| Reducing the amount of loss during grain storage is the main problem in warehousing.There are many factors affecting it.Controlling the temperature of the grain storage in the storage is an effective method to reduce the amount of grain loss.In recent years,the method of controlling the temperature of the grain pile is mainly to reduce the temperature by mechanical ventilation in the silo.However,the above method has the following deficiencies in the implementation: the mechanical ventilation parameters in the silo are not easy to achieve targeted local control,and the mechanical ventilation inside the grain pile has a great influence on the humidity of the grain pile,and it is difficult to ensure the quality of the stored grain pile.80% of the externally introduced heat that causes the temperature rise of the grain pile comes from the roof of the silo.Insulating the roof of the silo is an effective measure to suppress the temperature rise of the stored grain pile in the active grain silo.In view of the temperature situation of the grain pile during the storage in the hot season of the large warehouse,this topic designed a forced circulation roof insulation system,which uses an insulation system of overhead layer system combined with mechanical ventilation to reduce the heat transferred from the top of the warehouse and reduce the grain pile.The temperature is controlled within the range of "normal temperature storage"(?25 ° C),and the storage period is extended,so that the grain heap can safely pass the high temperature season.The subject designed a simulation test platform for a large warehouse with a volume of 1.2m3.The experimental variables are the net height of the overhead layer and the ventilation in the layer.The temperature control equipment with reasonable cooling capacity and accounting radiation is designed to control the temperature of the experimental warehouse and make a determination.Duration heating experiment with constant radiation.This paper analyzes the thermal insulation effect of the system through simulation experiments,numerical calculations and dimensionless analysis.The temperature-increasing experiments and numerical calculations are carried out on the simulated experimental warehouses with different cross-sections of overhead floors,and the effects of structural parameters and ventilation conditions parameters(double-skin roof height,air volume in the floors)on the forced circulation roof insulation performance are analyzed;The simulation experiment chamber of the cross-section double-skin roof is used for temperature rise experiments and numerical calculations,and the degree of optimization of the thermal insulation performance of the double-skin roof by the increase in flow velocity caused by the tapered opening design is analyzed.The realization results show that the experimental study is carried out with the heating process of fixed length and constant radiation,and the effect of the inlet section of turbulent heat transfer in the dominant wind direction can improve the heat exchange efficiency,effectively reduce the heat accumulation in the silo,and control the temperature of the grain pile in the silo.It is within the range of normal temperature storage,and expanded the scope of "cold core" of grain pile.For the simulated bunker warehouse,under the design air volume conditions,there is a more suitable height of the double-skin roof to match it,so that the flow formed in the double-skin roof can effectively take away the heat introduced by the board,and block the transmission of the house facing the warehouse.heat.Based on the experimental platform of the simulated bunker warehouse,a threedimensional equal-scale mathematical model is established,the storage grain pile is defined as a porous medium,the UDF file is used to define the ambient temperature and the roof temperature,and multiple sets of calculations are established by changing the inlet wind speed and the slope of the overhead plate.The model is given the same boundary conditions for different working conditions models;based on the unsteady state algorithm,combined with the k-? model in fluent to numerically solve the temperature field and velocity field in the simulated cottage,and analyze the inlet wind speed and the height of the double-skin roof.Influence of thermal insulation performance;the error of numerical simulation and simulation experiment results is less than 10%,which verifies the rationality of numerical simulation parameters.Through simulation,the influence of design variables on the thermal insulation performance of the double-skin roof is determined,and the parameter limits and relevant characteristic data about the design of the double-skin roof are obtained.According to the simulation experiments and calculation results,the experimental variables that affect the insulation performance of the double-skin roof are classified into temperature parameters,height parameters,speed parameters and natural convection parameters.According to the numerical calculation,the insulation coefficient is expressed in a dimensionless criterion.The formula can be The project provides a reference. |
PDF Full Text Request