Understanding Baffle Types in Shell and Tube Heat Exchangers: A Comprehensive Guide

Explore the different types of baffles used in shell and tube heat exchangers, their purposes, and benefits, including transverse and longitudinal baffles, plate baffles, and grid baffles.

Baffles may be classified as transverse and longitudinal types. The purpose of longitudinal baffles is to control the overall flow direction of the shell fluid such that a desired overall flow arrangement of the two fluid streams is achieved. For example, F, G, and H shells have longitudinal baffles (see Fig. 1.6).

Transverse baffles may be classified as plate baffles and grid (rod, strip, and other axial-flow) baffles. Plate baffles are used to support the tubes during assembly and operation and to direct the fluid in the tube bundle approximately at right angles to the tubes to achieve higher heat transfer coefficients. Plate baffles increase the turbulence of the shell fluid and minimize tube-to-tube temperature differences and thermal stresses due to the crossflow. Shown in Fig. 1.10 are single- and multi segmental baffles and disk and doughnut baffles.

Single- and double-segmental baffles are used most frequently due to their ability to assist maximum heat transfer (due to a high-shell-side heat transfer coefficient) for a given pressure drop in a minimum amount of space. Triple and no-tubes-in-window segmental baffles are used for low-pressure-drop applications. The choice of baffle type, spacing, and cut is determined largely by flow rate, desired heat transfer rate, allowable pressure drop, tube support, and flow-induced vibrations. Disk and doughnut baffles/ support plates are used primarily in nuclear heat exchangers. These baffles for nuclear exchangers have small perforations between tube holes to allow a combination of crossflow and longitudinal flow for lower shell-side pressure drop. The combined flow results in a slightly higher heat transfer coefficient than that for pure longitudinal flow and minimizes tube-to-tube temperature differences. Rod (or bar) baffles, the most common type of grid baffle, used to support the tubes and increase the turbulence of the shell fluid, are shown in Fig. 1.11. 

The flow in a rod baffle heat exchanger is parallel to the tubes, and flow-induced vibrations are virtually eliminated by the baffle support of the tubes. One alternative to a rod baffle heat exchanger is the use of twisted tubes (after flattening the circular tubes, they are twisted), shown in Fig. 1.12. Twisted tubes provide rigidity and eliminate flow-induced tube vibrations, can be cleaned easily on the shell side with hydrojets, and can be cleaned easily inside the tubes, but cannot be retubed. Low-finned tubes are also available in a twisted-tube configuration. 

A helical baffle shell-and-tube exchanger with baffles as shown in Fig. 1.13 also has the following advantages: a lower shell-side pressure drop while maintaining the high heat transfer coefficient of a segmental exchanger, reduced leakage streams (Conventional shell-and-tube exchangers have segmental plate baffles. The shell-side flow is very complex in such a heat exchanger, due to a substantial portion of the fluid bypassing the tube bundle through necessary constructional clearances. As a result, the conventional heat transfer correlations and the MTD method applied to a shell and tube exchanger generally do not predict the actual performance.), and elimination of dead spots and recirculation zones (thus reducing fouling).

Every shell-and-tube exchanger has transverse baffles except for X and K shells, which have support plates because the sole purpose of these transverse baffles is to support the tubes.

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