Embedded vortices in internal flow: heat transfer and pressure loss enhancement

Abstract

Vortices depend strongly on the way they are generated. A class of wing-type vortex generators, which can easily be incorporated into heat transfer surfaces, is considered in fully developed and developing channel flows with respect to heat transfer enhancement and pressure loss penalty. Such configurations have been investigated in detail by the research group “Vortices and Heat Transfer” at the ITF of the Ruhr University. Three enhancement mechanisms are identified and discussed quantitatively: (1) developing boundary layers on the vortex generator surface; (2) swirl; and (3) flow destabilization. Experiments and calculations show that (1) winglets are more effective than wings, and (2) rectangular and delta winglets give similar performance. A base configuration with rectangular vortex generators is investigated in detail. Transition starts at Reynolds numbers below 300, and no dominant frequencies can be detected at Re= 1,000. At all Reynolds numbers, longitudinal vortices are more effective than transverse vortices; i.e., longitudinal vortex generators generate higher heat transfer enhancement for the same pressure penalty than transverse vortex generators.