Heat transfer and hydraulic drag in helical channels in gas flow

Abstract

Experimental results are given for heat transfer from convex and concave walls and for hydraulic drag in hydrodynamically and thermally stabilized air flow in rectangular helical channels over a wide range of operating conditions ( Re = 10 2–2 × 10 5) and geometric parameters ( D/h = 5.5–84.2, b/h = 2.4– 18.5). It is established that, with an increase in the channel curvature, heat transfer from the concave wall is enhanced, whereas that from the convex wall is reduced, and a transition to turbulent flow on both walls occurs at different Reynolds numbers, which are larger than those in a straight channel, and has different lengths. Applying artificial roughness to the convex surface is shown to allow its heat transfer enhancement even to the level of heat transfer from the concave surface. Correlations are obtained for the critical Reynolds numbers at which the transition from laminar-vortex to turbulent flow occurs, for heat transfer from separate walls and for hydraulic drag in the helical channels.