Abstract: Method and apparatus for improving convective heat transfer by mechanically stirring fluid over the outer surface of a heat exchanger. A stirring mechanism is described which revolves rapidly around a heat exchanger surface in a stream undergoing heat transfer. During rotation, the stirring mechanism is supported near an end of the stirred heat exchanger by a central bearing and drive means. It is also supported over an extended length of the stirred heat exchanger surface by the hydrodynamic action of the stirring mechanism relative to the heat exchange surface without need for an additional central support bearing. The stirring mechanism uniformly turbulates the fluid film over the outer surface of the heat exchanger where heat transfer resistance normally occurs without imposing a pressure drop in the fluid stream undergoing augmented heat transfer. Compact and inexpensive heat exchangers are described which may be used in refrigeration, heating-cooling, and energy conservation systems.