Baffles and Tube Supports

U-Tube Heat Exchangers For

Baffles and Tube Supports
U-Tube Duty

Baffles do two jobs that pull against each other. They direct shell-side flow across the tubes for heat transfer, and they support the tubes against vibration. Spacing them is a compromise between those two duties.

Segmental baffles are plates with a segment cut away, arranged alternately so the shell-side fluid weaves across the bundle. Cut is expressed as a percentage of shell diameter; around 20 to 25 percent is a normal starting point.

Spacing sets everything. Closer baffles mean higher cross-flow velocity, a better coefficient and higher pressure drop. They also shorten the unsupported tube span, which is the governing variable for vibration.

Bypass Is the Silent Performance Loss. Shell-side fluid takes the easiest path, and the clearances between bundle and shell, and between tube and baffle hole, are easy paths. Fluid that bypasses the bundle does no useful work.

Sealing strips placed in the bypass lanes push flow back through the tube field. On large bundles this is worth real percentage points of performance and is far cheaper than the extra surface area needed to compensate for its absence.