Abstract: 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.

Abstract: An apparatus for vaporizing a cryogenic fluid comprises a heat transfer fluid closed circulation loop at least partially defined by an ambient air heat exchanger, a heater, and a vaporizer. The heat exchanger is configured to direct air downward across a plurality of heat exchanger tubes. A cryogenic fluid flows through the vaporizer. The plurality of tubes comprise a first tube having a first fin of a height, h1, and a second tube spaced adjacent the first tube, where the second tube has a second fin of a height, h2, wherein h2 is different from h1.