Sandia researchers have developed a radically new architecture for air-cooled heat exchangers.

via Sandia National Laboratories : Licensing/Technology Transfer The Sandia Cooler.

In this new device architecture, heat is efficiently transferred from a stationary base plate to a rotating (counterclockwise) structure that combines the functionality of cooling fins with a centrifugal impeller.  Dead air enveloping the cooling fins is subjected to a powerful centrifugal pumping effect, providing a 10x reduction in boundary layer thickness at a speed of a few thousand rpm.  Additionally, high-speed rotation completely eliminates the problem of heat exchanger fouling.  The “direct drive advantage”, in which relative motion between the cooling fins and ambient air is created by rotating the heat exchanger, provides a drastic improvement in aerodynamic efficiency.  This translates to an extremely quiet operation.  The benefits have been quantified on a proof-of-concept prototype.