CFD-Based Analysis And Optimization Of Mechanical Aeration In Commercial Warehouse-Type Grain Bin

As an important industry technology and energy-saving engineering,mechanical aeration is widely used in grain storage in China.It is necessary to control the internal temperature and moisture of paddy bin by mechanical aeration,duo to the temperature and moisture are the most important factors which affecting the stability in the paddy storage.Based on theory of heat and mass transfer in porous medium,this paper used a CFD(computational fluid dynamics)commercial software Fluent 14.0 to numerically analyze the process of the aeration cooling.The distribution of temperature in different layer at grain bin,different types of aeration system and accuracy of the model were investigated.Meanwhile,the improvement about the mechanical aeration system were optimized,which aim to provide the technical guidance for warehousing-type grain bin.Results of this research involve that:1.Study on the physical parameters and moisture diffusion dynamic characteristic of paddy kernel.The physical parameters of different moisture content paddy were analyzed,and the dynamic parameters of paddy moisture diffusion ere determined according to the thin layer drying experiment.The results shown that the air temperature was higher and wind speed was faster,the speed of paddy moisture decrease was larger,and the effective moisture diffusion coefficient was higher,nearly 10-12 m2/s.2.Establishment and solution of heat and mass transfer model of paddy bulk.Based on the heat and mass transfer theory and FVM(finite volume method)theory,a 3-D warehouse-type paddy bin model was set up,which the paddy bulk considered as a uniform porosity zone.However,a user-defined function(UDF)was compiled for describing the coupling transfer mechanism of moisture and energy for paddy bulk,and a serials equations about the mass,energy and momentum for paddy bulk were successfully solved by using Fluent.3.Simulation about mechanical aeration for paddy bulk in warehouse-type bin based on the experimental.The gradient for the temperature and moisture content in paddy bulk after 30 h cooling aeration in warehouse-type grain bin were confirmed by both simulation and experiment.The difference between the simulated value and experimental were lower than 0.8 °C and 0.5%,respectively.4.CFD-based analysis of temperature decrease by comparison of different mechanical aeration strategies.There are three new types of cooling aeration system were supposed based on ground-cage aeration system(GCA),which are extended-cage aeration(ECA),assisted-intubation cage aeration(AICA)and double ground-cage aeration system(DGC),respectively.The result showed: DGC,ECA and AICA performed better,and the difference about the top layer of the paddy bulk were less than the GCA.Meanwhile,the DGC preformed a best temperature uniform and the most significant cooling results while after 30 h mechanical aeration between four types strategies.Conclusion,CFD-based analysis model about the distribution in warehousetype grain bin could successfully describe the changes under the reasonable mass,energy and momentum transfer equation solved,and also the simulation could provide more direct analysis of temperature and moisture distribution in paddy bulk.Hence,this study suggests that CFD-based simulation technology should be more widely used in grain industry or optimization of mechanical aeration system.