Thin layer convective solar drying and mathematical modeling of prickly pear peel (Opuntia ficus indica)

This paper presents the thin layer convective solar drying and mathematical modeling of prickly pear peel. For these purposes, an indirect forced convection solar dryer consisting of a solar air collector, an auxiliary heater, a circulation fan and a drying cabinet is used for drying experiments. Moreover, the prickly pear peel is sufficiently dried in the ranges of 32 to 36 °C of ambient air temperature, 50 to 60 °C of drying air temperature, 23 to 34% of relative humidity, 0.0277 to 0.0833 m3/s of drying air flow rate and 200 to 950 W/m2 of daily solar radiation. The experimental drying curves show only a falling drying rate period. The main factor in controlling the drying rate was found to be the drying air temperature. The drying rate equation is determined empirically from the characteristic drying curve. Also, the experimental drying curves obtained were fitted to a number of mathematical models. The Midilli-Kucuk drying model was found to satisfactorily describe the solar drying curves of prickly pear peel with a correlation coefficient (r) of 0.9998 and chi-square (χ 2) of 4.6572 10-5. © 2003 Elsevier Ltd. All rights reserved.