Performance analysis on root-soil separation of Panax notoginseng using DEM-CFD method and air-jet system

• Air-jet method to realize the separation of Panax notoginsen root and soil. • Building experimental devices in simulated and physical environments. • Soil separation rate and soil attachment rate were proposed as evaluation standards. • Nozzle diameter >10 cm, soil adhesion rate still >55 % when soil separation rate >90 %. • Nozzle diameter of 7 cm, soil separation rate >62 % at optimal angle-pressure-distance. PN (Panax notoginseng root) is a kind of Chinese traditional medicinal crop. A large amount of soil is attached to PN after the harvest. Therefore, PN-S (PN and soil mixture) separation operation is a key step in the postharvest processing of PN. However, the root and soil separation operation of PN suffers from two problems: poor root-soil separation effect and unclear separation process. In this study, a method for PN-S separation using jetting is proposed. The three-dimensional scales and geometries of PN and soil particles were measured and calibrated. A coupled fluid–solid separation model of PN-S was constructed using DEM-CFD (discrete element coupling method and computational fluid dynamics). Based on the structure of the air-jet soil separation device and the problems to be solved in the study, a new evaluation standard combining φ (soil separation rate) and η (soil attachment rate) was proposed to quantify the working effect of the air-jet device. This study established experimental platforms for PN and soil air-jet separation devices in both simulated and actual environments. Through the mutual corroboration of physical and simulation experiments, the results prove that the method is feasible. Obtain a clear process of PN and soil separation through the use of a simulation experimental platform. The optimum parameters of the air-jet device were further obtained through the BBD (Box-Behnken Design) method. The optimal parameters are: pressure of 2285 Pa, distance of 10 cm, angle of 90°, and φ of 62.06 %. The fluid–solid coupling model and the new evaluation criteria established in this study provide a theoretical basis for the effective separation of PN-S. The proposed air-jet separation method can effectively separate PN-S. The results of this study provide new ideas and technical support for the optimization and design of PN-S separation equipment.