On the Dynamics of Bubbles Passing Through a Sand Bed Layer

The present research paper reports the outcomes of an extensive laboratory investigation examining the effects of grain size and air discharge on bubble dynamics of bubble plumes passing through a sand bed layer. The effects of sand layer thickness and grain size on bubble characteristics such as bubble size, bubble concentration and velocity, and interfacial area within bubble plumes are studied for a wide range of air discharges. The experiments revealed 58% reduction on the mode bubble size when the sand bed thickness increased from 33 to 66 times of the nozzle diameter. The distribution of bubble size along the main axis of the plume indicated a linear correlation, while bubble size distribution became more uniform with relatively smaller bubbles when air passes through a sand bed layer. A sand bed layer significantly improved the formation of uniform bubbly flow with relatively smaller bubbles sizes. Moreover, an increase in the thickness of sand bed layer reduced the mean bubble velocity and consequently extended the residence time of bubbles. Nonlinear correlations were observed between particle size and bubble velocity, and empirical correlations were formulated to estimate mean bubble diameter and bubble velocity for different bed particle sizes and initial air discharges. The frequency of bubbles increased with increasing air discharge, and the sand bed layer almost doubled the frequency of bubbles. The interfacial area of bubbles, which is an indicator of the contact surface between air and water, increased by approximately 32% when the initial Reynolds number doubled.