Effect of Polarization on the Heat of Desorption of Water in Dielectrics

The heat of desorption characteristics of moisture in hygroscopic solid dielectrics during microwave drying was investigated. White bean seeds were used as the experimental material. A direct method for determining the heat of desorption of moisture was developed. Results indicate that the heat of desorption offree water during microwave heating is lower than that during conventional heating. However, the heat of desorption of bound water during microwave drying was above that for conventional drying. This indicates that polarization of solid dielectrics may induce additional binding forces for bound moisture thus increasing the heat of desorption. The implication of this is that microwave drying of solids that do not become polarized is likely to be more energy efficient than those that become polarized in the microwave field. The lower the level of polarization ofa solid, the greater the microwave drying efficiency and effectiveness.