Abstract

Spray drying is the process by which a fluid feed material is transformed into a dry powder by spraying the feed into a hot drying medium. The drying behavior of suspension droplets is important in many industrial applications (material processing, ceramic, chemical or food industry). The main aim of drying by this method is to obtain dry particles with desired properties. In this work, the drying behavior of acoustically levitated multiphase droplets has been experimentally investigated. The experiments have been performed using ceramic suspensions like those used in the manufacture of porcelain tiles. High load and temperature conditions close to those found in industrial applications have been used. The experiments have been carried out in an acoustic tube levitator modified in order to allow experiments at high temperature conditions. The flow rate, temperature and relative humidity of this air stream can be controlled by an air conditioning system. A CMOS camera and a back-light illumination system are used to measure the droplet cross-sectional area and vertical position of the droplet during the drying process. An experimental matrix based in a factorial design 2^k has been chosen to study the effect of the flocculation state (flocculated-deflocculated), solid mass load (0.65 < Y_S < 0.70), particle size distribution of the porcelain composition (1.95 < d_P50 < 3.25 μm), ambient air temperature (70ºC < T < 100ºC) and initial droplet volume (0.4 μl < V₀ < 0.7 μl) on the mean porosity of the grain and its mechanical strength.