Page 116 - Mechanical Engineer's Data Handbook

THERMODYNAMICS AND HEAT TRANSFER 10.5

3.2. I I Mixtures of gases

The thermodynamic properties of a mixture of gases
can be determined in the same way as for a single gas,
the most common example being air for which the
properties are well known. Using Dalton’s law of
W= PlVl -P2V2 partial pressures as a basis, the properties of mixtures
n-1 can be found as follows.
Q= w(g) Symbols used:

m=total mass of mixture
m,, mB, etc.=masses of constituent gases
p = pressure of mixture
PA, pe, etc. =pressures of constituents
R,, RE, etc. =gas constants of constituents
T= temperature of mixture
V= volume of mixture
Dalton’s law:
Polytropic process P=PA+PB+P~+. . . +Pi
m=rnA+m,+m,+. . . +mi
where: pi=miRi(T/V)
3.2. IO Irreversible processes
Z(miRi)
Apparent gas constant R = -
Throttling (constant enthalpy process) m
Apparent molecular weight M = R,/R
h,=h2, where: R,= universal gas constant.
For perfect gas T, = T,
Wi4)
Internal energy u = -
h h m

%vi)
Entropy s=-
m
Throttling process
Specific heats:
Adiabatic mixing

When two flows of a gas rkl and m2 at temperatures T,
and T2 mix:
mT, +m2T,
Final temperature T3 =
m, +m,