Experimental Analysis of Spraying and Drying Characteristics in Vacuum Spray Dryer

Abstract

Vacuum Spray Drying (VSD) produces powders at lower temperature (40-60℃) due to vacuuming of the drying chamber to low atmospheric pressures (10-20 kPa). In this study the spraying and drying characteristics in the vacuumed drying chamber was investigated experimentally to have fundamental data on the design and operation of VSD. Condensed milk and yogurt slurry as feeding materials were sprayed in the vacuumed or non-vacuumed drying chamber and the sprayed droplet diameters were determined. Analysis of the relationships between droplet diameter and volumetric flow rate of spray air or spray pressure revealed that the droplets sprayed into the vacuumed chamber became smaller and these fine droplets were produced even at lower flow rate of spray air. However the drying in VSD was insufficient when the spray was conducted at the lower flow rate of spray air. On the contrary higher flow rate resulted in the discharge of fine powders out of the drying chamber so that some methods to collect those fine powders easily should be devised to improve the drying performance of VSD.