Numerical Study On Nanoparticle Capture Efficiency And Filtration Resistance In Fibrous Media

Fiber filter plays an irreplaceable role in air purification,industrial dust removal and other fields.It is very important to study the filtration resistance and filtration efficiency of fiber filter for optimal design of fiber filter.In this paper,a single fiber model and a random fiber arrangement model are established,and the filtration resistance and filtration efficiency are studied by computer simulation.In terms of single fiber calculation,this paper mainly explores the factors influencing the capture efficiency of nano-particles（particles with aerodynamic diameter less than1um）by fiber medium,and establishes the fitting formula of capture efficiency by Using Lagrange method and Euler method.In the multi-fiber research,the correction coefficients of filtration resistance and filtration efficiency are proposed respectively.The main research results are as follows:1.The Kuwabara flow field and Happel flow field are compared by dimensionless resistance and ideal intercepting single fiber efficiency.The results show that the Kuwabara flow field is in good agreement with the simulation results,and is better than the Happel flow field in accuracy.2.The single fiber filtration resistance is simulated and the distribution characteristics of the velocity field and pressure field of the single fiber are explored.The dimensionless resistance of the single fiber simulated is compared with the results of others.The results show that the dimensionless resistance value of Kuwabara single fiber is very close to the simulation results of this paper.The Happel and Davies equations result in lower estimated dimensionless drag values,which also reflects the accuracy of Kuwabara flow field.3.Lagrange method is used to solve the diffusion efficiency of single fiber,and statistical method is used to define the calculation formula of single fiber efficiency（4-6）.According to the simulation results,the influences of filtration speed,particle diameter,volume ratio and Pe number on the diffusion efficiency of single fiber are discussed.4.Lagrange method is used to solve the diffusion efficiency of single fiber,and statistical method is used to define the calculation formula of single fiber efficiency（5-5）.According to the simulation results,the influences of filtration speed,particle diameter,volumetric ratio and Pe number on the diffusion efficiency of single fiber are discussed.The results show that the increase of filtration speed,particle diameter and Pe number will lead to the decrease of filtration efficiency,while the change of volumetric ratio has almost no effect on the filtration efficiency.4.Euler method was used to solve the diffusion efficiency of single fiber,and the results were compared with those obtained by Lagrange method and other scholars’ formulas.The results show that the euler method is in good agreement with the Lagrange method,which is better than Kirsch’s（1968）and Wang’s（2006）formula.Compared with Lagrange method,Euler method has the advantages of low cost and high accuracy,but it can only be used to calculate the diffusion efficiency of small particles due to the limitation of its own principle.By contrast,Lagrange method is more suitable for calculating the capture efficiency of inertial particles.Euler method is the most suitable method for the trapping process of nanoparticles studied in this paper.According to the data obtained by euler method,the single fiber diffusion efficiency formula（4-10）is fitted,and the applicable range is 0 < 0)< 1000,0 < < 0.1.5.Due to the inhomogeneity of random arrangement of fibers,the resistance value and efficiency value calculated theoretically are always higher than the actual situation.In this paper,the two-dimensional random arrangement model was used to represent the real fiber distribution.Through a large number of data fitting,the correction coefficients of filtration resistance and filtration efficiency were finally obtained,as shown in Equations（5-2）and（5-4）respectively.Through the test,the coefficient can be well applied to the correction calculation under various working conditions.The applicable conditions are respectively 0)<< 1,0 < < 0.1 and 0 < < 0.1,0 < 0)< 1000.