Experimental investigations of heat transfer enhancement and flow losses in a channel with double rows of longitudinal vortex generators

Abstract

Flow structure, heat transfer, and drag by longitudinal vortices generated by double rows of delta winglets in transition channel flow are investigated for the reduction of the gas side heat transfer resistance of compact heat exchangers. The experiments consist of flow visualization by laser light sheets, liquid crystal thermography for local heat transfer and balance measurements for drag. Angle of attack and channel Reynolds number have been varied. Aligned delta winglet double rows show higher heat transfer enhancement than staggered. The critical angle of attack for the formation of longitudinal vortices is smaller behind the second row than behind the first. Heat transfer enhancements of 80% and drag increases of 160% have been found on wall areas 40 times the winglet area. The ratio of heat transfer enhancement and drag increase is larger for higher Reynolds numbers.