Source code for RCAIDE.Library.Attributes.Gases.Air
# RCAIDE/Library/Attributes/Gases/Air.py
#
#
# Created: Mar 2024, M. Clarke
# ----------------------------------------------------------------------------------------------------------------------
# Imports
# ----------------------------------------------------------------------------------------------------------------------
from .Gas import Gas
import numpy as np
# ----------------------------------------------------------------------------------------------------------------------
# Air Class
# ----------------------------------------------------------------------------------------------------------------------
[docs]
class Air(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.
Attributes
----------
tag : str
Identifier for the gas type ('air')
molecular_mass : float
Molecular mass of air in kg/kmol
gas_specific_constant : float
Specific gas constant in m²/s²-K
specific_heat_capacity : float
Specific heat capacity in J/kg·K
composition : Data
Chemical composition of air
- O2 : float
Mass fraction of oxygen (0.20946)
- Ar : float
Mass fraction of argon (0.00934)
- CO2 : float
Mass fraction of carbon dioxide (0.00036)
- N2 : float
Mass fraction of nitrogen (0.78084)
- other : float
Mass fraction of other components (0.00)
Notes
-----
This class implements standard atmospheric air properties and various methods
for computing thermodynamic and transport properties.
"""
def __defaults__(self):
"""This sets the default values.
Assumptions:
None
Source:
None
"""
self.tag = 'air'
self.molecular_mass = 28.96442 # kg/kmol
self.gas_specific_constant = 287.0528742 # m^2/s^2-K, specific gas constant
self.specific_heat_capacity = 1006 # J/kgK
self.composition.O2 = 0.20946
self.composition.Ar = 0.00934
self.composition.CO2 = 0.00036
self.composition.N2 = 0.78084
self.composition.other = 0.00
self.air_surrogate = {'O2':0.2095, 'N2':0.7809, 'AR':0.0096} # [-] Mole fractions of air surrogate species
self.kinetic_mechanism = 'Air.yaml'
[docs]
def compute_density(self,T=300.,p=101325.):
"""
Computes air density using the ideal gas law.
Parameters
----------
T : float
Temperature in Kelvin
p : float
Pressure in Pascal
Returns
-------
rho : float
Density in kg/m³
Notes
-----
**Major Assumptions**
* Air behaves as an ideal gas
"""
return p/(self.gas_specific_constant*T)
[docs]
def compute_speed_of_sound(self,T=300.,p=101325.,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 : float
Speed of sound in m/s
Notes
-----
**Major Assumptions**
* If variable_gamma is False, assumes γ = 1.4
* Air behaves as an ideal gas
"""
if variable_gamma:
g = self.compute_gamma(T,p)
else:
g = 1.4*np.ones_like(T)
return np.sqrt(g*self.gas_specific_constant*T)
[docs]
def compute_cp(self,T=300.,p=101325.):
"""
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 : float
Specific heat capacity in J/(kg·K)
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.
"""
c = [-7.357e-007, 0.001307, -0.5558, 1074.0]
cp = c[0]*T*T*T + c[1]*T*T + c[2]*T + c[3]
return cp
[docs]
def compute_gamma(self,T=300.,p=101325.):
"""
Computes specific heat ratio using a 3rd-order polynomial fit.
Parameters
----------
T : float
Temperature in Kelvin
p : float
Pressure in Pascal
Returns
-------
g : float
Specific heat ratio (gamma) [unitless]
Notes
-----
**Major Assumptions**
* Valid for temperature range: 233 K < T < 1273 K
"""
c = [1.629e-010, -3.588e-007, 0.0001418, 1.386]
g = c[0]*T*T*T + c[1]*T*T + c[2]*T + c[3]
return g
[docs]
def compute_absolute_viscosity(self,T=300.,p=101325.):
"""
Computes absolute (dynamic) viscosity using Sutherland's law.
Parameters
----------
T : float
Temperature in Kelvin
p : float
Pressure in Pascal
Returns
-------
mu : float
Absolute viscosity in kg/(m·s)
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
"""
S = 110.4 # constant in deg K (Sutherland's Formula)
C1 = 1.458e-6 # kg/m-s-sqrt(K), constant (Sutherland's Formula)
return C1*(T**(1.5))/(T + S)
[docs]
def compute_thermal_conductivity(self,T=300.,p=101325.):
"""
Computes thermal conductivity of air.
Parameters
----------
T : float
Temperature in Kelvin
p : float
Pressure in Pascal
Returns
-------
k : float
Thermal conductivity in W/(m·K)
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].
"""
return 3.99E-4 + 9.89E-5*(T) -4.57E-8*(T**2) + 1.4E-11*(T**3)
[docs]
def compute_prandtl_number(self,T=300.):
"""
Computes Prandtl number.
Parameters
----------
T : float
Temperature in Kelvin
Returns
-------
Pr : float
Prandtl number [unitless]
Notes
-----
**Theory**
.. math::
Pr = \\frac{\\mu C_p}{k}
"""
Cp = self.specific_heat_capacity
mu = self.compute_absolute_viscosity(T)
K = self.compute_thermal_conductivity(T)
return mu*Cp/K
[docs]
def compute_R(self,T=300.,p=101325.):
"""
Computes specific gas constant.
Parameters
----------
T : float
Temperature in Kelvin
p : float
Pressure in Pascal
Returns
-------
R : float
Specific gas constant in J/(kg·K)
Notes
-----
**Theory**
.. math::
R = \\frac{\\gamma - 1}{\\gamma}c_p
"""
gamma = self.compute_gamma(T,p)
cp = self.compute_cp(T,p)
R = ((gamma - 1)/gamma)*cp
return R
