Mass transfer between fluid and immersed surfaces in liquid fluidized beds of coarse spherical inert particles

Abstract

Mass transfer coefficients between fluid and immersed surfaces in liquid fluidized beds of spherical inert particles have been studied experimentally using fluidization columns 40 mm and 70 mm in diameter. Mass transfer data were obtained in three experimental systems: i) transfer of methylene blue dye from very dilute aqueous methylene blue solution as the fluidizing fluid to plane solid surfaces using the adsorption method [Končar-Djurdjević, Nature, 172 (1953) 858]; ii) transfer of benzoic acid from a large spherical particle to flowing water using the dissolution method, and iii) transfer of benzoic acid from a plane solid surface to flowing water also using the dissolution method. In all runs mass transfer rates were determined in the presence of inert fluidized particles 1.20, 1.94 and 2.98 mm in diameter. Measurements covered a particle range having Reynolds number from 15 to 400, and two Schmidt numbers (20 °C), 1361 and 1932. Experimental data are correlated by the widely used formula j D =0.261 Ga 0.324Re p −0.97 ( j D = mass transfer number; Ga = Galileo number; Re p = Reynolds number). The data show that an analogy exists between the mass transfer factor and fluid–particle interphase drag coefficient, since both quantities vary with voidage in a similar way. The normalized mass transfer factor in liquid–phase fluidized beds of active or inert particles and the dimensionless drag coefficient are shown to be the same. Experimental data agree reasonably well with the proposed model.