Chemical Engineering

Department, BUET, 2019

Dr. Md Shahinoor Islam

Dr. Easir Arafat Khan
 CHE 453: Transport Phenomena
 Instructors: Md Shahinoor Islam and
Easir Arafat Khan
 3 Credit Hours:
Sunday (9:00 am)
Tuesday (10:00 am)
Wednesday (11:00 am)
 Course Outlines
 Marks distributions
Class tests: 20%
Attendance: 10%
Final exam: 70%
 Four (4) class tests will be taken during the course and
best three (3) of them will be counted to cover 20% of
the total marks.
Topics
1. Momentum Transport
 viscosity and the mechanism of momentum
transport
 Velocity distribution of laminar flow
 Equation of change for isothermal systems
 Velocity distribution with more than one
variable
 Velocity distribution in turbulent flow
2. Energy Transport
 Thermal conductivity and mechanism of
energy transport
 Temperature distribution in solids and in
laminar flow
 Equation of change for non isothermal
systems
 Temperature distribution with more than one
variable
 Temperature distribution in turbulent flow
3. Mass Transport
 Diffusivity and the mechanism of mass
transport
 Concentration distribution in solids and
laminar flow
 Equation of change in multicomponent
systems
4. Analogy among momentum, energy and
mass transfer
Text books
 Bird, R.B., WE. Stewart and E. N. Lightfoot,
Transport Phenomena, John Wiley (1960) or
second edition (2002)
 Other references will be given during the
lectures as needed
Chapter Topic Week Teac CT
her
Introduction 1 SI
1-2 Viscosity and Application of shell balances 1-3 SI 1
for momentum transfer (Laminar flow)
3 Application of equation of change for 3-5 SI 2
momentum transfer (Laminar flow)
4 Velocity distribution with more than one 6 SI
independent variable
5 Velocity distribution in turbulent flows 6 SI
8-9 Thermal conductivity and Application of 7-8 EAK 3
shell balances energy transfer
10-12 Application of equation of change for 9-11 EAK 4
nonisothermal system(heat transfer)
16-18 Mass transfer and multi-component 12-13 EAK
systems.
Hand out Analogy equations for momentum, energy 14 SI
and mass transfer
By the end of this course, you should be able to:
1) understand the three types of transport phenomena
(momentum, heat and mass)
2) explain the mechanisms of transport phenomena
3) understand the differential momentum, heat and
mass balance and set up a mathematical model for a
physical/chemical process.
4) derive and apply equation of change in curvilinear
coordinate systems
5) analyze the relations and similarities among 3 types
of transport that may occur in a system.
 Transport Phenomena is the subject which deals
with the movement of different physical
quantities in any chemical or mechanical process
and describes the basic principles and laws of
transport.
 It also describes the relations and similarities
among different types of transport that may occur
in any system.
Transport in a chemical or mechanical process can be
classified into three types:
 Momentum transport deals with the transport of
momentum in fluids and is also known as fluid
dynamics.
 Energy transport deals with the transport of different
forms of energy in a system and is also known as heat
transfer.
 Mass transport deals with the transport of various
chemical species themselves.
3 level at which transport phenomena can be studied
 The transport equations are developed by
balancing of physical quantities as input and
output streams in a control volume which may
provide a fair idea about overall performance
of systems.
 But it cannot provide information at local
level.
 The transport equations are developed by
balancing physical quantities for a small control
volume and then allowing the control volume to
approach zero results in transport equations
which are valid at each point in the fluid.
 Theses equations may be solved by using
appropriate assumptions and boundary
conditions.
 Microscopic level of study of system gives the
chance to study the systems in much more
details and provides more accurate description
of the transport phenomena occurring in the
system.
 If required, these equations may be integrated
for the whole system for better understanding
of the overall performance of the system.
 The transport phenomena are described in
terms of molecular structure and
intermolecular forces.
 Study of transport phenomena at this level may
be important for theoretical physicist/chemist.
 MOMENTUM TRANSPORT
1) Fluid flow is a simple example of momentum
transfer. The driving force for fluid flow is a
pressure difference.
2) On a molecular scale that means that the
molecules knock into each other transfer their
momentum to other molecules.
3) On a larger scale, these molecules knock into
each other determine how the fluid is going to
flow that is, if it will just flow smoothly
(laminar), or if it will be rough (turbulent).
Example: Water flow in a drinking fountain. What
will happen if the valve in a drinking fountain is
opened?

When the valve in a drinking fountain is opened, the

water flows out in a jet because the water pressure inside
the fountain is much higher than the atmospheric
pressure into which the jet discharges.
 HEAT TRANSFER
1) Deals with the transfer of energy and difference
in temperature is the driving force for the heat
transfer.
2) The process of increasing the kinetic energy of a
material's particles from a material of high
temperature to one of lower temperature.
3) Once the material at the same temperature, no
more energy can be transferred.
 CONDUCTION
The transfer of heat through solid objects
e.g: touch something hot

CONVECTION
Typical methods of The transfer of heat
heat transfer through liquids or gases
e.g: Heat from burner is
transferred to the
circulating water
RADIATION
The transfer of heat, in the form of
electromagnetic energy, through space.
e.g: Expose to the sun – felt warmth
Example: Molecular transport for conduction of heat
from a high-temperature region to a low-temperature
region through a metal rod, shown in Figure below.
What happen to the metal rod after a few minute?
rod

Flow Direction

When metal heated on one end, will soon be hot on the

other end too.
The hot molecules in the fire have more energy than the
cooler molecules of the other end rod. As the molecules
collide, energy is transferred from the hotter molecules to
the cooler molecules.
 MASS TRANSPORT

1) Mass transfer deals with the transfer of mass.

Concentration is the driving force.

2) Once the concentration is the same everywhere,

no more mass transfer can take place.

3) If you take a glass of water and put one drop of

red dye in it. Even if you don't stir the water,
eventually the water is all the same pinkish color.
 Example: How the red dye spreads out in the
water?

The red dye when it is first dropped into the water

is at a high concentration and the water is at zero
concentration. But, as the dye spreads out, the
concentration of the dye slowly increases, until, it
is all at the same low concentration everywhere.
Once the concentration of the dye in the water is
the same everywhere, no more mass transfer can
take place.
 They frequently occur simultaneously in
industrial, biological, agricultural, and
meteorological problems; in fact, the
occurrence of any one transport process
by itself is the exception rather than the
rule.
 The basic equations that describe the
three transport phenomena are closely
related. The similarity of the equations
under simple conditions is the basis for
solving problems "by analogy.”
 The mathematical tools needed for
describing these phenomena are very similar.
 The molecular mechanisms underlying the
various transport phenomena are very closely
related. All materials are made up of
molecules, and the same molecular motions
and interactions are responsible for
viscosity, thermal conductivity, and
diffusion.
 How are they all related?

• They all are similar in their behaviour.

• They all move stuff (Momentum, Heat, or Mass)

from a place where there is a lot of the “stuff” to a
place where there is less “stuff”.
Relation among mass, momentum and
energy
 Flux is proportional to the gradient of a potential
 Momentum transport deals with the transport
of momentum which is responsible for flow
in fluids.
 Momentum transport describes the science of
fluid flow also called fluid dynamics.
 A few basic assumptions are involved in fluid
flow and these are discussed below.
 In Fig. 1.1-1 we show a pair of large parallel
plates, each one with area A, separated by a
distance Y. In the space between them is a
fluid-either a gas or a liquid. This system is
initially at rest.
 At time t = 0 the lower plate is set in motion
in the positive x direction at a constant
velocity V.
 As time proceeds, the fluid gains momentum,
and ultimately the linear steady-state
velocity profile shown in the figure is
established and the flow is laminar.
Momentum Transport
 Momentum Transport

:flux of x-momentum in the positive y direction, where the term "flux"

means "flow per unit area."