Simulation Method Optimization Of The Cohesive Particle Deposited On The Fiber

Due to the fine particles in the atmosphere has caused serious hazards on the natural environment and public health, the air pollution is increasingly serious. Therefore, it is very important to reduce the content of fine particles in the air for protecting the human health and natural environmental. As an effective tool to remove fine particles, it is seriously important to study the effect of the deposition characteristics of particles in the fiber body of the fibrous media on its filtration performance. As an important research tool, numerical simulation has been increasingly applied in this field. Therefore, it has important theoretical research value and practical significance for optimizing the geometry of the fibrous media, improving the atmospheric environment and energy saving and emission reduction to study the numerical simulation method of the fine particle deposition characteristics on the fiber body.Firstly, the discrete phase model(Discrete Phase Model) in ANSYS-Fluent was used for the gas-solid two-phase flow numerical simulation of single fiber body in this study. Based on the user defined function(UDF), which considers the Van der Weal’s force to the particle trapped effect, and combined with Matlab, the visual simulation of the cohesive particles deposition on a single fiber body was realized, and the influence of different operating parameters and particle properties parameters on the particle deposition characteristics was also analyzed. Secondary, the coupling method of discrete element method(DEM) and computational fluid dynamics(CFD) was utilized to study the dynamic deposition characteristics of the cohesive particle on the single fiber body, such as collision and cluster, with different restoration coefficient of particle and fiber and filtration velocity. Finally, the drag model was loaded to DEM based on the API interface of EDEM software, and the dynamic simulation of cohesive particle deposition on the fiber body was also studied, and the calculated results with the CFD-DPM, CFD-DEM and DEM were compared to realize the optimization of numerical simulation method. The results show that:(1) Implemented of Van der Waals’ force can be realized by using the method of CFD-DPM based on the Fluent UDF interface. This method can accurately simulate the deposition process of the cohesive particles on the fiber body and the particle trajectory. Moreover, through combining Fluent and Matlab data, the visual simulation of particle motion is also realized. The simulation results by this simulation method show that, for the particle with the small size(Rp ≤1μm)which the Brown effect plays a leading role, constantly increasing the filtration velocity does not cause the filtration efficiency promote; for the particle with the large size(2μm≤Rp ≤4μm)which the inertial collision effect plays a leading role, the filtration efficiency significant decreases with the filtration velocity. This method is not highly required for the computer configuration, and the simulation time is also short(2h-4h), but the deposition pattern of the cohesive particles in the fiber body is not intuitive.(2) The cohesive particles deposition on the fiber body was simulated through the coupling algorithm of CFD-DEM, and the intuitive visualization of the particles deposition morphology on the fiber body was presented, but the computing time of the simulation condition is long(12h-24h). For the different collision recovery coefficients between the particle and fiber, the trap number of cohesive particles increases first and then decreases with the collision recovery coefficient, finally reaches the steady state. As for the particle and fiber in this study, when the CFD-DEM coupling calculation is used, the collision recovery coefficient between particle and fiber set to 0.3 is reasonable. The trapped number of cohesive particle is related to the particle size under the different filtration velocity. When the cohesive particle diameter is less than 2μm, the cohesive particles are prone to flow around the surface of fiber without trapped by the fiber, and the cohesive particles deposition on the fiber body is small. When the cohesive particle diameter is larger than 2μm, the number of cohesive particles trapped by fiber body is significantly increased, and the number of cohesive particles deposition on the fiber body decreases with the filtration velocity. When the CFD-DEM simulation of gas–solid two-phase flow was carried on in this study, the filtration velocity set to 0.1m/s can get the best filtration effect.(3) The drag model was loaded to DEM by the API interface of EDEM software, and the cohesive particles deposition on the fiber body was dynamically simulated, and then the results were compared to those of CFD-DPM and CFD-DEM coupling. The results show that DEM can accurately describe the characteristics of the cohesive particles deposition on the fiber body, at the same time, the computer configuration requirements is also low, and the simulation time is greatly reduced to 30-60 min compared with the traditional CFD simulation. Therefore, the numerical simulation method optimization of the cohesive particles deposition on the fiber body is realized. As for the cohesive particles deposition on the fiber body with the different surface energy, the number of the cohesive particles deposition on the fiber body increases and the filtration effect improves when the surface energy is small. As for the different particle diameter, while the collision recovery coefficient between particle and fiber body remains unchanged, the particles with the bigger size are more easily trapped and the amount is more. The number of the cohesive particles which trapped by the fiber body decreases with the particle Reynolds number, and the number of the cohesive particles which trapped by the fiber body increases with the Stokes number. Meanwhile, the number amplitude of the cohesive particles trapped by the fiber body increases when the Stokes number is bigger. In addition, under the variety of particle diameter distribution, the cohesive particles deposition on the fiber body forms to the dendrite structure. The cohesive particle with the larger diameter deposits on the surface of the fiber body, a part of the cohesive particles with the smaller diameter are trapped by the surface of the fiber body, and the other part are trapped by the bigger particles which deposited on the surface of the fiber body and forms to the dendrite structure.