Research On The Dense Forming Mechanism Of Salix Fine Particles Based On Discrete Element Method

Salix as an energy plant in the desert area of northwest China,its tiny branches are important raw material resources for the development of biomass forming fuels.However,most of these resources are wasted due to the use of suffering,because this type resources possess these disadvantages of inconvenient transportation and high transportation costs.Therefore,the dense processing of salix twigs resources is imminent.This paper analyses the pressure transfer mechanism and force chain evolution mechanism during salix twigs particles compact forming process.It aims to further analyze the transmission path of the external load during salix twigs particles compression process,deepen the cognition of salix twigs particles dense forming process,and provide a theoretical basis for the promotion of biomass.This paper mainly analyzes the salix particles micromechanical behavior and forming mechanism of single mode under one way compression.Discrete element method is used to simulation the dense forming process,which suitable for bulk materials numerical simulation,and the dense forming test of material moisture content,compression speed and mold pore size are carried out on an electronic universal material testing machine to analyze the influence of single factor on forming specific energy consumption and product density.The experimental date are compared with the simulated date and hypothetical test to verify the validity of the discrete element model established in this paper.According to the variation trend of compression force,the whole compact process is divided into three stages: loose stage,compaction stage and conformal stage,and the distribution law of each stage contact force is analyzed.The evolution process of axial and circumferential force chain is obtained through the contact force values in each measuring block.The macroscopic morphology of the sample is illustrated by force-chain distribution.According to the trajectory of the individual particle,the motion characteristics of different sizes particles are obtained.By changing the influence parameters of different molding processes and comparing the changes of voidage and force chain number under different parameters,the effects of different factors on forming quality and energy consumption are obtained.The results show that the contact force between plunger bottom and particles fluctuating increase with the plunger depth.At each stage,the contact force distribution law of each type do not change significantly,and showing an gradually decreased and then tended to be stable.The strong-chain experiences the process that it is first transmitted from top to bottom,then uniformly distributed after reflection,and then transmitted from both ends to center and finally evenly distributed in axial direction.The strong-chain evolves from the uniform distribution at the beginning to the penetration from edge to center and finally to the uniform distribution in circumferential direction.When dense particles are extruded,the strong-chain mainly distributes outside of molding chamber.The result not only confirms that the friction between particles and mold is larger than that between particles,but also verifies the axial unevenness and circumferential delamination of biomass particle fuels during the test.The hardness showes a gradual increase from 93.4 HBW to 148.1 HBW from center to outside measured by using a test sample on a Brinell hardness machine.The result also reflects the effect of force-chain evolution.During the compression process,the trajectory of large particles is quasi-linear,and the trajectories of small particles are first linear and then rotated.The small size spherical particles have a better forming effect,but the energy consumption is increased.It is an effective method to simulate the dense forming process of salix particles by discrete element method,and it provides a theoretical basis for the research and development of biomass.