Simulaiton Study Of The Filtration Performance Of Particle Matters In The Fibrous Filtration Media

The rapid development of modern industry had brought serious environmentpollution problem, and the air contains lots of harmful gases and fine suspendedparticles, which harm the ecological environment and human health. As the public’senvironmental protection consciousness strengthens and the standards of the pollutantsdischarge gradually improve, the work that optimizes and improves the structure of theexisting filtration media to adapt to the new standard is imminent. Fiber filtrationtechnology has high filtration efficiency for particle pollutants, especially for fineparticles, and can achieve the increasingly strict environmental emissions standards.Therefore, understanding of the mechanism of fiber filtration further, improving thefiltration performance of the media, and optimization the design of the filtrationmaterial still are the current research focuses.The effect of the particle deposition on the single fiber filtration efficiency, theeffect of the particle size and outline fractal dimension on the deposition morphologyof the particle branches were studied in this study utilizing (Computational FluidDynamics) CFD method and based on the grid “frozen” technology and the fractaltheory, respectively. The filtration media models with random structure and a certaincurvature, k were established, and the effects of filtration velocity, U, fiber curvature, k,and particle size, Rpon the filtration performance of the filtration media were analyzed,then the results were compared with the conventional empirical models. In addition,the Discrete Element Method (DEM) and CFD-DEM were introduced to this study,and the effects of the particle group characteristics, including particle rebound,agglomerate, particle group components and particle size distribution, etc, on thefiltration performance were simulated and analyzed. The results show that:The mechanisms of particle captured vary with the particle size, when the particlesize, Rp, is between1and4μm, the inertial collision plays a leading role, and thefiltration efficiency increases with the filtration velocity, simultaneously, the pressuredrop increases with the filtration velocity linearly. When the particle size, Rp, is lessthan1μm, Brown diffusion plays an important role in the filtration process, and thefiltration efficiency decreases with the filtration velocity. Meanwhile, when the StokesNumber of the particle, St is less than1.2, the filtration efficiency of the mediaincreases with St significantly, and when St>1.2, the filtration efficiency decreases due to the particle rebound. Therefore, it is necessary to control the value of St in practicalapplication.The particle branches help to enhance the filtration efficiency of the media, and inits early growth, this effect is significant. Furthermore, the filtration efficiency isrelated with the contact area between the particle and the media, and the probability ofthe particle collision increases with the contact area, consequently, the probability thatparticles captured is higher, too. The fractal dimension of the outline, D’cancharacterize the complexity degree of the particle branches surface, and the smaller thevalue of D’is, the more even the outline of the particle branches deposition is, and then,the more simpler the structure is. In addition, the fractal dimension of the particle size,D characterizes the distribution property of the particle size in the particle group, andthe fraction of fine particles in the system increases with D. Meanwhile, the particlegroup is more sophisticated when D increases.The pressure drops of the multi-fiber model with the random structure and a certaincurvature, k are good agreement with the classical Davies experimental correlations.The filtration efficiency of k equal to1, is superior to the value of k equal to0, which isconsistent with the results in engineering application. The results also show that themulti-fiber model with the random structure and a certain curvature can truly reflectthe structural characteristics of the actual filtration media.The gas-solid flow characteristic and the fine particle deposition morphology onthe surface of the filtration media in the filtration process can be obtained throughCFD-DEM simulation. The simulation results show that the surface filtration hasimportant contribution to the filtration efficiency, and the depth filtration mainlyinfluences fine particles. At the same time, the qualitative comparison between thesimulation results and experimental observation ones in the literature was conducted inthis study, and the results show that it is feasible to calculate the filtration characteristicin the filtration media by means of numerical simulation, which can provide theoreticalbasis and practical guide for optimizing the design parameters and operating conditionsof the filtration media, developing a new type filtration material.