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Seminar - Advances in Nanofiber Filtration of Nano-aerosols by Prof. Wallace Woon-Fong LEUNG
日期:2018 年 02 月 13 日 ( 星期二)
Time:11:00 am – 12:00 pm


Nano-aerosols/ultrafine particles (<100nm) in high concentration (50-500+ MM/m3) are found in polluted air both indoors and outdoors. Air-borne viruses are also typically in the same size range. By their small sizes, these invisible killers can be inhaled readily into our bodies causing health problems. Nanofiber filters are very effective to capture these invisible killers. This presentation will discuss various technologies being developed in the past decade on filtration of nano-aerosols to achieve high capture efficiency and to maintain low pressure drop.

Depth filtration on submicron aerosols and nano-aerosols using nanofiber filter as function of face velocity, filter thickness, and fiber packing density has been well established. This includes low Peclet number (Pe<10) condition for which diffusion dominates over convection/interception capture. To achieve high capture efficiency for a given aerosol size, a certain basis weight (grams of nanofibers per square meter) of filter is required. When the same weight of nanofibers is divided into multiple layers, each separated by a permeable scrim material, the pressure drop of the entire filter is much reduced as compared to the case with all nanofibers all incorporated in a single layer due to introduction of the macropores between the nanofiber layers with the micropores. This novel multilayer nanofiber technology has been proven for different polymeric and natural materials.

For extended aerosol loading, a cake formed on the filter surface. The transition from depth to surface/cake filtration has been studied recently both experimentally and theoretically. It has been found that more aerosols are captured at the upstream end of the filter forming a skin layer, followed by plugging of pores in the skin layer by aerosol deposit, building of dendritic bridges above the plugged pores of the capillaries in the skin layer, and finally cake forming above the filter.

The cake formed above a nanofiber filter is quite dense, resulting in higher pressure drop across the entire filter. It can be made less dense and more permeable when a microfiber filter is installed upstream of the nanofiber filter. This composite filter technology has been proven experimentally and also by numerical simulation.

Other technologies such as cleaning of a loaded nanofiber filter by backpulse-and-backblow, and electrostatically charging of a nanofiber filter will also be discussed.


Prof. Wallace W-F Leung received his BS in Mechanical and Aerospace from Cornell University, and MS and ScD both in Mechanical Engineering from MIT. For the past 40 years, he has worked on filtration and separation from ultrafiltration of protein solution, centrifugation of process stream, vacuum filtration of minerals, to air filtration. For 18 years, he was with Bird/Baker Hughes as Senior Research Scientist and Director of Process Technologies directing centrifugal separation/filtration. Earlier, he has worked for Gulf Oil and Schlumberger on production/testing of petroleum reservoirs and wells. For the past 14 years, he is Chair Professor of Innovative Products and Technologies at The Hong Kong Polytechnic University. Besides air filtration, he is also interested in applications of nanofiber technologies in renewable energy (photovoltaics, and recently hydrogen production using water splitting), air and water purification (photocatalysis), and health technologies (wound dressing). He is a fellow of American Institute of Chemical Engineers, American Society of Mechanical Engineers, American Filtration and Separations Society, Hong Kong Institute of Engineers, and Hong Kong Academy of Engineering Sciences. He has 47 US patents and two books to his credit. He is the Chair of International Delegation on Filtration with 13 member countries including US, UK, Germany, France, Scandinavia, Austria, Hungary, Japan, Australia, Taipei, China, S. Korea, and India. He is also the chair of the World Filtration Congress, San Diego, CA, USA, 2020.