مطالعه و شبيه سازي فرآيند خشك كردن ورقه هاي گوجه فرنگي بوسيله خشك كن هواي داغ مجهز به پمپ حرارتي

چكيده انگليسي :

Study and Simulation of Heat Pump Drying of Tomato Slices Khaled Gomar k gomar@ag iut ac ir January 30 2012 Department of Agricultural Machinery Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisors Morteza Sadeghi sadeghimor@cc iut ac ir Ali Esehaghbeygi esehaghbeygi@cc iut ac ir AbstractMost agricultural products are harvested at high moisture content that is not proper to storage Therefore to prevent deterioration drying operation is used Heat pump dryers have been widely considered fordrying fruits vegetables and biological materials due to the low power consumption high efficiency high quality of final product good consistency with environmental laws ability to control the dryingprocess as well as being independent of the environmental conditions The objectives of this study wereinvestigation the drying kinetics and qualitative parameters of tomato slices during heat pump dryingoperation empirical and analytical modeling of the process as well as assessing the heat pump systemperformance Fresh tomato samples Shanoon variety were purchased from a local greenhouse in Isfahan central Iran Heat pump drying and hot air drying conventional method were conducted at threetemperatures 40 50 and 60 C and two air flow velocities 1 and 1 5 m s 1 with three replications Theheat pump system consisted of two condensers a compressor an expansion valve and two evaporators which were connected to each other using copper tubes The refrigerant A404 was chosen for workingfluid The color indices L a and b were measured by a digital camera and Photoshop software Volume change caused by shrinkage was determined using the displacement of toluene with density of0 87 g cm 3 To modeling mass transfer of tomato slices the equation of Fick s second law for infiniteplane sheet was explicitly solved Empirical modeling of drying data was also done by fitting 12commonly used empirical and semi empirical thin layer drying models According to the drying curves the constant rate period was not observed for all treatments and the drying kinetics of the samplesoccurred continuously Drying time with heat pump was shorter than that of conventional method Theminimum and maximum values of effective moisture diffusion coefficient of dried tomato slices in theheat pump dryer were 3 04001 10 9 m2 s 1 at the temperature of 40 C and air flow velocity of 1 m s 1 and6 18135 10 9 m2 s 1 at the temperature of 60 C and air flow velocity of 1 5 m s 1 respectively Inaddition maximum and minimum values of the effective moisture diffusion coefficient of the samplesdried with hot air dryer were 2 53334 10 9 m2 s 1 at the temperature of 40 C and air flow velocity of 1 ms 1 and 5 26935 10 9 m2 s 1 at the temperature of 60 C and air flow velocity of 1 5 m s 1 respectively The prediction of models based on the explicit solutiuon of the equation of the second Fickian lawshowed a good correlation with the experimental data at all drying temperatures and air flow velocity forboth methods According to the maximum coefficient of determination R 2 and minimum value of rootmean square of error RMSE between the observed and predicted moisture ratios the diffusion approachmodel indicated the close prediction compared to the observed values With decreasing moisture content the color parameters L a and b decreased and the shrinkage increased for all treatments Thecoefficient of performance COP of the heat pump system increased with increasing air temperature andair flow velocity The maximum and minimum values of COP were 5 77 and 2 21 at the temperature of60 C and air flow velocity of 1 5 m s 1 and at the temperature of 50 C and air flow velocity of 1 m s 1 respectively Keywords Coeffecint of perfomance Energy consumption Heat pump Mathematical modeling Shrinkage

گمار، خالد

مطالعه و شبيه سازي فرآيند خشك كردن ورقه هاي گوجه فرنگي بوسيله خشك كن هواي داغ مجهز به پمپ حرارتي

چروكيدگي , ضريب عملكرد , مدل سازي رياضي , مصرف انرژي