TITLE.PM5

GASES AND VAPOUR MIXTURES 419

dharm

\M-therm\Th9-1.pm5

Fig. 9.4
Applying steady-flow energy equation to the mixing section (neglecting changes in kinetic
and potential energy), we get

mh&&AA 11 +mhBB+ Q = mh&&AA 22 +mhBB+ W

In case of adiabatic flow : Q = 0, and also W = 0 in this case

∴ mh&&AA 11 +mhBB = mh&&AA 22 +mhBB

Also h = cpT, hence,

mc T&&ApAA+mc TBpBB = mc T mc T&&ApAB+ pB

For any number of gases this becomes

Σ mc T&ipii = T Σ mc&ipi

i.e., T =

Σ

Σ

mc T

mc

i pii

i pi

...(9.28)

Also, Cp = Mcp and M = m/n

∴ nCp = mcp

Hence, T =

Σ

Σ

nC T

nC

i pii

i pi

...(9.29)

Eqns. (9.28) and (9.29) represent one condition which must be satisfied in an adiabatic mixing
process of perfect gas in steady flow. In a particular problem some other information must be known
(e.g., specific volume or the final pressure) before a complete solution is possible.

9.7. Gas and Vapour Mixtures

Fig. 9.5 (i) shows a vessel of fixed volume which is maintained at a constant temperature. The
vessel is evacuated and the absolute pressure is therefore zero.

p=0

T

Vessel

(evocuated)

p

T

patTg

T

(1–x)kg

water

xkg

Vapour

(i)(ii)(iii)

Fig. 9.5