Effect of Drying Temperature on the Drying Kinetics of Red Rice Paddy (Oryza sativa L.) in a Tray Dryer

Abstract

Understanding the temperature-dependent drying kinetics and convective transport mechanism is critical for the characterization of the drying process of red rice paddy under controlled conditions. This present study evaluates the drying behavior and heat and mass transfer characteristics of red rice paddy in a laboratory-scale tray dryer over a temperature range of 30 – 80 °C, with sun drying functioning as a reference. The drying kinetics were evaluated using several thin-layer models, while convective heat and mass transfer characteristics were estimated from dimensionless-number correlations. Increasing the drying temperature enhanced moisture removal, with the average drying rate increasing from 0.0012 kg moisture/(kg dry paddy·min) during sun drying to 0.0020 kg moisture/(kg dry paddy·min) at 80 °C tray drying. Among the evaluated models, the Page model demonstrated the optimal overall fit, with an average coefficient of determination of 0.9904 and a sum of squared errors of 0.0050. The estimated convective heat transfer coefficient remained nearly constant at 68.43 ± 0.40 W/(m2·K). Conversely, the convective mass transfer coefficient exhibited an increase, rising from 0.0649 to 0.0799 m/s across the temperature range of 30 to 80 °C. The activation energy for convective mass transfer was found to be 3.70 kJ/mol. The results obtained characterize the temperature-dependent drying and convective transport behavior within the investigated drying configuration and observation period.