Abstract: A method and means of exchanging heat in fluids is described herein. The heat exchanger device is comprised of a primary compartment which is separated into at least two longitudinal compartments by a vertically disposed heat exchanger plate. Each longitudinal compartment is divided into a plurality of sub-compartments by walls that extend outwardly from the heat exchanger plate to the sidewalls of the primary compartment. Fluid inlet means are provided at the lower portion and at opposite ends of each longitudinal compartment. Fluid outlet means are provided at the upper portion and at opposite ends of each longitudinal compartment. The sidewalls of each sub-compartment are shorter than the height of the heat exchanger plate to provide a common fluid flow way in each longitudinal compartment over the sub-compartments. The sidewalls of the sub-compartments are progressively lowered at their upper ends in the direction of fluid flow through the flow ways.