Solar drying of Roselle (Hibiscus sabdariffa L.): Mathematical modelling, drying experiments, and effects of the drying conditions

Abstract

Imad Eldin Saeed

(Dept. of Mech. and Materials Eng., Faculty of Engineering, National University of Malaysia (UKM), 43600 Bangi, S.D.E., Malaysia)

Abstract: Thin-layer drying experiments were conducted in a solar-assisted dehumidification drying system for agricultural products.  The experiments were carried out to determine the influences of drying conditions on the drying behaviour of Roselle’s calyces (Hibiscus sabdariffa L.).  The Investigations were carried out at five different air temperatures and two different air velocities.  Drying air temperature was the main factor affecting the drying behaviour of Roselle since raising the temperature (from 35℃ to 65℃) dramatically reduced the drying time.  At the low temperature (35℃), increasing the drying-air velocity (from 1.5 m/s to 3.0 m/s) resulted in shorter drying time.  Twelve thin-layer drying models were fitted to the solar drying experimental data.  Statistical analysis was carried out and comparison between drying models was made to select the best-fitting model for the drying curves.  Among the 12 tested models, the logarithmic model was found to be superior to other models; and it adequately represents the drying characteristics of Roselle in the range of applied drying conditions.

Keywords: Roselle (Hibiscus sabdariffa L.), solar drying, drying kinetics, mathematical models

Citation: Imad Eldin Saeed.  Solar drying of Roselle (Hibiscus sabdariffa L.): Mathematical modelling, drying experiments, and effects of the drying conditions.  Agric Eng Int: CIGR Journal, 2010, 12(3): 115-123.