Particle Scale Modelling of Bubble Dynamics in a Single Jet Fluidized Beds
Fluidized beds are widely applied in many industrial processes, and have many inherent features such as good mixing and excellent heat and mass transfer which are directly related to the presence of bubbles. The objective of the present work is to study the bubble properties mainly bubble size, bubble size distribution and bubble shape (aspect ratio and shape factor) in a bubbling gas solid fluidized bed operated with a continuous central jet. The results show that generally, the continuous injection of a central air jet to the bed leads to the formation of series of bubbles which rises through the bed and then finally bursts at the top of the bed. Initially, after the introduction of a central air jet to the bed, the first bubble is formed at a certain height above the distributor. Then there are several successive bubbles formed one after another. The average bubble diameters increase with the increase of jet velocity. The bubble size distribution in the overall bed follow gamma distribution function. A mono-peak positively skewed distribution is found for all the jet velocities. As the jet velocity increases, the long tail end pointing towards the right expands. At the upper part of the bed, the distribution is more scattered signifying the presence of small and large bubbles. The distributions of bubble shape in terms of aspect ratio are also examined, showing a normal distribution. The bubble aspect ratio has a very high scattered distribution at lower part of the bed compared to that at the upper part. The distribution of bubble aspect ratio shifts towards the left and the mode increases as the height of the bed increases. The analysis of the bubble size and bubble shape provides useful information for understanding the gas-solid contact and mixing in gas fluidisation.