Chapter 8 Fundamentals of mass transfer page 8-1
Chapter 8 Fundamentals of mass transfer
1. Drying T-Shirt
dM Ak c sat c
2. Dissolving benzoic acid walls
From Table 5.2-1, the diffusion coefficient of benzoic acid is 110-5 cm2/s.
or dc
dz = 2k
Rv (csat – c)
subject to c = 0 at z = 0, and csat = 0.003 g/cm3
csat – c
3. Permeation of benzoic acid through cellulose acetate
The total mass transfer coefficient is
1
k + l
D
-1
1
5.9710-5 + 0.01
10-5
-1
Following Problem 8.2,
Chapter 8 Fundamentals of mass transfer page 8-2
4. Permeation through cellulose acetate into benzene
From Table 5.2-2, the diffusion coefficient of benzoic acid in benzene is 1.3810-5 cm2/s
1 –
0
c = 1 – exp(-2*7.0210 *50/0.4/0.1) = 13.1%
13.1% of benzoic acid has been removed.
5. Spinning disk
6. Dissolving photoresist
7. Mass transfer into a reactive liquid
a) Balance on interface:
Chapter 8 Fundamentals of mass transfer page 8-3
b)
y = 0.01
gas liquid
x
=
0
xi = 0.0065
8. Mass transfer in an SO2 scrubber
9. Water evaporating from a falling film
From Table 8.3-2, for falling films,
0.5
10. Dissolution of a cholesterol gallstone
This is a case of free convection around a solid sphere. From Table 8.3-3,
D = 2 + 0.6
2
1/4
D
1/3
Chapter 8 Fundamentals of mass transfer page 8-4
13*0.003*980
1/4
0.06
1/3 = 1.8910-4 cm/s
11. I2 evaporation into air stream
This is a case of packed bed. From Table 8.3-3,
-0.42
2/3
12. Dewaxing of lubricants
ft3hr
3600 sec
ft3
1.15 62.4 lbs
0.0024
sec
13. Mass transfer into hydrogels
First we calculate kB:
cm
s
cm
D
2
6
1036
6
Chapter 8 Fundamentals of mass transfer page 8-5
g
cm
g
c
K
kkcK
y
BSy
2
4
3109.4
3.1
1111
14. Drying of pipe insulation
Assume as a basic 1 ft of pipe. Then the amount of water is
Saturated water vapor pressure at 80 °F (299.7 K) is 0.50683 psi (0.0345 atm).
For stagnant air, the mass transfer coefficient is about
From a mole balance, N = N1At = k[c(sat) – c(bulk)]At
-6
Since the air is certainly not stagnant, this time is too long, probably by several order of
magnitude.