Numerical Simulation And Optimization Of Gas-Particle Flow In The Separation Chamber Of The Air-Screening Classification Machine

The seed selection plays an important role in agricultural production.The most important procedure in the seed selection is the air-screening classification,whose working principle is to remove light and heavy impurities from seeds based on the different suspension velocity of them in the separation chamber and then precisely grade different levels seed through the sieve bed.The traditional control of air-screening classification machine,e.g.adjusting the fan frequency,air outlet magnitude and feeding speed,depends mainly on the experience of operators,and therefore it is difficult to achieve the best classification effects.Hence,the research on the relationship between the working parameters and the cleaning performance has great contributions to design and optimization of air-screening classification machine.As the motion of the airflow field and seeds in the separation chamber belongs to typical gas-solid two-phase flow,it is too complex and random to get ideal results by the analytic method or experimental method.So far,the Computational Fluid Dynamics has become an important tool for research on the two-phase flow.In this paper,the RNG k-? turbulence model of Fluent software was used to simulate airflow field distribution in the separation chamber.And then the characteristics of flow field were analyzed on three aspects of the velocity field,pressure field and turbulence flow.Based on the study of single-phase flow,the movement of seeds in the separation chamber was simulated by the Discrete Phase Model.Based on the gas-solid two-phase flow simulation research,the orthogonal experiment method was adopted to calculate the optimal working parameters of the separation chamber.The research results show that the influence degree of the working parameters on the cleaning performance is the fan frequency,air outlet magnitude and feeding speed.In addition,the feeding speed was set to a fixed value to get rid of the influence of the change of feeding speed.Based on the conclusion of the orthogonal simulation experiment,we designed a new simulation experiment.The cleaning performance of separation chamber was expressed by a binary cubic function that the fan frequency and air outlet magnitude were chosen as independent variables.According to the function,we drew the three-dimensional surface diagrams of cleaning performance.Converting discrete simulation data to continuous cleaning performance index function helps us to investigate the relationship between working parameters,i.e.fan frequency and air outlet magnitude,and cleaning performance more accurately.A comprehensive evaluation index was proposed,which is called the cleaning efficiency.This index is obtained by weighted operation of the cleaning rate and the loss rate.The optimal working parameters of the separation chamber for different production requirements were calculated by selecting different weights.On this basis,the basic rules of selecting the optimal working parameters for the different seeds were studied by the simulation method.The validation experiment was carried out on the FLX-150 A airscreening classification machine.Chinese cabbage seeds were chosen as the particle phase of validation experiment.The airflow velocity field distribution in the lifting pipeline and the cleaning performance under different working conditions of the simulation results and the experiment results were compared.It was found that the simulation results and the experiment results are in good agreement.It is proven that the gas-solid twophase flow simulation is effective and convenient to the research on the separation chamber and the optimization of working parameters.The modeling and simulation methods for the two-phase flow physical phenomena in the separation chamber can provide the reference for the performance research and the structure optimization for the equipment of the seed air cleaning and grain pneumatic transportation in the agricultural field.The binary polynomial fitting method for the simulation data processing is established.And a comprehensive evaluation index for the evaluation of seeds cleaning is proposed,which provides a scientific method for the calculation of the optimal working parameters and the comprehensive evaluation of the cleaning effect.