The hydrodynamics of pseudo-2D and 3D bubbling fluidized beds: A magnetic resonance imaging study

• Magnetic resonance imaging is used to study pseudo-two-dimensional and three-dimensional fluidized beds • Particle distribution and velocity are measured to investigate fluidized beds with varying thicknesses • Pseudo-2D fluidized beds show enhanced radial bubble distribution and reduced equivalent bubble diameter compared to a 3D bed • Reduced bubble rise velocity in thinner beds leads to slower average particle velocity • Bubble shape remains largely unaffected by variations in bed thickness Real-time magnetic resonance imaging (MRI) was used to compare the hydrodynamics of three-dimensional (3D) and pseudo-two-dimensional (2D) gas-solid fluidized beds of various wall separation distances by measuring the particle distribution and velocity. Five different superficial gas velocities from one to two times the minimum fluidization velocity and four pseudo-2D bed thicknesses between 15 and 50 mm were investigated. A neural network model was used to segment gas bubbles, revealing that thinner beds homogenize the radial bubble distribution and reduce the average equivalent bubble diameter compared to 3D beds. Furthermore, pseudo-2D beds showed lower bubble rise and average particle velocities. Based on the findings, an existing correlation for predicting bubble rise velocity is extended by incorporating an additional term that accounts for the influence of bed thickness. The minimum fluidization velocity and the expansion ratio increases as the bed thickness decreases. Yet, the shape of the bubbles in pseudo-2D fluidized bed remains unaffected when compared to 3D fluidized beds. Pseudo-2D fluidized beds with a smaller thickness, typically employed in optical experiments, exhibited the greatest deviation in hydrodynamics compared to 3D fluidized beds.