Study On Induced Airflow Flow Law Of Bulk Materials In Freefall

The air pollution caused by dust dispersion is a serious threat to the safety of industrial and agricultural production and the quality of air environment,which is a major problem to be solved urgently.The entrainment and release of the free falling of the bulk material to the surrounding air flow is a major inducement of dust dispersion.However,because the airflow induced by free falling is an unstable and weakly dynamicvariation,the interaction mechanism between airflow and particles,particles and particles are very complex.At present,there is not deep enough research on the dynamic behavior of gas phase and particle phase in the falling process of bulk material.Therefore,in-depth study of the coupling mechanism of particles and airflow in the falling process of bulk material,and analysis of the flow law of induced airflow and the dynamic evolution behavior of particles can provide theoretical and scientific basis for the suppression of dust dispersion in the process of industrial and agricultural production.In this work,based on the transport process of food crops,an experimental model was established,and the food crops are selected as the granular materials to explore the free blanking induced airflow and particle movement characteristics.The induced airflow is characterized by measuring the total airflow velocity in the whole blanking process,and the power function fitting relationship is quantitatively analyzed by using the single factor method.The relationship between the induced airflow and the relevant factors such as blanking height,mass flow,particle size and blanking pipe space is discussed.The results are as follows:the induced airflowvelocity is directly proportional to the 1.29 power of the blankingheight,and to the 0.35 power of the mass flow of the blanking;in the range of the experimental particle size,the induced airflow velocityincreases with the increase of the particle size,and the power function fitting coefficient and index increase from 0.2236 and 0.2691 to 0.4580 and 0.3843respectively;under the condition of the experimental blanking diameter,the induced airflow is the largest at the 120mm diameter,and Whether the diameter of the pipe increases or decreases,the induced airflow velocity show decreasing trend.Based on the experimental data,a semi empirical model for the calculation of induced airflow is established by using dimensional analysis method,and the error of the model is less than 20%after verification.The applicability of other calculation models under the experimental conditions in this paper is compared and analyzed.The results show that the particle size is one of the key factors to determine the applicability of the calculation model.The CFD-DEM coupling method is used to simulate the free blanking process.The dynamic flow process of particle flow,the characteristics of particle diffusion,induced airflow velocity and pressure are analyzed,which are difficult to observe in the experiment.It is found that the particle velocity is directly proportional to the blanking height and increases with the blanking time;when mungbean particles drop155 cm at a mass flow rate of 0.68 kg/s,the numerical relationship between the diameter of particle flow beam d_h and the blanking height H can be expressed by the formula d_h=0.109H+0.049,the airflow velocity distribution and pressure distribution trend of different height sections are roughly the same,and the numerical value increase with the increase of the blanking height,in addition,the flow fluidity near the blankingplate is the strongest.This paper contains 33 figures,7 tables and 110 references.