Tube layout there are two standard types of tube

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Tube layoutThere are two standard types of tube layout: a)Square layout b)Triangular layout Triangular pitch is preferred when the cleaning of the shell is not needed or chemical cleaning can suffice. It provides a more compact arrangement resulting in smaller shell. It is preferred when the operating pressure difference between the two fluids is large. Triangular layouts give more tubes in a given shell and also provide a better heat transfer coefficient in the tube side. Square pitch is used when mechanical cleaning is necessary on the shell side. It is generally not used in the fixed header sheet design because cleaning is not feasible in this case.
35 Fig. 5: Layouts of the tubes The 90-degree layout has the lowest heat transfer coefficient and the lowest pressure drop. Baffles Baffles are used to support the tubes, enable a desirable velocity to be maintained and flow induced vibration. They increase the heat transfer by producing cross flow and turbulence. As per TEMA standard, the baffle spacing is one-fifth of the shell diameter. Closer baffle spacing will result in poor bundle penetration by shell side fluid and difficulty in the mechanical cleaning of the outside of the tubes. As the baffle spacing is decreased, the pressure drop also increases more rapidly than the heat transfer coefficient. The baffle cut vary from 15% to 45%. Types of baffle: Segmental baffle Rod baffle
36 Single segmental baffle Double Segmental baffle No tubes in window Fig. 6: Types of the Baffles Shell side flow pattern The actual flow of the main stream of fluid will be a mixture of cross flow between the baffles, coupled with the axial flow in the baffle windows. Some fluid will leak through the gaps formed by the clearances that have to be allowed for fabrication and assembly of the exchanger. Fig. 7:Idealized main stream flow
37 Fig. 8: Shell side leakage and by-pass paths Stream A: It is the tube to baffle leakage stream. The fluid flows through the clearance between the tube outside diameter and the tube hole in the baffle. Stream B: It is the actual cross-flow stream. Stream C: It is the bundle to shell by-pass stream. The fluid flows through the clearance between the outer tubes in the bundle and the shell. Stream E: It is the baffle to shell leakage stream. The fluid flows through the clearance between the edge of the baffle and the shell wall. Stream F: It is the pass partition stream. The fluid flows through the gap in the tube arrangement due to the pass partition plates. The stream C is the main by-pass stream and can be considerably reduced by using sealing strips, horizontal strips that block the gap between the bundle and the shell. Impingement plate, Tie rods and spacers, Tube sheet The impingement plates are used to prevent the damage to the tubes due to the oncoming shell side fluid.

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