Particle dispersion and fluctuations in viscous liquid–solid fluidised Beds

Abstract

Particle dispersion and fluctuations were investigated in a liquid–solid fluidised bed with viscous liquid media by employing the relaxation method based on the stochastic model. The bed expansion or contraction during the transient state was analysed by means of the histogram of pressure drop variation with elapsed time. The relaxation behaviour of the liquid–solid fluidised bed appeared to be heterogeneous followed by homogeneous expansion or contraction. Effects of liquid velocity (UL), particle size (dP), liquid viscosity (µL) and liquid holdup or bed porosity (εL) on the fluctuating frequency (F) and dispersion coefficient (DP) of fluidised solid particles were examined. The values of F and DP increased with an increase in dP but decreased with µL and exhibited local maxima with variations of UL and εL. The flow pattern of solid particles could be changed from uniform or pseudo‐homogeneous to turbulent random behaviour with an increase in the liquid velocity and liquid holdup or bed porosity. © 2012 Canadian Society for Chemical Engineering

A simple model for predicting solid concentration distribution in binary‐solid liquid fluidized beds

“…Another type of approach to describe the solid concentration distribution in liquid fluidized beds originates from the stochastic model proposed by Yutani et al The particle dispersion was calculated by the temporal variance of particle parameters, e.g., velocity and number, during the relaxation of bed expansion or contraction, which was manipulated by step‐wisely changing the superficial liquid velocity. The concept of the model has also been adopted by other researchers for predicting the solid concentration distribution in liquid fluidized beds that operate under unsteady or steady state conditions with flow patterns ranging from uniform or pseudo‐homogeneous to turbulent random regimes . However, the application of this category of models is not straightforward, requiring experimental inputs of microscopic information on the particle motion, which are extremely difficult (if not impossible) to attain due to limitations of experimental instrumentation and measuring methodologies.…”

“…A transition zone that contains both particle species 1 and 2 is formed between the two mono‐component zones. Figure depicts the schematic of the binary‐solid liquid system at the equilibrium state, which can be simply characterized by the length ( h ) of each zone and the axial distribution of solid concentration of each particle species ( ϕ ) …”

Model for Predicting Solids Velocity Fluctuations in Sedimenting Suspensions

“…Fluidized beds have found widespread use in the process industry, e.g., in the chemical, biochemical, energy, environmental, and food sectors . In a typical fluidized bed, sufficient fluid is allowed to flow upwards through the bed of particles to create enough drag force to balance the weight force of the particulate solids present.…”