The objective of this study is analysis of heat-up process of wet woody particles on a backward acting grate including dynamics motion investigation by implementing XDEM （extended discrete element method） as a novel...The objective of this study is analysis of heat-up process of wet woody particles on a backward acting grate including dynamics motion investigation by implementing XDEM （extended discrete element method） as a novel approach. In this method, the particles are resolved as the discrete phase （individual elements） coupled via heat, mass and momentum transfer to the continuous gas phase. The temperature of particulates along the backward acting grate is investigated by evaluating effects of operating parameters such as bar amplitude and period. Furthermore, the bar motion has effects largely on the heat-up process of the packed bed on the backward acting grate which is considered here as well. In other words, motion of particles caused by bar motion influences the heat transfer of particles and totally the packed bed. In fact, the particles＇ heat-up is performed by a radiative heat flux facing the packed bed surface so that heat transfer of particles as radiation and conduction with surrounding particles is taken into account in addition to convection heat transfer between particles and surrounding gas phase.展开更多
Numerical simulation of gas-solid flow behaviors in a rectangular fluidized bed is carried out three dimensionally by the discrete element method (DEM).Euler method and Lagrange method are employed to deal with the ga...Numerical simulation of gas-solid flow behaviors in a rectangular fluidized bed is carried out three dimensionally by the discrete element method (DEM).Euler method and Lagrange method are employed to deal with the gas phase and solid phase respectively.The collided force among particles,striking force between particle and wall,drag force,gravity,Magnus lift force and Saffman lift force are considered when establishing the mathematic models.Soft-sphere model is used to describe the collision of particles.In addition,the Euler method is also used for modeling the solid phase to compare with the results of DEM.The flow patterns,particle mean velocities,particles' diffusion and pressure drop of the bed under typical operating conditions are obtained.The results show that the DEM method can describe the detailed information among particles,while the Euler-Euler method cannot capture the micro-scale character.No matter which method is used,the diffusion of particles increases with the increase of gas velocity.But the gathering and crushing of particles cannot be simulated,so the energy loss of particles' collision cannot be calculated and the diffusion by using the Euler-Euler method is larger.In addition,it is shown by DEM method,with strengthening of the carrying capacity,more and more particles can be schlepped upward and the dense suspension upflow pattern can be formed.However,the results given by the Euler-Euler method are not consistent with the real situation.展开更多
文摘The objective of this study is analysis of heat-up process of wet woody particles on a backward acting grate including dynamics motion investigation by implementing XDEM （extended discrete element method） as a novel approach. In this method, the particles are resolved as the discrete phase （individual elements） coupled via heat, mass and momentum transfer to the continuous gas phase. The temperature of particulates along the backward acting grate is investigated by evaluating effects of operating parameters such as bar amplitude and period. Furthermore, the bar motion has effects largely on the heat-up process of the packed bed on the backward acting grate which is considered here as well. In other words, motion of particles caused by bar motion influences the heat transfer of particles and totally the packed bed. In fact, the particles＇ heat-up is performed by a radiative heat flux facing the packed bed surface so that heat transfer of particles as radiation and conduction with surrounding particles is taken into account in addition to convection heat transfer between particles and surrounding gas phase.
基金Supported by National Natural Science Foundation of China(51006106)National High Technology Research and Development of China 863 Program(2006AA05A103)
文摘Numerical simulation of gas-solid flow behaviors in a rectangular fluidized bed is carried out three dimensionally by the discrete element method (DEM).Euler method and Lagrange method are employed to deal with the gas phase and solid phase respectively.The collided force among particles,striking force between particle and wall,drag force,gravity,Magnus lift force and Saffman lift force are considered when establishing the mathematic models.Soft-sphere model is used to describe the collision of particles.In addition,the Euler method is also used for modeling the solid phase to compare with the results of DEM.The flow patterns,particle mean velocities,particles' diffusion and pressure drop of the bed under typical operating conditions are obtained.The results show that the DEM method can describe the detailed information among particles,while the Euler-Euler method cannot capture the micro-scale character.No matter which method is used,the diffusion of particles increases with the increase of gas velocity.But the gathering and crushing of particles cannot be simulated,so the energy loss of particles' collision cannot be calculated and the diffusion by using the Euler-Euler method is larger.In addition,it is shown by DEM method,with strengthening of the carrying capacity,more and more particles can be schlepped upward and the dense suspension upflow pattern can be formed.However,the results given by the Euler-Euler method are not consistent with the real situation.
