Abstract
Particle adhesion is of great importance to coating processes due to its effect on fluidization. Currently, Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) has become a powerful tool for the study of multiphase flows. Various contact force models have also been proposed. However, particle dynamics in high temperature will be changed with particle surface properties changing. In view of this, an adhesion model is developed based on approaching-loading-unloading-detaching idea and particle surface change under high temperature in this paper. Analyses of the adhesion model are given through two particle collision process and validated by experiment. Effects of inlet gas velocity and adhesion intensity on spouted bed dynamics are investigated. It is concluded that fluidization cycle will be accelerated by adhesion, and intensity of fluidization will be marginally enhanced by slight adhesion. Within a certain range, increasing inlet gas velocity will lead to strong intensity of particle motion. A parameter sensitivity comparison of linear spring-damping model and Hertz-Mindlin Model is given, which shows in case of small overlaps, forces calculated by both models have little distinction, diametrically opposed to that of large overlaps.
Highlights
Spouted beds (SBs) have drawn much attention in recent years for a broad range of applications, such as coating [1], drying [2], biomass [3] or waste pyrolysis [4,5] and gasification [6]. These processes are conducted at high temperatures and particle adhesion can give way to severe operational problems, even causing bed de-fluidization [7]
Due to the high fluid-solid contact efficiency, especially for coarse particles in drying and coating processes [8,9,10], the spouted bed has unique characteristics as a prototype reactor for research. In addition to their ability to handle coarse particles, spouted beds possess certain structural and flow characteristics that are very desirable in some chemical reaction systems because of their perfect particle periodic dynamics
Based on comparison results, an adhesion particle contact force model which is suitable for describing particle surface changed is developed, combining the linear hysteresis model, JKR model and heat conduction derivation under high temperature as a typical case
Summary
Spouted beds (SBs) have drawn much attention in recent years for a broad range of applications, such as coating [1], drying [2], biomass [3] or waste pyrolysis [4,5] and gasification [6]. Due to the high fluid-solid contact efficiency, especially for coarse particles in drying and coating processes [8,9,10], the spouted bed has unique characteristics as a prototype reactor for research. Based on comparison results, an adhesion particle contact force model which is suitable for describing particle surface changed is developed, combining the linear hysteresis model, JKR model and heat conduction derivation under high temperature as a typical case. The drag scaling factor is applied considering the nonuniformity effect of fluid drag on the particles inside and outside an agglomerate [30] This particle contact force shown as Eequation (11) can be calculated by linear spring model and Hertz-Mindlin model.
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