| With the rapid development of facilities horticulture in china, a large number of horticultural crops straw and stubble are produced to pollute the environment and increase the pests and diseases. It is found that crushing nearby, mixing and fermentation are the effective methods to deal with the horticultural crops at the low cost. One of the key issues that need to be solved is how to realize the efficient mixing of straw and fermentation strains. In this paper, the main research object is the crushed material of tomato straw as the matrix material. According to the technology of the mixture of tomato straw crushed and fermentation bacteria and the requirement of energy saving and high efficiency, the research on vertical spiral belt mixing method and its mechanism system are conducted to provide theoretical basis for the research and development of the special equipment for the high efficiency mixing of the straw crushed and fermentation of horticultural crops. The main research contents and conclusions are as follows:(1) Vertical spiral belt mixing method and its theoretical researchAccording to the existing solid mixing equipment selection decision logic, the paper proposes a vertical spiral belt mixing method and carries out theoretical analysis and research to deal with the problem of the mixture of tomato straw crushed and fermentation bacteria. Firstly, the structure model of vertical spiral belt type mixing equipment is designed, which is composed of a material bucket and a vertical inner and outer double helix mixing blade; Then the mixing process and mechanism of vertical spiral belt type mixing equipment are analyzed qualitatively, It is found that the mixed material in the whole area of the material barrel is mainly mixed with convection, which is accompanied by the complex process of shear mixing and diffusion mixing, and the generation of a large number of turbulent phenomena. Then do the dynamic analysis of the mixed materials to find the main performance and influence factors of the mixing blades. It is found that the radius, the pitch and the rotational speed of the mixing blades have a nonlinear effect on the axial velocity of the mixture. Finally through the stirring power calculation of the material mixing, it is V found that the height of the packing, the width and the rotation speed of the mixing blades have a linear increasing influence on the power of the power of the mixed material, and the radius of the mixing blades have a two linear increasing effect on the power.(2) Measurement and experimental analysis of the characteristics of tomato straw crushed materialResearch on the measurement of tomato straw crushed material in mature period which is obtained by the 3FC-500 type straw cutting and crushing mill. Observe its geometry characteristics and simply to a cylindrical, measured the length of the mean of 6.93 mm, diameter of 2.09 mm. Use TA.XTPLUS test instrument drawing module suite, shear module kit and friction module kit to measure tomato straw crushed material that the elastic modulus is 235.2Mpa, the shear modulus is 538 Mpa, the static friction coefficient between tomato straw material is 1.17, the dynamic friction coefficient between tomato material is 1.02, the static friction coefficient between the crushed material and steel is 0.97, the dynamic friction coefficient between the crushed material and steel is 0.84. The average moisture content of tomato straw crushed material measured by MJ33 moisture measuring instrument is 22.61%. The JA31002 electronic balance was used to measure the bulk density which is 188.02 kg.m-3, and the porosity which is 58.56% by filling method and calculate the true density is 188.02 kg.m-3. High speed camera technology is used to measure the recovery coefficient of the tomato straw crushed material which is 0.2029 and the recovery coefficient between the straw and steel is 0.1935. The characteristics of these straw crushed material provide the basis and foundation for further research on vertical spiral band mixing using discrete element simulation.(3) Simulation and experimental study of vertical spiral belt mixing using discrete element methodCreate the discrete element model and compare the simulation results with the actual test by means of orthogonal test to determine the suitable test parameters for the simulation for tomato straw crushed, The static friction coefficient of particles is 1.1, the particle density is 450 kg.m-3, the viscosity coefficient of particles is 2000. Carry on the discrete element simulation test:(1) Through the simulation of the motion process of a single material particle, it is found that the material particles in the center region of the upper surface of the material particle swarm spiral down along the spiral blade and the speed is stable; the material particles in the radial external region of the bottom area of the material barrel oscillation rise along the outer spiral blade and the speed is slow.(2) Through the simulation of the axial average displacement of multiple material particles in radial center region under different factors, it is found that due to the influence of diffusion mixing, the axial average velocity of the multiple material particles is much slower than that of the single particle. In the case of different rotational speed, the order of the axial mean displacement is that: 30r/min>60r/min>90r/min. In the case of different pitch, the order of the axial mean displacement is that: 275mm>150mm>400mm. In the case of different packing height, the order of the axial mean displacement is that: 400mm>360mm>440mm.(3) Through the simulation of axial average displacement of multiple material particles in radial outward edge region under different factors, it is found that the axial rise mean displacement of multiple material particles is less affected by diffusion mixing. In the case of different rotational speed, the order of the axial mean displacement is that: 90r/min>60r/min>30r/min. In the case of different pitch, the order of the axial mean displacement is that: 150mm>275mm>400mm. In the case of different packing height, the order of the axial mean displacement is that: 400mm>360mm>440mm.(4) Study on the mixing performance of vertical spiral band under different factors, through the simulation of the mixing process of tomato straw crushed and the mixture of straw crushed material with fermentation bacteria by single factor test method. It is found that with the blade pitch increasing,the mixing uniformity is improved, the power increases firstly and decreases then;with the rotational speed of blade increasing,the mixing uniformity is improved as the same, the power increases substantially;with the filler height increasing,the mixing uniformity is decreased, the power increases.(4) Prototype trial manufacture and experimental researchDesign and set up a vertical spiral belt type mixing device for testing. According to the test requirement, the device can precisely control the rotation speed, reclaim and feed the material, rapidly replace the mixing blades and collect the real time torque Carry out experiments with a single factor of the pitch, the rotational speed and the packing height using this test device. Carry out regression orthogonal test with multiple factors of the pitch, the rotational speed and the packing height. The research results show that with the blade pitch increasing,the mixing uniformity is improved, the power increases firstly and decreases then;with the rotational speed of blade increasing,the mixing uniformity is improved as the same, the power increases substantially;with the filler height increasing,the mixing uniformity is decreased, the power increases. There is a linear relationship between the mixing uniformity and the pitch, the packing height and the rotation speed. The important order of the effect for the mixing uniformity is :the blade pitch,the rotational speed of blade and the filler height. The mathematical model of mixing uniformity and structure and working parameters is constructed. Through the solution and optimization of the Math CAD software, the material mixing uniformity is 4.3 when the height of the filling material is 440 mm, the speed is 30r/min, and the pitch is 400 mm. It reveals its efficient mixing mechanism. |
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