Q. Draw Temperature Profile For 2-4 Shell and Tube Heat Exchanger

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Raj Khare (181113044)

Chemical Engineering,7th Sem
PED-II Assignment - 2
Q. Draw Temperature Profile for 2-4 Shell and Tube Heat Exchanger.
Figure (a) represents temperature profile for 1-2 Shell & Tube Heat Exchangers
Figure (b) represents temperature profile for 2-4 Shell & Tube Heat Exchangers
Where: 𝑇ℎ𝑎 = 𝐼𝑛𝑙𝑒𝑡 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 ℎ𝑜𝑡 𝑓𝑙𝑢𝑖𝑑

𝑇ℎ𝑏 = 𝑂𝑢𝑡𝑙𝑒𝑡 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 ℎ𝑜𝑡 𝑓𝑙𝑢𝑖𝑑
𝑇𝑐𝑎 = 𝐼𝑛𝑙𝑒𝑡 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑐𝑜𝑙𝑑 𝑓𝑙𝑢𝑖𝑑
𝑇𝑐𝑏 = 𝑂𝑢𝑡𝑙𝑒𝑡 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑐𝑜𝑙𝑑 𝑓𝑙𝑢𝑖𝑑
𝑇𝑐𝑖 = 𝐼𝑛𝑡𝑒𝑟𝑚𝑒𝑑𝑖𝑎𝑡𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑐𝑜𝑙𝑑 𝑓𝑙𝑢𝑖𝑑
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Q. Application of 1-2, 2-4, 3-6 Shell and Tube heat exchanger and why they are used.
1-2, 2-4 and 3-6 Shell and Tube heat exchangers fall under Multipass heat exchangers. Multipass
heat exchangers are the heat exchangers that allow fluid to pass through the heat exchangers
several times, thereby increasing the heat transfer. Multipass heat exchangers have a certain edge
over normal heat exchangers due to following reasons:-
 For a given exchanger length multipass flows create a thermally long heat exchanger
while maintaining the same compact exchanger design.
 They allow thermal expansion.
 Mechanical cleaning is easy.
 Multipass flow results in higher tube fluid velocities which help in achieving higher heat
transfer coefficients.
 Surface fouling is reduced.
Hence for the above reasons multipass heat exchangers are widely used.
Applications of Multipass Heat Exchangers (1-2, 2-4, & 3-6)

 1-2 Shell and Tube heat exchangers are predominantly used in liquid CDU’s for data
centre cooling.
 They are used as Carbon dioxide gas coolers in industries.
 They are widely used in vapor recovery systems and industrial paint systems.
 They find application in Boiler blowdown heat recovery units and steam generation units.
 The 2-4 exchanger is used when process temperatures gives a correction factor Ft less
than 0.75 for a 1-2 exchangers
 The 3-6 exchanger is used when process temperatures give a correction factor less than
0.9 (for removable longitudinal baffle arrangement) and 0.85 (for welded longitudinal
baffle arrangement).
Q. Why is there a change in correction factor Ft for 1-2 and 2-4 STHE and What is the
impact of change?
1-2 STHE involves only a single shell while 2-4 and higher shell pass STHE involves two or
more shells in series or parallel arrangement. The fluid enters the shell flows across it for
multiple times as per number of tube passes and then enters the next shell. The flow conditions
are neither parallel nor counter flow but a combination of both. Hence a Hence a different
correction factor ‘F’ should be taken as compared to single shell 1-2 exchanger. Correction
factor depends on the number of shells of the heat exchanger and on the terminal temperatures of
the heat exchanger. This correction factor value can be found through a graph.
If there is no change in correction factor value for 2-4 exchanger and same values are taken for
both arrangements then resulting calculated heat transfer rate will be less and absurd. The
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correction factor for 2-4 STHE is always higher than the 1-2 STHE and hence will result in
higher heat transfer rate in a 2-4 heat exchanger than a 1-2 heat exchanger. The correction factor
approaches unity as the number of shell-side passes is increased for any value of P and R which
is expected since multipass heat exchanger approaches the behavior of an ideal countercurrent
heat exchanger.
Q. What most significant or minimum Ft value must be selected for 1-2 & 2-4 STHE.
1-2 STHE – The minimum value of 𝐹𝑇 for a efficient design of 1-2 heat exchanger is 0.75. If the
value is less than 0.75 than a 2-4 heat exchanger is preferred.
2-4 STHE – The Minimum value of 𝐹𝑇 for efficient design of a 2-4 heat exchanger with
removable longitudinal baffles is 0.90 while for a 2-4 heat exchanger with welded longitudinal
baffles is 0.85. If 𝐹𝑇 value is below the minimum value then an arrangement with larger number
of shell passes is preferred such that the 𝐹𝑇 value for new arrangement is above the minimum
value.
Q. Write the importance and application of horizontal and vertical segmented baffles?
Vertically Segmental baffles.

 These are similar to the segmental baffles used in 1-2 Exchangers.
 The flow area is crosshatch section and flow area is one half the flow area of 1-2 STHE
per inch of baffle spacing. The flow distribution is identical with 1-2 STHE.
 Mass velocity for a given weight of fluid is twice the mass velocity of same weight of
fluid in 1-2 heat exchangers with identical diameter and baffle spacing.
Importance:
 Vertical segmented baffles make the fabrication of two pass heat exchangers simple.
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 Vertical segmented baffles provides the lowest pressure drops

 Vertical segmental baffles provide reduced flow area, increased mass velocity and film
coefficient which is highly desirable in majority of application.
Application:
 Vertical segmented baffles are best suited for operations that involve condensation of
fluid on shell side.
 They are best suited for operations where a lower pressure drop is highly desirable.
Horizontally segmental baffles

 These are similar to ordinary Segmental baffles.
 The mass velocity for a given weight of fluid is same as 1-2 exchangers.
 The fluid traverses half the depth equivalent to inside diameter.
Importance:
 The use of horizontal segmented baffles prevents deposits from building up on the
bottom side of exchanger.
 They prevent stratification of fluid enabling proper mixing of the warmer fluid in upper
region with the colder fluid in lower region.
 Horizontal baffles help in achieving higher heat transfer rates even at lower flow velocity.
 They are seldom used in comparison to vertically segmented baffles as pressure drops are
much higher.
Applications:
 Horizontal segmented baffles are best suited for operations that involve single phase fluid
on the shell side.
 They are best suited for operations where higher heat transfer rates are highly desirable.
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References :
● Chemical Engineering Design by Coulson and Richardson

● Perry’s Chemical Engineers’ Handbook
● Research paper – Design and optimization of multipass heat exchangers
 https://www.theengineeringconcepts.com/temperature-profile-in-single-multi-pass-heat-
exchanger/
 https://www.stalwartint.com/application-and-advantages-of-shell-and-tube-heat-
exchanger.html
 https://www.thomasnet.com/articles/process-equipment/understanding-heat-exchangers/
 https://www.swep.net/technology/multi-pass-flows/
 https://www.enerquip.com/2018/07/31/horizontal-vs-vertical-baffles-which-to-choose-
for-your-shell-and-tube-heat-exchanger/

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Raj Khare (181113044)

Where: 𝑇ℎ𝑎 = 𝐼𝑛𝑙𝑒𝑡 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 ℎ𝑜𝑡 𝑓𝑙𝑢𝑖𝑑

Applications of Multipass Heat Exchangers (1-2, 2-4, & 3-6)

Vertically Segmental baffles.

 Vertical segmented baffles provides the lowest pressure drops

Horizontally segmental baffles

● Chemical Engineering Design by Coulson and Richardson

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