Abstract: A rotary kiln is formed by a helical tube secured inside a cylindrical shell, and fitted with flow spoiler baffles between each turn of the helical tube. Inside the helical tube, one solid particle stream flows uphill in the manner of the classical Archimedes screw. Another stream of particles is tumbled by the flow spoiler baffles and flows under gravity downhill through the center of the helical tube, tumbling over the successive convolutions of the helical tube. This downhill flow occurs because the particles collide with the interflute spoiler baffles, tumble and fall off the helical flutes, thus causing the countercurrent flow. A wide range of surface-to-volume ratios of, and heat transfer through, the helical tube may be achieved by a proper design of the relative width of the tube. This helical tube in a drum device provides heat transfer for a varied number of process applications, such as oil shale or tar sands retorting.