Abstract: A high pressure heat exchanger has a body with spaced apart parallel plates with side walls joined to the peripheral edge of each plate; a tubular high pressure liquid inlet header external of the body; a tubular high pressure liquid outlet header external of the body; a plurality of separate tubular runs in communication with the inlet and outlet headers; each tubular run including a tubular portion between substantially all adjacent plates of the body; the tubular portions of the same run being interconnected at one end by a tubular liquid return with a tubular portion on the opposite side of a first adjacent body plate and interconnected at the other end by a tubular liquid return with a tubular portion on the opposite side of a second adjacent body plate; the body internal plates having a liquid communication opening which permits a second liquid to flow from the space on one side of a baffle plate to the space on the other side of the baffle plate in a serpentine flow path through the body while in heat