Heat And Mass Transfer Characteristics Of Convective Drying In Porous Packed Bed About Zanthoxylum Bungeanum Maxim

In addition to the natural drying of crops on a household basis,hot-air convection factory-based mechanical drying greatly reduces labor and ensures the cleanliness of dried agricultural products.In particular,it can avoid the impact of bad weather and ensure the quality of product drying has been widely studied.Among them,the gas-solid heat and mass transfer characteristics of the porous packed bed of crops and the drying medium are important parameters that affect the energy consumption and drying quality of the equipment.Mastering the dry heat and mass transfer characteristics of the porous packed bed of crops is useful for the theoretical research and industrial practice of drying.The optimal design of the structure is of great significance.At present,there is almost no research on heat and mass transfer of Zanthoxylum bungeanum in drying,and there is no research on the relationship between the pores of Zanthoxylum bungeanum stacked packed bed and the coupling characteristics of gas-solid flow heat and mass transfer.A numerical model of heat and mass transfer in gas-solid flow of Zanthoxylum bungeanum was developed by using thin layer drying model,porous medium theory and local non-thermal balance principle in order to reduce the design cost and develop a more suitable drying system in the future.The main research work is as follows:(1)The specific heat capacity and thermal conductivity of Zanthoxylum bungeanum were measured by the thermophysical parameter instrument,and the non-linear fitting was performed using Origin software.The thermal conductivity under different moisture content and the specific heat capacity curve law of dried Zanthoxylum bungeanum particles with temperature changes were obtained.The curve shows that the thermal conductivity of Zanthoxylum bungeanum decreases gradually as the moisture content decreases,and the range of thermal conductivity belongs to the range of crops;as the temperature is before 60℃,the specific heat of Zanthoxylum bungeanum increases to the highest point and then begins to decrease,which is because Caused by the volatilization of the oil.The density,bulk porosity and specific surface area of Zanthoxylum bungeanum were measured using the pycnometer method.(2)According to the basic requirements of the hot-air drying experiment,the experiment platform was designed and built by itself,and the characteristics of the pepper under common drying conditions were studied using the method of thin-layer drying.Combining with the drying kinetics theory,the effect of hot air temperature and wind speed in different experimental sections on the drying rate is analyzed.The results show that pepper is basically in two stages in the use of hot air drying:the drying rate rise stage and the lower stage.stage.Two suitable drying models are obtained by fitting the commonly used thin-layer drying model.One is that the Newton model is suitable for numerical simulation,and the other is that the Wang and Singh model is suitable for predicting the actual drying time of pepper.The drying constant in the Newton model is fitted to the temperature curve,and a complete fitting formula is obtained for use in the numerical simulation.(3)The effective water diffusion coefficient and thermodynamic properties of Zanthoxylum bungeanum were obtained by thin-layer drying experimental data combined with drying kinetics theory.The results show that the effective water diffusion coefficient of v is between 1.43923 × 10-11～4.74770 × 10-11m2/s,and the drying activation energy is between 16.81～18.17 kJ/mol.Entropy,Enthalpy and Gibbs free energy are used in thermodynamic properties to explain the essence of pepper dehydration.(4)The porous media model is used to model the convection drying of Zanthoxylum bungeanum,and the local non-thermal equilibrium multi-physical field transport equation of the drying process is deduced by using the above-mentioned geometric parameters,thermal physical parameters and thin-layer drying model.The Fluent numerical simulation software is used to UDF the program development and numerical simulation of each transport equation.The experimental results show that the developed program can be applied to the hot air convection drying of Zanthoxylum bungeanum.