![Page 1: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/1.jpg)
Geometrical Details of Baffles & Shell Side Fluid Dynamics
P M V SubbaraoProfessor
Mechanical Engineering Department
I I T Delhi
Ideas to Achieve Optimal Combination of Axial & Cross
flow……
![Page 2: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/2.jpg)
Segmental Baffle Cut Geometry
Segmental baffle cut height :Lbch
Assuming that the segmental baffle is centered within the shell inside diameter .
The small difference between the shell and baffle diameter is called the clearance Lsb and it is important for leakage corrections.
![Page 3: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/3.jpg)
Selection of Baffle Cut
• Baffle cut can vary between 15% and 45% of the shell inside diameter.
• Both very small and very large baffle cuts are detrimental to efficient heat transfer on the shellside due to large deviation from an ideal situation.
![Page 4: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/4.jpg)
Role of Baffle Cut on Flow Distribution
• If the baffle cut is too small, the flow will jet through the window area and flow unevenly through the baffle compartment.
• If the baffle cut is too large, the flow will short-cut close to the baffle edge and avoid cross-mixing within the baffle compartment.
• A baffle cut that is either too large or too small can increase the potential for fouling in the shell.
• In both cases, recirculation zones of poorly mixed flow cause thermal maldistribution that reduces heat transfer.
• To divert as much heat-carrying flow across the tube bundle as possible, adjacent baffles should overlap by at least one tube row.
• This requires a baffle cut that is less than one-half of the shell inside diameter.
![Page 5: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/5.jpg)
Non-Optimal Baffle Cut & Fouling Zones
Too small Baffle Cut Too Large Baffle Cut
LBCH
LBCH/Ds
Ds
![Page 6: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/6.jpg)
Optimal Baffle Cut
• It is strongly recommended that only baffle cuts between 20% and 35% be employed.
• Reducing baffle cut below 20% to increase the shellside heat-transfer coefficient or increasing the baffle cut beyond 35% to decrease the shellside pressure drop usually lead to poor designs.
• Other aspects of tube bundle geometry should be changed instead to achieve those goals.
• For example, double segmental baffles or a divided-flow shell, or even a cross-flow shell, may be used to reduce the shellside pressure drop.
![Page 7: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/7.jpg)
Equalize cross-flow and window velocities
• Flow across tubes is referred to as cross-flow, whereas flow through the window area (that is, through the baffle cut area) is referred to as window flow.
• The window velocity and the cross-flow velocity should be as close as possible — preferably within 20% of each other.
• If they differ by more than that, repeated acceleration and deceleration take place along the length of the tube bundle, resulting in inefficient conversion of pressure drop to heat transfer.
![Page 8: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/8.jpg)
Recommended segmental baffle cut values
![Page 9: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/9.jpg)
Orientation of Baffle Cut• For single-phase fluids on the shellside,
a horizontal baffle cut is recommended.
• This minimizes accumulation of deposits at the bottom of the shell and also prevents stratification.
• In the case of a two-pass shell (TEMA F), a vertical cut is preferred for ease of fabrication and bundle assembly.
![Page 10: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/10.jpg)
Vertical Vs Horizontal Cut
![Page 11: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/11.jpg)
Selection of Baffle Cut Orientation
• For single-phase service, single-segmental baffles with a perpendicular (horizontal) baffle-cut orientation in an E- or J-shell are preferred to improve flow distribution in the inlet and outlet regions.
• With vertical inlet or outlet nozzles, parallel-cut (vertical) baffles are preferred if the shellside process fluid condenses and needs a means of drainage.
• Parallel-cut baffles should also be used when the shellside fluid has the potential for particulate fouling, and in multipass F-, G-, or H-type shells to facilitate flow distribution.
• However, parallel-cut (vertical) baffles have the potential for significant flow and temperature maldistribution in the end zones.
• This can induce local tube vibration and reduce the effective heat transfer rate in the inlet and outlet baffle spaces
![Page 12: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/12.jpg)
Helical Baffles
![Page 13: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/13.jpg)
Superiority of Helical Baffling
![Page 14: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/14.jpg)
Closing thoughts
• Baffling is the most crucial shellside consideration in shell-and-tube heat exchanger design, because baffles regulate shellside fluid flow and improve heat transfer while offering significant tube support.
• Although TEMA baffles are easier to fabricate, they usually have higher pressure drops than non-TEMA-type baffles.
• It is equally important to consider how baffle selection affects other shellside parameters, such as tube pitch ratio, tube layout pattern, tube size, shell type, and shell diameter.
• A basic understanding of the various baffle types and their advantages and disadvantages is essential to choosing an effective baffle configuration.
![Page 15: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/15.jpg)
Basic baffle geometry relations
![Page 16: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/16.jpg)
Basic baffle geometry relations
Dotl : Diameter of circle touching the outer surface of outermost tubes.
Dctl : Diameter of circle passing through the centers of of outermost tubes.
Lbb: Diametric clearance between tube bundle and shell inside diameter.
ctl: The angle intersecting Dctl due
to baffle cut.
ds: The angle intersecting Ds due
to extended baffle cut.
![Page 17: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/17.jpg)
Historical Development of the Delaware Method • The Department of Chemical Engineering at the University of
Delaware started a comprehensive research program on shell-side design of shell-and-tube heat exchangers in 1947.
• This project is called Delaware Project and it finished in 1963.
• In 1947, the project started under ASME sponsorship using funds from:– the Tubular Exchanger Manufacturers Association,
– the American Petroleum Institute,
– Standard Oil Development Co.,
– Andale Company, Downingtown Iron Works,
– Davis Engineering Co., E.I. du Pont de Nemours and Company, and
– York Corporation.
• The principal investigators were Professors Olaf Bergelin and Allan Colburn of the University of Delaware.
![Page 18: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/18.jpg)
Methodology of Development
• In 1947, the experimental program started with measurements of heat transfer and pressure drop during flow across ideal tube banks.
• Then several baffle cut and spacing configurations were studied inside a cylindrical shell with no baffle leakage first.
• Baffle leakages between baffles and the shell and between the tubes and baffles were added afterwards.
• Finally, the bypass flow around the bundle between the outer tube limit and the shell inner diameter was investigated.
• The first report was published in 1950 and the second report, in 1958.
• In 1960, a preliminary design method for E shell heat exchangers was issued.
• In 1963, the final report was published.
![Page 19: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/19.jpg)
Shell-side stream analysis• On the shell side, there is not just one stream.• There are essentially two models that address the
flow on the shell side. • The ideal flow and real flow models.
Ideal Shell side flow
A nearly ideal flow can only exist in a heat exchanger if it is manufactured with the special mechanical features.
![Page 20: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/20.jpg)
Realization of Ideal Flow : Condition - 1
• Each baffle is welded to the shell inside diameter at the contact line so that there is no possibility of leakage between the shell and the baffle.
![Page 21: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/21.jpg)
Realization of Ideal Flow : Condition - 2
• The annular space between the tube and the baffle hole is either mechanically closed or a bushing is inserted to eliminate any fluid leak across the clearance between the baffle hole and the tube.
![Page 22: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/22.jpg)
Realization of Ideal Flow : Condition - 3
• The tube bundle layout is such that there are no lands and extra spaces for ribs and impingement plates.
![Page 23: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/23.jpg)
Realization of Ideal Flow : Condition - 4
• The outer tube limit (OTL) almost touches the inner diameter of the shell.
![Page 24: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/24.jpg)
Shell side Real Flow
• When the tube bundle employs baffles, the velocity of fluid fluctuates because of the constricted area between adjacent tubes across the bundle.
• Only part of the fluid takes the desired path through the tube bundle, whereas a potentially substantial portion flows through the ‘leakage’ areas.
• However, these clearances are inherent to the manufacturing and assembly process of shell-and-tube exchangers, and the flow distribution within the exchanger must be taken into account.
![Page 25: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/25.jpg)
Flow Path lines
![Page 26: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/26.jpg)
Temperatures of Path-lines
![Page 27: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/27.jpg)
Velocity Contours in Mid-plane
![Page 28: Geometrical Details of Baffles & Shell Side Fluid Dynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas to Achieve Optimal](https://reader030.vdocuments.net/reader030/viewer/2022032803/56649e365503460f94b25d14/html5/thumbnails/28.jpg)
The Role of Fluid Viscosity• The shell side fluid viscosity also affects stream analysis
profoundly.
• In addition to influencing the shell side heat transfer and pressure drop performance, the stream analysis also affects the mean temperature difference (MTD) of the exchanger.
• It is important to realize that the
• LMTD and F factor concept assumes that there is no significant variation in the overall heat-transfer coefficient along the length of the shell.
• In the case of cooling of a viscous liquid — as the liquid is cooled, its viscosity increases, and this results in a progressive reduction in the shellside heat-transfer coefficient.
• In this case, the simplistic overall MTD approach will be inaccurate, and the exchanger must be broken into several sections and the calculations performed zone-wise.