Numerical Simulation On The Filtration Characteristic Of Fiber Filter

Pressure drop and collection efficiency are two main performance parameters of fiber filter, to which scholars from domestic and overseas have made researches. But most researches simply regard the real fiber filter as regulation structure, and only concentrate on 2D space and low speed filtration stage, which can't meet the reality that the air-solid two-phase flow inside fiber filter occurs in 3D space. It is concluded that the performance predicted by these models are different from what real fiber filter do. By far although several scholars have done mathematical calculation to 3D models of fiber filter media, but they are based on suppose that the air flow meets Darcy's law, and there is very little research on collection efficiency of fiber filter media. Besides, there is little research to fractural dimension of complicated structure of fiber filter media, so the research to the air-solid two-phase flow in 3D fiber filter media and the fractural dimension will play significant role to the optimization of filter design parameter and performance parameter.In order to obtain actual microstructure of fiber filter, the paper establishes a series of virtual 3D fiber filter models, and simulates and studies the status of air-solid two-phase flow in different operation conditions by using the software FLUENT 6.3. Besides based on the fractural theory, corresponding fractural dimension of each model are calculated, and the relationship with filtration performance are studied. The main research and conclusions are as following:(1) Fiber filter models are established randomly by computer program, which make the micro structure close to actual non-woven fabric.(2) The paper puts emphasis on study of air phase flow in 3D random fiber filter media model. Research conclusion:as the filling density of filter increases, the pressure drop increases nonlinearly; as face velocity increases, pressure drop increases linearly at first, then increases nonlinearly, and flow distribution can be separated as linear flow area and nonlinear flow area. In linear flow area, flow distribution meets Darcy law, and research conclusion is very close to Davies experiment expression, while in nonlinear flow area, Darcy law can't describe the flow precisely, but Forchheimer Equation can be used to describe. Besides, based on analysis to simulation data, the paper concludes the critical velocity of linear flow and nonlinear flow, and obtains the pressure drop expression for both linear and nonlinear flow area according to simulation calculation.(3) On basis of the air flow in random model, use DPM model to simulate the particle phase flow at stable filter stage in different conditions. The research finds the collection efficiency of random model increases as the particle diameter increasing, and increases gradually till it can't increase as the filtering rate increasing. Besides, collection efficiency of random model increases as infilling rate increasing. But regarding the micro-particles, the collection efficiency is unaffected by the filtration velocity.(4) Based on fractural theory, the paper calculates the fractural dimension of random model, and study the relationship between fractural dimension and random model's filtration performance. The conclusion is the fractural dimension of random model has related to pressure drop and collection efficiency.