Abstract: A heavy duty heat exchanger consisting of a large number of plates of tapered cross-section, selectively provided with essentially lengthwise parallel grooves and land areas at the lengthwise edges. Upon being stacked together and joined, the plates form an inherently leaktight, rugged and compact heat transfer core with axially directed fluid passages and integral with it two fluid transition zones, all of radially symmetrical, annular cross-section, throughout. Very large fluid flow rates can be accommodated and very high heat transfer effectiveness attained without increased design complexity or cost escalation.