Experiment And Simulation On Local Temperature Control Of Squat Silo Grain Storage

In the process of long-term grain storage,due to the low heat conduction coefficient of grain,the phenomenon of"hot skin and cold core"often occurs with the change of external temperature in the grain bulk.How to reduce the impact of this phenomenon on the grain quality is a big problem in storage process.In order to solve this problem,warehouse managers mainly use comprehensive ventilation to control the temperature of the grain bulk,but the expenditure on grain storage rises sharply due to the large energy consumption of this ventilation mode.According to previous research and actual warehouse data,it is found that the high temperature with condensation in grain bulk appears mostly near the warehouse wall.If the temperature of the condensation-prone position can be controlled by a targeted ventilation,the cooling cost on stored grain can be effectively reduced.Firstly,a top-supply and down-return targeted ventilation with temperature control system was set up to control the temperature of the condensation-prone position in the bulk.The temperature and humidity changes in the grain bulk were taken as the analysis parameters.A series of comparative experiments were carried out under different working conditions for the temperature control system.The results showed an obvious effect on temperature control in the condensation-prone position through the top-supply and down-return targeted ventilation.From the perspective of energy saving,there’s an optimal ventilation volume for local temperature control.That is,when the ventilation volume is higher than 667 m~3/h,the targeted ventilation cannot generate more effective temperature control in the grain bulk with the volume increasing.In the process of temperature control,the condensation-prone position occurred in the upper area of the bulk.Through the targeted ventilation,the risk of condensation was reduced in the position near the wall of the storage.Furthermore,through Gambit 2.4.6,a geometric model with a size equal to the experiment one was established,and numerical simulations under different parameters were carried out by Fluent 19.0.The results showed that when the ventilation volume is 667 m3/h and the supply air temperature is 15℃,the duration should be set within 8.83～28.83 h.Considering of the shortcomings in the ventilation and cooling process for practical application,an optimization was taken on the structure of the targeted ventilation and temperature control system.With the optimized system,a series of performance parameters were calculated.The results showed that the flow rate of the condensation-prone position was increased by 30%,and the changing rate of that is increased by 32%.The effect on temperature control was enhanced by the optimized system.Moreover,an analysis of dimensionless speed(ζ)and dimensionless excess temperature(θ)was carried out.Under the constant dimensionless parameters(ζ=4666.38,θ=0.66),the optimized targeted ventilation and temperature control system was used to simulate the effects in practical application.The calculation results showed that the temperature control can be expected through the targeted ventilation system for the condensation-prone position in squat silos.Finally,the prospect of the top-supply and down-return ventilation system was discussed and the further efforts on research were suggested.