A Cleaning System for Urban Air Pollution Removal
2019-11
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A Cleaning System for Urban Air Pollution Removal
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2019-11
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Abstract
Air pollution is a severe issue worldwide, which is adversely affecting the health and living environment of urban population. A novel outdoor air cleaner, named Solar-Assisted Large-Scale Cleaning System (SALSCS), was proposed as an innovative approach to facilitate the separation of particulate matter (PM) from atmospheric air by installing pleated filters in the system. This work first proposed the basic concept of SALSCS, which is composed of a flat-plate solar collector, a chimney, a filter bank, and fans if necessary. A three-dimensional numerical model of the system was developed by using the ANSYS Fluent fluid solver. The numerical results indicated that a full-scale system can generate a total flow rate of 2.64 × 105 m3 s-1 with the pressure drop of installed filter bank considered. In addition, the numerical model was applied to design a demonstration unit constructed in Xi’an with a tower of 60 m in height and a solar collector of 43 × 60 m2 in the horizontal directions. Field measurements were conducted and the obtained experimental data was used to validate the numerical model of SALSCS, which was further applied to investigate the performance characteristics of systems in the dimensional range of 10–120 m. The parameters that considerably influence the system performance have been identified. Meanwhile, atmospheric simulations over the terrain of Beijing were carried out by using the Weather Research and Forecasting (WRF) model to investigate the effectiveness of SALSCS for PM2.5 mitigation. A derived tendency term in the potential temperature equation was applied to simulate the buoyancy effect of SALSCS created with solar heating on its nearby atmosphere. PM2.5 pollutant and SALSCS clean air were simulated in the model domain by passive tracer scalars. Simulation conditions with two system flow rates of 2.64 × 105 m3 s-1 and 3.80 × 105 m3 s-1 were tested for seven air pollution episodes of Beijing during the winters of 2015–2017. The numerical results showed that with eight SALSCSs installed along the 6th Ring Road of the city, 11.2% and 14.6% of PM2.5 concentrations were reduced under the two flow-rate simulation conditions, respectively. To further improve the system’s effectiveness, an air cleaner with a reverse-flow configuration was proposed to be directly installed inside city blocks. An open-source large-eddy simulation (LES) model, called PALM, has been utilized to study the nearby atmospheric flow behavior and investigate its effectiveness in reducing air pollution. A method of incorporating the flow pattern of the air cleaner into the surrounding atmospheric flows was developed. A scenario of two systems operating together has also been investigated. The simulations illustrated that there is a clean air plume with higher turbulence intensity arising near the SALSCS providing a cleaner region within the polluted atmospheric flows. The numerical results indicated that as high as 60-100% of the nearby air pollution can be reduced, depending on its operating conditions and urban topographies. The filtration elements in SALSCS is one of the many applications of pleated filters. This dissertation also presents our experimental study on the flow fields of pleated filters by using the Particle Image Velocimetry (PIV) method. Flow patterns and pressure drop across pleated filters with various pleat configurations have been measured under our laboratory setup. It was found that the pleat geometry impacts the downstream flow pattern more significantly than the upstream pattern. The obtained downstream flow distributions indicated lower permeability at the pleat corner regions due to compression of the fibers. We discovered that when pleat geometry stays unchanged, similarity exists among downstream flow structures of pleated filters with different pleat numbers. These four studies below comprise parts of the main body of this dissertation and have already been published. Chapter 2: Q. Cao, D.Y.H. Pui, W. Lipiński. A concept of a novel Solar-Assisted Large-Scale Cleaning System (SALSCS) for urban air remediation. (2015). Aerosol. Air. Qual. Res. 15 (1), 1-10. Chapter 3: Q. Cao, T.H. Kuehn, L. Shen, S.-C. Chen, N. Zhang, Y. Huang, J. Cao, D.Y.H. Pui. Urban-scale SALSCS, part I: Experimental evaluation and numerical modeling of a demonstration unit. (2018). Aerosol. Air. Qual. Res. 18, 2865-2878. Chapter 4: Q. Cao, M. Huang, T.H. Kuehn, L. Shen, W.-Q. Tao, J. Cao, D.Y.H. Pui. Urban-scale SALSCS, part II: A parametric study of system performance. (2018). Aerosol. Air. Qual. Res. 18, 2879-2894. Chapter 5: Q. Cao, L. Shen, S.-C. Chen, D.Y.H. Pui. WRF modeling of PM2.5 remediation by SALSCS and its clean air flow over Beijing terrain. (2018). Sci. Total Environ. 626, 134-46.
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University of Minnesota Ph.D. dissertation. November 2019. Major: Mechanical Engineering. Advisors: David Pui, Lian Shen. 1 computer file (PDF); xi, 152 pages.
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Cao, Qingfeng. (2019). A Cleaning System for Urban Air Pollution Removal. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/211323.
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