mass transfer in multiphase systems - Greenleaf University

MASS TRANSFER IN MULTIPHASE SYSTEMS: VOLATILE ORGANIC COMPOUND
REMOVAL IN THREE-PHASE SYSTEMS
1 1 1 1 1
(15)
oa
KL kskD ksLkD kL kGHA
The mass flux of component A is therefore:
oa s* v*
A L A A
N K C C
(16)
The above result uses two nonexistent or virtual concentrations. C A s* is the nonexistent liquid
concentration of the solid and C A v* is the nonexistent concentration of the liquid in the gas phase.
The nonexistent variables are common usages in mass transfer and illustrate one of the major
differences with heat transfer. Since the desired results are in terms of bulk solid concentrations
and bulk partial pressures, the above equation becomes:
N
A
K
X
p
oa A A
L
kD
HA
(17)
If the value of k s is large, true for most VOCs, the first is neglected. However, the k D
could be large, e.g., activated carbon which would have the opposite effect. This is the main risk
and uncertainty that testing would help elucidate. For this project, the k D s’ appeared low enough
that it was more like a porous mineral and could be neglected in the overall mass transfer
coefficient. For low solubility VOCs, the last term is also neglected, i.e., the liquid coefficient is
controlling (Sherwood 1939). The differential equation f based on the nonexistent liquid phase is:
dC
dt
s*
A
oa
L
s* v*
A A
K a C C
(18)
f Note the use of a, the specific area discussed later
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