Analysis of particle dispersion coefficient in solid-liquid fluidised beds

Solid liquid fluidised beds (SLFB) are frequently encountered in the mineral processing applications including ore leaching/washing and particle size classification based on difference in settling velocity. Due to complex phase interactions, SLFB shows interesting characteristics such as phase segregation and mixing depending on variation in particle diameter, density difference and slip velocity. To characterise the multifaceted hydrodynamics of SLFB, often a diffusion-like parameter called dispersion coefficient is utilised. In literature, various empirical correlations of this parameter have been proposed however they are mostly system specific and lack a theoretical foundation. In this work, we report a model for dispersion coefficient along the line of definition for diffusion coefficient incorporating the mean free path of collision and interstitial fluid velocity as the characteristic velocity of collision. The model is tuned based on the available experimental data for mono as well as multi-particle system covering wide range of particle diameter (0.39 to 23 mm), liquid superficial velocity (0.0009 to 0.6 m s-1) and Reynolds number (4 to 2820). To evaluate the capability of the proposed dispersion coefficient, mixing and segregation behaviour in binary SLFB system is simulated using a one dimensional convective-diffusive numerical model to predict the volume fraction distribution of each solid phase. Validation of the numerical model against available experimental data shows reasonably good agreement.