Shell-tube bundle clearance, heat exchanger

The U-tube bundle has the advantage of providing minimum clearance between the outer tube hmit and the inside of the shell for any of the removable-tube-bundle constructions. Clearances are of the same magnitude as for fixed-tube-sheet heat exchangers. 

In conjunction with this, the shell side fluid generally will take the path of least resistance and will travel at a greater velocity in the free areas or by-pass lanes, than it will through the bundle proper, where the tubes are on a closely spaced pitch. All factors considered, it appears a formidable task to accurately predict heat transfer characteristics of a shell and tube exchanger. The problem is further complicated by the manufacturing tolerances or clearances that are specified to allow assembly and disassembly of the heat exchanger. 

Sufficient clearance should be provided for removal of tube bundles from shell and tube heat exchangers for maintenance, inspection, or replacement. 

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