Performance evaluation and parameter optimization of a walnut shell-kernel winnowing device

To design a walnut shell-kernel winnowing device, the aerodynamic characteristics of walnut shells and kernels were studied by combining theoretical computation and empirical tests. A winnowing method was developed for shell-kernel separation based on an analysis of suspending velocity. The performance of the walnut shell-kernel winnowing device was evaluated based on the screening rate and loss rate. Influences of feeding rate, wind speed, and vibration frequency on the performance of the device were simulated, and the optimal operating parameters were acquired. Research results demonstrated that the suspending velocity ranges of walnut shells and kernels were 8.96-13.89 and 11.81-20.78 m/s, respectively. Vibration frequency was the primary factor that influenced the screening rate of the device, followed by wind speed and then feeding rate. Feeding rate was the primary factor influencing the loss rate of the device, followed by vibration frequency and then wind speed. The optimal operating parameters were as follows: feeding rate = 246.61 g/s, wind speed = 19.77 m/s, and vibration frequency = 41.17 Hz. Under these conditions, the winnowing device's screening rate and loss rate were 79.22% and 7.38%, respectively. The performance of the designed walnut shell-kernel winnowing device conforms to practical operational requirements. This study provides a potential reference for future investigation into the optimization of shell-kernel winnowing devices for other agricultural products.Practical applicationsIn order to explore the influence of each factor on the performance of the device, the windward area of the crushed materials was obtained by Image Processing. Meanwhile the "3 sigma criterion" was used to establish an equivalent sphere of equal windward area to replace the real shape of the walnut particles, and the range of the suspending velocity of the walnut crushed material was explored. Based on the Computational Fluid Dynamics Discrete Eement Method (CFD-DEM) coupling method, and taking the screening rate and loss rate as the evaluation indicators, the effects of feed flow, wind speed, and vibration frequency on the performance of the device were simulated and analyzed, and the optimal operating parameter combination was obtained. The performance of the walnut shell-kernel winnowing device designed in this paper meets the actual operation requirements, and the research method can provide a reference for the development and optimization of other agricultural product separation equipments. The walnut shell-kernel winnowing separation is a typical coupled gas-solid two-phase flow process, and the material exhibits complex kinetic properties. The coupled CFD-DEM method simulates the winnowing separation of walnut shells and kernels.image