Microwave vacuum drying of porous media: Verification of a semi-empirical formulation of the total absorbed power

Vacuum drying,experiments were performed on a laboratory scale dryer with t wo porous materials: a packing of initially saturated glass beads and of un saturated pharmaceutical granules. Several incident powers and two vacuum p ressure levels were tested in order to demonstrate different drying mechani sms. The drying kinetics, temperature of the product and the absorbed power are presented and the coupling between the drying rate and the absorbed po wer is shown. A semi-empirical formulation of the total absorbed power is p roposed taking into account the water content, the temperature and the diel ectric properties of each phase. This formulation is based on a quasi-stati c assumption which allows the local electric field inside the material to b e expressed with an analytical equation.