Experimental investigations of occupied volume effect on the microwave heating and drying kinetics of cement powder in a mono-mode cavity

This paper deals with the microwave heating and drying of cement powder in a mono-mode waveguide. The rapid volumetric heating and drying spare cement hardening and allow recuperation of the powder for reuse, as required from an industrial user. Based upon pilot scale extrapolation, the effect of occupied volume on microwave heating and drying kinetics constitutes the important aim of this experimental work. For different diameters, the parameters measured simultaneously in time are the temperature, the moisture and the mean absorbed power. The change in time of the dielectric properties according to the moisture is observed for different diameters of cylindrical glass support. The volumetric power density decreases while the diameter decreases resulting in rapidity of drying kinetics. This is in agreement with the heating rate before evaporation. The dielectric relaxation coefficient of the humidified powder presents a threshold value of the normalised moisture (45%), which corresponds to the decreasing of absorbed power. (C) 2001 Elsevier Science Ltd. All rights reserved.