Heat transfer and wake characteristics in three-phase fluidized beds with floating bubble breakers

Abstract

The ratio of the total wake volume to the mean bubble volume, k̄, and the heat transfer coefficient h in three-phase fluidized beds with and without floating bubble breakers (ϱ f = 1500–2280 kg/m 3; V f = 2.0 × 10 −6−3.8 × 10 −6 m 3) have been determined. The effects of gas velocities (0.02–0.14 m/s) and liquid velocities (0.02–0.09 m/s), the ratio of the volume of the floating bubble breakers to the volume of the solid particles, V f/ V s, and the properties of the floating bubble breakers (density, contact angle, projected area) on k̄ and h have been determined. The total wake volume to mean bubble volume decreases with increasing gas velocity and increases with increasing liquid velocity in the beds with floating bubble breakers. The heat transfer coefficient increases with increasing gas velocity, and reaches its maximum values when the liquid velocity or bed porosity are varied. Also, k̄ decreases with an increase in V f/ V s up to around 0.15; thereafter, it decreases with increasing V f/ V s and h exhibits a reverse trend to that of k̄ with variation of V f/ V s. The total wake volume to mean bubble volume decreases and h increases with increasing density, projected area of the breakers, and contact angle between the breakers and the water. The heat transfer coefficient data in three-phase fluidized beds with floating bubble breakers have been correlated in terms of the energy dissipation rate based on the local isotropic turbulence theory.