Abstract

The spray drying process is used in many industrial applications to produce powders with different characteristics. Drying models based on the reaction engineering approach (REA) have been found promising due to its simplicity and high accuracy at different drying conditions. In this work single droplets of silica-water nanofluids were dried in an acoustic levitator under different experimental conditions of initial solid mass fraction (0.02 < Y_S < 0.20), pH value (2 < pH < 10), salt concentration (0 M < [NaCl] < 0.05 M), air temperature (80ºC < T < 120ºC), and initial droplet volume (0.3 μl < V₀ < 0.8 μl). The drying curves (X=f(t)) were experimentally obtained for each test conducted and the REA model was used to model the experimental data. The grains were collected and observed by SEM in order to measure the thickness of the shell formed. Finally, the packing of particles inside the droplet was checked to be constant and equal to the random close packing. This packing can be obtained from the modelling of the viscosity data to the Quemada equation. The final diameter and the packing fraction were used to calculate the shell thickness. Experimental results from the SEM micrographs and theoretical results show a good agreement.