CE 318: Transport Process 2(Heat and Mass Transfer)

Lecture 18: Convective Mass Transfer(Chapter 28)

NSC 2104/16/2015

2

Overview of Mass Transfer

• Steady State Molecular Diffusion

Fick’s Law for Molecular Diffusion

DA: gas, liquid, solid, biological materials

calculation: different geometries and flow conditions

• Convective Mass-Transfer Coefficient

• Unsteady State Diffusion

dx

dCDJ AAA

dx

dCA

21 AAAA CCkJ )(Re,ScfkA

2

2

x

CD

t

C AA

A

Different parameters for driving forceMulti-components

3

Mass Convective Transfer: Drying the Paint

4

Mass Convective Transfer: Dryer

5

Mass Convective Transfer: Membrane Coater

Film Concept: Convective Mass TransferFilm Concept: Convective Mass Transfer

6

2,1,, AAczA CCkN

• Fundamental view of heat convection

Dimensional analysis

Exact analysis of the boundary layer

Approximate integral analysis of the boundary layer

Analogy between momentum and heat transfer

• Empirical equations (next lecture)

7

Outline: h Values ?

TThA

qs

x

Pr)(Re,fk

hLNu

8

Heat Convective Transfer

9

Heat Convective Transfer

LTT

yTT

k

hLNu

s

ys

0/

Combining of Momentum and Heat Transfer

10(Chapter 12)

Blasius’s Solution for Heat Transfer

11

Semi-Empirical Method to Estimate h

12

k

c

ckp

p

Pr

Prandtl Number

Nusselt Number

Pr)(Re,fk

hLNu

13

Outline: h Values ?

1Pr pck

14

Outline: h Values ?

• 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)

15

Outline: kc Values ?

)(Re,ScfD

LkSh

AB

c

ABDSc

2,1,, AAczA CCkN

16

Momentum, Heat and Mass Transfer

pCv

ydiffusivitthermal

ydiffusivitmomentumPr

17

Mass Convective Transfer

18

Mass Convective Transfer

)(Re,ScfD

LkSh

AB

c

Combining Momentum and Mass Transfer

19

25.17

Blasius’s Solution

20

Blasius’s solution:

Blasius’s Solution (See Chapter 12)

21

Blasius’s Solution for Mass Transfer

22

1Pr pck

Blasius’s Solution for Mass Transfer

23

When Sc=1

Blasius’s Solution for Mass Transfer

24

Average mass convective coefficient

Semi-Empirical Method to Estimate kc

25

Schmidt Number

Sherwood Number

• 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)

26

Outline: kc Values ?

)(Re,ScfD

LkSh

AB

c

ABDSc

2,1,, AAczA CCkN

27

Outline: h Values ?

Sc = Pr = 1

28

Outline: h Values ?

29

kc Values ?

• Fundamental view of heat convection

Dimensional analysis

Exact analysis of the boundary layer

Approximate integral analysis of the boundary layer

Analogy between momentum and heat transfer

• Empirical equations (next lecture)

30

Outline: h Values ?

TThA

qs

x

Pr)(Re,fk

hLNu

pck

Pr

• 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)

31

Outline: kc Values ?

)(Re,ScfD

LkSh

AB

c

ABDSc

2,1,, AAczA CCkN

Example