperature measurements: Cryostat design, material properties and superconductor critical-current testing. Oxford University Press.

compute_gamma(T=300.0, p=101325.0)

Computes specific heat ratio using a 3rd-order polynomial fit.

Parameters:

• T (float) – Temperature in Kelvin

• p (float) – Pressure in Pascal

Returns:

g – Specific heat ratio (gamma) [unitless]

Return type:

float

Notes

Major Assumptions * Valid for temperature range: 233 K < T < 1273 K

compute_absolute_viscosity(T=300.0, p=101325.0)

Computes absolute (dynamic) viscosity using Sutherland’s law.

Parameters:

• T (float) – Temperature in Kelvin

• p (float) – Pressure in Pascal

Returns:

mu – Absolute viscosity in kg/(m·s)

Return type:

float

Notes

Theory Uses Sutherland’s formula with S = 110.4K and C1 = 1.458e-6 kg/m-s-sqrt(K)

References

[1] Sutherland’s law

compute_thermal_conductivity(T=300.0, p=101325.0)

Computes thermal conductivity of air.

Parameters:

• T (float) – Temperature in Kelvin

• p (float) – Pressure in Pascal

Returns:

k – Thermal conductivity in W/(m·K)

Return type:

float

Notes

Major Assumptions

• Properties computed at 1 bar (14.5 psia)

References

[1] The Engineering ToolBox (2009). Air - Thermal Conductivity vs. Temperature and Pressure. [online] Available at: https://www.engineeringtoolbox.com/air-properties-viscosity-conductivity-heat-capacity-d_1509.html [Accessed 8 January 2025].

compute_prandtl_number(T=300.0)

Computes Prandtl number.

Parameters:

T (float) – Temperature in Kelvin

Returns:

Pr – Prandtl number [unitless]

Return type:

float

Notes

Theory .. math:

Pr = \frac{\mu C_p}{k}

compute_R(T=300.0, p=101325.0)

Computes specific gas constant.

Parameters:

• T (float) – Temperature in Kelvin

• p (float) – Pressure in Pascal

Returns:

R – Specific gas constant in J/(kg·K)

Return type:

float

Notes

Theory .. math:

R = \frac{\gamma - 1}{\gamma}c_p