Model development and validation of structural two-fluid model for heat transfer in a gas-solid bubbling fluidized bed

The mesoscale structures such as clusters and bubbles have a significant impact on the flow, transfer, and reaction process of heterogeneous gas-solid systems. This article proposes a structural two-fluid model for simulating the hydrodynamics and heat transfer in a complex gas-solid system. Based on the different flow control mechanisms, the bubbling fluidized bed system is treated as two interpenetrating fluids that are the fluids of gas-dominated bubble phase and the particle-dominated emulsion phase. With this fundamental idea, we establish the governing equations and constitutive relationships considering the influence of mesoscale structure. Reasonable empirical correlations are utilized to close the interphase drag force, the emulsion phase viscosity, the interphase heat transfer coefficient, and the thermal conductivity of each fluid. Present structural two-fluid model in conjunction with an explicit resolution of hydrodynamic and thermal boundary layer is employed to simulate a bubbling fluidized bed system with a vertical heating tube. The simulation results demonstrate that the structural two-fluid model accurately predicts the axial distribution of solid holdup as well as the bed-to-wall heat transfer coefficient, specifically, the relative error between the simulated and experimental values of the wall heat transfer coefficient in the dense phase regime is less than 10%, and the simulated wall heat transfer coefficient in the dilute phase regime is in the same order of magnitude as the experimental value. It shows that the structural two-fluid heat transfer model can accurately describe the flow heat transfer characteristics of the gas-solid two-phase in the bubbling bed system. © 2024 Materials China. All rights reserved.