Three kinds of heat transfer augmentation in perforated surfaces

Abstract

Heat exchanger cores, each consisting of a number of single or composite perforated plates separated by wooden spacers to form parallel flow channels, were tested in a subsonic wind tunnel. Three distinct types of augmentation in the heat transfer and friction loss performance have been identified: the transition-turbulent flow enhancement, the "second" laminar flow enhancement and the laminar flow enhancement. The first kind is observed to occur in the transition and turbulent flow regimes on low porosity surfaces [1]. The second type is detected in the "second" laminar flow regime on high porosity surfaces [2]. The present study has revealed the existence of the third pattern which occurs over the entire laminar flow region on low-porosity composite surfaces consisting of a short upstream section for producing vortices and a main section for heat transfer. An attempt is made to explain the enhancement mechanisms.