Large brazed aluminum, plate-fin heat exchangers are frequently used in applications involving three or more separate fluid streams. Important applications include the liquefaction or separation of gas mixtures. They are used extensively in the cryogenic separation of industrial gases, large-scale production of petrochemicals, natural gas processing (NGP), and liquefaction of natural gas (LNG). Their compact design yields minimum size and surface area for environmental heat leaks.

The brazed aluminum heat exchanger is ideally suited for this service. Applications may involve use of multiple fluid streams. The heat transfer and pressure drop requirements for each stream are satisfied by varying the fin geometry (type, fin spacing, height), and the number of flow channels apportioned to each fluid stream. Further, barriers can be provided within the channel stack to allocate one channel to more than one fluid over the length of the heat exchanger. Headers and flow distributors are located on the core, as required, to accommodate the number of fluids involved. The flow distribution areas are usually constructed of plain fins that direct the fluid from the nozzles to the heat transfer area. Within a single core, heat may be transferred between boiling, condensing, or sensible streams. The size of a single brazed core is limited by the vendor’s brazing furnace. Current furnaces permit fabrication of a single core up to about 1.6 m square cross section and 8 m in length. Headers are welded on after brazing.

The following several factors place limits on the use of brazed aluminum heat exchangers.

Typical design temperatures and pressures for large brazed aluminum applications are given in Table 1, taken from the ALPEMA (2009) Standards.