In previous research articles on solar drying of Roselle (karkade), statistical analyses on twelve thin-layer drying models proved the superiority of the logarithmic model.  This article investigated the effects of the drying conditions on the drying constant (k), coefficients, and drying rate.  Validation of the model as well was presented.  The rate constant (k) was highly affected by the drying temperature.  It increased linearly with the temperature.  Air velocity to a lesser extent influenced (k). Coefficient (a) showed a positive relation with both drying-air temperature and velocity.  In contrast to coefficient (a), parameter (c) showed an inverse relation with the drying temperature and a moderate dependence on the air velocity.  The drying rate was highly influenced by the drying temperature.  Raising the temperature increased the drying rate.  Furthermore, two criteria were applied to validate the developed model.

Keywords: roselle, drying constant, coefficients, rate, logarithmic model, model validation

Citation: Saeed I.E.  Solar drying of roselle (Hibiscus sabdariffa L.): Effects of drying conditions on the drying constant and coefficients, and validation of the logarithmic model.  Agric Eng Int: CIGR Journal. 2010, 12(1): 167－181.