Research On Walnut Winnowing Based On CFD-DEM Coupling

With the integrated development of the primary and secondary industries,the walnut industry is not only related to agricultural engineering,but also to the machinery industry,food industry and other industries.Separation of shell and kernel is one of the most important processes before the deep processing of walnut.The quality of the operation directly affects the added value of the product.Improving the performance of the separation device will become a critical link to promote the overall improvement of the quality of walnut processing.The winnowing separation method was widely used in hard-shell nut ShellKernel Winnowing Device.However,the complex Gas-Solid Two-Phase Flow was involved in the air cleaning process,which was difficult to accurately describe by traditional research methods.With the promotion of Computer Aided Engineering(CAE),the development and design of gas-solid two-phase flow devices has already surpassed the traditional research methods.Using CAE technology to numerically simulate the working conditions of agricultural product cleaning has become an important means to clear its working principle,but the simulation of only considering a single physical field cannot reflect the characteristics of the flow field.The Gas-Solid Two-Phase Flow Coupling method which based on computational fluid dynamics and discrete element theory enables the gas phase and the solid phase to be calculated in their respective computational domains,and then comprehensively analyzed to realize the gas cleaning process of the walnut shell and kernel mixture in the simulation of Shell-Kernel Winnowing Device.In this paper,the CFD-DEM coupling method was used as the research method,and the separation performance evaluation index of the Shell-Kernel Winnowing Device was used to study the Winnowing Device.Firstly,the structure model of the Winnowing Device was determined through the analysis of the flow field,and the windward area distribution of the shell-kernel mixture after shell breaking was analyzed to determine the particle size distribution of the typical shell-kernel mixture.Mixture modeling,based on the basic principle of Gas-Solid Two-Phase Flow Coupling,the motion state of different material particles in the Winnowing Device was explored and analyzed from the two scales of single particle and particle group,and the CFD-DEM coupling method was verified in hard-shell nut ShellKernel Separation.Meanwhile,the aerodynamic characteristics test of the singleparticle shell-kernel mixture was carried out to determine the difference in the suspension velocity of the shell-kernel mixtures.The single-factor simulation test of the group Winnowing Separation was carried out to determine the optimal level range,and the multi-factor combination test was carried out accordingly to determine the best working parameter combination.The research results showed that the simulated suspension velocity of the shell and kernel mixture can be obtained by using the CFD-DEM coupling method,and the suspension velocity of each shell and kernel mixture was tested.The average suspension speed range of walnut shell is8.03m/s-14.79m/s,and the average suspension speed range of walnut kernel was11.29m/s-20.19m/s.Compared with the test results,the deviations were 0.1% and3.4% respectively.The single factor test showed that with the increase of the inlet wind speed,the removal rate and separation loss rate of shell kernels was increasing.With the increase of the baffle opening,the clean rate and loss rate of Shell-Kernels mixture decreased firstly and then increased.With the increase of the inclination angle of the air inlet,the clean rate was decreased and the loss rate was increased;Meanwhile,the combined test results showed that: the baffle opening has the most significant effect on the clean rate of Shell-Kernel Mixture,and the inclination angle of the air inlet has the greatest effect on the loss rate.The best working parameter combination was obtained as follows: the inlet wind speed was 24m/s,the baffle opening was 7cm,and the air inlet inclination was 10°.