Simulation Experiment And Numerical Simulation Of Ventilation System Above The Grain Bulk For Insulating In Flat Warehouse

China has always attached great importance to people’s livelihood issues.Since2004,the grain production in China has achieved “17 consecutive harvests”.This year’s grain output is expected to continue to exceed 1.3 trillion catties.The rations will be fully self-sufficient and the self-sufficiency rate of grains has been maintained at 95%.While the grain production is in good form,there are certain problems with grain storage.The Food and Agriculture Organization of the United Nations report shows that the global grain loss rate is 20%.China’s domestic food loss exceeds 35 million due to poor storage conditions after grain production and poor equipment each year.Improving grain storage conditions and reducing storage losses are equivalent to increasing actual grain output.At present,most of the warehouses in my country are grain warehouses.This type of warehouses were designed and constructed earlier.With the development of society,they can no longer meet the needs of energy-saving grain storage and "green grain storage".In summer,as the outside temperature rises,the warehouse temperature and grain temperature of the grain warehouse also rise,thus endangering the quality of food and the safety of storage.Because of the large radiation area,the roof of the grain warehouse is the main source of heat introduced from the outside.Therefore,if the heat introduced from the roof of the warehouse can be isolated,food security can be ensured to a large extent.Mature roof insulation technologies include green roofs,water-film roofs,overhead roof layers and indoor ceilings.However,because granary buildings have special requirements for airtightness,commonly used roof insulation renovation technologies are difficult to use in flat houses.Some storage sites in southern my country do not carry out roof construction,but from the perspective of heat insulation on the surface of grain piles,some grain storage depots adopt the technology of cold airbags on the surface of grain piles,that is,to lay double-layer sealing films on the grain piles.The circulating cold air is introduced to dynamically take away the heat insulation device from the roof of the silo.The excellent heat insulation of the cold airbag technology is supported by measured data and numerical simulations.However,due to material reasons,the real warehouse cold airbag system used in the warehouse has caused irregular processes in the system,making it difficult to quantify the factors affecting the heat transfer effect..The system data in the bungalow only measured the temperature state of the grain pile under a single working condition,and did not design variable experiments and rules for the parameters that affect the system’s thermal insulation performance.The numerical simulation results performed by previous scholars also lack experimental verification.This article is based on the cold airbag heat insulation technology on the surface of grain piles used in the southern grain storage depot,and proposes a thermal insulation and temperature control system for the surface of the grain pile in the flat warehouse after improvement.A heat insulation temperature control system test bench is designed for the heat insulation temperature control system.The test bench includes a test chamber with a capacity of 1m3,a heat insulation temperature control system,a refrigeration device,a measuring device,an external climate control system and a test grain pile.During the test,the height,air supply speed and air supply temperature of the system can be adjusted to obtain the temperature data of grain piles under different working conditions,and the law of the thermal insulation performance of the system changing with the working conditions can be summarized.The error of the system measurement data is an inevitable measurement factor.The accuracy is ±0.003℃ for temperature and ±0.8% for humidity,which is better than the specified value of the specification and meets the standard of use.This paper uses CFD software to establish the model and numerical simulation of the test chamber,and the correctness of the model is verified by the measured data.The test warehouse and the flat warehouse are compared and analyzed,and the test warehouse model is combined to obtain the flat warehouse model for the numerical simulation of the flat warehouse.Based on the actual situation,a certain grain warehouse in Zhengzhou is selected for model establishment and numerical analysis,and the optimal working condition interval of the insulation system is given by using the simulation data of multiple sets of insulation temperature control system of the warehouse.At the same time,combined with energy consumption,the best value of working conditions is given in terms of economy.For the problem of convective heat transfer,the core purpose is to obtain the dimensionless criterion correlation.This paper analyzes the heat transfer process of the grain pile in the single-story warehouse,and obtains a dimensionless number describing the thermal insulation performance of the system.Three working condition parameters that affect the thermal insulation performance of the system: air supply speed,air temperature and system height are transformed into dimensionless Reynolds number,dimensionless temperature and dimensionless height.46 sets of numerical simulations under different working conditions are carried out,and the non-dimensional thermal insulation performance of the system in the simulation data is integrated with the non-dimensional number of the working conditions to obtain the thermal insulation criterion correlation formula.It can provide a certain reference for the design of heat insulation system under different conditions.