Heat transfer enhancement through the use of an oscillatory flow in circular-orifice baffled tubes: ane xperimental study

Abstract

This work presents an experimental study of the flow pattern in tubes with equally-spaced circular-orifice baffles. Particle Image Velocimetry (PIV) technique is employed in order to obtain the velocity field of the oscillatory flow in the symmetry plane of the region between two consecutive baffles. Experiments have been carried out for oscillatory Reynolds numbers ranging from Reosc =26to Reosc =1500. Theinstantaneousand cycle average f low fields have been obtained for the experiments. The flow has been found to have laminar regime characteristics for Reosc < 100 and to be unstable for about Reosc > 140. For all tested conditions, a recirculation bubble has been detected when the change in direction of the oscillatory motion takes place. Besides, the bubble is displaced along the cell tank by the flow. This bubble results in some mass transfer between core and peripheral regions of the flow. Furthermore, when the limit of about Reosc ≈ 140 is overcome, additional instabilities and vortexes appear, which increase with the Reynolds number, and also increase mass transfer.