Simulation And Experimental Research On Drying Of Fruit And Vegetable Porous Media

In recent years, the research on porous media drying has attracted more and more people’s attention, and the research hot spot is to study the drying process by the model simulation method. Due to the complexity of the internal structure of the porous media for fruits and vegetables, and the difference between the traditional continuum medium model simulation results and the actual drying of fruit and vegetable drying is very significant, it can’t give a reasonable description of heat and mass transfer during drying process of porous media, and which is necessary for the research of improving the quality of fruit and vegetable drying. In view of these problems, in this paper, the apple was used as a typical representative of fruit and vegetable porous media to study these problems:Establishment of the physical model of irregular pore network. First use the experimental method to determine the porosity, pore density and pore diameter distribution about the freeze-dried apple slices, and the parameters such as pore coordination number is determined; and then build the irregular pore network physical model of the apple porous medium, the parameters of the model is the parameters of the apple porous medium that actual measured, so the simulation of the pore network can be better applied to the actual drying process of apple porous medium.With the apple slices porous media as the experiment object, the hot air drying test is carried out, in the experiment, the temperature and the moisture content of the apple slices were measured, and its drying curves, moisture field, temperature curves and temperature field were obtained.Based on the established pore network physical model, the mathematical model of pore scale is established, including the heat transfer equation, mass transfer equation and momentum equation, the capillary effect and Kelvin effect in the pores on the heat and mass transfer during the drying process are considered comprehensively in the mathematical model. The numerical calculation and simulation of mathematical model. The mesh of the heat and mass transfer about the pore network physical model was divided, and the difference discretization of the mathematical model was conducted by using the control volume balance method, then solve the temperature field and moisture filed distribution of the model. By using VC++ simulation software and MATLAB programming to simulate the drying of pore network.Through the comparison of the test results and the simulation results, it shows that the pore network model can describe the heat and mass transfer process of the actual fruit and vegetable porous media very well. The drying curve of simulation and the actual material drying curve is relatively close, simulation of moisture field distribution can reflect the moisture field distribution characteristic of actual materials drying process; the change trend between the temperature curve of simulated and the temperature curve of the actual materials drying process is almost the same, the temperature value of the simulation is higher than the experiment. The drying experiment of different material structure parameters shows that:The parameters such as porosity and the average coordination number have great influence on the drying simulation. The greater the porosity, the longer the drying time, the lower the average temperature; the greater the average coordination number, the longer the drying time, the higher the average temperature.