i

Acknowledgments
I would like to thank to all of the teachers in the department petrochemical,
oil and gas faculty, Hanoi University of Mining and Geology was dedicated teach
me during the time I study and practice at school.
I am deeply extending my sincere appreciation to my instructor, Dr. Vũ Văn
Toàn, for his valuable advice, constant support, commitment, dedication,
encouragement and precious guidance, creative suggestions and critical comments,
and for his being everlasting enthusiastic from the beginning to the end of the
seminar. Without his urge, no doubt, this work would not have been possible at all.
And finally, I would like to thank my parents, friends who always there
encouraging me during 5 years as well as during I do my graduation thesis.


ii

Contents
Acknowledgments ............................................................................................ i
List of figure .................................................................................................. iv
List of table ..................................................................................................... v
NOMENCLATURE ...................................................................................... vi
Preface .......................................................................................................... vii
Chapter 1: Introduction ................................................................................. 1
1.1.

Heat exchanger......................................................................................................... 1

1.2.

Classification of heat exchanger ............................................................................... 1

1.2.1.

Fixed tube sheet exchanger............................................................................................ 2

1.2.2.

Removable tube bundle ................................................................................................. 3

1.2.2.1.

U – Tube ........................................................................................................................ 3

1.2.2.2.

Floating head ................................................................................................................. 4

Chapter 2: Thermal Design Considerations ................................................... 6
2.1.

Shell .......................................................................................................................... 6

2.2.

Tube .......................................................................................................................... 7

2.3.

Tube pitch and tube-layout ....................................................................................... 8


2.4.

Tube passes ............................................................................................................... 9

2.5.

Tube sheet ............................................................................................................... 10

2.6.

Baffles..................................................................................................................... 11

2.7.

Fouling Considerations .......................................................................................... 13

2.8.

Selection of fluids for tube and the shell side .......................................................... 15

Chapter 3: Thermal Design Process ............................................................. 16
Chapter 4: Design problem .......................................................................... 20
4.1.

Problem statement .................................................................................................. 20

4.2.

Fluid properties ...................................................................................................... 21


4.2.1.

Crude oil ...................................................................................................................... 21

4.2.2.

Kerosene ...................................................................................................................... 22

4.3.

Assign fluid to shell and fluid to tube...................................................................... 24

4.4.

Evaluate heat duty and outlet temperature of crude oil .......................................... 25

4.5.

Estimate the overall heat transfer coefficient.......................................................... 27


iii

4.6.

Calculate Logarithmic mean temperature different ................................................ 30

4.7.

Calculate heat transfer area.................................................................................... 32


4.8.

Decide appropriate tubes......................................................................................... 33

4.9.

Calculate tube – side heat transfer coefficient ........................................................ 35

4.10.

Calculate shell diameter.......................................................................................... 37

4.11.

Calculate shell – side heat transfer coefficient........................................................ 39

4.12.

Overall heat transfer coefficient ............................................................................. 41

4.13.

Pressure drop .......................................................................................................... 42

Conclusion .................................................................................................... 47
Reference ...................................................................................................... 48


iv


List of figure
Figure 1.1: Classification of shell and tube heat exchanger .....................................2
Figure 1.2: Fixed tube sheet heat exchanger ............................................................3
Figure 1.3: U - tube heat exchanger .........................................................................4
Figure 1.4: Floating head heat exchanger ................................................................5
Figure 2.1: Shell of a heat exchanger ......................................................................6
Figure 2.2: Tube of a straight tube heat exchanger ..................................................7
Figure 2.3: Heat exchanger tube layout ...................................................................8
Figure 2.4: Straight tube heat exchanger one and two pass tube side .......................9
Figure 2.5: Tube passes arrangement ......................................................................9
Figure 2.6: Stainless tube sheet .............................................................................10
Figure 2.7: Different type of heat exchanger baffles ..............................................11
Figure 2.8: Baffle cut ............................................................................................12
Figure 2.9: Baffle cut and fouling in shell .............................................................12
Figure 2.10: The fouling in heat exchanger ...........................................................13
Figure 4.1: Specific heat of hydrocarbon liquid .....................................................25
Figure 4.2: Overall heat transfer coefficient ..........................................................28
Figure 4.3: Correction factor F ..............................................................................31
Figure 4.4: Tube side heat transfer factor ..............................................................35
Figure 4.5: Shell bundle clearance.........................................................................38
Figure 4.6: Shell side heat transfer factor ..............................................................40
Figure 4.7: Tube side friction factor ......................................................................42
Figure 4.8: Shell side friction factor ......................................................................43


v

List of table
Table 2.1: Typical values of fouling coefficients and resistances...........................14

Table 2.2: Guidelines for placing the fluid in order of priority ..............................15
Table 4.1: Typical overall heat transfer coefficient ................................................27
Table 4.2: Constant for calculating shell diameter.................................................. 37
Table 4.3: The common tube per pass..................................................................... 45


vi

NOMENCLATURE
Symbol
q̇
mh
mc
Cp,h
Cp,c
Th,i
Th,o
Tc,i
Tc,o
U
A
ΔTm
do
di
Nt
Np
At
Pt
As
Ds

De
Db
Cb
L
ht
hs
Ua
U0
u
P
k
Re
Pr
Nu

Description
Total heat transfer
Mass of hot fluid
Mass of cold fluid
Specific heat of hot fluid
Specific heat of cold fluid
Hot fluid temperature at inlet
Hot fluid temperature at outlet
Cold fluid temperature at inlet
Cold fluid temperature at outlet
Overall heat transfer coefficient
Heat transfer area
Logarithmic mean temperature different
Outer diameter of tube
Inner diameter of tube

Number of tubes
Number of tube pass
Cross area of tube
Tube pitch
Shell side cross flow area
Internal shell diameter
Equivalent diameter
Bundle diameter
Clearance
Length of shell
Tube – side heat transfer coefficient
Shell – side heat transfer coefficient
Assumed over all heat transfer coefficient
Calculated over all heat transfer coefficient
Velocity
Pressure
Thermal conductivity
Renoldous number
Pranditle number
Nussult number

Unit
W
kg
kg
kJ/kg.oC
kJ/kg.oC
o
C
o

C
o
C
o
C
W/m2.oC
m2
o
C
m
m
m2
m
m2
m
m
m
m
m
W/m2.oC
W/m2.oC
W/m2.oC
W/m2.oC
m/s
Bar
W/m.oC


vii


Preface
Heat exchangers are systems of thermal engineering in which its
applications are occurred in different industries. Heat exchangers are the basic or
heart of once organized plant since it transfers energy to the processing plant. This
paper describes about thermal design considerations and the thermal design of shell
and tube heat exchangers.


1

Chapter 1: Introduction
1.1. Heat exchanger
Heat exchanger is a device that is used to transfer thermal energy no mixing
between two or more fluids, between a solid surface and a fluid, or between solid
particulates and a fluid. For the heat transfer to occur two fluids must be at different
temperatures and they must be thermal contact. Heat exchange involves convection
in each fluid and conduction through the separating wall. Heat can flow only from
hotter to cooler fluids. However, they are not only used in heating applications but
are also used in cooling applications, such as refrigerators and air conditioners.

1.2. Classification of heat exchanger
Many types of heat exchangers can be distinguished from on another based
on the direction the liquids flow. In such applications, the heat exchangers can be
and be parallel-flow, cross-flow, or countercurrent. In parallel-flow heat
exchangers, both fluid involved move in the same direction, entering and exiting
the exchanger side by side. In cross-flow heat exchangers, the fluid paths run
perpendicular to one another. In countercurrent heat exchangers, the fluid paths
flow in opposite directions, with each exiting where the other enters.
Countercurrent heat exchangers tend to be more effective than other types of
exchangers.

Heat exchangers are also typically classified according to transfer processes,
number of fluids, surface compactness, construction features and heat transfer
mechanisms. Amongst of all type of exchangers, shell and tube exchangers are
most commonly used heat exchange equipment.


2

Figure 1.1:
.1: Classification of shell and tube heat exchanger

1.2.1. Fixed tube sheet exchanger
Mostly, it is used in high pressure and high temperature applications. Fixed
tube sheet heat exchangers are the one that are very much used in process chemical
industries and refinery services, as there is absolutely no chance for intermixing of
fluids. This type of heat exchanger is employed where even slightest intermixing of
fluids can’t be tolerated. A fixed tube sheet heat exchanger has straight tubes that
are secured at both ends to tube sheets welded to the shell.
The principal advantage of the fixed tube sheet construction is its low cost
because of its simple construction. In fact, the fixed tube sheet is the least
expensive construction type.
The disadvantage of fixed tube sheet heat exchanger is shell pass cannot be
cleaned with the mechanical method and can be cleaned with chemical method
only. Their maintenance process is difficult.
The Fixed tube -sheet heat exchanger
changer is applicable to all services where the
temperature difference between the shell and tube is small. The temperature
difference is slightly great but the pressure of shell pass is not high with media in
the shell pass not easy to scale.



3

Figure 1.2: Fixed tube sheet heat exchanger

1.2.2. Removable tube bundle
A fixed tube sheet heat exchanger is the cheapest because of the ease of
fabrication. This heat exchanger requires periodic cleaning, replacement of tubes
etc. and inside of the tubes can be easily cleaned by mechanical means (by forcing
wire brush or worm) and cleaning of the tubes from outside require removal of the
tubes bundles from the heat exchanger, in addition to the above cited difficulty
many heat exchangers are provided with removable tubes bundles. So as to make
removal of the tube bundles possible and to allow for considerable expansion of the
tubes, a removable tube bundle exchanger is used.
1.2.2.1.

U – Tube

In the U-tube exchanger, a bundle of nested tubes, each bent in a series of
concentrically tighter U-shapes, is attached to a single tube sheet. Each tube is free
to move relative to the shell, and relative to one another, so the design is ideal for
situations that accommodate large differential temperatures between the shell side
and the tube side fluids during service. Such flexibility makes the U-tube exchanger
ideal for applications that are prone to thermal shock or intermittent service. The Utube bundle provides minimum clearance between the outer tube and the inside of
the shell for any of the removable-tube-bundle constructions. Clearances are of the
same magnitude as for fixed-tube-sheet heat exchangers.


4


The advantage of U – tube exchanger is it allows for differential thermal
expansion between shell and tubes as well as between individual tubes and capable
of withstanding thermal shock. High heat transfer surface area forgiven shell and
tube size. Shell side can be steam or mechanically cleaned. Bundle can be removed
for shell side cleaning and maintenance.
The disadvantage: individual tube replacement is difficult. The exchanger
cannot be made single-pass on tube side, so true countercurrent flow not possible.
Draining tube side is difficult in vertical (head-up) position. Tube side can be
cleaned by chemical means only.

Figure 1.3: U - tube heat exchanger

1.2.2.2.

Floating head

In this, exchanger tubes are fixed at both the ends in the floating and
stationary tubes sheet. The stationary tubes sheet is clamped between shells.
The floating tubes sheet is clamped between the floating head and a clamp
ring. The ring which is split in half to permit dismantling is placed at the back of
the tube sheet shows the details of a split ring assembly. The floating tubes sheet is
kept slightly smaller in diameter than the inside diameter of shell so as to withdraw
the entire tube bundle from channel end. The channel is provided with inlet and
outlet connection for tubes side fluid. The shell is closed by shell cover or bonnet
on a floating head side. Shell cover at the floating head end is larger than the other
end so as to enable the tubes to be placed as near as possible to the edge of the


5


fixed tube sheet. The tube sheet along with floating head is free to move and take
the differential thermal expansion between the shell and the tubes bundle.
The advantage of floating head type is the tube of the exchanger is
removable for inspection and mechanical cleaning of outside of the tubes. It is
widely used in chemical industry and suitable for rigorous duties associated with
high pressure and temperature and also with dirty fluids.

Figure 1.4: Floating head heat exchanger


6

Chapter 2: Thermal Design
Considerations
The flow rates of both hot and cold streams, their terminal temperatures and
fluid properties are the primary inputs of thermal design of heat exchangers.
Thermal design of a shell and tube heat exchanger typically includes the
determination of heat transfer area, number of tubes, tube length and diameter, tube
layout, number of shell and tube passes, type of heat exchanger (fixed tube sheet,
removable tube bundle etc), tube pitch, number of baffles, its type and size, shell
and tube side pressure drop etc.

2.1. Shell
Shell is the container for the shell fluid and the tube bundle is placed inside
the shell. Usually, it is cylindrical in shape with a circular cross section, although
shells of different shapes are used in specific applications and in nuclear heat
exchangers to conform to the tube bundle shape. Shell diameter should be selected
in such a way to give a close fit of the tube bundle. The clearance between the tube
bundle and inner shell wall depends on the type of exchanger. Shells are usually
fabricated from standard steel pipe with satisfactory corrosion allowance.


Figure 2.1: Shell of a heat exchanger


7

2.2. Tube
Tube OD of ¾ and 1‟ are very common to design a compact heat exchanger.
The most efficient condition for heat transfer is to have the maximum number of
tubes in the shell to increase turbulence. The tube thickness should be enough to
withstand the internal pressure along with the adequate corrosion allowance. The
tube length of 6, 8, 12, 16, 20 and 24 ft are preferably used. Longer tube reduces
shell diameter at the expense of higher shell pressure drop. Finned tubes are also
used when fluid with low heat transfer coefficient flows in the shell side. Stainless
steel, admiralty brass, copper, bronze and alloys of copper-nickel are the commonly
used tube materials.

Figure 2.2: Tube of a straight tube heat exchanger


8

2.3. Tube pitch and tube
tube-layout
Tube pitch is the shortes
shortestt center to center distance between the adjacent
tubes. The tubes are generally placed in square or triangular patterns in the tube
sheets. The square layouts are required where it is necessary to get at the tube
surface for mechanical cleaning. The triang
triangular

ular arrangement allows more tubes in a
given space. The tube spacing is given by the tube pitch/tube diameter ratio, which
is normally 1.25 or 1.33. Since a square layout is used for cleaning purposes, a
minimum gap of 6.35 mm (0.25 in) is allowed between tubes.

Figure 2.3: Heat exchanger tube layout


9

2.4. Tube passes
The tube passes vary from 1 to 16. The tube passes of 1, 2 and 4 are
common in application. The number of passes is chosen to get the required tube
side fluid velocity to obtain greater heat transfer coefficient and also to reduce scale
formation. Increasing the number of tube pass that will increase velocity of fluid of
tube side. The partition built into exchanger head known as partition plate (also
called pass partition) is used to direct the tube side flow.

Figure 2.4: Straight tube heat exchanger one and two pass tube side

The arrangement of tube pass can be illustrated in the figure below.

Figure 2.5: Tube passes arrangement


10

2.5. Tube sheet
The tubes are fixed with tube sheet that form the barrier between the tube
and shell fluids. The tubes can be fixed with the tube sheet using ferrule and a soft

metal packing ring. The tubes are attached to tube sheet with two or more grooves
in the tube sheet wall by “tube rolling‟. The tube metal is forced to move into the
grooves forming an excellent tight seal. This is the most common type of fixing
arrangement in large industrial exchangers. The tube sheet thickness should be
greater than the tube outside diameter to make a good seal. The design of tube
sheets is a fairly precise and complex process; the exact number of tubes needs to
be established and a pattern of holes calculated to spreads them evenly over the
tube sheet surface. Large exchangers may have several thousand tubes running
through them arranged into precisely calculated groups or bundles.

Figure 2.6: Stainless tube sheet


11

2.6. Baffles
Baffles are used to increase the fluid velocity by diverting the flow across
the tube bundle to obtain higher transfer coefficient. Baffles also serve as support s
for the tubes during operation and help in preventing vibration from flow induced
eddies. The distance between adjacent baffles is called baffle-spacing. The baffle
spacing of 0.2 to 1 times of the inside shell diameter is commonly used. Baffles are
held in positioned by means of baffle spacers. Closer baffle spacing gives greater
transfer coefficient by inducing higher turbulence. The pressure drop is more with
closer baffle spacing.

Figure 2.7: Different type of heat exchanger baffles

Baffle cut is the height of the segment that is cut in each baffle to permit the
shell side fluid to flow across the baffle. In case of cut segmental baffle, a segment
(called baffle cut) is removed to form the baffle expressed as a percentage of the

baffle diameter.


12

Figure 2.8: Baffle cut

Baffle cut, either too much or too little, creates velocity changes in the shellside fluid. Baffle cuts can vary between 15% and 45% and are expressed as ratio of
segment opening height to shell inside diameter. The upper limit ensures every pair
of baffles will support each tube. A baffle cut of 20 to 25% provide a good heat
transfer with the reasonable pressure drop. The following figure compares too
much flow restriction, just right, and too little flow restriction for a shell and tube
exchanger.

Figure 2.9: Baffle cut and fouling in shell


13

2.7. Fouling Considerations
Fouling is generally defined as the accumulation and formation of unwanted
materials on the surfaces of processing equipment, which can seriously deteriorate
the capacity of the surface to transfer heat under the temperature difference
conditions for which it was designed. The most of the process fluids in the
exchanger foul the heat transfer surface. Therefore, net heat transfer with clean
surface should be higher to compensate the reduction in performance during
operation. Fouling of exchanger increases the cost of construction due to over
sizing, additional energy due to poor exchanger performance and cleaning to
remove deposited materials. A spare exchanger may be considered in design for
uninterrupted services to allow cleaning of exchanger.


Figure 2.10: The fouling in heat exchanger


14

The effect of fouling is allowed for in design by including the inside and
outside fouling coefficients in ca
calculation.
lculation. Fouling factors are usually quoted as
heat-transfer
transfer resistances, rather than coefficients. Typical values for the fouling
coefficients and factors for common process and service fluids are given in the
following table.

Table 2.1: Typical values of fouling coefficients and resistances


15

2.8. Selection of fluids for tube and the shell side
The routing of the shell side and tube side fluids has considerable effects on
the heat exchanger design. Some general guidelines for positioning the fluids are
given in the following table. It should be understood that these guidelines are not
ironclad rules and the optimal fluid placement depends on many factors that are
service specific.

Table 2.2: Guidelines for placing the fluid in order of priority

Tube-side fluid Shell-side fluid

Condensing vapor (unless corrosive)
Corrosive fluid
Fluid with large temperature difference (>40°C)
Cooling water
Fouling fluid
Less viscous fluid
High-pressure steam
Hotter fluid


16

Chapter 3: Thermal Design Process
1)
2)
3)
4)
5)

Obtain the required thermo physical properties of hot and cold fluids
Assign fluid to shell side or tube side
Perform energy balance and find out the heat duty (q̇ ) of the heat exchanger
Assume a reasonable value of overall heat transfer coefficient (Ua)
Determine Logarithmic mean temperature different (ΔTlm), correction factor
(F)
6) Calculate heat transfer area (A) required:
A=

q̇
∗F∗U


∆T

7) Design tube
 Decide the tube diameter (di, do), tube pitch (Pt), tube length L and tube
layout
 Calculate number of tubes (Nt) required to provide the heat transfer area
(A)
A
πd L

N =
 Tube cross area of tube
A =

π
∗d
4

 Decide the number tube pass (Np)
 Calculate tube side fluid velocity
u =

ṁ
A .ρ .N

 Calculate Renoldous number
Re =

ρu d

μ

 Calculate Pranditle number
Pr =

μC
k


17

 Calculate Nussult number
μ
μ

Nu = j ∗ Re ∗ Pr

.

 Calculate the tube – side heat transfer coefficient
h =

Nu. k
d

8) Design shell
 Calculate bundle diameter (Db)
D =d ∗

N

K

n1 and K1 can be look up in appendix
 Determine the shell clearance (Cb)
 Calculate shell diameter (Ds)
D =D +C
 Assign baffle cut and baffle space
 Calculate shell side cross flow area
A =

p −d
p

∗D ∗B

 Calculate the shell equivalent diameter
 Triangular pitch arrangement
D =

1.1
∗ (p − 0.917d )
d

 Square pitch arrangement
D =

1.27
∗ (p − 0.785d )
d


 Calculate shell – side velocity
u =

m
A .ρ


18

 Calculate Renoldous number
Re =

ud ρ
μ

 Calculate Pranditle number
Pr =

μC
k

 Calculate Nussult number
μ
μ

Nu = j ∗ Re ∗ Pr

.

 Calculate the shell – side heat transfer coefficient

h =

Nu. k
D

9) Calculate the overall heat transfer coefficient
1

U=
1
+R
h

d ln

d
+
d
2k

d
d

+

1
+R
h

ht: tube – side heat transfer coefficient

hs: shell – side heat transfer coefficient
do: outside diameter of tube
di: inside diameter of tube
Rt: fouling factor of fluid in tube side
Rs: fouling factor of fluid in shell side
kw: thermal conductivity of the wall
10) Check pressure drop. If it is too high, adjust design until it is pertinent.