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# Air - Thermophysical Properties

## Thermal properties of air at different temperatures - density, viscosity, critical temperature and pressure, triple point, enthalpi and entropi, thermal conductivity and diffusivity and more.

Thermophysical properties of air:

• Boiling temperature (at 1 bara):                            78.8 K = -194.4 °C = -317.8 °F
• Bulk modulus elasticity :                                         1.01325 x 10 5 Pa or N/m 2
• Condensation temperature (at 1 bara):                 81.8 K = -191.4 °C = -312.5 °F
• Critical temperature :                                              132.63 K = -140.52 °C = -220.94 °F
• Critical pressure :                                                    37.363 atm = 37.858 bar = 3.7858 MPa (MN/m 2 ) = 549.08 psi (=lb f /in 2 )
• Critical density:                                                      10.448 mol/dm 3 = 302.6 kg/m 3 = 0.5871 slug/ft 3 = 18.89 lb m /ft 3
• Density (at 0°C and 1 bara):                                 1.276 kg/m 3 = 0.00248 slug/ft 3 = 0.0797 lb/ft 3
• Density (at 60°F and 1 atm):                                  1.208 kg/m 3 = 0.00234 slug/ft 3 = 0.0754 lb/ft 3
• Enthalpy (heat) of air at 0°C  and 1 bara:              11.57  kJ/mol = 399.4  kJ/kg = 171.7 Btu(IT)/lb
• Entropy of air at 0°C  and 1 bara:                           0.1100 kJ/mol K = 3.796 kJ/kg K = 0.9067 Btu(IT)/lb °F
• Liquid density at boiling point and 1 bar:                875.50 kg/m 3 = 54.656 lb/ft 3
• Molar mass: 28.9647 g/mol
• Specific heat capacity (C p ) air at 0°C and 1 bara:  1.006 kJ/kgK = 0.24028 Btu(IT)/(lb m °F) or kcal/(kg K)
• Specific heat capacity (C v ) air at 0°C and 1 bara:  0.7171 kJ/kgK = 0.17128 Btu(IT)/(lb m °F) or kcal/(kg K)
• Thermal conductivity at 0°C and 1 bara:                 24.35 mW/(m K) = 0.02094 kcal(IT)/(h m K) = 0.01407 Btu(IT)/(h ft °F)
• Thermal expansion coefficient at 0°C and 1 bara:  0.00369 1/K  = 0.00205 1/°F
• Triple point pressure:                                              0.05196 atm = 0.05265 bar = 5265 Pa = 0.7636 psi (=lb f /in 2 )
• Triple point temperature:                                         59.75 K = -213.40 °C = -352.12 °F
• Viscosity, dynamic , at 0°C and 1 bara:                    17.22 μPa s = 0.01722 cP = 0.3596x 10 -6 ( lb f s)/ft 2 = 11.57 x10 -6 lb m /(ft s)
• Viscosity, kinematic , at 0°C and 1 bara:                   0.00001349 m 2 /s = 13.49 cSt = 0.0001452 ft 2 /s

Follow the links below to get values for the listed properties of air at varying pressure and temperature :

See also more about atmospheric pressure , and STP - Standard Temperature and Pressure & NTP - Normal Temperature and Pressure ,
as well as Thermophysical properties of: Acetone , Acetylene , Ammonia , Argon , Benzene , Butane , Carbon dioxide , Carbon monoxide , Ethane , Ethanol , Ethylene , Helium , Hydrogen , Hydrogen sulfide , Methane , Methanol , Nitrogen , Oxygen , Pentane , Propane , Toluene , Water and Heavy water, D 2 O .

Air is a mixture of gases at standard conditions. However, at low temperature and high pressures the gas mixture becomes a liquid. The phase diagram for air shows the phase behavior with changes in temperature and pressure. The curve between the triple point and the critical point shows the air boiling point with changes in pressure. At the critical point there is no change of state when pressure is increased or if heat is added.

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.  Example - Mass of Air at Temperature 100 o C

From the table above - the density of air is 0.946 kg/m 3 at 100 o C . The mass of 10 m 3 air can be calculated as

m = V ρ

= (10 m 3 ) (0.946 kg/m 3 )

= 9.46 kg

where

m = mass (kg)

V = volume (m 3 )

ρ = density (kg/m 3 )

Example - Mass of Air at Temperature 20 o C

From the table above - the density of air is 1.205 kg/m 3 at 20 o C . The mass of 10 m 3 air can be calculated as

m = (10 m 3 ) (1.205 kg/m 3 )

= 12.05 kg

Example - Lifting Force of a Hot Air Balloon

An air balloon with volume 10 m 3 is heated to 100 o C . The temperature of the surrounding air is 20 o C. The change in gravity force (weight) of the air volume is the potential lifting force of the balloon. The lifting force can be calculated as

F l = dm a g

= V d ρ a g

= (10 m 3 ) [(1.205 kg/m 3 ) - (0.946 kg/m 3 )] (9.81 m/s 2 )

= 25.4 N

where

F l = lifting force - change in gravity force (weight)  (N)

a g = acceleration of gravity (9.81 m/s 2 )

dm = V d ρ = change of mass in the balloon (kg)

dρ = change in density due to temperature difference (kg/m 3 )

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Viscosities of products and chemical species at varying conditions.

## Related Documents

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Chemical, physical and thermal properties of acetone, also called 2-propanone, dimethyl ketone and pyroacetic acid. Phase diagram included.
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Air density at pressure ranging 1 to 10 000 bara (14.5 - 145000 psi) and constant selected temperatures.
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Figures and tables with isobaric (Cp) and isochoric (Cv) specific heat of air at constant temperature and pressure ranging 0.01 to 10000 bara.
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Figures and table with changes in Prandtl number for carbon dioxide with changes in temperature and pressure.
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Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.
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Enthalpy change and temperature rise when heating humid air without adding moisture.
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Density, specific heat, thermal conductivity, viscosity and Prandtls no. of liquid ammonia at saturation pressure.
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Volumetric - or cubical - expansion coefficients for common liquids.
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Chemical, Physical and Thermal Properties of Methane - CH4. Phase diagram included.
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Chemical, physical and thermal properties of methanol, CH3OH (also called carbinol, wood alcohol, hydroxy methyl and methyl alcohol). Phase diagram included.
• ### Mixing of Humid Air

The change in state wwhen mixing moist air - enthalpy, heat, temperature and specific humidity.
• ### Moist Air - Density vs. Pressure

Density of moist air vs. pressure ranging 75 - 1000 mmHg.
• ### Moist Air - Enthalpy

Sensible and latent heat of moist air.
• ### Moist Air - Psychrometric Table for Pressure 29.92 inHg

Dry and wet bulb temperatures, saturation pressure, water vapor weight, specific volume, heat and more.
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Chemical, physical and thermal properties of pentane, also called n-pentane. Phase diagram included.
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Calculating heat removed with air by measuring the wet bulb temperature.
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## Citation

• The Engineering ToolBox (2003). Air - Thermophysical Properties. [online] Available at: https://www.engineeringtoolbox.com/air-properties-d_156.html [Accessed Day Month Year].

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