Interaction of counter rotating longitudinal vortices and the effect on fluid flow and heat transfer

Abstract

The flow with longitudinal vortices is an important phenomenon in fluid dynamics and heat transfer. As the longitudinal vortices can potentially enhance heat transfer with small pressure loss penalty, vortex generators (VGs) which can generate longitudinal vortices are widely used to enhance the heat transfer of compact heat exchanger. In order to obtain a better heat transfer performance, researchers always try to punch lots of VGs out of the fin surface. But the increasing number of VGs is not necessarily linked with the rise in heat transfer performance augmentation. This is because the longitudinal vortices will interact with each other when they meet in the flow channel and the interaction between the longitudinal vortices is always disadvantage for the heat transfer enhancement. In this paper, numerical simulation of the interaction between two counter-rotating longitudinal vortices was carried out for the plate–fin heat exchanger using two rows of delta winglet type vortex generators. The effect of the transversal distance between the two VGs on the interaction of vortices and the effect of such interaction on heat transfer enhancement are studied in detail. New and important understandings about the interaction of counterrotating longitudinal vortices are obtained. The intensity of the longitudinal vortices and the heat transfer performance are sensitive to the interaction between longitudinal vortices. The interaction between counterrotating vortices decreases the average intensity of vortices, but does not necessarily decrease the heat transfer performance of longitudinal vortices. The common flow region formed between the counterrotating longitudinal vortices is beneficial to the heat transfer enhancement though interaction takes place in the common flow region between longitudinal vortices. An optimum arrangement of VGs exists for obtaining the best heat transfer performance. The arrangement of VGs with the transversal distance is zero must be avoided due to the serious interaction between longitudinal vortices.