Study On Effects Of Discharge Hopper Geometric Parameters Flow Field Characteristics Of Free-falling Particle Stream

Duning the process of industrial production, transportation and unloading of buik materials (such as sand, coal and food particles, etc), it can be seen everywhere that free-fall motion of granular flow; in the process of free-fall motion, due to the impact of gravity, buoyancy, the frictional resistance between particles, and the force ambient air and particles, some fine particles are attracted to flow field of particle beam by ambient air due to the unbalance force, then a particle stream was formed. In the process of particle stream free-fall motion, the dust escape into the surrounding environment when particle stream confronted at the bottom of the receiving device due to the influence of gravity of material itself, which caused air pollution as well as a huge damage on human health and mind.The topic tracked the international forefront as well as for practical application, which took discharge hopper structure as research object and used EDEM particles element software and Fluent software conduct the numerical simulation on the relationship between bulk material when the bulk materials fell freely though discharge hopper and ambient air and physical parameters of discharge hopper as well as physical parameters of particulate material. Based on the multi-functional experimental platform of the relationship between the existing free falling particles and the environment air, by improving the discharge hopper structure (angle of inclination, initial drop diameter), the dust production was real-time measured when particle stream falling freely in ambient air, which was in order to obtain discharge hopper structure with minimum amount of dust production. The following conclusions were acquired through numerical simulation and experimental research:(1) The numerical simulation results showed that:a) The mass flow Ws of material decreased with increasing of tilt angle、internal friction coefficient μ and wall friction coefficient μw. When 53°<a< 55°, the mass flow Ws of material reduced greatly with increasing of tilt angle α; when 55°<α< 60°, the mass flow Ws of material reduced a smaller range with increasing of tilt angle α. The relationship between the mass flow Ws of material and the internal friction coefficient μ could be expressed as follows:Ws= 195.83×exp[0.095/(μ+0.176)], the relationship between the mass flow Ws of material and the wall friction μw could also be expressed as follows: Ws=322.5-416.3μw+736.2/μw2-638.6/4+211.4μw4b) The concentration of particles in the calculation area increased with increasing of initial drop diameter D and particle flow velocity v. When the initial drop diameter was 0.01m, the minimum the concentration of particles was and when the initial drop diameter was 0.03m, the maximum the concentration of particles was. In the initial stage of the falling of particle, the particles flow velocity increased as the drop height increases, when the drop height increased to a certain value, the particle flow velocity tended to be stable. When the initial drop diameter was 0.01m, the particle flow velocity vmax was 2.28m/s, but when the initial drop diameter was 0.03m, and the particle flow velocity vmax was 3.5m/s.c) The diffusion radius of particles in the calculation area decreased with increasing of particle density. In the initial stage of the falling of particle, the particles flow velocity increased as the drop height increased when the drop height increased to a certain value and the particle flow velocity tends to be stable. The particle flow velocity increased with increasing of particle density, when the particle density was 790kg/m3, the particle flow velocity was 1.21m/s. However, when the particle density was 2590kg/m3, the particle flow velocity was 2.83m/s.d) The diffusion radius of particle in the calculation area decreased with increasing of particle size and the residence time of particle decreased at the same time. When the particle size was 186.42 X 10"6m, the degree of mixing between particle and ambient air was better, and the residence time of particle in the calculation area was longer, and diffusion radius was larger. However, when the particle size was 767.13 X 10-6m, the residence time of particle in the calculation area was shorter, and diffusion radius was smaller. In the initial stage of the falling of particle, the particles flow velocity increased as the drop height increased, when the drop height increased to a certain value, the particle flow velocity tended to be stable. The particle flow velocity increased with increasing of particle size, when the particle size was 186.42 X 10"6m, the particle flow velocity was. However, when the particle size was 767.13 X 10"6m, the particle flow velocity was.(2) The experimental results showed that the discharge hopper with various structures (inclination angles) had its proper using scope. In practical engineering application, a suitable discharge hopper with proper structure should be selected. For example, the angle of the discharge hopper which made the dust production was different. When the angle of the discharge hopper was 58°, the dust production for the sand particles was the least, and when the discharge hopper was 57 °, the dust production for the corn particles was the least. However, when the angle of the discharge hopper was 54°, the dust production for the silica particles was the greatest.(3) By comparing and analyzing of experimental data and simulation data, it could be found that experimental results of speed in the process of fall was basically consistent with the simulation results. Therefore, experimental research and numerical simulation could be used to study the influence that structure of the discharge hopper on the free-fall particle flow field characteristics and the dust production.(4) Using mathematical methods, a large amount of experimental data were fitted linearly by using of the theorem and multiple linear regression analysis. Finally, empirical formula among the dust production of free falling particle stream, the initial drop diameter, the drop height, the particle density, the air density, the particle size, and the inclination angle of discharge hopper was aquired as follows: G=228e20.D1.55648.dp-0.30275.H1.85923ρp1.31621·ρa-1.31621.α-7.05578...