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Quotes - Engineering - SalesE-Shell U-Tube Heat Exchangers
The Single-Pass Standard
Shell-side fluid enters through a nozzle at one end and leaves at the other, crossing the bundle repeatedly as segmental baffles direct it back and forth. That cross-flow is where most of the shell-side heat transfer happens.
Baffle cut and spacing. Cut is the fraction of shell diameter the baffle leaves open; spacing is the distance between baffles. Together they set velocity, coefficient and pressure drop. Around a quarter of shell diameter is a common starting cut, adjusted from there.
Where the E shell runs out. Paired with a two-pass tube side it cannot produce a counterflow profile, so a temperature cross defeats it regardless of surface area. The LMTD correction factor is the warning sign, and below roughly 0.8 the configuration needs rethinking.
Vibration. Unsupported span between baffles is the variable that decides whether tubes vibrate. On a U-bundle the bend region needs particular attention, since those tubes are the longest and least restrained in the assembly.
Typical Construction
- Shell type: E - single pass
- Shell-side flow: Cross-flow over segmental baffles
- Typical baffle cut: Approximately 20 to 25 percent of shell diameter
- Baffle spacing: Set by velocity, pressure drop and unsupported span limits
- Pressure drop: Higher than J or X shells for the same flow
- Temperature profile: Cannot achieve a true cross with a two-pass tube side
- Cost: Lowest of the shell types
- Bundle: Removable U-tube
- Vibration check: Required, especially in the bend region
- Codes: ASME Section VIII, TEMA R, B or C
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Reading a Low Correction Factor
When a rating comes back with an LMTD correction factor below about 0.8, the exchanger is being asked to do something its configuration does not suit. Adding surface area barely helps, and performance becomes sensitive to small changes in operating temperature.
The fixes are an F shell, two shells in series, or a rear head that permits a single tube pass. Recognising the signal early avoids buying an exchanger that only works on paper.
