A glass transition-based controller algorithm to manage rice intermittent drying

Abstract

Understanding the glass transition of different layers of a rice kernel makes it possible to control its drying and tempering operation. In our previous study, a validated numerical model was developed to simulate the intra-kernel behavior during intermittent drying and predict dependent values considering the glass transition concept. The kinetics of state change of different layers was determined using a quantitative function defined based on the glass transition line. This study is a lateral extension on the basis of our previous model to plan a controller algorithm aiming to dry rice in the rubbery zone preventing the expansion of moisture content gradients and accomplishing the process as quickly as possible. Through coupling the model with the controller algorithm the number of stages, drying duration, and tempering duration at any stage of the drying process were determined at various temperatures. The findings revealed that the number of drying stages decreased as the drying temperature increased. The third drying stage at 40 and 50 °C caused the surface and middle layers to migrate into the glassy region, increasing cracking possibilities. As temperatures increased to more than 60 °C, the rice kernel was dried completely in the rubbery region. The maximum (11.3%d.b.) and minimum (6.9%d.b.) created moisture content gradient were related to 70 °C and 40 °C, respectively. The rubbery area was 0%, 9.2%, 66.3%, and 85% of the total kernel's area at the end of the drying process, respectively at temperatures of 40, 50, 60, and 70 °C. Drying at 60 °C in a two-stage intermittent method led to the best performance in terms of state changes, maximum moisture content gradients, and total drying duration.