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Drying Dynamics of Particulate Solids in Spouted Beds With/Without Draft Plates: Numerical and Experimental Investigation

Zarghamzadeh, Mohammad Reza | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58748 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Molaei Dehkordi, Asghar
  7. Abstract:
  8. Owing to their circulating flow, spouted beds are widely used for convective drying, and the use of draft plates to stabilize the spout and optimize gas-solid contact is increasingly common. This study examines the drying behavior of wet particles in three configurations, a conventional spouted bed, a bed equipped with non-Perforated draft plates, and a bed equipped with open-sided draft plates, via a combined experimental and Eulerian-Eulerian CFD program. All three systems were built at laboratory scale with their real geometries; “drying time of solid particles” was defined as the time for particle moisture content to fall below 1%. The numerical model employed geometry conforming meshing, Grid Convergence Index (GCI) control, and post-processing that reconstructs the moisture history by integrating the outlet mass flux of water vapor at fixed time steps. Validation against experiments for the three laboratory controllable variables, initial particle moisture content, inlet gas velocity, and initial stagnant bed height, showed that the model reproduces trends, slopes, and the ranking of configurations. The model systematically under-predicts drying time, primarily because of simplifying assumptions (dominance of surface moisture with intraparticle diffusion and internal resistance neglected), understated boundary-layer resistance and lateral heat losses, and homogenized temperature and concentration fields; nevertheless, these discrepancies remain within the experimental uncertainty, and for design purposes, faithful reproduction of trends and sensitivities is paramount. Using the validated model, parametric analysis indicated that increasing the gas velocity from 12 to 16 m.s⁻¹ reduces drying time by roughly 24%, 45%, and 58% in the conventional, open-sided, and non-Perforated configurations, respectively; increasing the stagnant bed height from 10.5 to 12.5 cm increases it by about 85%, 86%, and 170%; enlarging the plate spacing from 8 to 12 mm cuts the time by ~34-37% in the two plate equipped beds; increasing the open-sided fraction yields an additional ~20% reduction; and a larger conical bed angle exerts a mild, monotonic increase. Among the configurations, the conventional spouted bed yields the shortest drying time, the bed equipped with non-Perforated draft plates the longest, and the bed equipped with open-sided draft plates performs intermediate. The validated framework and the resulting design maps provide a reliable basis for selecting configurations and operating and geometry settings in spouted bed dryers and for reducing energy costs
  9. Keywords:
  10. Drying ; Spouted Bed ; Eulerian-Eulerian Computational Fluid Dynamics (CFD) ; Model Validation ; Design Optimization ; Open-Sided Draft Plates ; Moisture Content

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