The aim of this research work was to study the drying behavior of onion slices using infrared radiation refractance window drying system, which the infrared radiation passed throw plastic membrane surface , where the water in the moist product creates a window, that allows for the passage of infrared energy and heat behaves as it and directly transferred to water present in the product, the water in the product on the plastic membrane surface evaporates, and the window of infrared energy closes and refracts back into the heated source, no longer exposing the product to heat and good quality product.
The experiments of this work carried out at food engineering and packaging research dept. , Food Techn. Res. Institute, Agric. Research center. The drying behavior of onion slices using suggested dryer was examined and simulated for three different thin layer drying models
( Page , modified Page and Hendreson and Padis ) .
Four levels of radiation intensity ( 1100 , 1750 , 2400 , 3050 W / m2) and for levels of drying air velocity ( 0.1 , 0.5 , 1 and 1.5 m / s ) were studied at 45 ºC temperature and 20 % relative humidity .
The results showed that :
The recorded drying time for drying whole onion slices from an initial moisture content of about 612 - 614.28 % d.b. to a final moisture content of about 13.75 – 15 % d.b. were 50 – 140 minutes under different drying parameters .
- The following equation can described the relation ship between drying time ( T ) , radiation intensity ( I ) and air velocity ( V ) with the best fit :
T = 80 + 100V - 1600 I, (R² = 0.9911)
- The thermal efficiency of the IR-refractance window drying system was varied between 54.47% to 46.43% , specific energy consumption varied between 4.39 KJkgˉ¹to5.15 KJkgˉ¹under different drying parameters.
- The total capacity of the dryer is a bout 0.326 Kg/h the calculated operation cost of the dryer approaches about 8.89 LE/kg of dried whole onion slices .