Combined Radiant and Conductive Vacuum Drying in a Vibrated Bed

Wet particles are often difficult to dry due to their stickiness and tendency to form lumps. Mechanical vibration can assist in separating such particles as well as in mixing beds of dissimilar particles if necessary. Delumping also exposes surfaces for evaporation. The objective of this experimental project is to design, build and test a laboratory size vibrated drum dryer under vacuum. The basic concept is to design a variable frequency, variable amplitude vibratory unit on which a horizontal drum is seated. An experimental approach was employed to permit simultaneous or individual mode of conduction and radiation heat input. Cube shaped potatoes and apples were used as model samples for experimental tests. Experiments were also performed using spherical shaped silica gel. Five different drying conditions were compared experimentally. These are: case-1, effect of vacuum; case-2, vacuum with vertical sinusoidal vibration (Amplitude: 0-5mm, frequency: 10-50 Hz); case-3, vacuum with vibration and conduction heat input (40C); case-4, vacuum with vibration and radiation heat input (1875 W/m2); case-5, vacuum using vibrating bed dryer with simultaneous conduction and radiation heat input. An energy savings strategy for drying is proposed based on the study. Results indicated that the proposed system is a variable option to reduce the process time under vacuum compared to other drying methods.