Parameters affecting the localized fluidization in a particle medium

Abstract

The current study presents experiments for the initial stages of fluidization induced by a localized fluid injection. The process was studied by recording high-speed videos in a 2-D-region far from the boundaries using Planar Laser Induced Fluorescence and Refractive Index Matching. The experimental setup allowed for several parameters to be systematically studied including particle sizes, initial bed heights, and injection port diameters. The results show that the critical flow rate required for fluidization is primarily dependent on the initial height of the granular bed. However, this dependence is not a linear relation but progressively plateaus for larger heights. Conversely, the diameter of the chimney relates only slightly to the injection port diameter and significantly more to the diameter of the particles. (c) are average of the video sequence; (d), (e), and (f) are standard deviations of the video sequence. (a) and (d) are of a static bed, (b) and (e) show a bed with a fluidized cavity and pictures (c) and (f) show a chimney. Figure (d) is solid black indicating no movement and resulting zero standard deviation. Image processing done by ImageJ. 37 Solid symbols are for the injection port of D 5 10 mm and open symbols are for D 5 40 mm. Symbols are as follow: Circles, 3 mm particles; squares, 5 mm; triangles, 7 mm; hexagon, 10 mm. [Color figure can be viewed at wileyonlinelibrary.com]

Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods

“…V C. It should also be noted that the range of injection velocity where the fluidized cavity regime is observed tends to extend slightly with an increase in the bed height as shown in Fig. 10(a) and is consistent with previous experimental evidences [23,37,38].…”

“…V B, the reason for this discrepancy between experimental and numerical results could be related to the difference in terms of space dimensionality since the experiments are intrinsically 3D whereas our simulations are solely two dimensional. However, similarly to previous experimental results [37,38], a fourth stationary regime, called potential fluidized cavity, can be observed in the velocity domain where the sample remained static during the increasing phase but was still locally fluidized during the decreasing phase, even if, as already mentioned, this domain is quite limited compared to experimental findings. It is to be noted also that this new regime exists even when the fluidized cavity regime has not, or evanescently, been observed during the prior increasing velocity phase, as is the case for parameter set A in Fig.…”

“…Of great interest is then the behavior of the system when the injection velocity is decreased back by a reverse sequence. Indeed, previous experiments [37,38] have reported that the fluidized cavity regime is then sustained until values of U are drastically smaller than U cav . This tremendous hysteresis effect was interpreted in terms of the creation of arches within the newly formed upper grain layer of the sample when the fluidized chimney closes back and then as the fluidized cavity progressively diminishes [38].…”

“…More recently, some noninvasive volume probing techniques have been implemented, such as positron emission particle tracking and electrical capacitance tomography in a study focusing on bed elevation in steady spout-fluidized beds [30] and magnetic resonance imaging for the identification of a fluidized chimney during its formation [35,36]. A direct observation of localized fluidization through an artificial granular medium has also been obtained [37,38], combining two optical techniques, refractive index matching and planar laser induced fluorescence [38][39][40]. The available experimental data and phenomenological observations given in Ref.…”

“…Building on some previous works of DEM-LBM modeling [54,58], the present study proposed a 2D modeling of partial fluidization inside a cohesionless granular sample by an upward fluid flow injected at the bottom of the grain layer with a variable width. Part of the numerical results were directly compared to previous experiments carried out in similar configurations [22][23][24]34,37,38].…”