Heat exchangers

A heat exchanger including a series of fluid pathways, said heat exchanger comprising:

• a plurality of primary surfaces, each fluid pathway being defined by primary surfaces in the form of surfaces of two parallel unperforated primary plates;
• at least two secondary plates extending along the fluid pathway between each two primary plates, each secondary plate being flat and being unperforated edges, each secondary plate having their a plurality of perforations, the perforations in adjacent secondary plates being staggered but overlying such that each perforation, other than at edges of the secondary plates, overlies two laterally and two longitudinally adjacent perforations in an adjacent secondary plate;
• means for securing the primary plates to the secondary plates and for securing the secondary plates together at positions where the secondary plates contact one another to form heat conducting pathways between the two primary surfaces, area of secondary plates not in contact with plates constituting secondary surfaces, said unperforated edges of the secondary sheets combining to form sealing strips;
• the series of fluid pathways being stacked together such that adjacent fluid pathways have a common primary plate;
• inlet and outlet means connected to said fluid pathways, whereby first and second fluids are supplied to the heat exchanger such that the first and second fluids flow through adjacent fluid pathways.