Achieve high heat transfer rates between 2 fluids in a small volume. (strict limitations on the weight & volume of HE).
Large surface area is obtained by attaching closely spaced thin plate or corrugated fins to the walls separating the two fluids.
In compact HE, the two fluids usually move perpendicular to each other is called cross-flow. It’s further classified as unmixed & mixed flow, depending on the flow configuration.
Unmixed: The plate fins force the fluid to flow through a particular interfin spacing and prevent it form moving in the transverse direction (i.e., parallel to the tubes)
Fluid is free to move in the transverse direction.