Effect of Viscosity on Wall-to-Bed Mass Transfer Coefficient in a Three-Phase Fluidized Bed

Abstract

Investigations have been carried out experimentally to study the effect of viscosity on wall-to-bed mass transfer coefficient in a three-phase fluidized bed. The system chosen was an electrolyte as liquid phase, glass spheres of different diameters as solid phase and inert nitrogen as gaseous phase. The electrolyte was an equimolar solution of 0.01 N potassium ferricyanide and potassium ferrocyanide with 0.4 N NaHCO3/Na2CO3 as indifferent electrolyte. To vary the viscosity, Carboxy Methyl Cellulose (CMC) sodium salt in 0.1, 0.2 and 0.4 wt% was added to the electrolyte. The reaction considered was the reduction of ferricyanide ion. The experiment was conducted at a constant temperature of 25 oC at which the physical property values of the electrolyte were obtained from literature. The mass transfer coefficient was computed from the measured limiting current. It was found that the mass transfer coefficient was relatively independent of liquid velocity within the range covered in the present experiment. The kL increased with increasing gas velocity and approached a constant value. kL was also observed to increase with increasing particle size and decreased with increasing CMC concentration. The entire experimental data was correlated in terms of modified Coulburn j-factor and modified Reynolds number.

Keywords: Gas-liquid-solid fluidization, Three-phase fluidization, Wall-to-bed mass transfer, Ionic mass transfer, Viscosity