CFD Investigation into transition from depth to surface filtration during loading a nanofiber filter using nano-aerosols

H. Guo, W. W.-F. Leung*, The Hong Kong Polytechnic University, China

Nanofibers have been proven to be effective to capture nano-aerosols with sizes less than 100nm. During initial loading of nano-aerosols, the aerosols are captured in the nanofiber filter. Over long period of loading, the nanofiber filter changes from depth filtration to surface filtration where a cake forms on the filter surface and the cake, from aerosol deposit, serves subsequently as the effective filter media.

A computational fluid dynamics (CFD) model has been developed to simulate the depth-to-cake filtration process, in particularly the transition between these two regimes. For simplicity, the filter is represented by a spaced out tri-cylinders with diameter equivalent to that of the nanofibers, which is assumed 200nm in the numerical model. First, the mechanical capture of nano-aerosols taken to be 80nm by diffusion and interception capture has been modelled. There is provision in the CFD model that the captured nano-aerosols can further capture incoming aerosols forming dendritic structures. The flow field is also changed by these dendritic structures and the pressure drop is increased by flow being blocked off by these dendritic structures. After further loading, nano-aerosols accumulate at the upstream end of the filter forming a skin layer which assumes majority of the pressure drop across the filter. Further captured aerosols start to saturate the skin region and build up above the filter to form a cake. This cake grows and the deposited aerosols continue to trap more aerosols even better than the original nanofibers. Eventually all aerosols are captured by the cake and at that point the efficiency of capture reaches 100% and the pressure drop increases...

Session: G6 - Nanofibre Filter Media
Day: 14 March 2018
Time: 10:45 - 12:00 h

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