Study Of Numerical Simulation Of Multi-tube High Efficiency Particulate Air Filters

The velocity field and the pressure distribution in the multi-tube high efficiency particulate air filters (HEPA filter) are investigated numerically using simulation method. Based on the real object, hypothesis and simplification are made for building up the numerical simulation model. In this model, the standard k-ε turbulent current model is adopted. The upwind differencing scheme is used to represent the diffusion terms, which appear on the differential equation. Wall Functions is employed to represent the effect of the wall boundaries. As for the porous medium, the Darcy Law is suitable. The SIMPLE algorithm gives satisfactory solutions for the pressure- velocity coupling in steady flows based on the staggered grid. Several cases on the structure of the HEPA filter are compared for selection of the rational one. Meanwhile the variation of flow rate is carried out as well for the investigation of applicability. Errors between the experimental data and the numerical simulation ones are less than 5%. Thus the reliability and accuracy of the numerical simulation method introduced in this paper is demonstrated. Based on the numerical simulation data, velocity and pressure distribution is investigated. Firstly, it is proved that the difference of the flow rate between filter tubes is less than 6%. For most types, the difference is only 2%. This result shows the distribution of the filter tubes is rational. Secondly, the flow rate along the tube axis changes linearly. It is in accord with another result that the filtration velocity keeps stable along the length of filter tubes. Similarly, the pressure drop along the filter lengths also shows the stability. Thirdly, the pressure drop of the filter material is the main factor of the total pressure drop of the HEPA filter. The proportion varies from 75% to 99%. Furthermore, the resistance formulae, AP= 1608v_i~0.9 is obtained through the least-square fit according to the numerical simulation data. It could be used to forecast and calculate the pressure drop of this type of HEPA filter. At the same time, it gives the modification to the conventional resistance formulae, and puts forward a more accurate one based on the analysis and the comparison of two resistance formulae.