CE 318: Transport Process 2(Heat and Mass Transfer)
Lecture 19: Convective Mass Transfer Between Phases
(Chapter 29)
NSC 2104/21/2015
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About Midterm and Schedule Change
• Midterm will be posted at UBLearns at 9am Friday (4/24).
• Midterm covers chapters 24-28.
• No recitation this week (4/24).
• Homework 9 is due on 4/30 (Thursday).
The 3rd Quiz
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Quiz 1st 2nd 3rd
Average 4.9/10 6.2/10
Median grade 5.0 6.0
Standard deviation 2.4 1.8
>= (Av. + SD) 12 24
Av. – (Av.+SD) 30 9
(Av.-SD) – Av. 15 26
< (Av.-SD) 15 13
Random Thoughts: Tips on Test-Taking
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Richard Felder
Random Thoughts: Tips on Test-Taking
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Richard Felder
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Overview of Mass Transfer
• Steady State Molecular Diffusion
Fick’s Law for Molecular Diffusion
DA: gas, liquid, solid, biological materials
calculation: • Counter-diffusion;
• Unimolecular diffusion;
• diffusion/reaction
• Convective Mass-Transfer Coefficient
• Unsteady State Diffusion
• Mass Transfer Equipment
dx
dCDJ AAA
dx
dCA
21 AAAA CCkJ )(Re,ScfkA
2
2
x
CD
t
C AA
A
Multi-componentsDiscontinuous interface
zBzAAA
ABzA NNydz
dycDN ,,,
General equation for diffusion & convection
Case I: Equimolar counterdiffusion
Case II: B is stagnant (NB = 0)
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Basic Processes
zBzAAA
ABzA NNxdz
dx
RT
PDN ,,,
L
PP
RT
DJN AAAB
zAzA21
,,
0, ln
A
ALABzA PP
PP
RT
P
L
DN
• Fundamental view of heat convection
Dimensional analysis
Exact analysis of the boundary layer
Approximate boundary layer analysis
Analogy between momentum, energy and mass transfer
• Empirical equations (in the future lecture)
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Outline: kc Values ?
)(Re,ScfD
LkSh
AB
c
ABDSc
2,1,, AAczA CCkN
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Mass Convective Transfer
)(Re,ScfD
LkSh
AB
c
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Analogies of Transfers
• Equilibrium
• Two-resistance theory
– Individual film mass transfer coefficients
– Overall mass transfer coefficients
• Example
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Outline: Convective MT between Phases
Multi-componentsDiscontinuous interface
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Discontinuous Interface in Mass Transfer:Gas Absorption/Stripping
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Discontinuous Interface in Mass Transfer:Distillation
Solvent ExtractionSolvent Extraction
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Solvent Extraction: Soybean Oil ProductionSolvent Extraction: Soybean Oil Production
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Convective Mass Transfer: Discontinuous Interface
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Phases at Equilibrium
Raoult’s Law
Henry’s Law
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Gas Absorption
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Convective Mass Transfer: Discontinuous Interface
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Convective Mass Transfer: Discontinuous Interface
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Convective Mass Transfer: Discontinuous Interface
“Uphill” Transport
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Hydrophobic Solute Diffuses From Organophobic (Water) to Organophilic (PEG) Environment
Progesterone:
LogP=3.5[octanol]/[water] = 103.5 = 3,200
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“One-Way” Diffusion Based on Differential Solubility
Sudan IV Dye: logP = 6.7 [octanol]/[water] = 106.7 = 5,000,000
Water
(hydrophilic)
Vegetable Oil
(hydrophobic)
PDMS (hydrophobic) + dye
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Experimental Demonstration of “One-Way” Diffusion
25 PDMS (hydrophobic) + dye
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Gas Absorption
Heat Transfer in Series: Plane Walls
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AR
TTq 21
Ak
xR
A
AA
qAk
xR
A
AA
Ak
xR
B
BB
Ak
xR
C
CC
CBA RRR
TTq
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Mass Transfer in Series: Plane Walls
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AA R
TTN 21
AD
xR
AB
AA
qAk
xR
A
AA
Ak
xR
B
BB
Ak
xR
C
CC
CBA
AAA RRR
CCN
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NA
CA1CA2
CA3 CA4
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Convective Mass Transfer: Discontinuous Interface
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Convective Mass Transfer: Discontinuous Interface
AA mxy
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Example
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Example 7.4.1
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