Abstract: A heat exchanger is formed by a plurality of parallel spaced plates (33,34,35,36) with the spaces between the plates defining fluid receiving passageways (38,39). Each plate includes protuberances (41,42,44,46,49,51) which are staggered with respect to the protuberances on each adjacent plate so that the protuberances of one plate rest against the adjacent plate between the protuberances thereof. Bars (43,48,52) are positioned on the periphery of each plate to close off the passageways and to permit the ingress and egress of a fluid at one temperature and a fluid at a second temperature through adjacent passageways.