Two-pass shell

A solid longitudinal baffle is provided to form a two-pass shell (Fig. 11-35F). It may be insulated to improve thermal efficiency. (See further discussion on baffles). A two-pass shell can improve thermal effectiveness at a cost lower than for two shells in series. 

The shell types are E, F, G, H. i, and K. E is a one-pass shell. The fluid comes in on one side and goes out the other side, F is a two-pass shell with a longitudinal plate in it. The fluid in the shell makes two passes. 

Figure 10-1J. Split-ring removable floating head, four-pass tube-side and two-pass shell-side. (Used by permission Engineers Fabricators, Inc., Houston.)...

Figure 10-22B. Assembled two-pass shell baffle for installation in shell of exchanger. (Used by permission Struthers-Wells Corp. Bui. A-22.).

Figure 12.12. Shell types (pass arrangements), (a) One-pass shell (E shell) (b) Split flow (G shell) (c) Divided flow (J shell) (d) Two-pass shell with longitudinal baffle (F shell) (e) Double split flow (H shell)...

These values do not intercept on the figure for a single shell-pass exchanger, Figure 12.19, so use the figure for a two-pass shell, Figure 12.20, which gives... 

Most of the heat exchangers in your plant are designed with the shell-side inlet and shell-side outlet at opposite ends of the shell, as shown in Fig. 19.6. However, you may have noted a few exchangers in which both the shell-side inlet and shell-side outlet are next to the channel head. This is a two-pass shell-side exchanger, of the type shown in Fig. 19.8. 

This would make it seem that the two-pass shell configuration is inherently more efficient than the ordinary single-pass shell exchanger. And it is, in theory. Then why do we see so few of these exchangers in service ... 

Two-pass shell-and-tube heat exchanger showing construction details. (Ross Heat Ixdtattgrr Division of American-Standard.)... 

D) Eixed-tube sheet exchanger with removable channel and cover, bonnet-type rear head, two-pass shell, 841-mm (33V6-in) diameter with tubes 2.4 m (8-ft) long. SIZE 33-96 TYPE AEM. 

This is a two-pass shell-side exchanger of the type shown in Fig. 26.8. 

This would make it seem that the two-pass shell configuration is inherently more efficient than the ordinary single-pass shell exchanger. 

I have seen new exchangers of "two-pass shell" configurations work well when new. However, with time and typically after a turnaround, performance has been degraded, due to leakage around the cross-flow (longitudinal) baffle. 

My former employer, American Oil, prohibited their use because of this problem. I also adhere to this practice and thus will select placing two exchangers in series, which is the more expensive option, as opposed to relying on the two-pass shell alternate design. 

Fig. 17-2. Common arrangeme of flow (a) countercurrent, two-pass shell, 2 tube passes (b),parallel flow, two-pass shell, two tube passes (c) ipixed flow, single-pass shell, two tube passes (d) constant-temperature ccioling medium (e) constant-temperature heating medium, and (/) combination condensing and subcooling.

Fio 17-6. Conventional segmental shell baffling (a) indicates lognitudinal baffle for a two-pass shell, and (b) shows cross baffles (for either single or two-pass shell). 

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