Bubble Dynamics in Gas Fluidisation of Nonspherical Particles

Bubbling fluidized beds (BFB) have widespread applications in various industrial process because they have unique features such as high chemical conversion, heat and mass transfer and mixing. Bubbles generated are generally regarded as the driving force influencing the performance and efficiency of BFB. Several variables can affect the bubble dynamics such as fluidization gas velocity, particle shape, inter-particle force, etc. Understanding the effect of these variables is of paramount importance to the improvement of design, operation and control of BFB. In this presentation, the aim is to report how the particle shape affects bubble dynamics under via numerical simulation under different conditions. Ellipsoidal particles are used as they have the advantage in representing a large range of particle shapes varying from disc-like to rod-like. The results reveal that for the case of continuous single jet, particle shape can alter the mechanisms of bubble behavior such as splitting and coalescence. Ellipsoids have larger bubble equivalent diameters, more irregular bubble shape, and lower bubble frequency and bubble velocities. For the case of uniform BFB, the results show that bubble flow patterns for ellipsoids are asymmetric leading to different solid flow pattern, solid mass flux, and mixing characteristics in the whole bed. The ellipsoids have a smaller bubble size and lower bubble rising velocity than spheres. The combined effects of particle shape and van der Waals force on bubble dynamics are also examined. It is found that the bubble coalescence and splitting phenomena are suppressed with the increase of van der Waals force. The bubble diameter and velocity decrease with the increase in extent of van der Waals force for particle of different shapes. Moreover, the oblate/prolate spheroids transform to non-bubbling fluidization under the influence of high cohesive force while spheres form channels.