Experimental and simulation study on fluidization behavior of high⁃density particles in a shallow spouted bed
Journal Title: China Powder Science and Technology - Year 2025, Vol 31, Issue 2
Abstract
[Objective] Tristructural-isotropic （TRISO） nuclear fuel particles serve as the primary barrier to ensure the inherent safety of high-temperature gas-cooled reactors （HTGRs）. These particles are coated with four layers using the fluidized bed-chemical vapor deposition （FB-CVD） technique. The fluidizing medium contains high-density uranium dioxide particles， reaching up to 10.8 g/cm3， and the particle motion directly affects the coating quality. Therefore， it is necessary to measure the motion characteristics of high-density particles in a shallow spouted bed and analyze the mathematical relationship between fluidization states and operating parameters. [Methods] Initially， bed pressure drop curves and minimum spouting velocities were obtained for particle systems with different loadings， and the fluidization behavior of high-density particles was explored. Then， magnetic particle tracking （MPT） and computational fluid dynamics-discrete element method （CFD-DEM） were employed. The local residence time of particles in the annular region was measured experimentally under different particle loadings （N=500， 1 000， 2 000） and gas inlet velocities， and the results were compared with simulation results. Finally， fast Fourier transform （FFT） analysis was applied to the signal curves of magnetic field strength， enabling rapid determination of particle flow patterns under certain loadings and gas velocities. [Results and Discussion] The results showed that in high-density particle systems， the bed pressure drop increased continuously with increasing inlet gas velocity， and the flow pattern transitioned from a fixed state to a spouted bed state， without a distinct pressure drop or a plateau phase. The turning point on the fluidization curve， corresponding to the transition in flow pattern， determined the minimum spouting velocity and was influenced by particle density， loading， and gas inlet diameter. MPT measurements showed that the local residence time of individual particles in the three-dimensional space tracked by two detectors varied randomly. Increased loading stabilized fluidization and facilitated particle circulation in a "spouting-fountain-annular region" pattern. Simulation results showed that at a particle loadingof 2 000 （N=2 000）， as the inlet gas velocity increased from 45 m/s to 55 m/s， the local residence time （TL） fluctuated randomly within a certain value range， with the average time decreasing from 0.032 s to 0.028 s. The experimental results were highly consistent with the simulation results. FFT analysis of detector-1's signal curves showed a dominant frequency and regular spouting pattern at a moderate gas velocity （e.g. Ug=55.26 m/s）. [Conclusion] The distinctive fluidization characteristics for high-density particles， including bed pressure drop behavior and minimum spouting gas velocity， are revealed. A novel method for tracking the motion of individual particles in three-dimensional space is established. The MPT method can effectively measure the TL of high-density particles in a shallow spouted bed under different operating conditions and quickly identify flow patterns and fluidization states. The method can support the process optimization and scale-up design for coating applications.
Authors and Affiliations
Lin JIANG, Tongwang ZHANG, Rongzheng LIU, Youlin SHAO, Bing LIU, Malin LIU
Keywords
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- EP ID EP760570
- DOI 10.13732/j.issn.1008-5548.2025.02.001
- Views 38
- Downloads 0
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