Modeling some properties of almond kernels in a semi industrial continuous dryer

In this study, the drying properties of Azar variety of almond kernels in a semi industrial continuous dryer with microwave pretreatment were investigated. The aim of this research work was study the effects of air temperature, microwave power and belt linear speed on drying process of almond kernel. Three drying air temperatures (45, 60, 75 °C), three microwave powers (270, 450 and 630 W) and three belt speeds (2.5, 6.5 and 10.5 mm/s) were applies under constant air velocity of 1.5 m/s. Seven mathematical models were fitted to the experimental data of almond kernels drying. The results indicated that the Midilli et al. model had the best performance. The highest values of effective moisture diffusivity (4.73×10-9 m2/s) achieved at air temperature of 75°C, microwave power of 630 W and belt speed of 10.5 mm/s and the lowest value (4.96×10-10 m2/s) at air temperature of 45°C, microwave power of 270 W and belt speed of 2.5 mm/s. The activation energy for almond kernels was between 10.29 and 28.15 kJ/mol. The highest and lowest values of specific energy consumption were 83.17 and 8.17 GJ/kg, respectively. Maximum and minimum values of shrinkage were 10.86% and 6.12%, respectively, computed. The highest and lowest values of total color change were 9.46 and 4.76, respectively. Based on the quality indices, it is recommended to achieve the least values of shrinkage and color changes, the almond kernels will be dry in air temperature of 45 °C, microwave power of 270 W and belt speed of 6.5 mm/s.