Liquid-wall mass transfer in three phase fluidized beds with cross-flow of electrolyte

Abstract

Liquid-wall mass transfer coefficients were computed in a gas–liquid fluidized bed from the limiting current data obtained at the outer surface of different cross electrodes for both the cases of oxidation of ferrocyanide and reduction of ferricyanide ion. Particles of different sizes and densities were used as bed material and electrodes of five different diameters of length 44.5 mm were used. The fluid electrolyte velocities were varied from minimum fluidization velocities to well below the terminal velocities of the particles before the gas phase enters the test section. The liquid-wall mass transfer coefficient increased with increasing superficial gas velocity at a constant superficial liquid velocity upto a certain extent and reached a plateau. At constant superficial gas velocity, k L increased with increasing superficial liquid velocity. k L decreased with increase in electrode diameter. The effect of particle size on k L was found to segregate into two regions, one for d p > 4 mm and the other for d p < 4 mm. k L increased with increase in ɛ , reached a maximum and beyond an ɛ value of 0.85 showed a declining trend. The liquid-wall mass transfer coefficient data for both oxidation and reduction were correlated in terms of Coulburn factor j D , void fraction ɛ , Reynolds number based on electrode diameter Re , Froude number based on gas velocity Fr g and gas to liquid mass velocity ratio G mr .