Research Of Influencing Factors Of Thermal Conductivity And Internal Temperature Field Numerical Analyzation For Fruit And Vegetables

Along with the rapid advancement of modern science and technology,the output of agricultural products is also constantly improving.However,due to insufficient preservation method of fruits and vegetables during storage and transportation,the annual loss due to decay is 30%.The thermal properties of fruits and vegetables are important parameters for refrigeration and processing.However,nowadays,the research on the thermal conductivity and specific heat capacity of fruits and vegetables is very small.At the same time,there are problems like coverage of the prediction model is small,data is too old to competent in the present form,and the reference value deviation is obvious.The quality and storage of fruits and vegetables are related to their storage temperature.Nowadays,there are many ways of temperature change to maintain the quality of fruits and vegetables and improve their storage time.Therefore,the heat transfer characteristics of fruits and vegetables are simulated and experimentally verified.The heat transfer law inside the tissues of fruits and vegetables is researched,and the real-time changes of internal temperature field are quantitatively analyzed.Therefore,this paper has completed researches from the following aspects:(1)Research on thermal conductivity of fruits and vegetables.Nine representative fruits and vegetables were selected,and the thermal conductivity of the two different temperatures in the range of-50 °C to 20 °C was measured by Hot Disk thermal constant analyzer.At the same time,red Fuji apples with different water content(MC)and soluble solids content(SSC)were selected,and the thermal conductivity of eggplant was measured.The effects of MC and SSC content on the thermal conductivity of the same fruits and vegetables were analyzed.When the increase was made,the thermal conductivity become small,and as the MC increased,the thermal conductivity become larger.At the same time,a linear regression equation was established for the MC,SSC,density and thermal conductivity of fruits and vegetables,and variance analysis was performed.(2)Research on stratified heat transfer model of cylindrical fruits and vegetablesThe layered heat transfer model of cylindrical fruits and vegetables was established according to the physiological structure of fruits and vegetables.The change of internal temperature field during the refrigeration process was studied and simulated by COMSOL.It was found that during the initial stage of internal cooling,the temperature of the tissue near the epidermis changed rapidly,while the temperature of the tissue at the center changed slowly.As time went on,the temperature inside and outside gradually approached.The temperature gradually decreases throughout the process,and the rate of decrease in internal temperature lags significantly from the outside.The accuracy of the model was verified by experimental determination with eggplant test materials.(3)Research on stratified heat transfer model of spherical fruits and vegetablesAccording to the physiological structure of fruits and vegetables,the layered heat transfer model of spherical fruits and vegetables was established.The hot air was used as the treatment medium,and apple was used as the testing material.The process of heat treatment of spherical fruits and vegetables was simulated by COMSOL.The simulation found that during the initial warming period of apple,the tissue temperature near the epidermis changed rapidly,while the tissue temperature at the center changed slowly.As time went on,the temperature inside and outside the apple gradually approached.At the same time,the effects of medium flow rate,material size,structure thermal properties and stacking method on the heat treatment process were analyzed.