Gas density

The sources are:

Values for 0, 15, and 25°C are taken from encyclopedia.airliquide.com
Values for 50, 75, and 100°C are taken from nist.gov
Values for 50, 75, and 100°C for dry air have been calculated using the equation from Dumas & Trancossi, 2009.
Equation for humid air is taken from paper by P.T. Tsilingiris: 'Thermophysical and transport properties of humid air at temperature range between 0 and 100°C', 2007
Equation for air is taken from paper by A. Dumas and M. Trancossi: 'Design of Exchangers Based on Heat Pipes for Hot Exhaust Thermal Flux, with the Capability of Thermal Shocks Absorption and Low Level Energy Recovery', 2009
Equation for humid air is taken from paper by P.T. Tsilingiris: 'Thermophysical and transport properties of humid air at temperature range between 0 and 100°C', 2007
Equation for air is taken from paper by A. Dumas and M. Trancossi: 'Design of Exchangers Based on Heat Pipes for Hot Exhaust Thermal Flux, with the Capability of Thermal Shocks Absorption and Low Level Energy Recovery', 2009. They are calculated from polynomial curve fits to a data set for 100 K to 1600 K in the SFPE Handbook of Fire Protection Engineering, 2nd Edition Table B-2. You may find a free air property calculator from Pierre Bouteloup
Equations for N₂ and SF₆ are taken from paper by J. Vermeer: 'A simple formula for the calculation of the convective heat transfer between conductor and sheath in compressed gas insulated (CGI) cables', 1983 as published in Elektra 87
The factor 353.0 in the formula for Air was calculated by multiplying $1.1840\cdot(273.15+25)$.
The factor 538.9 in the formula for CO₂ was calculated by multiplying $1.8075\cdot(273.15+25)$.
The factor 390.1 in the formula for O₂ was calculated by multiplying $1.3085\cdot(273.15+25)$.

Symbol

$\rho_{gas}$

Unit

kg/m$^3$

Formulae

$1.293393662-5.538444326{\cdot}{10}^{-3} \theta_{gas}+3.860201577{\cdot}{10}^{-5} {\theta_{gas}}^2-5.2536065{\cdot}{10}^{-7} {\theta_{gas}}^3$	humid air @ 1 atm (Tsilingiris2007)
$360.77819{T_{gas}}^{-1.00336}$	air @ 1 bar (Dumas&Trancossi2009)
$\frac{351.99}{T_{gas}}+\frac{344.84}{{T_{gas}}^2}$	dry air @ 1 bar (UW/MHTL 8406, 1984)
$\frac{353p_{gas}}{T_{gas}}$	air (ideal gas)
$\frac{337.4p_{gas}}{T_{gas}}$	N₂ (Vermeer1983)
$\frac{1666p_{gas}}{230+\theta_{gas}}$	SF₆ (Vermeer1983)
$\frac{538.9p_{gas}}{\theta_{gas}+\theta_{abs}}$	CO₂ (linear interpolation)
$\frac{\frac{1}{R_{gas}} p_{gas}}{T_{gas}}$	ideal gas
$\frac{390.1p_{gas}}{\theta_{gas}+\theta_{abs}}$	O₂ (linear interpolation)

Related

$p_{gas}$

Gas pressure [Pa]

$R_{gas}$

Specific gas constant [J/(kg.K)]

$T_{gas}$

Absolute gas temperature [K]

$\theta_{abs}$

Absolute temperature [K]

$\theta_{gas}$

Gas temperature [°C]

Used in

$\alpha_{gas}$

Thermal diffusivity for gas [m$^2$/s]

$\eta_{gas}$

Dynamic viscosity of gas [Pa.s]

$F_{pt}$

Function of pressure and temperature

$\nu_{gas}$

Kinematic viscosity for gas [m$^2$/s]

$p_{gas}$

Gas pressure [Pa]

$T_{conv,ce}$

Thermal resistance by convection, conductor to enclosure [K.m/W]

$W_{a,L}$

Heat removed by air at outlet [W/m]

Choices

Gas	Formula	0°C	15°C	25°C	50°C	75°C	100°C
Air	78%N₂+21%O₂+minor	1.292	1.225	1.184	1.0934	1.0143	0.9462
N2	N₂	1.2501	1.1848	1.145	1.0562	0.9802	0.9145
SF6	SF₆	6.6161	6.2563	6.0383	5.5554	5.1466	4.7949
CO2	CO₂	1.9763	1.8714	1.8075	1.6657	1.5448	1.4403
CO	CO	1.2502	1.1849	1.145	1.0562	0.9802	0.9144
O2	O₂	1.4287	1.354	1.3085	1.207	1.1201	1.0449
H2	H₂	0.0899	0.0852	0.0823	0.076	0.0705	0.0658
NH3	NH₃	0.7713	0.7289	0.7033	0.6471	0.5995	0.5586
SO2	SO₂	2.9305	2.7633	2.6636	2.4459	2.2634	2.1073
He	He	0.1784	0.1692	0.1635	0.1509	0.14	0.1306
Ar	Ar	1.7835	1.6903	1.6335	1.5068	1.3983	1.3045
Kr	Kr	3.748	3.5514	3.4314	3.1644	2.9361	2.7386
Xe	Xe	5.8965	5.584	5.3937	4.9707	4.6099	4.2983
Ne	Ne	0.8996	0.8528	0.8242	0.7605	0.7059	0.6586