Abstract: A channel for moving gas between an entry into which gas is introduced and an exit through which gas exits, comprising a plurality of adjoining adjacent guides, each guide comprising an outer portion of a smoothly-curved, modified torus whose inner wall has concave curvature on the gas inlet and convex curvature on the gas outlet and has an inflection point of curvature axially downstream of the inlet of the respective guide. Each guide forms a smoothly curved internal cavity with a cavity mouth opening into the gas flow channel, the cavities shaped such that a vortex forms within each of the cavities as gas passes through the channel. Flow of fluid in the channel is unidirectional and axial from the entry to the exit.