A simulation model of hybrid solar drying as alternative sustainable drying system for herbal and medicinal plants was developed. Heat absorbed from the solar radiation. Heat gained by the collector and supplemented by the burner. Heat gained or lost by the product, heat gained or lost through the drying bin wall, and the latent heat of the moisture evaporation from the product were the main components of the equations describing the drying system. The model was able to predict the moisture loss from the product at wide ranges of temperatures (55, 60, 65 and 70 C and air circulation percentages (10, 20 and 30%). The model showed a dramatic effect of the drying air temperature on the moisture loss at the beginning of the drying process and became constant. Energy consumption at different drying temperatures was studied. Air recirculation has a profound effect on energy saving while drying herbs. In the next stages, high temperature without forcing air should be used. The model was validated by using experimental data of the drying temperatures and moisture loss under both direct sun and solar drying systems for herbal plants. The predicted values were in a reasonable agreement with the experimental data. |
