The plate-fin heat exchanger is similar to the plate-type exchanger, except that an extended surface is used between the two separating sheets as shown in Figure 1. A unique feature of plate-fin heat exchangers is their high-heat transfer surface area per unit volume. Heat transfer surface area of 1,300 m²/m³ of volume is not uncommon. For this reason, they are commonly called "compact heat exchangers," although sometimes in the United Kingdom the term "matrix heat exchanger" is used.

Figure 1 Basic components of plate fin stack, courtesy of the Trane Company

There are two important subclasses of plate-fin heat exchangers, namely, the plate-fin-plate-fin construction and the plate-fin-tube construction. The plate-fin-plate-fin construction, which consists of a number of laminations of the elements in Figure 1, is normally used for gas-to-gas (or two-phase) applications. The plate-fin-tube construction, which has tubes normal to the plate structure, is used for gas-to-liquid or gas change of phase applications; the liquid or two-phase mixture flows through the tubes. The passenger car radiator and air-conditioning condenser are examples of this construction.

The most common construction material is all aluminum, which yields what are called "brazed aluminum heat exchangers." These have an extremely wide variation in core size-from the gargantuan sizes used in industrial gas processing to quite small sizes used in automotive applications (e.g., a heater cores) or aircraft (e.g., oil coolers).

First, we describe the construction of large, industrial "plate-fin-plate-fin" exchangers, and then, the construction of small plate-fin-tube exchangers.