|
Abstract
|
This work aimed in modeling some physical and thermal properties of walnut kernel undergoing various drying techniques include microwave semi-industrial continuous drying (M-CD), microwave infrared-vacuum drying (M-IVD), and microwave infrared-fluidized bed drying (M-IFD) methods. By using the verifications of experimental parameters, ten drying models for describing combined effects of independent variables were derived and the parameters of these models were determined by multiple regression analysis. In the case of the model, comprised of collective effects of drying independents, the Midilli model gave the best result in describing drying behavior of walnut kernel in all experimental domains. Minimum values of shrinkage (6.53%) and color change (5.54%) were obtained in the M-CD with the microwave power of 270 W, air temperature of 45°C, and belt linear speed of 10.5 mm/s, however maximum shrinkage (14.65%) and color change (18.28%) were related to the M-IVD with microwave power of 630 W, drying temperature of 75°C, and absolute pressure of 60 kPa. The lowest and highest values of effective moisture diffusivity (1.04×10-8 and 9.74×10-8 m2/s, respectively) belonged to the M-CD. Based on the quality indices including shrinkage and total color difference M-CD was found an adequate arrangement among applied techniques in walnut kernel drying, hence it produced the most similar dried samples to fresh ones.
|