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Mass-transfer enhancement in a wavy-walled tube by imposed fluid oscillation



The present experimental study deals with mass-transfer enhancement and fluid dynamic behavior in a wavy-walled tube for pulsatile flow. Three flow parameters are considered here: the net flow Reynolds number, the oscillatory fraction of the flow rate, and the Strouhal number. Among them, we especially focused on the effect of Strouhal number on mass-transfer enhancement under the condition of no reverse flow. Time-averaged transport enhancement by means of imposed fluid oscillation is found to vary with the net flow Reynolds number and with the oscillatory fraction of the flow rate. The most effective mass-transfer enhancement is registered when the net flow falls on just before the transitional flow regime for steady flow. Furthermore, there is an optimum Strouhal number, corresponding to the maximum transport enhancement, that depends on the oscillatory fraction of the flow rate. The results of time variation for flow behavior show that stable and unstable flow states exist during one oscillation cycle. The duration of the unstable flow state, corresponding to the optimum Strouhal number, is found to be the longest, and it leads to a remarkable fluid exchange between the mainstream and the recirculation zone, thus contributing to the mass transfer enhancement. These results indicate that the transport enhancement mechanism for the wavy-walled tube is quite different from the resonant transport enhancement observed in the two-dimensional (2-D) wavy-walled channel. © 2004 American Institute of Chemical Engineers AIChE J, 50: 762-770, 2004