Jiang, Shuxian; (2025) Hydrodynamics and Heat Transfer in Dynamically Structured Fluidised Beds. Doctoral thesis (Ph.D), UCL (University College London).

Text Thesis_ShuxianJiang_edited_version.pdf - Published Version Access restricted to UCL open access staff until 1 February 2026. Download (7MB)

Abstract

Gas-solid fluidised beds are widely employed in the chemical and process industries due to their high mass and heat transfer rates and effective solids mixing. They are used in both non-reactive processes (e.g. drying, coating) and reactive processes (e.g. fluid catalytic cracking, gasification). Substantial research has been conducted on heat and mass transfer in fluidised beds. However, their nonlinear, chaotic hydrodynamic behaviours make operation and scale-up challenging. Inspired by naturally occurring ordered structures from periodic oscillating gas flows, such as sandy ripples on beaches, this research explores creating a "dynamically structured fluidised bed" by applying an oscillating gas flow near the minimum fluidisation state. The pulsed flow introduces order into the system, resulting in a state between fixed and fluidised beds where bubbles form a hexagonal array. This unique condition offers opportunities for process intensification through improved gas-solid contact efficiency and enhanced micro-mixing, despite reduced macroscopic solids mixing. While previous studies have investigated the hydrodynamics of dynamically structured fluidised beds, the effects on heat transfer coefficients remain poorly understood. This research advances understanding of hydrodynamics and thermal dynamics in structured bubbling fluidised beds, revealing the relationship between structured patterns and system performance. A machine learning-assisted image segmentation method was developed to enhance bubble identification in gas-solid quasi-2D fluidised beds, providing a robust foundation for analysing spatiotemporally structured flows. By comparing flow properties between quasi-2D rectangular and annular configurations, the influence of curvature and lateral walls on flow behaviours was quantified. This finding indicates the adaptability of these flow patterns across different configurations, which is valuable for particle processing and process intensification. Heat transfer characteristics were investigated using CFD-DEM simulations and infrared thermography. A CFD-DEM-based model, coupled with a modified heat transfer model, was employed and validated against experimental data. Results demonstrated that oscillatory gas flows can achieve similar overall heat transfer coefficients compared to constant gas flows, but with the added benefits of more intensive solid mixing and controlled local heat transfer. Analysis of the local temperature fields uncovered the formation of cellular thermal patterns, reminiscent of Rayleigh-Bénard convection cells, but induced by the oscillatory gas flow. This structured thermal behaviour indicates that oscillatory flows regulate spatial and temporal temperature distributions in the solid phase, enhancing powder mixing and increasing particle-level conductive heat transfer by 64%, without the need to increase the gas flow rate.

Downloads since deposit

Loading...

4Downloads

Download activity - last month

Export as CSVJSONXML

Loading...

Download activity - last 12 months

Export as XMLJSONCSV

Loading...

Downloads by country - last 12 months

Export as CSVJSONXML

1.

United Kingdom

4

102550all

Archive Staff Only

View Item