The Possibility of Harvesting Useful Energy from the Thermal Motion of Air Molecules

Graeme A. Bird


Direct simulation methods have been used to model the motion of initially stationary microscopic spheres following their release into the atmosphere. The spheres have diameters of the order of 10 nm and acquire energy from the slightly cooled air as they develop Brownian motion. While the individual trajectories vary wildly, an ensemble average over tens of thousands of trajectories yields a classical relaxation curve. The initial energy input from the air to a sphere is determined as a function of its diameter and mass. The energy flux to and from the fluctuations is also calculated along with the inward heat flux at the molecular level. The values of these quantities indicate that, while a sufficiently large number of sufficiently small devices might extract useful energy from air, the requirements with regard to size are beyond current nano-technology.