 Open Access
 Total Downloads : 1280
 Authors : Swarup Shrikant Deshpande, Shreeniket Ashok Hinge
 Paper ID : IJERTV3IS110752
 Volume & Issue : Volume 03, Issue 11 (November 2014)
 Published (First Online): 28112014
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Design and Performance Study of Shell and Tube Heat Exchanger with Single Segmental Baffle Having Perpendicular & ParallelCut Orientation.
Swarup S Deshpande Shreeniket A Hinge
Mechanical Engineering Intern Project Trainee
Excel Plants & Equipments Pvt Ltd Bharat Forge Ltd
Pune
Pune
Abstract: Shell and Tube Heat Exchangers are having special importance in boilers, oil coolers, condensers, preheaters .They are widely used for process operations as well as in the refrigeration and air conditions industries. Therefore a critical analysis of important parameters in needed in order to improve the overall efficiency and reduce the costs involved in processes. This paper primarily focuses on the design and comparative analysis of Single segmental Shell and tube Heat Exchanger with perpendicular & parallel baffle cut orientation. For designing Kern Method is used. It predicts heat transfer coefficient, Pressure drop of both arrangements. This method gives us clear idea that rate of heat transfer is greater in Perpendicularcut baffle orientation than Parallelcut , Pressure drop approximately remaining same. The Shell side fluid used is Lithiumbromide with average concentration of 58.5% and tube side fluid is hot water. All other parameters of fluid remaining same.
INTRODUCTION:
There are often numerous heat transfer problems involved in the petroleum, chemicals, power, metallurgy, energy and other industrial sectors. The shell and tube heat exchanger (STHE) is the heat transfer equipment most widely used in the current industrial production. Compared with other types, its main advantages are the large heat transfer area in the unit volume and good heat transfer characteristics. Combined with a simple structure, wide range of materials required in manufacturing, and greater operation flexibility, it is more and more widely used in the chemical engineering fields. In many heat exchangers, the uids are separated by a heat transfer surface, and ideally they do not mix or leak. Such exchangers are referred to as direct transfer type or simply recuperate. In contrast, exchanger which there is intermittent heat exchange between hot and cold fluid via thermal energy storage and release to the exchanger surface and matrix are referred to as indirect transfer type or simply regenerator.
To further optimize this existing STHE system, with the intentions of minimizing the energy consumption and finances involved. With this objective in mind, we concluded that the most important parameter that had to be worked upon was the heat transfer coefficient as it had a direct bearing on the energy consumption and the finances. For this a comparative analysis, including design, needed to be done.
Shell & Tube Heat Exchanger Design:
Shell & tube type heat exchangers are built of tubes (round or rectangular in general) mounted in shells (cylindrical, rectangular or arbitrary shape).
The differences lie mainly in the detailed features of construction and provisions for differential thermal expansion between the tubes and the shell.
Figure – Shell & Tube Heat Exchanger
BAFFLES:
Baffles are installed on the shell side to give a higher heat transfer rate due to increased turbulence and to support the tubes thus reducing the chance of damage due to vibration. One of the most important parts in shell and tube heat exchanger.
Baffles serve mainly two functions:

To fix the tubes in the proper position during assembly and prevent tube vibration caused by flow induced eddies.

Guiding the shellside fluid across the tube field, increasing the velocity and the heat transfer coefficient.
There are a number of different baffle types, which support the tubes and promote flow across the tubes. The different baffle arrangements used are given below:
Segmental:

Single Segmental (this is the most common)

Double Segmental (this is used to obtain a lower shell side velocity and pressure drop)

Disc and Doughnut.
Baffle Pitch:
The centretocentre distance between baffles is called the bafflepitch and this can be adjusted to vary the crossflow velocity. In practice the baffle pitch is not normally greater than a distance equal to the inside diameter of the shell or closer than a distance equal to onefifth the diameter or 50.8 mm (2 in) whichever is greater.
Baffle Cut:
In order to allow the fluid to flow backwards and forwards across the tubes part of the baffle is cut away. The height of this part is referred to as the bafflecut and is measured as a percentage of the shell diameter, e.g., 25 per cent bafflecut. The size of the bafflecut (or baffle window) needs to be considered along with the baffle pitch. It is normal to size the bafflecut and baffle pitch to approximately equalize the velocities through the window and in crossflow, respectively.
Horizontal Cut:

For singlephase fluids on the shell side, a horizontal baffle cut is recommended.

This minimizes accumulation of deposits at the bottom of the shell and also prevents stratification.
Vertical Cut:

In the case of a twopass shell (TEMA F), a vertical cut is preferred for ease of fabrication and bundle assembly.
ERNs Method:
Figure – Baffle Orientation
Figure: – Baffle Arrangement
Baffle Orientations:

For singlephase service, singlesegmental baffles with a perpendicular (horizontal) bafflecut orientation in an E or Jshell are preferred to improve flow distribution in the inlet and outlet regions.

With vertical inlet or outlet nozzles, parallelcut (vertical) baffles are preferred if the shell side process fluid condenses and needs a means of drainage.

Parallelcut baffles should also be used when the shell side fluid has the potential for particulate fouling, and in multipass F, G, or Htype shells to facilitate flow distribution.
This method was based on experimental work on commercial exchangers with standard tolerances and gives a reasonably satisfactory prediction of the heat transfer coefficient for standard designs. The prediction of pressure drop is less satisfactory as pressure drop is more affected by leakage and bypassing than heat transfer. The shell side heat transfer and friction factors are correlated in a similar manner to those for tube side flow by using hypothetical shell velocity and shell diameter. As the cross sectional area of flow will vary across the shell diameter, the linear and mass velocities are based on the maximum area for cross flow.
Shell side and factors for use in this method are given in the figures below for calculating the heat transfer:
The parameters required for calculating the heat transfer coefficient by this method are:


Area of Cross flow As

Shell side mass velocity Gs

Outer diameter of tubes do

Reynolds Number Re

Prandtl Number Pr

Heat transfer factor
BELL METHOD:
In Bell's method the heat transfer coefficient and pressure drop are estimated from correlations for flow over ideal tube banks, and the effects of leakage, bypassing and flow in the window zone are allowed for by applying correction factors. This approach will give more satisfactory predictions of the heat transfer coefficient and pressure drop than Kerns Method and, as it takes into account the effects of leakage and bypassing, can be used to investigate the effects of constuctional tolerances and the use of sealing strips .
Heat transfer coefficient:
The shell side heat transfer coefficient by this method is given by
Hs=hoc * Fn * Fw * Fb * FL Where,
Hoc = heat transfer coefficient calculated for cross flow over an ideal tube bank, no leakage no bypassing
Fn = correction factor to allow for the effect of the number of vertical tube rows
Fw = window effect correction factor Fb = Bypass stream correction factor FL = leakage correction factor
The total correction will vary from 006 for a poorly designed exchanger with large clearances to 0.94 for a well designed exchanger.
LithiumBromide solution specifications:
SrNo
Quantity
Symbol
Value
1
Lithium Bromide
Concentration dilute
57%
2
Lithium Bromide
Concentration strong
60%
3
Lithium Bromide
inlet temperature
Ti
68.3
4
Lithium bromide
outlet temperature
To
75.5
5
Flow rate dilute
12750 kg/hr
6
Flow rate strong
11983 kg/hr
7
Average flow rate
Ws
3.435 kg/sec
8
Density of lithium
bromide
1660 kg/
9
Viscosity
Âµ
9.80 kg/ m hr
10
Thermal
conductivity
0.392
11
Heat capacity
0.384 kcal/ kg C
12
Viscosity at wall
temperature
7.908 kg/m hr
Parallel Cut (Vertical baffle)
SrNo
Quantity
Symbol
Value
1
Shell side fluid
LiBr
2
Tube Side Fluid
Water
3
Tube outer diameter
do
0.019m
4
Tube length
l
3.7m
5
Number of Baffles
9
6
Tube transverse pitch
pt
0.0225m
7
Tube Vertical pitch
pt'
0.0195m
8
Number of tube
columns
27
9
Baffle width
0.326m
10
Shell length at c/s
0.5346 m
11
Baffle cut width
0.2086 m
12
Baffle cut fraction
39.65%
13
No of tube rows in
cross flow area
5
Perpendicular Cut (Horizontal baffle)
SrNo
Quantity
Symbol
Value
1
Shell Side Fluid
LiBr
2
Tube Side Fluid
Water
3
Tube outer diameter
do
0.019m
4
Tube length
l
3.7m
5
Number of Baffles
5
6
Tube transverse
pitch
pt
0.0195 m
7
Tube Vertical pitch
pt'
0.0225 m
8
Number of tube
columns
11
9
Shell length at c/s
0.243 m
10
Baffle width
0.1895 m
11
Baffle cut width
0.073 m
12
Baffle cut fraction
30.04 %
13
No of tube rows in
cross flow area
6
Leakage and bypass clearances:
Clearance between tube and shell bundle = 0.0055 m Bypass area ratio
Tube to baffle clearance = 0.0099 Shell to baffle clearance area = 0
Influence of Number of tube rows:
It is known that in laminar flow the heat transfer coefficient decreases with increasing distance from the start of heating. This is due to the fact that with increasing distance of the tube inlet, the temperature gradient at the tube wall decreases and it also decreases the heat transfer coefficient. This phenomenon also exists during flow across tube banks. For large heat exchangers in deep laminar flow, it can result in a decrease in the average heat transfer coefficient by a factor of 2 or more compared with what would have been predicted based on calculations. Therefore Bell proposed to introduce a
correction factor that depends on the total number of tube rows in the fluid path across the heat exchanger.
Graph for tube row correction factor
Effect of baffle window:
In order to correlate the experimental data properly it is important to take into account the effect of flow in the window area of the baffle. This factor corrects for the effect of flow through the baffle window and is a function of heat transfer area in the window zones and total heat transfer area. For this it is necessary to use a velocity defined as the geometric mean between the cross flow velocity and the window velocity. The need to define this velocity arises due to the fact that by increasing the baffle spacing, the pressure drop through the window changes but the velocity of flow through the window section is constant
The correction factor is shown the figure plotted vs. Rw, the ratio of the number tubes in the window zones to the total number of tubes in the bundle.
Effect of Leakage:
Owing to the leakage existing between baffles and tubes and between baffles and shell, both heat transfer coefficient and pressure drop differ from the values of an ideal bank. This was taken into account by Bell who simplified the calculations by assuming that the ratio between leakage flow rate and cross flow area is independent of the flow regime and depends only on the ratio between leakage area and cross flow area.
According to Bell, the ratio of between pressure drop for a heat exchanger with no leakage and pressure drop for a heat exchanger with leakage can be represented by a curve shown of the type shown in the figure below. The upper curve corresponds to a heat exchanger where the leakage occurs between tubes and baffle exclusively and the lower curve
corresponds to a heat exchanger with leakage only between shell and baffles
Thus the mathematical treatment can be simplified using a single curve which is that of tube – baffle leakage as shown in the figure below.
RESULTS:
After calculating with the help of Kerns method the results are obtained are more than satisfactory.
Parallel Cut Perpendicular Cut
SrNo
Quantity
Symbol
Value for Parallel
Cut
Value
for Perpendicular Cut
p>1 Maximum Area of Cross
flow
0.01967
0.034
2
Shell side
mass velocity
Gs
174.63
kg/sec
101.03 sec
3
Reynolds number
Re
1218.84
705.148
4
Prandtl number
Pr
9.675
9.675
5
Nusselts number
Nu
37.18
29.19
6
Heat transfer
coefficien t
ho
1458.24
1144.14
7
Total Pressure
drop
p
33.74 mm of LiBr
17.85 mm of LiBr
COMPARATIVE REPRESENTATION OF HTC, REYNOLDS NUMBER AND PRESSURE DROP
1400
1200
1000
800
600
400
200
0
Heat Transfer
Coefficient
Horizontal Flow Vertical Flow
COMPARISON OF NUSSELTS AND PRANDTL NUMBER
CON Condenser
H GEN Horizontal Flow Generator V GEN Vertical Flow Generator
TE1 – Temperature of Dilute solution of LiBr
TE2 – Temperature of Concentrated solution of LiBr TE3 – Temperature of Condensate
TE4 – Temperature of Condenser cooling water outlet TE5 – Temperature of Condenser cooling water inlet TE6 – Temperature of Hot water inlet
TE7 – Temperature of Hot water outlet
Purge Tank – Used to remove the noncondensable gases
CONCLUSION:
From the above graphic representation it is evident that there is significant drop in the Reynolds Number corresponding to vertical flow which in turn has a direct impact on the shell side heat transfer coefficient which is found to be lower than that for horizontal flow.
However the shellside pressure drop for the vertical flow is in the same range as that for the horizontal flow design. Also there is a noticeable drop in the Nusselts Number for the proposed design with the Prandtl number being the same for both designs.
Therefore based on the results we conclude that changing the flow pattern to vertical to improve the shellside heat transfer coefficient is not feasible.
BOOKS:
REFERENCES:
THE SCEMATIC DIAGRAM OF HEAT EXCHANGER WE DESIGNED FOR THIS STUDY IS AS FOLLOWING


"Chemical Engineering" , Coulson & Richardson, 3rd Edition Volume 6

"Heat Transfer in Process Engineering" , Eduardo Cao

"Chemical Engineering Design" , R.K. Sinnott and G.Towler, 4th Edition, 2008

"Investigation of the effects of baffle orientation , baffle cut , fluid viscosity on shell side pressure drop and heat transfer coefficient in an E type shell and tube heat exchanger" by Koorosh Mohammadi , Institute of Thermodynamics and Thermal Engineering University of Stuttgart, Germany Feb 2011
LINKS:

http://nptel.iitm.ac.in/courses/103103032/module8/lec33/4.html

http://www.wermac.org/equipment/heatexchanger_part4.html

http://www.bestinnovativesource.com/2012/04/06/baffle

http://hwarts.blogspot.in/2011/11/industrialdesignand animationkettle.html

http://www.hwarts.blogspot.in/