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Due to the presence of liquid bridge forces, wet particles reveal totally different fluidization behaviours than dry fluidized beds. This paper studies the bubble dynamics of wet Geldart‐D particles in a wet 2D fluidized bed. A digital image analysis method is adopted to identify bubbles and extract bubble properties based on MATLAB software. During fluidization, the bubble feature analysis of optimized binary images captures the bubble size variation, bubble fraction, and bubble shape. The results show that the increasing liquid saturation promotes the gas holding capacity of the emulsion phase, leading to the decreasing bubble fraction. When the particle size grows, the stability of the emulsion phase is promoted and hence the average bubble diameter increases. As the liquid saturation increases, the enhancing liquid bridge forces limit the bubble growth and promote the bubble breakage, which contributes to the small bubbles. With respect to the wet particles, of which the diameter is 1 mm and the liquid saturation is over 15%, slugging is likely to be observed, resulting in the increasing equivalent bubble diameter. The growing liquid saturation increases the wide aspect ratio, decreases the shape factor, and disperses the dependence between the two parameters. This indicates that small and irregular bubbles are likely to be seen in wet fluidized beds. [ABSTRACT FROM AUTHOR]

In order to improve the mass transfer efficiency of the high‐temperature molten pool area in the oxygen coal combustion melting and separating furnace, water model experiment and VOF model were used to study the mechanism of bubble formation in the area, investigate the changing rules of oxygen lance parameters on the shape and frequency of bubbles. The results show that the basic law of bubble generation is the transition from lateral injection to longitudinal growth, and the bubble generation frequency is 7.5 Hz under standard conditions. Increasing the oxygen lance mass flow will reduce the generation frequency, but the local bubble distribution is more compact. Increasing the oxygen lance inclination angle increase the generation frequency, but it will cause local gas phase accumulation, if too close to the bottom of the furnace. Small oxygen lances diameter is beneficial to increase the generation frequency and enhance mass transfer efficiency. Increasing the oxygen lance immersion depth is conducive to increasing the generation frequency, the gas‐liquid interface and improving molten and separation efficiency. On the other hand, it will weaken the effect of "adherence to the wall" and reduce the erosion of furnace lining by inhibiting the flow of bubbles and slag. [ABSTRACT FROM AUTHOR]

The orifice size has a significant influence on hydrodynamic characteristics and bubble size distribution (BSD) in gas‐liquid flow. However, the mechanism of the influence of orifice size on BSD and hydrodynamic characteristics in an external loop airlift reactor (EL‐ALR) has not been fully revealed. In this work, the effects of the orifice size on hydrodynamic characteristics and BSD in a laboratory scale EL‐ALR were investigated using the particle image velocimetry (PIV) technique and digital image analysis (DIA). The results show that the transition superficial gas velocity becomes greater when the orifice size is reduced. The time‐averaged bubble velocity profiles along the riser radius are parabolic, and the shape of the time‐averaged bubble velocity curve is strongly dependent on the orifice diameter. The larger the orifice diameter, the steeper the parabolas. For sparger with lager orifice diameters, the BSD curve is bimodal even at low superficial gas velocity, and its peaks shift to a larger equivalent bubble diameter. The bubble aspect ratio appears to be related only to the equivalent diameter of the bubbles, regardless of the diameter of the orifice. It has a defined relationship between the bubble aspect ratio and the bubble equivalent diameter, and a new correlation is obtained based on the experimental data. This study will help to gain an understanding of the influence of sparger orifice size on the hydrodynamic characteristics and BSD and provide a basis for numerical simulation. [ABSTRACT FROM AUTHOR]

Based on experiments with single air bubbles rising in stagnant non‐Newtonian fluids, an innovative model containing the aspect ratio (E) and two parameters (α, β) was proposed and proved to be capable of characterizing the bubble shape from spherical/ellipsoidal to prolate/oblate‐tear with good accuracy. Several impacts on bubble deformation were investigated, involving the rheological properties of the fluids and different forces exerted on the bubble, which were quantified by multiple dimensionless numbers (e.g., Reynolds, Eötvös, and Deborah number). Within a wide range, the empirical correlations were obtained for parameter β, and between α and β. Together with the shape model, a complete system was set up for bubble shape characterization and prediction that will provide new ideas for future studies on bubble hydrodynamics. [ABSTRACT FROM AUTHOR]

The volume of fluid with the continuum surface force (VOF-CSF) model has been used in the present numerical study to investigate bubble formation and shapes in a bubble column. The effects of orifice sizes ranging from 0.5-1.5 mm on the bubble formation stages (i.e., expansion, elongation, and pinch-off), bubble contact angle, departure diameter, time, and shape of bubble are investigated under a constant inlet velocity (0.2 m/s) boundary condition (BC). It is found that the initial formation of a bubble is dependent on the orifice diameter. Consequently, the formation of the bubble's hemispherical shape at the orifice is faster for a smaller orifice diameter than for a larger orifice diameter which forms a bigger bubble. A leading bubble requires a longer time to detach itself from an orifice in comparison to the next bubble (the second bubble), but interestingly the third bubble detaches much faster than the second. This model was also used to investigate the effect of the Bond number (Bo σ). An increase of the Bond number (Bo σ) from 0.047 to 0.16 speeds up the bubble pinch-off, but a further increase in the Bo σ (e.g. 0.17-0.47) slows it down. Based on the simulated cases used in this study, the findings demonstrate the capacity and accuracy of the CFD method in predicting bubble formation characteristics. The findings may be useful in the design of spargers for bubble column reactors. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Chemical Engineering is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Chemical Engineering is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Chemical Engineering is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper a three-dimensional (3-D) front-tracking (FT) model is presented featuring a new method to evaluate the surface force model that circumvents the explicit computation of the interface curvature. This method is based on a direct calculation of the net tensile forces acting on a differential element of the interface. Our model can handle a large density and viscosity ratio and a large value of the surface tension coefficient characteristic for gas-liquid systems. First, the results of a number of test cases are presented to assess the correctness of the implementation of the interface advection and remeshing algorithms and the surface tension model. Subsequently, the computed terminal Reynolds numbers and shapes of isolated gas bubbles rising in quiescent liquids are compared with data taken from the bubble diagram of Grace. In addition drag coefficients for rising air bubbles in water were successfully computed, a system that has proven difficult to simulate by other methods, and showed good agreement with existing correlations. Finally, a number of sample calculations involving multiple bubbles are reported to demonstrate the capabilities of our three-dimensional FT model. [ABSTRACT FROM AUTHOR]