滑移效应下纤维绕流场及过滤阻力的数值计算与分析

Numerical calculation and analysis of flow field and filtration resistance for fiber media with gas slip effect

考虑实际纳米/微米纤维表面的流体滑移效应,采用数值方法求解滑移流动机理下纳米/微米纤维绕流场及过滤阻力,分析讨论了Knudsen数Knf和填充率C对纤维近壁面速度分布及纤维过滤阻力的影响规律。结果表明,对纳米/亚微米纤维过滤情形,纤维表面流体的滑移效应导致纤维绕流场与非滑移条件下情形有显著差异,尤其在高填充率下,纤维表面最大滑移速度与来流风速相当;而对于大尺度微米级纤维,滑移效应对纤维绕流场及过滤阻力影响甚微。此外,已有纤维过滤阻力计算模型不能准确估计出具有强滑移效应的纳米纤维过滤阻力系数,且各纤维过滤阻力系数模型的估计结果存在跨数量级的偏差。根据数值分析结果,给出了一个适用于纳米/微米纤维过滤阻力系数的可靠估计式,适用参数范围为0.01≤C≤0.1,0.013≤Knf≤2。

A numerical method was developed to calculate the flow field and filtration drag around nanofiber/microfiber with consideration of gas slip effect,and the effects of Knudsen number Knf and the fiber volume fraction C on velocity distribution around the fiber surface and fiber filtration resistance were discussed and analyzed.The results indicated that significant differences could be found between flow field around the fiber in slip flow regime and in no-slip flow regime for nanofiber/sub-microfiber filtration,especially for the case of high fiber volume fraction where the maximum slip velocity along the fiber surface approached the filtration velocity,however,the gas slip effect had a negligible influence on flow field and filtration resistance for large-scale microfiber filtration.Moreover,existing filtration resistance coefficient models developed for fibrous filter were inadequate in predicting nanofiber filtration resistance coefficient in slip flow regime,and orders of magnitude deviation could be seen between the different filtration resistance coefficient expressions.Based on the simulation results,a reliable expression for the nanofiber/microfiber filtration resistance coefficient in the range of 0.01≤C≤0.1 and 0.013≤Knf≤2 was developed.