King Abdulaziz University
Mechanical Engineering Department
MEP 460
Heat Exchanger Design
Thermal Design of Shell
and tube heat Exchanger
March 2018
1
Contents
1-Introduction
2-Basic components
Shell types
Tube bundle types
Tube layouts
baffle types
3-Basic design procedure
Preliminary estimate of unit size
Rating of preliminary design
4 Shell side heat transfer and pressure drop
5-Bell-Delaware method for rating a shell and
tube heat exchangers
2
1-Introduction
 Most used heat exchangers
 Can accommodate high temperature high
pressure fluids
 In some designs tubes can be replaced
 Many options to choose from
 Different designs to choose from for shell,
tube layout and tube bundle
 Require more space when compared to
plate gasketed heat exchangers
3
1-Introduction
Main components of a shell & tube HX
A-Shell types
B- Tube bundle types
C- Tube layouts
D-Baffle types
4
A- Shell types
TEMA
Tubular Exchanger
Manufacturers Association
Standards
Most common
shell type are:
E, F, G
5
A- Shell types
V stands for vent
6
A- Shell types
Kettle re-boiler shell
7
B- Tube bundle types
U tube bundle
Tube can expand
Replacement of
tubes is not
possible except
maybe the outer
row
Tubes can have
fins
8
B-Tube bundle types
Fixed tube sheet
Design for ease cleaning of the
inside of the tubes
Not possible to access the outer
surface of the tubes
Has limited expansion
Individual tubes can be replaced
9
B-Tube bundle types
Floating head
pull-through floating head
Bundle can be removed and cleaned
Good for fouled fluids
10
C-Tube layouts
Only an E-shell with one tube pass and an F-shell with two tube
passes result in nominal counterflow. All other multiple tube passes
require a temperature correction (factor F),
Tube metal is usually:
Low carbon steel
Low alloy steel
Stainless steel
Copper
Admiralty
Cupronickel
Inconel
Aluminum (in the form of alloys),
or titanium.
The wall thickness of heat exchanger tubes is standardized in
terms of the Birmingham Wire Gage (BWG) of the tube. Tables
9.1 and 9.2 give data on heat exchanger tubes
11
C-Tubes & Tube layouts
Tube diameters (8–15 mm) are preferred for greater area/volume
density but are limited, for purposes of in-tube cleaning
Larger tube diameters are often required for condensers and
boilers.
The tubes may be either bare or have low fins on the outside. Low
fin tubes are used when the fluid on the outside of the tubes has a
substantially lower heat transfer coefficient than the fluid on the
inside of the tubes.
As the tube length is increased the heat transfer area
increased and the number of tubes decreased. Tube
length is dictated by space available and transportation
requirement.
shell-diameter-to-tube-length ratio is typically
between 1/5 to 1/15 [ Ds/L =1/5 to 1/15]
12
C-Tubes & Tube layouts
Commercial tube data
Birmingham
Wire Gage
(BWG)
13
C-Tubes & Tube layouts
Commercial tube data
14
C-Tubes & Tube layouts
15
C-Tube & tube layout
Pitch angle p

=

=

=
=
16
C-Tube & tube layout
PT is the tube pitch
do is the outside diameter
P /d , is between 1.25 and 1.5.
T
o
17
C-Tube & tube layout
Tube counts for different shell diameters and tube layout
18
Tube counts for different shell
diameter and tube layout
19
Table 9.3 Tube count
20
D-Baffle types
Baffle function:
Baffles serve two functions:
* Support the tubes for structural rigidity,
preventing tube vibration and sagging, and
* To divert the flow across the bundle to
obtain a higher heat transfer coefficient
baffle types
 Transverse and longitudinal
 Rod and plate
21
D-Baffle types
transverse and longitudinal baffles
Transverse baffles
Longitudinal baffle
22
D-Baffle types
Rod and plate baffles
Rod baffles
Plate baffles
23
D-Baffle types
Types of plate baffles
Single segmental
Double segmental
Triple segmental
No tubes in the window
Disk and doughnut
24
D-Baffle types
Types of plate baffles
25
D-Baffle types
Types of plate baffles
26
D-Baffle types
Types of plate baffles
27
D-Baffle types
Types of plate baffles
28
D-Baffle types
Types of plate baffles
Orifice baffle
29
D-Baffle types
Rod and ring baffle
30
Baffle spacing and baffle cut
Optimum baffle spacing is somewhere between 0.4
and 0.6 of the shell diameter and a baffle cut of 25% to
35% is usually recommended. The
B
31
Baffle cut
32
33
34
Procedure for
designing heat
exchangers
Select type of
shell & tube HX
Preliminary
sizing of key
parameters
Kern method
Bell Delaware
method
35
Preliminary procedure to size a unit
1-Calculate LMTD and estimate the correction
factor F
2-Estimate the overall heat transfer coefficient U
(use table 9.4 and table 9.5 for individual h)
3-Calculate q from the known mass flow rates and
the temperatures
4-Calculate approximately the heat transfer area Ao
using 𝐴𝑜 = 𝑞 𝑈𝑜 𝐿𝑀𝑇𝐷𝑐𝑓 𝐹
5-From the calculate Ao one can estimate the
number of tubes
36
Preliminary calculation for sizing shell and tube
heat exchangers
The size of a heat exchanger can be found using
𝑞
𝐴𝑜 =
𝑈𝑜 𝐿𝑀𝑇𝐷𝑐𝑓 𝐹
Provided all temperatures are known and an
approximate value of Uo is available
An estimate for Uo can be found based on
individual thermal resistances
𝑅𝑓𝑖
1
1
1
=
+
+ 𝐴𝑜 𝑅𝑤 + 𝑅𝑓𝑜 +
𝑈𝑜 ℎ𝑖 (𝐴𝑖 𝐴𝑜 ) (𝐴𝑖 𝐴𝑜 )
ℎ𝑜
37
Preliminary procedure
to size Shell & tube HX
Estimating the individual
heat transfer coefficient h
38
Preliminary procedure
to size a unit
Typical U value for
some heat
exchangers
39
Symbols and their meanings
L
Length of the tube [m]
De
Equivalent diameter [m] used in calculating Res by Kern method
do
Outside diameter of the tube [m]
di
Inside diameter of the tube [m]
Ds
Shell inside diameter[m]
Nt
No. of tubes
A1
Area taken by single tube [m2]
CL
Tube layout constant. CL=1 for 90 and 45 layout, CL=0.87 for others
CTP
Tube count calculation constant. One tube pass=0.93, two tube
passes=0.9, Three tube passes=0.85
Np
No of tube passes
B
Baffle spacing [m]
Bc
Baffle cut [m]
PT
Tube pitch [m]
PT/do
Pitch outside diameter ratio [-]
As
Min. flow area at the shell center line [m2]
Gs
Mass velocity
𝑚𝑠
[kg/(m2.s)]
𝐴𝑠
40
Preliminary procedure to size a unit
𝑞 = 𝑚𝑐 𝐶𝑝𝑐 (𝑇𝑐𝑜 − 𝑇𝑐𝑖 )
(1)
𝑞 = 𝑚ℎ 𝐶𝑝ℎ (𝑇ℎ𝑖 − 𝑇ℎ𝑜 )
(2)
𝑞 = 𝑈𝑜 𝐴𝑜 𝐿𝑀𝑇𝐷 𝐹
(3)
𝑞
𝐴𝑜 =
𝑈𝑜 𝐿𝑀𝑇𝐷 𝐹
(4)
𝐴𝑜 = 𝜋𝑑𝑜 𝑁𝑡 𝐿
(5)
𝜋𝐷𝑠2
𝑁𝑡 = 𝐶𝑇𝑃
4𝐴1
(6)
𝐶𝑇𝑃
𝐷𝑠2
𝑁𝑡 = 0.785
𝐶𝐿 𝑃𝑅2 𝑑𝑜2
𝐶𝐿 𝐴𝑜 𝑃𝑅2 𝑑𝑜
𝐷𝑠 = 0.637
𝐶𝑇𝑃
𝐿
PR=tube pitch ratio=PT/do
(8)
1 2
(9)
(10)
(7)
𝐴1 = 𝐶𝐿 𝑃𝑇2
CL =1
For 90 and 45
CL=0.87
For 30 and 60
One tube pass
CTP=0.93
Two tube pass
CTP=0.9
Three tube passes
CTP=0.85
1-From Eq. (4) Ao can be estimated
2-Assume a typical commonly used
shell and tube layout estimate CTP,
CL, PT and do
3-Use Eq. (9) to estimate shell
inside diameter Ds
4-Use Eq. (8) to get the number of
tubes Nt
41
Example 9.1 on preliminary sizing of a shell and
tube heat exchangers
42
Example 9.1 continue
Rf=0.000176 m2 .K/W
Thi= 67 C
mh=5000 kg/hr
Baffle spacing B=0.6 Ds
Tubes: do=19 mm, di=16 mm
Water condensate
40 C
heat exchanger length L<5 m
Tho
city Water
mc=30,000 kg/hr
Baffle cut= 25%
Δ𝑃𝑠 < 5 𝑝𝑠𝑖
17 C
kt=60 W/(m.K)
Required: Preliminary sizing of shell and
tube heat exchanger
¾” tube
PT/do=1.25
di=16 mm, do=19mm
43
Example 9.1 continue
hi =5000 W/(m^2.K)
ho=4000 W/m^2.K
44
Example 9.1 continue
45
Example 9.1 continue
46
Example 9.1 continue
47
Example 9.1 continued
48
Rating a heat exchanger
Kern and Bell-Delaware methods
for rating shell and tube heat exchangers
49
Shell-Side Heat Transfer and Pressure Drop (Kern)
McAdams expression for
finding the shell side
heat transfer coefficient
ℎ𝑜 𝐷𝑒
𝐷𝑒 𝐺𝑠
= 0.36
𝑘
𝜇
2 × 103 < 𝑅𝑒𝑠 =
0.55
𝑐𝑝 𝜇 1 3 𝜇𝑏
𝑘
𝜇𝑤
0.14
𝐺𝑠 𝐷𝑒
< 1 × 106
𝜇
ho shell side heat transfer coefficient
De equivalent diameter
Gs shell side mass velocity
𝐷𝑒 =
4𝑓𝑟𝑒𝑒 𝑓𝑙𝑜𝑤 𝑎𝑟𝑒𝑎
4𝐴𝑐
=
𝑊𝑒𝑡𝑡𝑒𝑑 𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟 𝑊𝑒𝑡𝑡𝑒𝑑 𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟
50
Shell-Side Heat Transfer and Pressure Drop (Kern)
4
For square pitch
For triangular pitch
𝐷𝑒 =
𝜋𝑑𝑜2
2
𝑃𝑇 − 4
𝜋𝑑𝑜
𝑃𝑇2 3 𝜋𝑑𝑜2
4 4 − 8
𝐷𝑒 =
𝜋𝑑𝑜 2
51
Shell-Side Heat Transfer and Pressure Drop (Kern)
The bundle cross flow area As at the centerline of the shell
depends on the shell inside diameter Ds, the tube layout pitch and
the clearance between the tubes
𝐷𝑠 𝐶𝐵
𝐴𝑠 =
𝑃𝑇
The shell side mass
velocity is given by
𝑚𝑠
𝐺𝑠 =
𝐴𝑠
52
Shell side pressure drop
The length is taken as the shell inside diameter and
the flow make crosses over the bundle (Nb+1) times
𝑓 𝐺𝑠2 𝑁𝑏 + 1 𝐷𝑠
Δ𝑝𝑠 =
2𝜌𝐷𝑒 𝜙𝑠
𝐺𝑠 =
𝑚𝑠
𝐴𝑠
𝑓 = exp(0.576 − 0.19 ln 𝑅𝑒𝑠 )
400 < 𝑅𝑒𝑠 =
𝐺𝑠 𝐷𝑒
≤ 1 ∗ 106
𝜇
𝜇𝑏
𝜙𝑠 =
𝜇𝑤
0.14
Where Nb is the number of baffles
𝑁𝑏 =
𝐿
−1
𝐵
B is the baffle spacing
53
Tube side pressure drop
Due to friction
2
𝐿 ∗ 𝑁𝑝 𝑢𝑚
𝐿𝑁𝑝 𝐺𝑡2
Δ𝑝𝑓 = 4𝑓
𝜌
= 4𝑓
𝑑𝑖
2
𝑑𝑖 2 𝜌
Np is the number of tube passes
Pressure drop due to change of
direction of the flow
2
𝜌𝑢𝑚
Δ𝑝𝑟 = 4𝑁𝑝
2
Which is taken as four velocity heads per pass
Therefore the total tube side pressure drop
2
𝐿𝑁𝑝
𝜌𝑢𝑚
Δ𝑝𝑡𝑜𝑡 = 4𝑓
+ 4𝑁𝑝
𝑑𝑖
2
54
Example 9.2 Rating of a preliminary design
It is required to rate the heat exchanger of
example 9.1
output results from example 9.1 are:
Thi= 67 C
mh=5000 kg/hr
Water condensate
40 C
Tho
Nt=117 tube
city Water
mc=30,000 kg/hr
55
Correct count of tubes in a shell
according to TEMA standards
56
Example 9.2 Rating of a preliminary design
Input data for rating the heat exchanger are:
No
parameter
value
1
Ds
15.25 “=0.39 m
2
Nt
124 tubes
3
di
16 [mm]
4
do
19 [mm]
5
k
60 [W/(m.K)]
6
B
0.2 and baffle cut =25%
7
PT
0.0254 [m]
8
Np
2 tube passes
57
Example 9.2 continue
58
Example 9.2 continue
59
Example 9.2
continue
60
Example 9.2 continue
61
Example 9.2 continue
62
Example 9.2 continue
Calculating heat exchanger length
63
Example 9.2 continue
64
Example 9.2 continued
65