Indirect and Mixed Mode Solar Drying Mathematical Models For Sultana Grape

Many research studies have been performed on forced convection (active) solar dryersfor fruit and vegetables. a short survey of these showed that applying the forcedconvection solar dryer not only significantly reduced the drying time but also resulted inmany improvements in the quality of the dried products. active indirect and mixed-modethin layer solar drying experiments were conducted on sultana grapes. a combination ofa solar air heater and a cabinet dryer was designed, constructed and tested for thisproduct in the agricultural engineering department at shiraz university, iran. three airflow rates (0.085, 0.126 and 0.171 m3 s-1) and two types of drying systems (indirect andmixed-mode) were adopted. the south wall of the drying chamber was covered by a sheetof glass for mixed-mode and the glass sheet was covered with a thick sheet of cloth for anindirect solar drying system. seven well-known thin layer drying models were usedseparately to fit the mixed-mode and indirect type experimental data for sultana grapes.for experimental indirect data, the modified page model (r= 0.998, ÷2= 0.000241) and forexperimental mixed-mode data, the page model (r= 0.999, ÷2= 0.000169) showed the bestcurve fitting results with highest r (correlation coefficient) and lowest ÷2 (reduced chisquare)values. the constants in these models explain the effects of drying parameters, airvelocity and temperature. to take account of these effects, the best correlation equationsbetween the constants and drying parameters were also introduced using multipleregression analysis.