There are a series of parallel corrugated metal plates placed above each other so that the formation allows for the fluids to flow between them. The plates are assembled between a frame and plate held together by tightening bolts. The plates have gaskets that are supposed to act as seals and direct the fluids into alternate channels. The corrugation helps to generate fluid turbulence and helps against the differential pressure. There are inlet and outlet portholes for the hot fluid to flow from one side and come out of the other, cold. There is an exchanger in the alternating channels to allow this to happen when the fluids are divided into parallel streams to produce a counter current.