Abstract
Bubble dynamics significantly affect the hydrodynamics of gas-solid fluidized bed since they influence the gas-solid mixing. In this study, simulations using CFD-DEM were carried out to characterize the bubble size and shape for a bubble formed at a single orifice in gas-solid fluidized bed. Impact of parameters such as jet velocity, orifice size and particle shape on bubble equivalent diameter and bubble aspect ratio were analysed and discussed. Bubble equivalent diameter was found to increase with increasing jet velocity, decreasing bed width to orifice width ratio, and particle shape deviating from spherical. The bubble shape illustrated by aspect ratio, was found to elongate more as it rise through the bed and then commence to expand horizontally after it was detached from the orifice. Aspect ratio was found to be closer to a circle for the bubble at higher jet velocity, lower orifice width to bed ratio and for non-spherical particles.
Highlights
Fluidization technology has been widely used in many industrial applications such as food, pharmaceuticals, energy and environment since they are associated with good heat and mass transfer
In order to extract the bubble characteristics, bubble boundary has to be defined which was evaluated from the simulated void fraction data
At 0.11s (Fig. 1 d, i and n), the bubble for U = 0.25 m/s is at the top of the bed while the bubble for U= 0.1 m/s is at the middle of the bed. This might be because the bubble rise velocity is greatly affected by the size of the bubble which is generally expressed as the bubble equivalent diameter
Summary
Fluidization technology has been widely used in many industrial applications such as food, pharmaceuticals, energy and environment since they are associated with good heat and mass transfer. A good understanding of bubble formation at an orifice and its dynamics is essential to aid in design and development of gas-solid fluidized beds. In recent years numerical techniques have been widely used to study gassolid fluidized beds and have become a significant approach to characterize bubble behaviour. Numerical techniques for gas-solid systems can be either continuumor discrete-based with respect to the solid phase The former is called two-fluid model (TFM), where both gas and solid phases are considered continuous and fully interpenetrating. Rong et al [11] studied the influence of particle properties (size and density), jet velocity and bed width on bubble characteristics. These parameters were found to affect the bubble dynamics. CFD-DEM is used to study the bubble formation at a single orifice and depict its size and shape with respect to jet velocity, orifice size and particle shape
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