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Quotes - Engineering - Sales| PRODUCT | STYLE | TEMA TYPE | BUNDLE |
| U-Tube Heat Exchanger | U-Tube, single tubesheet | BEU / AEU / BKU | Removable |
Two-Pass U-Tube Heat Exchangers
Even Passes, and Why It Matters
Because each tube doubles back, the tube-side fluid always makes at least two passes. Four, six and eight pass arrangements are built by adding partition plates to the channel so the fluid crosses the bundle multiple times before leaving. What never happens is an odd number of passes.
Why add passes at all? To raise tube-side velocity. Higher velocity means a better heat transfer coefficient and less fouling deposition, and it is the standard remedy when the tube-side flow is too low to be turbulent in a single pass. The cost is pressure drop, which climbs steeply with pass count.
The temperature cross problem. A two-pass tube side cannot achieve true countercurrent flow, because half the tube length runs one way and half the other. When the required duty produces a temperature cross — the cold stream leaving hotter than the hot stream leaves — a single two-pass exchanger cannot do it regardless of surface area.
The remedies. An F-shell with a longitudinal baffle creates two shell passes and restores counterflow. Two shells in series does the same thing with more hardware. Or the rear head changes to a fixed tubesheet or floating head design that permits a single tube pass. We would rather raise this at rating than let a correction factor quietly ruin the design.
Typical Construction
- Minimum passes: Two, set by the U-bend geometry
- Typical arrangements: Two, four, six or eight passes
- Odd passes: Not possible in U-tube construction
- Pass partitions: Plates in the channel or bonnet
- Velocity target: Selected for turbulence, fouling and erosion limits
- Pressure drop: Rises steeply with pass count
- Temperature cross: Requires F-shell, shells in series, or a different rear head
- Correction factor: LMTD F factor checked at rating; low F flags a poor configuration
- Gasket detail: Pass partition gasket rib required in the channel
- Nozzle arrangement: Inlet and outlet on the same head
Two-Pass U-Tube Heat Exchangers
U-TUBE • CONSTRUCTION
Stock Steam-to-Liquid
Stock two-pass steam-to-liquid U-tube heat exchangers in 304L and 316L. ASME hydro-tested and code stamped, tri-clamp process connections, shipping in
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U-TUBE • CONSTRUCTION
Custom U-Tube Exchangers
Custom engineered U-tube heat exchangers built to your conditions. Thermal rating, third-party inspection, applied nozzle loadings, seismic cases and
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U-TUBE • CONSTRUCTION
Sanitary U-Tube
Sanitary U-tube heat exchangers in 316L with tri-clamp connections, drainable geometry and removable bundles. Built for 3-A duty and CIP circuits.
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Reading the LMTD Correction Factor
Every multi-pass exchanger rating carries a correction factor applied to the log mean temperature difference. It accounts for the fact that flow is not purely countercurrent. When that factor drops much below about 0.8, the configuration is fighting the duty, and small changes in operating temperature produce large changes in performance.
A low correction factor is not something to solve by adding surface area. It is a signal that the configuration is wrong for the temperature profile, and the right response is an F-shell, shells in series, or a different design entirely.
Both Nozzles on One End
A practical consequence of U-tube construction that is easy to overlook during layout: the tube-side inlet and outlet are both on the same head, because the fluid comes back to where it started. That simplifies some pipe runs and complicates others.
It also means the tube-side connections sit at the end you need clear to withdraw the bundle. Plan the piping so those connections can be broken without dismantling half the skid, or the maintenance advantage of a removable bundle becomes theoretical.
