Experimental Study And Numerical Simulation Of Radial Ventilation And Cooling In Shallow Circular Silo

Grain is an important strategic resource on which a country depends for its survival,especially with the global outbreak and spread of the 2019-n Co V epidemic situation since this year,there has been endless concerns and discussions about global grain security.The safety of grain storage plays an important regulatory role in reducing fluctuations in grain supply,improving people’s livelihoods and promoting social stability in a country.Temperature is an important indicator in the grain storage process,and mechanical ventilation is the conventional method of preserving the quality of grain in storage in order to ensure grain security.Grain porosity is a key parameter for grain in storage,the porosity of the grain pile changes during storage,influencing the value of the side pressure of the silo wall and the mechanism of its generation,as well as a key parameter for grain storage and ventilation.As a new silo type,the proportion of squat silos applied in China’s grain silos is increasing,so it is of great practical significance to study the impact of radial ventilation process and variable porosity distribution on grain storage in squat silos.This paper firstly introduces several squat silos ventilation methods,selects the radial ventilation process according to the principles of fluid mechanics and other principles,uses a combination of numerical simulation and experiments to optimize the process of radial ventilation of squat silos,and compares and analyses the predicted data of airflow distribution and temperature change of the ventilated grain pile by numerical simulation.At the same time,a study was carried out on the variable porosity model for grain piles,comparing the temperature variation law of variable porosity grain piles during vertical and radial ventilation of squat silos,and verifying the correctness of the variable porosity model through experiments.Its main research contents are as follows:1)The severity of grain security is analyzed and the basic properties of soybeans and the structural characteristics of squat silos and the principles of ventilation methods are introduced;research is conducted on radial ventilation of squat silos and an optimization scheme for the new ventilation process of squat silos is proposed.2)This paper analyses the theoretical basis of radial ventilation and introduces the heat and moisture coupling heat and mass transfer in porous media,the theory of computational fluid dynamics and the physical parameters of air and grain piles during the ventilation process.Based on these theories,a mathematical and physical model for radial ventilation of squat silos is established,and the temperature changes of radially ventilated grain piles are simulated and predicted under different structure sizes of air collection ducts,different heights of vertical branch ducts,different ventilation volumes and different ventilation directions,and the optimal process solution for radial ventilation of squat silos is obtained by comparing the cooling rate,uniformity of ventilation and modification costs.3)A study was conducted on the variable porosity model for squat silos.Based on the distribution law of grain pile porosity and the distribution of impurities in the real bin,a non-linear equation formula for the relationship between grain pile porosity and location was determined.Using the numerical simulation method for vertical and radial ventilation of squat silos with variable porosity model of grain pile,the simulation prediction data of static pressure distribution,airflow movement and temperature field of grain pile were obtained,and the effect of variable porosity on temperature change of grain pile was concluded,and the correctness of variable porosity model was verified by experiment.4)Finally,a small experimental squat silos was built for radial ventilation experiments,and the results of this experiment were compared and summarized with the numerical simulation prediction data to verify the feasibility and superiority of radial ventilation for squat silos,and the variable porosity model for squat silos grain piles was obtained.The radial ventilation has no ventilation dead space,better grain temperature uniformity and lower energy consumption;the proposed model of variable porosity of grain piles can reduce the occurrence of abnormal grain conditions,improve the safety and stability of grain storage and reduce waste;and some outlook and suggestions on radial ventilation of squat silos are presented.