A state of the art review of gas solid t

Turbulent fluidization has only been widely recognized as a distinct flow regime for the past two decades, even though it is commonly utilized in industrial fluidized-bed reactors due to vigorous gas-solids contacting, favourable bed-to-surface heat transfer, high solids hold-ups (typically 25–35% by volume), and limited axial mixing of gas. Despite its practical importance, turbulent fluidization has received much less attention than the adjacent flow regimes of bubbling, slugging, and fast fluidization, due to the challenges of experimental and theoretical work related to this flow regime. However, recent years have seen an upsurge in interest in turbulent fluidization. Various methods—pressure fluctuations, visual observations, capacitance signals, optical fiber probes, and bed expansion—have been used to determine the transition velocity, usually denoted as /p65, at which turbulent fluidization begins. Different methods tend to give different results. There appear to be as many as three different types of turbulent fluidization, depending on factors such as mean particle size, particle size distribution, column diameter, and internal baffles, if any. When turbulent fluidization is preceded by bubbling, /p65 denotes a change from closed laminar bubble wakes to open turbulent wakes. The upper boundary of turbulent fluidization occurs when a distinct upper bed surface disappears due to substantial entrainment.