Heat Transfer Enhancement by Wing-Type Longitudinal Vortex Generators and their Application to Finned Oval Tube Heat Exchanger Elements

Abstract

Wing-type longitudinal vortex generators (LVGs) can be used as fins or fin modifications for heat transfer enhancement in compact heat exchangers. For the last 15 years a group at the Ruhr-University Bochum has studied systematically the characteristics of heat transfer surfaces with vortex generators. Recent results are reported here. Three heat transfer enhancement modes may be induced by LVGs: developing boundary layer, swirl (longitudinal vortices) and flow destabilization. First these enhancement modes were studied numerically and experimentally for a base configuration consisting of a rectangular winglet array in channel flow at a Reynolds number of 175. Then finned oval tube heat exchanger elements with and without punched delta winglets were studied numerically. Winglet number and arrangement on the fin were varied in the Re range from 100 to 500. Flow structure, temperature distribution, local and global heat transfer, and flow loss penalty were presented. Staggered winglet arrangements were superior to in-line arrangements. The fin heat transfer surface may be reduced by more than 50% compared to a plane fin for identical heat duty, pressure loss, mass flow rate and temperature difference of the hot and cold medium. Direction for further research is indicated.