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DESIGN AND FABRICATION OF
CROSS FLOW HEAT EXCHANGER
A PROJECT REPORT
Submitted by
JESU JAFFRIN.T.X. 312212114047
K.CHANDRA SHEKHAR 312212114027
ANIRUDDAN.M 312212114010
ASHWIN.S 312212114703
in partial fulfillment for the award of degree
of
BACHELOR OF ENGINEERING
In
MECHANICAL ENGINEERING
SSN COLLEGE OF ENGINEERING, CHENNAI – 603 110
ANNA UNIVERSITY: CHENNAI – 600 025
APRIL 2015
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ANNA UNIVERSITY: CHENNAI – 600 025
BONAFIDE CERTIFICATE
Certified that this project report “DESIGN AND FABRICATION OF CROSS
FLOW HEAT EXCHANGER“ is the bonafide work of “JESU JAFFRIN.T.X.,
K.CHANDRA SHEKHAR, M.ANIRUDDAN, ASHWIN.S” who carried out the
project work under my supervision.
SIGNATURE SIGNATURE
Dr. V. E. ANNAMALAI Dr. R.PRAKASH
HEAD OF THE DEPARMENT ASSOCIATE PROFESSOR
Mechanical Engineering, Mechanical Engineering
SSN College of Engineering, SSN College of Engineering
OMR, Kalavakkam – 603 110 OMR, Kalavakkam – 603 110
SUBMITTED FOR THE VIVA VOCE EXAM HELD ON: _______________
INTERNAL EXAMINER EXTERNAL EXAMINER
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ACKNOWLEDGEMENT
We are grateful to our Principal, Dr. S. Salivahanan for
providing us an opportunity to for carrying out on our project.
We sincerely thank our Head of the Department, Dr. V. E.
Annamalai for granting us permission to carry out our Design
and Fabrication Project.
We would like to express our gratitude to our guide
Dr.R.Prakash, for his valuable guidance and support
throughout the period of this project work.
We also like to thank Mr.J.R.Thomas Xavier,Annai Theres &
Co,Nagercoil for providing us the workspace and helping us
fabricate this project.
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TABLE OF CONTENTS
TITLE PAGE
ABSTRACT (v)
LIST OF SYMBOLS (vi)
1.INTRODUCTION
1.1.Exhaust Gas 1
1.1.1.Composition of Exhaust Gas
1.2.Heat Exchanger 2
` 1.2.1.Types of Heat Exchanger
1.2.2.Cross Flow Heat Exchanger
1.3.Objective 4
2.DESIGN MODEL CALCULATIONS 5
3.CAD MODELLING 9
4.FABRICATION OF HEAT EXCHANGER 11
5.EXPERIMENTAL SETUP 16
6.REFERENCES 21
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ABSTRACT
A heat exchanger is a device built for effective heat transfer
from one medium to another. The media may be separated
by a solid wall to prevent direct contact or they may be in
contact with one another. They are widely used in space
heating, refrigeration, air conditioning power plants,
chemical plants, petrochemical plants, petroleum refineries
etc. A heat exchanger is an important component of internal
combustion engines.
The objective of the present work is to design and fabricate
a multi-pass cross flow heat exchanger. Multi pass heat
exchangers provide better cooling effect when compared to
single pass heat exchangers. Instead of using fluid coolant,
air from a forced draft fan is used as the cooling medium.
The secondary objective of this project is to study the
feasibility of this heat exchanger to cool exhaust gases for
the purpose of Exhaust Gas Recirculation.
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LIST OF SYMBOLS:-
Re - Reynold’s number No unit
Nu – Nusselt’s number No unit
ρ – Density of fluid m³/kg
V’ – Volume flow rate m³/s
M’ – Mass flow rate kg/s
V – velocity of fluid m/s
Pr – Prandtl number No unit
h – Heat transfer coefficient W/m²-K
k – Thermal conductivity W/m-K
γ – Kinematic viscosity m²/s
ϵ - Effectiveness No unit
cp – Specific heat J/kg-K
N – No of Thermal units No unit
1
UNIT – I
INTRODUCTION
1.1.Exhaust Gas
Exhaust gas or flue gas is emitted as a result of the combustion
of fuels such as natural gas, gasoline/petrol, diesel fuel, fuel oil
or coal. According to the type of engine, it is discharged into the
atmosphere through an exhaust pipe, flue gas stack or propelling
nozzle. It often disperses downwind in a pattern called an
exhaust plume.
1.1.1 Compsition of Exhasut gas
The largest part of most combustion gas is nitrogen (N2), water
vapor (H2O) (except with pure-carbon fuels), and carbon
dioxide (CO2) (except for fuels without carbon); these are not
toxic or noxious (although carbon dioxide is a greenhouse gas
that contributes to global warming). A relatively small part of
combustion gas is undesirable noxious or toxic substances, such
as carbon monoxide (CO) from incomplete combustion,
hydrocarbons (properly indicated as CxHy, but typically shown
simply as "HC" on emissions-test slips) from unburnt fuel,
2
nitrogen oxides (NOx) from excessive combustion temperatures,
ozone (O3), and particulate matter (mostly soot).
1.2. Heat Exchanger
A heat exchanger is a piece of equipment built for efficient heat
transfer from one medium to another. The media may be
separated by a solid wall to prevent mixing or they may be in
direct contact. They are widely used in space heating,
refrigeration, air conditioning, power plants, chemical plants,
petrochemical plants, petroleum refineries, natural gas
processing, and sewage treatment. The classic example of a heat
exchanger is found in an internal combustion engine in which a
circulating fluid known as engine coolant flows through radiator
coils and air flows past the coils, which cools the coolant and
heats the incoming air.
1.2.1.Types of Heat Exchanger
Shell and tube heat exchanger
Plate heat exchanger
Plate and shell heat exchanger
Adiabatic wheel heat exchanger
Plate fin heat exchanger
3
Pillow plate heat exchanger
Fluid heat exchangers
Waste Heat Recovery Units
Dynamic scraped surface heat exchanger
Phase-change heat exchangers
Direct contact heat exchangers
1.2.2. Cross Flow Heat Exchanger
Cross flow heat exchangers are commonly used in gas heating or
cooling. A tube bundle carries a heating or cooling fluid (either
gas or liquid), normally perpendicular to a gas flow which
passes over the tubes and allows heat to be transferred between
the fluids. Cross flow heat exchangers can be of the mixed or
unmixed type. The mixed type is the simpler of these designs in
which the gas is mixed and not separated into channels.
A car radiator and an air conditioner evaporator coil are
examples of cross flow heat exchangers. In both cases
evaporator coil heat transfer is taking place between a liquid
flowing inside a tube or tubes and air flowing past the tubes.
With a car radiator, the hot water in the tubes is being cooled by
air flowing through the radiator between the tubes. With an air
conditioner evaporator coil, air flowing past the evaporator coils
4
is cooled by the cold refrigerant flowing inside the tube(s) of the
coil. Cross flow heat exchangers are typically used for heat
transfer between a gas and a liquid as in these two examples.
1.3.Objective
The objective of the present work is to design and fabricate a
multi pass cross flow heat exchanger for the purpose of cooling
exhaust gases from internal combustion engines. This setup
makes use of air from a forced draft fan flowing perpendicular
to the exhaust gases to cool the exhaust gases. The secondary
objective of this project is to study the feasibility of this heat
exchanger for the purpose of Exhaust gas Recirculation.
5
UNIT – II
DESIGN MODEL CALCULATIONS
For Exhaust gas [CO – Carbon monoxide]
Inlet Temperature, T hi = 100°C
Total inlet area across the bank of tubes, A e = 29 × 4 (.012 ×
.002) m²
Density, ρ e = 0.916 kg/m³
Volume Flow Rate, V’ e = 0.038976 m³/s
Mass Flow Rate, M’ e = V’ e × ρ e = 0.038976 × 0.916 = 0.0357
kg/s
Velocity of Exhaust Gas, v e = V’ e / A e = 0.038976
2.784 ×10³ = 14 m/s
Where, A e = 29 × 4 × 0.012 × 0.002 = 2.784 × 10³ m²
Reynold’s No, Re = 𝑣 𝑒 ×𝑑
𝛾, (d = 4A/P =
4∗29∗4∗.012∗.002
2∗(.012 + 0.002) = 3.43 ×
10³ m)
Prandtl No, Pr = 0.718
6
Specific heat, C p = 1043 J/kg-K
Thermal conductivity, k = 0.03012 W/m-K
Nusselt’s no, Nu = 3.66+5.597
2 = 4.6285 (pg 128) [2b/2a = 1/6]
Nu = hL/k
h , heat transfer coefficient = 𝑁𝑢 × 𝑘𝐿⁄ =
4.6285 ×0.03012
.45 × 2 =
0.1549 W/m²-K
For Coolant gas (Dry air)
Circular cross-section with diameter, d c = 0.1 m
Area of cross-section, 𝐴 𝑐 = 𝜋𝑟2 = 7.85 × 10⁻³ m²
Inlet temperature, T ci = 30°C
Density of dry air, ρ c =1.165 kg/m³
Kinematic viscosity, γ c = 16 × 10⁻⁶ m²/s
Prandtl no, Pr = 0.701
Specific heat, c pc = 1005 J/kg-K
Thermal conductivity, k c = 0.02675 W/m-K
7
Volume flow rate, V’ c = 20000 lph = 20000
3600 ×10³ = 5.554 × 10⁻³
m³/s
Mass flow rate, m’ c = V’ c × ρ c = 5.554 × 10⁻³ × 1.165 = 6.472
× 10⁻³ kg/s
Velocity of coolant gas, v c = 𝑉′𝑐
𝐴 𝑐 =
5.554 × 10⁻³
7.85 ×10⁻³ = 0.708 m/s
Reynold’s no, Re c = 𝑣𝑑
𝛾 =
0.708 ×0.1
16 ×10⁻⁶ = 4425 (Turbulent)
Nusselt’s no, Nu = 0.023 × 𝑅𝑒0˙8 × 𝑝𝑟⁰˙⁴ = 0.023 × (4425)⁰˙⁸
× (0.701)⁰˙⁴
= 16.47
Average Nusselt’s no, Nu’ = Nu[1 + 1.4
𝑥
𝑑
] = 247.05
(Fully developed x/d=.01/.1=.1)
Nu’ = ℎ𝑑
𝑘
h = 𝑁𝑢′𝑘
𝑑 =
247.05 ×0.02675
0.1 = 66.1 W/m²-K
8
Cross flow (both fluids unmixed)
Effectiveness, ε = 1 − 𝑒(𝑒(−𝑁𝐶𝑛)−1)×𝐶
𝑛
Overall heat transfer coefficient, U = 20 W/m²-K
Area, A = (29 × 4) × 2 × h (l + b) = 29 × 8 × 0.9 [0.012 + 0.002]
= 2.9232 m²
C min = (m c × c c) = 6.50436 W/K
C max = (m e × c e) = 37.2351 W/K
C= 𝐶 𝑚𝑎𝑥
𝐶 𝑚𝑖𝑛 = 5.725
N = 𝑈𝐴
𝐶 𝑚𝑖𝑛 =
20 ×2.9232
6.50436 = 8.988
n = N⁻⁰˙²² = 0.617
ε = 1 − 𝑒(𝑒(−8.988 ×5.725 ×0.617)−1)×5.725
0.617 =0.9
9
UNIT - III
CAD MODELLING
ISOMETRIC VIEW
10
TOP VIEW
11
UNIT - IV
FABRICATION OF HEAT EXCHANGER
The various processes involved in the fabrication of heat
exchanger are discussed briefly in this unit. The machining
processes are as follows:
SHIELDED METAL ARC WELDING:-
Shielded metal arc welding (SMAW), also known as manual
metal arc welding (MMA or MMAW), flux shielded arc welding
or informally as stick welding, is a manual arc welding process
that uses a consumable electrode coated in flux to lay the weld.
An electric current, in the form of either alternating current or
direct current from a welding power supply, is used to form an
electric arc between the electrode and the metals to be joined.
The workpiece and the electrode melts forming the weld pool
that cools to form a strong joint. As the weld is laid, the flux
coating of the electrode disintegrates, giving off vapors that
serve as a shielding gas and providing a layer of slag, both of
which protect the weld area from atmospheric contamination.
This process is used to weld the elements forming the base
12
GAS WELDING
Oxy-fuel welding (commonly called oxyacetylene
welding, oxy welding, or gas welding in the U.S.) and oxy-fuel
cutting are processes that use fuel gases and oxygen to weld and
cut metals, respectively. French engineers Edmond Fouché and
Charles Picard became the first to develop oxygen-
acetylene welding in 1903.Pure oxygen, instead of air, is used to
increase the flame temperature to allow localized melting of the
workpiece material (e.g. steel) in a room environment. A
common propane/air flame burns at about 2,000 °C (3,630 °F), a
propane/oxygen flame burns at about 2,500 °C (4,530 °F), and
an acetylene/oxygen flame burns at about 3,500 °C (6,330 °F).
Oxy-fuel is one of the oldest welding processes, besides forge
welding. Still used in industry, in recent decades it has been less
widely utilized in industrial applications as other specifically
devised technologies have been adopted. It is still widely used
for welding pipes and tubes, as well as repair work. It is also
frequently well-suited, and favored, for fabricating some types
of metal-based artwork. As well, oxy-fuel has an advantage over
electric welding and cutting processes in situations where
accessing electricity (e.g., via an extension cord or portable
13
generator) would present difficulties; it is more self-contained,
and, hence, often more portable.
SOLDERING
Soldering is a process in which two or more metal items are
joined together by melting and flowing a filler metal (solder)
into the joint, the filler metal having a lower melting point than
the adjoining metal. Soldering differs from welding in that
soldering does not involve melting the work pieces. In brazing,
the filler metal melts at a higher temperature, but the work piece
metal does not melt. In the past, nearly all solders
contained lead, but environmental concerns have increasingly
dictated use of lead-free alloys for electronics and plumbing
purposes.This process is used for joining the various electrical
connections
TURNING
Turning is a engineering machining process in which a cutting
tool, typically a non-rotary tool bit, describes a helical toolpath
by moving more or less linearly while the workpiece rotates.
The tool's axes of movement may be literally a straight line, or
they may be along some set of curves or angles, but they are
14
essentially linear (in the nonmathematical sense). Usually the
term "turning" is reserved for the generation of external surfaces
by this cutting action, whereas this same essential cutting action
when applied to internal surfaces (that is, holes, of one kind or
another) is called "boring". Thus the phrase "turning and boring"
categorizes the larger family of (essentially similar) processes.
The cutting of faces on the workpiece (that is, surfaces
perpendicular to its rotating axis), whether with a turning or
boring tool, is called "facing", and may be lumped into either
category as a subset. This process is used in the fabrication of
the forced draft fan.
BORING
In machining, boring is the process of enlarging a hole that has
already been drilled (or cast), by means of a single-point cutting
tool (or of a boring head containing several such tools), for
example as in boring a gun barrel or an engine cylinder. Boring
is used to achieve greater accuracy of the diameter of a hole, and
can be used to cut a tapered hole. Boring can be viewed as the
internal-diameter counterpart to turning, which cuts external
diameters.
15
There are various types of boring. The boring bar may be
supported on both ends (which only works if the existing hole is
a through hole), or it may be supported at one end(which works
both as through holes and blind holes). Lineboring (line boring,
line-boring) implies the former. Backboring (back boring, back-
boring) is the process of reaching through an existing hole and
then boring on the "back" side of the workpiece (relative to the
machine headstock).
Boring is used to machine the motor shaft to connect the motor
to the fan.
16
UNIT - V
EXPERIMENTAL SETUP
HEAT EXCHANGER:-
Cross flow heat exchangers are commonly used in gas heating or
cooling. A tube bundle carries a heating or cooling fluid (either
gas or liquid), normally perpendicular to a gas flow which
passes over the tubes and allows heat to be transferred between
the fluids. Cross flow heat exchangers can be of the mixed or
unmixed type. The mixed type is the simpler of these designs in
which the gas is mixed and not separated into channels.
The heat exchanger used is a cross flow, multi pass heat
exchanger with air cooling.
17
MOTOR AND FAN:-
The motor used is a 0.25hp,2880 rpm.
The fan is a 6 leaf, 25cfm
ENGINE:-
The engine used was a single cylinder , 4 stroke, 1500 rpm,
dieseil engine with a hydraulic dynamometer loading
arrangement.
18
PROCEDURE:-
1. Calculate the maximum load that can be applied to
dynamometer using the engine details.
2. Check the following before starting the engine as precautions,
(a) Lubricating oil level.
(b) Fuel level in the tank.
(c) Ensure that there is no load in the engine.
(d) Whether all the fuel values in the line to the engine is open
condition.
19
3. The engine is started rotating the crank by means of hand
crank lever.
4. Decompression lever is pressed for easy cranking.
5. Adjust the cooling water to the required level.
6.Switch on the forced draft fan and connect the exhaust gas the
heat exchanger by means of a connecting pipe.
7. Note the exhaust gas temperature at the inlet of the haet
exchanger and at the outlet of the heat exchanger.
8. The experiment is repeated for different values of load
applied to the engine and the readings are tabulated.
9. Note the following
Manometer reading
Time duration for 10 cc of fuel consumption in the burette.
Time duration for 3 rev. of energy meter Disc.
Load applied.
20
TABULATION:-
S.No Load
applied to
the
engine(kg)
Time taken for
10 cc fuel
consumption(s)
Exhaust
gas
temperature
at inlet
Exhaust
gas
temperature
at outlet
1. 0 99.6 89 35
2. 0.5 81.22 109 36
3. 1 73.22 122 38
4. 1.5 65.93 146 41
5. 2 59.56 164 44
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UNIT - VI
REFERENCES
1. “Automobile Engineering” vol.2 by Dr.Kirpalsingh,11th
edition pgs.335-351.
2. Heat and Mass transfer by Dr.Yahya
3. Method of operating heat exchangers by Hoechst Ceramtec
Aktiengesellschaft patent US5531265 dated.November 1, 1994
4. International Journal of Heat and Mass Transfer, Volume 81,
February 2015, Pages 542-553
5. Applied Thermal Engineering, Volume 30, Issue 10, July
2010, Pages 1170-1178