Sanitary Cooling
U-Tube Exchangers

Sanitary Product Cooling U-Tube Exchangers

Bringing Product to Fill or Storage Temperature

Post-process cooling takes product from a hot process step down to fill or storage temperature, usually against chilled water or glycol. It looks like the simplest duty in the plant and it contains two traps that catch people regularly.

The cold end works hardest for the least return. Two things happen there simultaneously. The temperature difference is at its smallest, and the product is at its most viscous, so both the driving force and the film coefficient are at their lowest. The last few degrees therefore cost disproportionate surface area. If the required outlet temperature can be relaxed even slightly, the exchanger often gets substantially smaller and cheaper.

Freezing is a real risk, not a theoretical one. Where the coolant runs well below the product's freezing point and flow is low or momentarily stopped, product freezes onto the tube wall. It insulates, so the surrounding surface works harder, and later it sloughs off in pieces. That is a quality problem as much as a thermal one. Coolant temperature control and minimum flow interlocks are the standard protections and they belong in the design rather than in the operating procedure.

Viscosity is a range, not a number. Send the property profile across the whole cooling range. Product entering thin and leaving thick changes flow regime through the exchanger, and a design based on an average will misjudge the coefficient, the pressure drop and often the required surface by a meaningful margin.

Drainability matters at the cold end too. Residue left in a cold exchanger between runs is still residue, and cold viscous product drains more slowly than hot. Vertical orientation or a properly sloped horizontal shell with a low-point drain is what makes the cleaning claim demonstrable rather than argued.

Which side for the product. Viscous and particulate-bearing products usually favour the shell side, where velocities are gentler and the surface can be reached once the bundle is out. Thin, clean products can run tube side, where drainage is straightforward and CIP solution follows exactly the same path the product took.

Related pages: sanitary product heating, pasteurization and HTST, process cooling and sanitary U-tube construction.