Temperature control of the continuous peanut drying process using microwave technology

The relationship between dielectric properties of peanuts (Arachis hypogaea L.), thermal and moisture distribution during continuous microwave drying, and automated control of the drying process was investigated. Dielectric properties (ϵ′, ϵ ″) of peanut pods and kernels were determined for several densities, temperatures, and moisture contents. An equation that determines the dielectric properties of bulk peanut pods and kernels as a function of their temperature and moisture content was determined using multiple linear regression.; Peanut dielectric properties were used in transport phenomena equations developed for a continuous microwave drying applicator. The theoretical equations, together with experimental methods, were used to determine the effect of microwave power level, initial moisture content and dielectric properties on the temperature profiles and the reduction in moisture content of peanuts. Temperature profiles were determined to be dependent on both moisture content and microwave power level. Although the maximum temperature in the microwave applicator was a function of power level only, the rate at which that maximum was attained was a function of dielectric properties and moisture contents of the peanuts. The surface temperature of the peanut bed measured using infrared pyrometry was well correlated with internal temperature profiles. Thermal imaging demonstrated that the temperature of the peanut bed surface at the exit of the microwave dryer was uniformly distributed.; The surface temperature determined as a function of power level was used to create a feedback control loop of the continuous microwave drying process. Process parameters were determined using process reaction curves and a PI (proportional, integral) controller was implemented in the software routine that controlled the microwave generator power level.; This study quantifies the relationships between the various parameters that influence the continuous microwave drying process of peanuts. The results of this study may be used as a foundation for development of optimum process conditions in microwave drying of peanuts and other agricultural commodities, as well as for development of advanced process control methods in continuous microwave processing.