Experimental study on the motion of isolated bubbles in a vertically vibrated fluidized bed

In this work the motion of isolated bubbles in a pseudo-2D fluidized bed subjected to vertical sinusoidal vibration is experimentally studied by means of Digital Image Analysis (DIA). The oscillatory behavior of the bed bulk as well as the bubble position, equivalent diameter and velocity, is studied using an averaging of cycles method that takes into account the intrinsic unsteadiness produced by the bed vibration. The results indicate that the bed is compressed and expanded by the system vibration, the movement of the bed surface being opposed to that of the bed vessel. Besides, the bubble diameter, centroid position and velocity oscillate with similar frequency as the bed vessel vibration. A phase delay was found between these bubble characteristics and the bed vessel displacement. This delay grows with the distance between the bubble centroid and the bed bottom, which suggests that the oscillation of the bubble characteristics is caused by compression-expansion waves traveling upwards through the bed. Both the phase delay and the amplitude of the oscillation of the bubble characteristics are affected differently by the frequency and the amplitude of vibration. The experimental results show that the amplitude of the vibration has an important role on the link between the average bubble diameter and velocity. In particular, increasing the amplitude of vibration produces a decrease of the average rising velocity of a bubble for a given bubble diameter. (C) 2014 Elsevier B.V. All rights reserved.