Page 445 - Modelling in Transport Phenomena A Conceptual Approach

PROBLEMS 425

in which da is the dimensionless bulk temperature defined by

d) Substitute Eq. (9) into Eq. (12) to get
OD
An e- 'f 9 (dG7a /cy) €=O
2
Sh= - n=l
3O0
x(An/Ai) e- At' (dGn/dt),+o
n=l
For large values of r) show that h. (14) reduces to

z
n
Sh= -A:
3
e) Use the method of Stodola and Vianello and show that the first approximation
gives
A: = 5.122 (16)
Hint: Use GI = [(C - 2) as a trial function.

9.18 Use Eq. (9.5-129) and show that CA CA, when
2
=2
J4 DABZ/vrnax
Therefore, conclude that the penetration distance for concentration, S,, is given by

9.19 H2S is being absorbed by pure water flowing down a vertical wall with a
volumetric flow rate of 6.5 x m3/s at 20°C. The height and the width of the
plate are 2m and 0.8m, respectively. If the diffusion coefficient of H2S in water is
1.3 x lo-' m2/s and its solubility is 0.1 kmol/m3, calculate the rate of absorption
of H2S into water.
(Answer: 6.5 x kmol/ s)

9.20 Water at 25 "C flows down a wetted wall column of 5 cm diameter and 1.5 m
height at a volumetric flow rate of 8.5 x m3/ s. Pure COa at a pressure of 1 atm
flows in the countercurrent direction. If the solubility of COz is 0.0336 kmol/ m3,
determine the rate of absorption of COP into water.
(Answer: 1.87 x kmol/ s)