The hydrodynamics of liquid slugs in gas-liquid Taylor flow in straight and meandering microchannels have been studied using micro Particle Image Velocimetry. The results confirm a recirculation motion in the liquid slug, which is symmetrical about the center line of the channel for the straight geometry and more complex and three-dimensional in the meandering channel. An attempt has also been made to quantify and characterize this recirculation motion in these short liquid slugs (L s /wo 1.5) by evaluating the recirculation rate, velocity and time. The recirculation velocity was found to increase linearly with the two-phase superficial velocity U TP. The product of the liquid slug residence time and the recirculation rate is independent of U TP under the studied flow conditions. These results suggest that the amount of heat or mass transferred between a given liquid slug and its surroundings is independent of the total flow rate and determined principally by the characteristics of the liquid slug.
This paper presents the results of an experimental investigation of the hydrodynamics of a countercurrent packed-bed column exposed to a step change in the liquid flow rate. For the first time in the literature, this paper reports observations of the overshoots of the transient curves of pressure as well as liquid holdup when the change in the liquid rate brings the hydrodynamic regime of the bed close to the flooding line. The experimental technique indicated that column flooding did not appear to occur, even temporarily. The experimental transient curves for the pressure along the packed section, the total pressure drop across the column, and the liquid holdup are interpreted in terms of a simple three-parameter transfer function. Plots of the magnitude of the overshoot and the instant of its appearance as functions of the gas-to-liquid mass flow rate ratio are presented and analyzed. On the basis of these results, the existence of a pressure overshoot is attributed to the extra energy required for redistribution of the gas and liquid flow according to the new prevailing flow regime.
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