Multi-field Coupled Numerical Simulation Of Bulk Grain Bulk In Flat Warehouse Based On COMSOL

The total grain output is as high as 500 million tons in China annually.Insect pests,heap fever and mildew of grain are three main causes of loss of grain storage.Temperature and moisture in wheat grain bulk are important influence factors of grain mildew,grain heats and insect pests.Based on the finite element software COMSOL Multiphysics,the distribution of micro-air flow,temperature and humidity in the static storage of wheat grain bulk is studied in this paper for improving the safety level of grain storage.The change of temperature,humidity and moisture in the process of cooling,drying and ventilation of wheat grain bulk in large warehouse is also studied in this paper.The main research work of this paper is as follows:(1)The basic parameters of wheat and wet air were determined.Based on the self-designed pressure-porosity testing device,the related experiments of wheat grain bulk under different pressures were carried out,and their laws were obtained.The pressure-porosity function model of wheat grain bulk was built.The model built is applied to the numerical simulation of the static storage process of the wheat grain stack test warehouse and the cooling,drying and ventilation process of the wheat grain bulk in the large warehouse.(2)According to the laws of mass conservation,energy conservation and momentum conservation,the mathematical models of static storage process of wheat grain bulk and cooling,drying and ventilation process of large warehouse were established.(3)Through the static storage mathematical model,the static storage process of wheat grain bulk in test warehouse was simulated,and the variation rules of micro-airflow field,water vapor partial pressure field,temperature and humidity field with static storage time were obtained.The results of numerical simulation are verified by the measured data of test warehouse.The simulation results show that temperature gradient is the driving force of the temperature front.The distribution of micro-airflow between the pores of wheat grain stack is mainly caused by temperature gradient of wheat grain bulk.The formation of water vapor partial pressure gradient of wheat grain stack is consistent with the direction of temperature gradient distribution.The relative humidity field of wheat grain bulk is negatively correlated with the distribution law of temperature field.(4)The cooling,drying and ventilation processes of a large warehouse in Shanghai were simulated by using the cooling,drying ventilation mathematical models.The distributions and variations of pressure field,velocity field,temperature field,humidity field and moisture field were obtained.The results of simulation were compared with the measured data of grainmonitoring system in the large warehouse.The numerical simulation results are consistent with the temperature variation laws of the wheat grain bulk in the warehouse.The simulation results show that there are obvious stratification phenomena in the distribution of pressure field,temperature and humidity field,moisture field and so on.There is an obvious cooling front in the cooling ventilation process,and an obvious drying front in the drying ventilation process.The average temperature and water content of the whole wheat grain bulk decrease gradually as ventilation time increase.The cooling rates and precipitation rates decrease gradually as ventilation time increase.Temperature and moisture in wheat grain bulk tended to the balances gradually.