Page 328 - Advanced thermodynamics for engineers

14.5 OTHER KINETICS-CONTROLLED POLLUTANTS 317

7:5319 10 1
x N 2 5 3
½N 2 Š ¼ 11086 ¼ 11086 ¼ 6:7941 10 mol=cm
e
7:7957 10 2
x O 2 6 3
½O 2 Š ¼ ¼ ¼ 7:0320 10 mol=cm :
e
11086 11086
Using a combination of Eqns (14.34) and (14.35) gives
d½NOŠ 13
¼ 2 7:6 10 e ð 38000=TÞ ½OŠ ½N 2 Š e
e
dt
¼ 15:2 10 13 e ð 38000=2000Þ 4:3051 10 9 6:7941 10 5 (14.42)
3

¼ 2:491 10 7 mol cm s
A similar value can be obtained from Eqn (14.37), which gives
d½NOŠ 6 10 16 1=2
¼ e ð 69090=TÞ ½O 2 Š e ½N 2 Š e
dt T 1=2
6 10 16 1=2 (14.43)
¼ 1=2 e ð 69090=2000Þ 7:0320 10 6 6:7941 10 5
2000
3
¼ 2:4022 10 7 mol cm s:

These values can be converted from mole concentrations to more useful parameters and, in this
case, they will be depicted as rate of formation of mole fraction. Rearranging Eqn (14.40) gives
x M ¼½MŠv m ; where M is a general substance: (14.44)
Hence, the rate of production of NO in terms of mol fraction is given by

dðx NO Þ d½NOŠ
¼ v m (14.45)
dt dt
For this condition

dðx NO Þ 7 3 1
¼ 11086 2:491 10 ¼ 2:762 10 s (14.46)
dt
The curves on Fig. 14.5 were calculated in this manner. It can be seen that either Eqns (14.34) and
(14.35),or Eqn (14.37) gives similar results. This indicates that the dissociation equation, Eqn (14.36)
for oxygen is similar to that used in the program for calculating the values of mole fraction of atomic
oxygen.

14.5 OTHER KINETICS-CONTROLLED POLLUTANTS
Carbon monoxide (CO) is formed in processes in which a hydrocarbon is burned in the presence of
oxygen. If the mixture is rich (i.e. there is more fuel than oxygen available to oxidise it) then there is
bound to be some carbon monoxide formed. However, even if the mixture is lean there will be some
carbon monoxide due to the dissociation of the carbon dioxide; this was discussed in Chapters 12 and 13.