Drying kinetics of prickly pear fruit (Opuntia ficus indica) Original Research Article

The present work examines the effect of drying air conditions on drying kinetics of the prickly pear fruit in a convective solar drier operating with an auxiliary heating system under air controlled conditions. Moreover, the prickly pear fruits are sufficiently dried in the ranges between 32 and 36 °C of ambient air temperature, 50–60 °C of drying air temperature, 23–34% of relative humidity, 0.0277–0.0833 m3/s of drying air flow rate and 200–950 W/m2 of solar radiation. The results verified with good reproducibility that drying air temperature is the main factor in controlling the drying rate and the experimental drying curves show only a falling rate period. The expression of the drying rate equation is determined empirically from the characteristic drying curve. Eight different thin layer drying models were compared according to their coefficients of determination to estimate solar drying curves. The two-term model was found to satisfactorily describe the solar drying curves of prickly pear fruit with a correlation coefficient (r) of 0.9999. The constants and coefficients of this model could be explained by the effect of drying air temperature with a correlation coefficient (r) of 1.0000.