Doc Number: AFG005
Revision 1.6
Properties of air and flue gas
The ideal gas law can be used for density calculations of air and flue gas, using the following specific gas
constants:
Air ideal gas constant:
 J 
Rair = 287.1 

 kg ⋅ K 
Flue gas ideal gas constant:
 J 
R fg = 276.3 

 kg ⋅ K 
For simplicity, one may assume that the properties of air and flue gas are the same. Note that the enthalpy
is also dependent on the moisture content, w, which is different for flue gas compared to air because of
the additional moisture introduced by the fuel.
Note that w is defined as the kg moisture per kg dry air. If the mass fraction x of moisture in the gas is
known, the following conversion must be used: w =
x
1− x
hair /fg (T ,w
=) 1.006 ⋅ T + w(2501 + 1.86 ⋅ T )
Air and Flue gas Enthalpy:
Air and Flue gas Prandtl number:
 kg moisture 
T in [°C ] and w in 

 kg dry air 
Prair /fg = 0.7
µair /fg (T ) =
T
 kg 


a + b ⋅T − c ⋅T 2 m ⋅ s 
a 1.2635 ⋅ 107
=
Air and Flue gas viscosity:
b 1.2618 ⋅ 104
=
c = 1.6929
T in [K ]
 kJ 
 kg 
 
Doc Number: AFG005
Revision 1.6
 W 
kair /fg (T ) =a ⋅ bT ⋅ T c 
 m ⋅ K 
Air and Flue gas conductivity:
=
a 9.1446 ⋅ 10 −5
b = 0.99958
c = 1.0148
T in [K ]