Applications of Chemical Kinetics in Environmental Systems - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 279

The concentration leaving the j th reactor is given by

e − n(t/ τ ) 1

j − 1 . (6.31)

n t
τ

2 n t

τ

C j
C( 0 ) =

n t

1
2

1

1 − +

τ +

+···+

! ( j − 1 ) !

E XAMPLE 6.4 D ISPERSION IN A S OIL C OLUMN

Chloride is a tracer used to determine the dispersivity in a soil column. It is conservative
and does not react with soil particles. A pulse input is introduced at the bottom of a soil
column of height 6.35 cm at an interstitial porewater velocity of 5.37 × 10 − 4 cm/s. The
soil has a porosity of 0.574. The chloride concentration at the exit (top) as a function of
time is given below:

t (min) C ( L , t ) / C (0)

125 0.05

150 0.15

180 0.30

200 0.40

250 0.90

Determine the dispersivity in the column.

260

240

220

200

180

160

140

120

.01 .1 1 5 10 20 30 50 70 80 90 95 99 99.9 99.99

Percent

FIGURE 6.8 Probability plot of dimensionless concentration versus time to obtain
the dispersion coefficient from experimental data.

continued