US Patent 7913512 Air-heated heat exchanger

A heat exchanger comprises a first tube having a first fin of a first predetermined height extending outward therefrom. A second tube is vertically spaced above the first tube. The second tube has a second fin of a second predetermined height extending outward therefrom. A fan is positioned to force ambient air across the second tube and then across the first tube to heat a fluid flowing therethrough. A method of heating a fluid comprises sequentially flowing the fluid upward through a plurality of vertically spaced rows of substantially horizontal tubes, and forcing air downward over the plurality of tubes to heat the fluid.