Experimental Investigation of Laminar Heat Transfer in Chaotic Heat Exchangers. Comparison of Four Geometries

In many applications, fluid flows are laminar and convective heat transfer is not as important as in turbulent regime. Chaotic geometry is a way to improve heat transfer in laminar regime at the same time as producing flow mixing. The present work is an attempt to study Chaotic Laminar Mixers (CLMs) from the viewpoint of heat transfer efficiency. In such a device a secondary flow normal to the main flow is created in order to mix the streamlines and to steer the fluid from the flow core to the walls. Such a secondary flow can be created in curving a duct to make profit of the centrifugal force applied to the fluid, so producing Dean vortices. A practical way is to form a succession of curved ducts whose orientation of the curvature plane is varied. This process superimposes different vortex zones in order to induce chaotic trajectories. This aspect can be improved by splitting the fluid into several flows and then recombining them. Four heat exchangers have been built in varying the number of bends and of the splitting/recombination sequences. Heat transfer has been experimentally studied to determine the best geometry.