The Transfer Function and Flow Field in the Aerosol Particle Mass Analyzer

• Main Authors: Weng, Kai-Yi, 翁愷邑
• Other Authors: Tsai, Chuen-Jinn
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/2zcx37

碩士 === 國立交通大學 === 環境工程系所 === 106 === The Aerosol Particle Mass Analyzer (APM) is an instrument to measure the mass of particles based on the force balance of centrifugal force and electrostatic force. Several models have been developed to simulate the APM transfer function. However, no model can accurately predict the APM transfer function of nanoparticles (Ehara et al., 1996; Lall et al., 2009; Tajima et al., 2011; Lin et al., 2014), and the exact mechanism of how APM underestimate the mass of nanoparticles is still unknown. In this study, a 2-D model is developed to simulate the transfer function in the whole APM region. The flow fields are calculated with the Navier-Stokes equations and continuity equation, and the particle concentration fields are calculated based on the convection-diffusion equations. The recirculation flows were observed in the APM’s inlet and outlet region, but no Taylor vortex was observed in the classifying region. The velocity profile of the flow field in the classifying region is almost identical to analytical solution, showing that the impact of the recirculation flows on the particle retention time and centrifugal force in the classifying region is minor. Comparison of the transfer functions predicted by present model with those by Ehara model (Ehara et al., 1996) showed that the Brownian diffusion loss and the convection-diffusion loss in the APM’s inlet and outlet region are the reason why Ehara model overestimate the transfer functions of nanoparticles. The response spectra predicted by present model agree well in both height and width with the experimental data present in a previous study for particles larger than 30 nm. However, present model still cannot reproduce the shift of the transfer function and response spectra of nanoparticles, showing that in addition to centrifugal force, electrostatic force, inertial force and Brownian motion, there should be other factors causing the shift of the transfer function and response spectra.