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