Based On Curved Hopper To Improve Particle Flow Characteristics In Silo Discharge

Silos are widely used in the storage of particulate matter in various industries such as agriculture,food and chemical industry.In the process of silo discharging,due to the complex flow phenomenon of bulk materials,it is easy to produce engineering problems,such as flow rate fluctuation,discharging flow pattern change and even blockage,which will bring great hidden dangers to the safe operation of the silo.Because of its constant contraction rate,the curved hopper is used to prevent blockage in order to obtain a stable flow rate.However,the design of curved hopper mostly depends on discharging experiment,and the effect of contraction rate on the complex motion behavior of particle system is not clear.Clarifying the flow characteristics of particles in the silo discharge process not only has important engineering significance for the design and optimization of curved hopper,but also enriches the theory and method of gravity-driven discharge flow in silos.This paper takes the discharging process of silo with curved hopper as the research object,combines the advantages of theoretical,experimental and simulation,and combines with the grain physical properties and silo structural properties,the critical flow conditions of the curved hopper,the effect of contraction rate on the particle flow characteristics,and the applicability of curved hopper to the discharging process of grain were studied respectively,and the discharging performance was compared with that of the traditional hopper.The main conclusions of the study are as follows:(1)The critical flow condition of curved hopper is clarified.By using the method of theory with experiment,the prediction model of critical orifice size of curved hopper is established.The model takes into account the effects of contraction rate,material properties and arch structure on the critical hole size,which can provide a theoretical basis for the selection of curved hopper orifice size of the curved hopper.(2)The influence of the contraction rate on the flow characteristics of particle discharge is clarified.With the contraction rate increases,the critical height of flow transition rises,the velocity of particles decreases,the porosity decreases,the discharge flow rate decreases,and the discharge fluctuation increases.Through the analysis of the flow characteristics,it is found that there is a critical value in the range of contraction rate.In this working condition,when the contraction rate is greater than 0.11,it no longer has a significant effect on improving the discharging fluidity of particles.Finally,the Froude number is used to quantitatively evaluate the flow characteristics,in which the power function can be used to describe the relationship between contraction rate and flow characteristics.(3)It is proved that the curved hopper can obviously improve the discharging fluidity of all kinds of grains.Compared with the traditional hopper,the discharge rates of grains in the curved hopper are higher and the discharge fluctuations are smaller;the curved hopper can obviously improve the discharging fluidity of all kinds of grains.The discharge flow rate of grains in the curved hopper is faster,and the discharge fluctuation is smaller.The curved hopper has the most significant effect on improving the discharging fluidity of irregularly shaped particles,and the grain which is similar to a perfect sphere and has a small volume density has the best discharging fluidity.When the ratio of hopper height to silo inner diameter reaches 0.6,the effect of curved hopper on improving particle discharging fluidity reaches the peak.