Gas interchange between bubble and emulsion phases in a 2D fluidized bed as revealed by two-fluid model simulations

Abstract

Using two fluid model simulations, the present work aims at characterizing the interchange due to gas advection between the emulsion phase and bubbles in fully bubbling beds of Geldart group B particles that are fluidized with air. In the studied beds the bubbles are slow, which means that the advection transport of gas through the bubble boundary is the main mechanism of gas interchange. In an initial ver ification step, the pressure distribution and the gas interchange coefficient for isolated bubbles obtained in the two fluid simulation are compared with the classical potential flow theory of fluidized beds, pro viding concordant results. In a second step, the work analyzes the gas interchange in fully bubbling beds and the effects of the superficial velocity, bed height, and particle diameter on the interchange coefficient and the crossflow ratio. The results indicate that both the interchange coefficient and the crossflow ratio in bubbling beds are about two times those predicted by the potential theory of isolated bubbles. A cor rected model for the gas interchange is proposed based on the introduction of the gas throughflow into the classical potential flow theory. As a consequence, the gas interchange coefficient in the corrected model is a function of the superficial gas velocity instead of the minimum fluidization velocity.

Compressible-gas two-fluid modeling of isolated bubbles in a vertically vibrated fluidized bed and comparison with experiments

“…Thus, for each simulation frame of solid volume fraction, a point in the image was assigned a value of 0 if ε p < ε p,th or 1 if ε p > ε p,th , making the contour of the bubble easily identifiable. Following previous works [19,39,40], the bubble equivalent diameter was calculated as the diameter of a circle having the same area of the bubble.…”

Critical comparison of electrostatic effects on hydrodynamics and heat transfer in a bubbling fluidized bed with a central jet

“…However, there are strong interactions between the bubbles in the bubbling bed with central jet, and the factors such as particle vorticity and electrostatic effect will change the througflow coefficient, affecting the heat transfer within the fluidized bed. Hernández (Hernandez-Jimenez et al, 2013) calculated the gas exchange coefficient and the cross-flow ratio in the bubbling fluidized bed using the corrected velocity, where U / Umf had a maximum of 2.75, where Uth is the throughflow velocity:…”

Effect of scraper movement on the separation performance of air dense medium fluidized bed

“…Because of the viscosity of the quasi-liquid (fluidized bed), the moving medium in upper layer would drive the lower layer medium to move in the same directionat a lower speed. Due to the back-mixing of the dense medium powders in ADMFB (Luo et al, 1996;Luo et al, 2008), the merge and breakage of the bubbles are quite complicated in the practical experimental operation (Hernández-Jiménez et al, 2013;Sánchez-Delgado et al, 2011;Zou et al, 2011). As a result, the actual distribution of the bed velocity varies and becomes complicated.…”