Drying characteristics of Roselle (1): Mathematical Modeling and Drying Experiments

Abstract

The effects of drying conditions on the drying behavior of Roselle (Hibiscus sabdariffa .L) and the applicability of twelve thin-layer drying models to predict the drying curves of Roselle were studied. The experiments were conducted in Constant Temperature and Humidity Chamber. Four temperatures (35, 45, 55 and 65°C) and five relative humidities (30, 35, 40, 45 and 50%RH) were studied. Drying air temperature was found to be the main factor affecting the drying kinetics of Roselle; raising the drying temperature from 35°C to 65°C dramatically reduced the drying times. The effect of the relative humidity was lower than that of temperature; increasing the relative humidity resulted on longer drying times. Higher equilibrium moisture contents were obtained with high relative humidities and low temperatures. Furthermore, drying was observed only in the falling-rate period. Statistical analysis was carried out and comparison among drying models was made to select the best-fitted model for the drying curves. Among twelve tested models, the two-term exponential model was found to be superior to the other models in terms of fitting performance.