Parts of shell and tube heat exchanger Shell Shell Side Pass Partition Plate Baffles Tube Tube Side Pass Partition Plate Tie Rods Spacers Tube Sheet Expansion Joint

1. VARIOUS
PARTS OF
SHELL AND
TUBE HEAT
EXCHANGERS

3. Shell
• Shell is the costliest part of the heat exchanger. Cost of shell and tube
heat exchanger sensitively changes with change in the diameter of
shell. As per the TEMA standard, shell size ranges from 6 in (152 mm)
to 60 in (1520 mm).
• Standard pipes are available up to 24 in size (600 mm NB). If shell
size is greater than 24 in, it is fabricated by rolling a plate.
• Shell diameter depends on tube bundle diameter. For fixed tube sheet
shell and tube heat exchanger, the gap between shell and tube bundle
is minimum, ranging from 10 to 20 mm. For pull through floating
head heat exchanger, it is maximum, ranging from 90 to 100 mm.

4. Shell Side Pass Partition Plate
• Single pass shell is used in the most of the cases. Two pass shell is
rarely used and is recommended where shell and tube temperature
difference is unfavorable for the single shell side pass. For such cases,
normally two or more smaller size 1-1 heat exchangers, connected in
series, are recommended.
• Shell side pass partition plate is not provided to improve shell side
heat transfer coefficient but it is provided to avoid the unfavorable
temperature difference or to avoid the cross of temperatures between
hot fluid and cold fluid.

5. Baffles
• There are two functions of baffles:
• 1. Baffles are used in the shell to direct the fluid stream across the tubes to
increase the velocity of shell side flow and thereby to improve the shell side
heat transfer coefficient. In other words, baffles are used in shell to increase
the turbulence in shell side fluid.
• 2. Baffles indirectly support the tubes and thereby reduce the vibrations in
tubes. If shell side liquid velocity is higher; say more than 3 m/s, vibration
analysis calculations should be carried out to check whether baffle spacing
is sufficient or not. Similarly, for very high velocity of gas or vapour and
also for the higher baffle spacing (higher than shell ID), vibration analysis
calculation must be carried out to check the baffle spacing. Vibration
analysis calculations are given in TEMA standard.

8. • Different types of baffles are used in shell and tube heat exchangers; (i) Segmental baffle,
(ii) Nest baffle, (iii) Segmental and Strip baffle, (iv) Disk and Doughnut baffle, (v)
Orifice baffle, (vi) Dam baffle, etc. Figure 6.2 shows various types of baffles.
• Most widely used type of baffle is segmental baffle. Other types of baffles like nest baffle,
segmental and strip baffle and disk and doughnut baffle provide less pressure drop for the
same baffle spacing but provide lower heat transfer coefficients as compared to segmental
baffle. Situations when other types of
• baffles might be used could be as given below.
• 1. For shell and tube heat exchangers shell side pressure drop controls the overalldesign.
For example, intercoolers of compressors and heat exchangers used in very high vacuum
system. In intercoolers of compressors maximum allowable shell side pressure drop may
be as low as 3.45 kPa. For such cases different types of shells are also used. Split flow (G
shell) or divided flow (J shell) designs provide low shell side pressure drop compared to
commonly used single pass (E shell) as shown in Fig.

9. • 2. For shell and tube heat exchanger in which boiling or condenout on
shell side. In such a case baffles are required only to reduce the
vibrations in tubes. For other type of baffles (other than segmental
baffle) correlations for finding heat transfer coefficient and pressure
drop are not easily available in open literature.
• Helical baffles are also developed by some heat exchanger
manufacturers. These are claimed to substantially alter the shell side
flow pattern by inducing a swirling pattern with a velocity component
parallel to the tubes. Optimum helix angle of 40° is recommended.
This arrangement is expected to improve the heat transfer and reduce
the pressure drop. However, its design procedure is proprietary.sation
is carried

10. Tube
• Tube size range from 1/4 in (6.35 mm) to 2.5 in (63.5 mm) in shell and
tube heat exchanger. Data for standard tubes are given in TEMA
standard and in Ref.
• For the standard tubes, its size is equal to outer diameter of tube.
Thickness of standard tubes are expressed in BWG (Birmingham Wire
Gauge). Increase in the value of BWG means decrease in tube
thickness. For no phase change heat exchangers and for condensers,
3/4 in (19.05 mm) OD tube is widely used in practice. While for
reboiler 1 in (25.4 mm) OD tube size is common. Tubes are available
in standard lengths like 6 ft (1.83 m), 8 ft (2.44 m), 12 ft (3.66 m), 16
ft (4.88 m) and 6 m.

11. Tube Side Pass Partition Plate
• Tube side passes are provided to decrease the tube side flow area and to increase tube side
fluid velocity thereby to improve the tube side heat transfer coefficient at the expense of
pressure drop. This is true only if there is no phase change on tube side. Hence, more
number of tube side passes are recommended only if there is no change in the phase of
tube side fluid.
• For example, at the design stage, if the number of tube side passes are increased from one
to two, then for the given volumetric flow rate, flow area becomes half and velocity
becomes double. Since, tube side heat transfer coefficient, hi ∝ ut 0.8 (where ut is tube side
fluid velocity), on increasing number of tube side passes from 1 to 2, hi nearly becomes
1.74 times. But, Δpt ∝ ut 2.8, so the pressure drop increases by 6.96 times. Increase in hi
means decrease in heat transfer area required and decrease in fixed cost. Increase in Δpt
means increase in power required for pumping the tube side fluid and increase in
operating cost. Hence, ideally optimum number of tube side passes must be decided.
Many a times, tube side velocity in a single pass could be calculated very low (say 0.3 to
0.5 m/s). Under such circumstances, two passes or four passes could be beneficial. It is
recommended that ut > 1 m/s. This is essential if tubeside fluid is cooling water; otherwise
rate of fouling will be higher.

12. • Tube side passes are very common and are advantageously used for
improving
• tube side heat transfer coefficient. These passes can be achieved in
many waysby locating partition plates in channel covers. Figure gives
different designs
• for achieving desired tube passes.

14. Tie Rods
• Baffles are supported by tie rods. Tie rods are made from solid metal
• bar. Normally four or more tie rods are required to support the baffles.
Diameter
• of tie rod is less than the diameter of tube. Diameter and number of tie
rods
• required for given shell diameter are specified by TEMA standard and
IS:4503.

16. Spacers
• Spacers are used to maintain the space between baffles. Spacers are
the pieces of pipes or in the most of the cases they are the pieces of
extra available tubes. Spacers are passed over the tie rods and because
of them baffles do notslide over tie rods under the effect of the force of
fluid. Hence, spacers fix the location of baffles and maintain the space
between them. Length of spacer is equal to space between the baffles.

17. Tube Sheet
• Tubes and one end of tierods are attached to tube sheet (also called
tube plate).
• Hence, entire load of tube bundle is transferred to one or two tube
sheets. In Utube shell and tube heat exchanger only one tube sheet is
used. While in fixed tube sheet shell and tube heat exchanger, two tube
sheets are used. One surface of tube sheet is exposed to tube side fluid
and other surface is exposed to shell side fluid. This point is very
important in the selection of material for tube sheet and also in
determining tube sheet thickness.
• In majority cases tube to tube sheet joints are two types; (a Expanded
joint, and (b) Welded joint as shown in fig.

19. • In expanded type joint, tube holes are drilled in a tube sheet with a
slightly greater diameter than the tube OD. Two or more grooves are
cut in the wall of each hole. The tube is placed inside the tube hole and
a tube roller is inserted into the end of the tube. Roller is slightly
tapered. On application of the roller, tube expands and tube material
flows into grooves and forms an extremely tight seal. Welding joint is
used only for the cases where leakage of fluid can be disastrous.

20. Sealing Strip
• It is a shell side component. Sealing strips are attached on the inside
surface of
• shell as shown in Fig. throughout the length of shell.

21. • There are two functions of sealing strips:
• 1. Sealing strips reduce the amount of bypass stream of shell side fluid
flowing through the clearance between shell inside diameter and tube
bundle diameter and thereby improve the shell side heat transfer
coefficient. (This is valid only if there is no phase change of shell side
fluid).
• 2. Sealing strips also make the removal of tube bundle from the shell
easy. Hence, they are also known as sliding strips.

22. Expansion Joint
• Expansion joint is attached to shell wall. In this case, shell is made from two pipe
pieces. Two pipe pieces are joined together by an expansion joint as shown In fig.
• Expansion joint is used in fixed tube heat exchanger to permit the differential
thermal expansion or contraction between shell and tubes which otherwise is not
permitted by fixed tube sheet heat exchanger. Differential thermal expansion
between shell and tube is significant if there is a large temperature difference
between temperature of shell material and temperature of tube material during
operation or if tube material and shell material are different. For the given case of
fixed tube sheet heat exchanger, whether an expansion joint is required or not can
be determined by calculations given in TEMA. If expansion joint is not provided
in fixed tube sheet heat exchanger, then fixed tube sheet does not permit the
unequal expansion or contraction between shell and tube and it can result in the
development of thermal stress across the tube sheet.

24. • If this thermal stress is higher than permissible value, then it may
develop a crack in tube sheet, and can result in leakage at tube to tube
sheet joint. Other options, available to avoid the development of
thermal stress in the tube sheet, are use of either Utube heat exchanger
or floating head heat exchanger.