بررسي و مدل سازي فرآيند خشك كردن تركيبي همرفتي

چكيده انگليسي :

Investigation and Modeling of Combined Convective Microwave Drying of Lemon Slices Omid Mirzabeigi Kesbi O kesbi@ag iut ac ir October 2010 Department of Agricultural Machinery Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Morteza Sadeghi sadeghimor@cc iut ac ir Abstract Drying is one of the oldest familiar post harvest processes of agricultural crops Employing microwave power in drying is a novel approach in the last two decades Microwave radiation causes molecular dipoles to rotate and ions to move in the material Friction generated because of dipoles rotation and ions movements warm the material and causes water evaporation In this study a combined convective microwave dryer was developed by modification of a domestic microwave oven Thin layer drying of lemon slices was investigated in convective drying at 50 55 and 60 0C inlet air temperatures microwave drying at 180 W microwave power and combined drying by applying 180 and 360 W microwave powers at 50 55 and 60 0C inlet air temperatures in three replications In all tests the initial sample weight air velocity and relative humidity were constants values of 190 g 1 5 m s and 25 respectively In drying experiments the initial moisture content was reduced from about 5 66 g g d b to approximately final amount of 0 15 g g d b Quality evaluation of the dried sample was determined by color parameters L a b and rehydration capacity measurements Convective and combined experiments were analyzed in random factorial design 3 3 Analysis of variance ANOVA was performed to determine significant differences between drying durations color parameters and rehydration capacities of the dried samples Dependent variable means were compared by Duncan s Multiple Range test Moisture reduction kinetics was investigated through moisture content versus time drying rate versus moisture content and moisture ratio versus time curves Drying experiments were occurred in one constant and tow falling rate periods Analytical modeling of drying data was performed in three methods Newton model in which the model constant drying coefficient obtained between 1 91 10 5 and 9 57 10 4 1 s Crank s solution of second Fick s equation for infinite plane sheet in which the effective moisture diffusivity obtained between 8 11 10 11 and 2 67 10 9 m2 s and Dincer and Dost method in which the Biot number obtained between 0 17 and 2 06 the moisture transfer coefficient between 3 25 10 8 and 3 38 10 6 m s and the moisture diffusivity between 2 21 10 10 and 7 21 10 9 m2 s The values of drying coefficient moisture diffusivity and moisture tensfer coefficient increased whereas the drying time decreased with increase in microwave power Mathematical modeling of drying data was done by fitting to 9 commonly used thin layer drying models namely Page modified Page logarithmic two term two term exponential Wang and Singh diffusion approach Midilli et al and Verma et al The performances of these models were compared by statistical procedure According to the maximum coefficient of determination R2 and minimum value of root mean square of error RMSE between the observed and predicted moisture ratios the Midilli et al model had the best close prediction to the observed data Regarding simultaneous attention to the drying time quality and energy consumption the combined convective microwave drying with 180 W microwave power and 500C inlet air temperature was the best treatment for drying of lemon slices amongst all treatments Key words Lemon Drying Microwave Moisture Diffusivity

ميرزا بيگي كسبي، اميد

بررسي و مدل سازي فرآيند خشك كردن تركيبي همرفتي - مايكروويو ورقه هاي ليموترش

خشك كردن , ضريب انتشار رطوبت