The effects of chaotic advection on heat transfer

Abstract

The objective of this study is to characterize a new heating process in fluids, chaotic advection. The main mechanism generating this flow is the production of spatially chaotic trajectories in an alternating Dean flow. The present work examines the effects of chaotic advection on heat transfer at low Reynolds numbers. In order to assess the enhancement of heat transfer by chaotic advection, a helical heat exchanger and a chaotic heat exchanger (both of shell-and-tube type) of the same heat-transfer surface area and the same tube length were tested. The coils were assembled from 90° bends, and the chaotic coil was produced merely by turning each bend at a ± 90° angle with respect to the previous one. Experiments were performed for Reynolds numbers ranging from 60 to 200. Temperature profiles measured in the cross-section of the coils show that chaotic advection substantially homogenizes and enhances heating. Moreover, it is shown that the homogeneity of heating in chaotic flow is almost independent of the Reynolds number. Parallel to the temperature profiles measurements, axial velocity profiles were measured by laser Doppler velocimetry at the exit from the coils and used to characterize the flow in the isothermal regime and compare the temperature profiles to the velocity profiles. Global heat-transfer measurements show that the chaotic heat exchanger is more efficient than the helical one, with an efficiency enhancement between 13 and 27%.