Effect of temperature on gas-solid flow structure in bubbling fluidized beds

The gas–solid flow structure in dense fluidized beds has been understood to be a bubble-emulsion two-phase flow characteristically dominated by bubble dynamics. Recent studies have suggested that bed temperature significantly affects this flow, but a clear understanding remains elusive. To address the issue, we investigate the impact of temperature on the gas–solid flow structure in bubbling fluidized beds by analyzing pressure fluctuation signals at various axial positions from ambient to 1500 °C. The results reveal that depending on bed temperature, two distinct flow structures can be observed in fluidized beds: a bubble-dominated flow structure below approximately 1200 °C, characterized by noticeable axial variations in the standard deviation and dominant frequency of pressure fluctuations resulting from bubble formation, coalescence, growth, and breakup along the axial direction; a homogeneous and stable bed structure above 1200 °C, featured by axially constant standard deviation and dominant frequency attributed to uniformly distributed small bubbles within constantly agglomerating and dispersing particles.