Mathematical modeling of thin layer solar drying of sultana grapes

Thin layer solar drying experiments were conducted for Sultana grapes (cv. Thompson seedless) grown in Antalya, Turkey. An indirect forced convection solar dryer consisting of a solar air heater and a drying cabinet was used in the experiments. Air heated by the solar air heater was forced through the product by an electric fan. In order to examine the effect of drying air temperature and velocity on a thin layer drying of Sultana grapes, twenty-two experiments were performed. Eight different thin layer mathematical drying models were compared according to their coefficient of determination to estimate solar drying curves. The effects of drying air temperature and velocity on the model constants and coefficients were predicted by the regression models. According to the results, a two-term drying model could satisfactorily describe the solar drying curve of Sultana grapes with a correlation coefficient (r) of 0.979. The constants and coefficients of this model could be explained by the effect of drying air temperature and velocity. (C) 2001 Elsevier Science Ltd. All rights reserved.