THE EFFECTS OF CHAOTIC ADVECTION ON HEAT-TRANSFER

The objective of this study is to characterize a new heating process i n fluids, chaotic advection. The main mechanism generating this Row is the production of spatially chaotic trajectories in an alternating De an flow. The present work examines the effects of chaotic advection on heat transfer at low Reynolds numbers. in order to assess the enhance ment of heat transfer by chaotic advection, a helical heat exchanger a nd 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 c oils were assembled from 90 degrees bends, and the chaotic coil was pr oduced merely by turning each bend at a +/-90 degrees angle with respe ct to the previous one. Experiments were performed for Reynolds number s ranging from 60 to 200. Temperature profiles measured in the cross-s ection of the coils show that chaotic advection substantially homogeni zes and enhances heating. Moreover, it is shown that the homogeneity o f heating in chaotic flow is almost independent of the Reynolds number . Parallel to the temperature profiles measurements, axial velocity pr ofiles 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 ef ficient than the helical one, with an efficiency enhancement between 1 3 and 27%. (C) 1997 Elsevier Science Ltd.