EXPERIMENTAL-STUDY OF FLOW AND HEAT-TRANSFER IN RIB-ROUGHENED RECTANGULAR CHANNELS

Secondary flow patterns, pressure drop and hear transfer in rib-roughe ned rectangular channels have been investigated. The aspect ratio of t he channels is 1-8, and ribs are attached to the wide channel walls in order to set up swirling motions. The geometries tested consist of ch annels having cross ribs, parallel ribs, cross V-ribs, parallel V-ribs , and multiple V-ribs (Swirl Flow Tube). The flow patterns were invest igated using smoke wire visualization and LDV measurements. The smoke wire experiments have been performed at Re = 1100 and the LDV measurem ents at Re = 3000 at periodic fully developed conditions. The heat tra nsfer and pressure drop are described by j and f factors for Reynolds numbers from 500 to 15000. The distributions of axial mean velocity an d turbulent fluctuations are strongly influenced by the secondary flow s. Large mean velocities and small fluctuations are found in regions w here the secondary flow is directed towards a surface, while small mea n velocities and large fluctuations are found in regions where the sec ondary flow is directed away from a surface. The Swirl Flow Tube provi des a significant increase in the j factor at Reynolds numbers from 10 00 to 2000, but unfortunately also an increase in the f factor.At high er Reynolds numbers, the j and f factors of the Swirl Flow Tube are of the same order of magnitude as for the other rib-roughened channels. It is found that the flow direction in a channel with parallel V-ribs has important influence on the j/f ratio. At Reynolds numbers above 40 00, this channel provides the highest j/f ratio if the V-ribs are poin ting upstream; while it provides the lowest j/f ratio of all rib confi gurations, if the V-ribs are pointing downstream. (C) 1998 Elsevier Sc ience Inc. All rights reserved.