Design and experimental study of an ultrasonically assisted shell-and-tube heat exchanger
Résumé
With the aim of studying heat transfer in the presence of low frequency ultrasound, a shell-and-tube heat exchanger has been designed [ 1]. It has been built from a tubular ultrasonic emitter resulting in what might be named a "sonoexchanger". This new type of shell-and-tube heat exchanger can be regarded as a vibrating exchanger since the shell transmits a low frequency ultrasonic field. To our knowledge, there is no reference in the literature with a heat exchanger involving an acoustic field. Experiments have been performed using a specific experimental set-up involving this homemade heat exchanger. A data acquisition system coupled with several temperature sensors and flowmeters is used. Attention is focused on the inlet and outlet temperatures of the cooling and heating water and on the corresponding flowrates. In a first step, experiments have been performed to study heat transfer without ultrasound under several hydrodynamical conditions. The second set of experiments was devoted to the study of heat exchange under the same experimental conditions but in the presence of the ultrasonic waves. Comparison was made between overall heat transfer coefficient with and without ultrasound, the determination of which is based upon the energy balance on the heat exchanger. Comparison has been performed for several ultrasonic powers at different flowrates. It has been shown that when ultrasound operates, heat flow rates are increased on both sides of the heat exchanger in all cases. Furthermore, the heat transfer coefficient is enhanced. This positive effect of ultrasound was expressed through an enhancement factor EF defined as the ratio of the overall heat transfer with ultrasound on the overall heat transfer under the same conditions without ultrasound. As illustrated in the figure below, the enhancement factor ranges from 120 to 257 % . Other operating parameter studies are now in progress in order to demonstrate the feasibility of such a new type of heat exchanger. [no pdf]
