1. Bansal Institute of Science and Technology, Bhopal
Coolingof water through Convectionprocess
FUNDAMENTALS OF HEAT
TRANSFER
A study on Heat Exchangers and its applications

2. SYNOPSIS ON HEAT TRANSFER AND ITS APPLICATIONS
Bansal institute of Science and Technology, Bhopal
(B.I.S.T)
Guided by: Submitted By:
Miss Mamta Varma Ajay Verma (08)
Professor ME Dept. Ashish Samuel Dass (25)
BIST Bhopal Deepak Kumar (31)
Dheerendra Patel (35)
Yogesh Sahu (121)
MECHANICAL ENGINEERING DEPT. VII SEM BIST BHOPAL

3. TABLE OF CONTENTS
1. HEAT TRANSFER
2. MODES OF HEAT TRANSFER
2.a. Conduction
2.b. Convection
2.b.1. Free or Natural Convection
2.b.2. Forced Convection
2.c. Radiation
3. HEAT EXCHANGERS
3.a.Types of Heat Exchangers
3.a.1. On the basis of nature of heat exchange process
3.a.2. On the basis of relative direction of fluid motion
3.a.3. On the basis of design and constructional features
3.a.4. On the basis of physical state of fluids
4. LOGARITHMIC MEAN TEMPERATUREDIFFERENCE (LMTD)
5. OUR VISION
5.a. Advantages of the desired design

4. HEAT TRANSFER
Heat transfer is the exchange of thermal energy between physical systems,
depending on the temperature and pressureby dissipating heat. Heat transfer is a
process function (path function). Heat transfer always occurs froma region of high
temperature to another region of lower temperature.
MODES OF HEATTRANSFER:-
The fundamental modes of heat transfer are:
a)Conduction; b)Convection; c)Radiation;
(a)Conduction: ‘Conduction’ is the transfer of heat from one partof the substance
to another part of the same substance, without appreciable displacement of
molecules forming the substance.
Heat transfer by conduction is evaluated by “Fourier’s law of heat conduction”.
Fourier’s law of heat conduction is an empirical law based on observation and
states as follows:
‘‘The rate of flow of heat through a simple homogeneous solid is directly
proportionalto the area of the section at right angles to the direction of heat flow,
and to change of temperature with respect to the length of the path of the heat
flow’’.
Mathematically, it can be represented by the equation:
Q ∝ A. (dt/dx)
Where, Q = Heat flow through a body per unit time (in watts), W,
A = Surface area of heat flow (perpendicular to the direction of flow), m^2,
dt = Temperaturedifferenceof the faces of block (homogeneoussolid) of thickness
‘dx’ through which heat flows, °C or K, and
dx = Thickness of body in the direction of flow, m.

5. (b) Convection: ‘Convection’ is the transfer of heat within a fluid by mixing of one
portion of the fluid with another. The types of heat transfer are:
(i) Free or natural convection: Free or natural convection occurs where the fluid
circulates by virtue of the natural differences in densities of hot and cold fluids; the
denser portions of the fluid move downward because of the greater force of
gravity, as compared with the force on the less dense.
(ii) Forcedconvection: When the work is done to blow or pump the fluid, it is said
to be forced convection.
The rate equation for the convective heat transfer (regardless of particular nature)
between a surface and an adjacent fluid is prescribed by Newton’s law of cooling
is:
Q = hA(ts – tf)
Where, Q = Rate of conductive heat transfer,
A = Area exposed to heat transfer,
ts = Surface temperature,
tf = Fluid temperature, and
h = Co-efficient of conductive heat transfer.
Fig. Concept of Conduction, Convection and Radiation
(c) Radiation: ‘Radiation’ is the transfer of heat through space or matter by means
other than conduction or convection. Radiation heat is thought of as
electromagnetic wavesor quanta (asconvenient) an emanation of the samenature

6. as light and radio waves.Radiantenergy (being electromagnetic radiation) requires
no medium for propagation and will pass through a vacuum.
HEAT EXCHANGERS:-
A ‘heat exchanger’ may be defined as an equipment which transfers theenergy
froma hot fluid to a cold fluid, with maximum rate and minimum investment and
running costs.
Examples of heat exchangers:
(i) Intercoolers and preheaters; (ii) Condensers and boilers in steam plant;
Types of Heat Exchangers:
In order to meet the widely varying applications, severaltypes of heat exchangers
have been developed which are classified on the basis of nature of heat exchange
process, relativedirection of fluid motion, design and constructionalfeatures, and
physicalstate of fluids.
1. Nature of heat exchange process:
Heat exchangers, on the basis of nature of heat exchange process, areclassified
as follows:
(i) Direct contact (or open) heat exchangers.
(ii) Indirectcontact heat exchangers.
(a) Regenerators. (b) Recuperators.
2. Relative direction of fluid motion:
According to the relative directions of two fluid streams the heat exchangers are
classified into the following three categories:
(i) Parallel-flow or unidirection flow (ii) Counter-flow (iii) Cross-flow.
3. Design and constructionalfeatures:
On the basis of design and constructionalfeatures, the heat exchangers are
classified as under:

7. (i) Concentric tubes: In this type, two concentric tubes are used, each carrying
one of the fluids. This direction of flow may be parallel or counter. The
effectiveness of the heat exchanger is increased by using swirling flow.
(ii) Shell and tube: In this type of heat exchanger one of the fluids flows through a
bundle of tubes enclosed by a shell. The other fluid is forced through the shell and
it flows over the outside surfaceof the tubes.
(iii) Multiple shell andtube passes: Multiple shell and tube passes areused for
enhancing the overall heat transfer.
4. Physical state of fluids:
Depending upon the physical state of fluids the heat exchangers are classified as
follows:
(i) Condensers (ii) Evaporators
(i) Condensers: In a condenser, the condensing fluid remains at constant
temperature throughout the exchanger while the temperature of the colder fluid
gradually increases from inlet to outlet.

8. (ii) Evaporators: In this case, the boiling fluid (cold fluid) remains at constant
temperature while the temperature of hot fluid gradually decreases from inlet to
outlet.
Logarithmic Mean Temperature Difference (LMTD):
Logarithmic mean temperature difference (LMTD) is defined as that temperature
difference which, if constant, would give the samerate of heat transfer as actually
occurs under variable conditions of temperature difference.
Fig. LMTD considerations for Parallel flow and Counter flow Heat Exchangers
OUR VISION:-
Our aim is to use the abovestated concept of convective heat transfer process
and the basic working principlebehind heat exchangers to develop a water cooler
that can be effective as well as efficient fromcustomer point of view taking rural
crowd under major consideration.
Advantages of thedesireddesign:
1. There is no need of any auxiliary adjustments/installations to cool the water.
2. It is eco-friendly as there is no emission of CFC or any other environment
polluting element.
3. In a minimum investment, the serviceof refrigerator like cooled water can be
afforded.