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

I. E. Saeed, K. Sopian, Z. Zainol Abidin


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.

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