Investigation of the flow characteristics in a multirow finned-tube heat exchanger model by means of PIV measurements

Multirow plain fin-and-tube heat exchangers (PFTHEs) are widely encountered in industrial processes. The airflow between the interfin spaces generates three-dimensional vortical structures at fin-tube junctions which increase local flow mixing. In this paper, two-components PIV velocity measurements were used to investigate the flow characteristics in a model of a four-row staggered PFTHE at Reynolds number ReD = 2000. For each row, the flow structure was analyzed in radial planes at the fin-tube junction in order to characterize the spatial evolution of the vortical structures around the tube. These vortical structures generated in the vicinity of fin-tube junctions were visualized by analyzing the velocity gradient tensor and their spatial evolution and dissipation was characterized. This study highlights the complexity of both row-by-row and angular evolutions of the flow structure. Significant vorticity concentration was found in the vicinity of fin-tube junctions, in the flow core where horseshoe vortices develop. The maximum primary vortex strength throughout the heat exchanger model is observed at the second fin-tube junction.