MICROWAVE VACUUM DRYING OF POROUS MEDIA: VERIFICATION OF A SEMI-EMPIRICAL FORMULATION OF THE TOTAL ABSORBED POWER

Abstract

Vacuum drying experiments were performed on a laboratory scale dryer with two porous materials: a packing of initially saturated glass beads and of unsaturated pharmaceutical granules. Several incident powers and two vacuum pressure levels were tested in order to demonstrate different drying mechanisms. The drying kinetics, temperature of the product and the absorbed power are presented and the coupling between the drying rate and the absorbed power is shown. A semi-empirical formulation of the total absorbed power is proposed taking into account the water content, the temperature and the dielectric properties of each phase. This formulation is based on a quasi-static assumption which allows the local electric field inside the material to be expressed with an analytical equation.

Keywords:

• Electrostatic assumption
• Evaporation
• Experiments
• Dielectric properties
• Glass beads
• Pharmaceutical granules
• Vaporization

ACKNOWLEDGMENTS

The authors wish to thank the research institute of pharmaceutical company Pierre Fabre for the financial support of this work, Institut de Recherche Pierre Fabre, Centre de Développement, Rue Jean Rostand, BP 687, 31319 Labège Innopole, France.