Distinguished McKnight University Professor, University of Minnesota
David Y. H. Pui, Ph.D, a Distinguished McKnight University Professor, is the L.M. Fingerson/TSI Inc. Chair in Mechanical Engineering and the Director of the Particle Technology Laboratory and of the Center for Filtration Research, University of Minnesota. He has a broad range of research experience in aerosol science and technology and has over 220 journal papers and 20 patents. He has developed/co‐developed several widely used commercial aerosol instruments. Dr. Pui is a fellow of the American Society of Mechanical Engineers (ASME), and has received many awards, including the Max Planck Research Award (1993), the Humboldt Research Award for Senior U.S. Scientists (2000), the Fuchs Memorial Award (2010)‐‐the highest disciplinary award conferred jointly by the American, German, and Japanese Aerosol Associations, and the Einstein Professorship Award (2013) by the Chinese Academy of Sciences (CAS). He was a past President of the American Association for Aerosol Research (AAAR) and of the International Aerosol Research Assembly (IARA) consisting of 15 international aerosol associations.
The filter dust holding capacity depends on the size distribution and morphological property of particles collected. In the conventional test method, test particles with a single mode of coarse particles are typically used. However, depending on the application and service location, many filters are used in an outdoor environment where particles exhibit a bi-modal size distribution or an indoor environment where the particles exist in a fine mode. Examples are the mechanical engine intake filters used in ambient environment for collecting atmospheric aerosols and indoor electret HVAC or air cleaner filters for collecting fine particles, or PM2.5, infiltrated from outdoor or generated from indoor activities. To more precisely predict the lifetime of the filters utilized in the ambient and indoor condition, these filters need to be tested with particles of similar size and morphological properties as atmospheric and indoor aerosols. In this study, filter loading behaviors were tested with particles with bi-modal size distribution that mimic the atmospheric aerosols and PM2.5 only to mimic the indoor fine aerosols. Factors that affect the filter loading behaviors were investigated.
Arizona road dust was dispersed by an ejection pump to represent the coarse mode particles in the atmosphere. Three different methods, namely, an atomizer, a tube furnace, and a propane flame, were used to generate particles to mimic fine mode particles in the atmosphere. Coarse mode and fine mode particles were mixed with different ratios to represent the atmospheric aerosols in different locations. The pressure drop of the tested filter media was monitored during the loading process. The penetration evolution of coarse mode and fine mode particles during the loading were measured by Aerodynamic Particle Sizer (APS) and Scanning Mobility Particle Sizer (SMPS) respectively.
For the engine intake filter testing, it was found that increasing the fine mode aerosol fraction dramatically increased the pressure drop increase rate. A small fraction (25%) of the fine mode particles significantly increased the pressure drop of a loaded filter compared to the pure coarse mode condition. The pressure drop evolution was also found to be affected by the morphology of fine mode aerosols. The pressure drop was the slowest when loaded by spherical particles, and the fastest when loaded by fractal-like soot agglomerates. Detailed results will be given in the talk. In the electret HVAC and air cleaner filters testing, the pressure drop evolution of fine mode aerosol loading varied significantly with the mass concentration of the fine aerosols in the feed. The lower concentration of fine mode aerosols resulted in a slower increasing rate of pressure drop, which was expected to be associated with the collapse and formation dynamics of the fine particle dendrite.