The large surface area in compact heat exchangers is obtained by attaching
closely spaced thin plate or corrugated fins to the walls separating the two fluids.
Compact heat exchangers are commonly used in gas-to-gas and gas-toliquid
(or liquid-to-gas) heat exchangers to counteract the low heat transfer
coefficient associated with gas flow with increased surface area. In a car radiator,
which is a water-to-air compact heat exchanger, for example, it is no surprise
that fins are attached to the air side of the tube surface.