In procurement language 'shell and tube' often means any tubular exchanger. Mechanically, a U-tube unit is a shell-and-tube exchanger with a U rear head (TEMA type U). A fixed-tubesheet unit has two tubesheets welded to the shell (TEMA L/M/N rear ends). Compare those two — not 'U-tube vs plate' — when the plant has already decided on tubular construction.
Thermal expansion
Straight tubes clamped in two tubesheets cannot grow independently of the shell. Large metal-temperature differences need a shell expansion joint, a floating head, or a U-tube bundle. U-bends flex; that is why U-tube is the usual first alternative to bellows.
Cleaning and inspection
Straight tubes with a removable channel cover can be mechanically cleaned tube-side. U-bends cannot be rodded through. Shell-side of a U-bundle can be cleaned after bundle withdrawal. Fixed tubesheets cannot be withdrawn; shell-side cleaning is chemical or, in some designs, not practical.
Maintenance of individual tubes
A leaking straight tube can often be plugged from both ends. A leak in a U-bend region is harder to isolate. Plants that expect frequent tube plugging often prefer straight tubes.
Cost and complexity
U-tube avoids a second tubesheet and floating-head hardware, so it is often less expensive than a TEMA S/T floating head. Versus a simple fixed tubesheet without bellows, U-tube is usually more expensive. The right comparison is against the expansion solution you would otherwise buy.
Ohm manufacturing note
Ohm Engineers manufactures both configurations. Send the process case; do not specify U-tube only because it is familiar if the tube side is dirty.
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