10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Rational Design a Dilution Sampler for Probing Nanoparticles in Flames
ZUWEI XU, Jianlong Wan, Zhijing Su, Haibo Zhao, Huazhong University of Science and Technology
Abstract Number: 351 Working Group: Instrumentation
Abstract Dilution sampling technology is used in many process diagnostic occasions from emission monitoring to nanoparticle manufacturing (Goudeli et al. 2016; Zhao et al. 2003). This study focuses on developing a dilution sampler for online diagnostics of flame synthesis processes, with a quantitative understanding of the probe effects and reducing the perturbations on flames. Computational fluid dynamics (CFD) simulations are used to study the effects of probe geometry and working conditions on the probe performance, and ultimately to help rationalize the design of the sampling probe. It is mainly considered that changing the pressure drop, nozzle angle, sample gas temperature, and nozzle thermal conductivity affects the dilution ratio. Firstly, an optimal geometry with 30° nozzle angle is in favor of expanding the ranges of operation pressure drop and dilution ratio. The effect of flame preheating diluent gas on the dilution ratio is investigated. It can be weakened or even ignored through reducing the heat conductivity of the nozzle. When the heat conductivity is less than 1 W/(m•K), the error of the dilution ratio derived from the non-preheating assumption is estimated no more than 2%. As thus, flint glass is screened as nozzle material with the heat conductivity of 0.8 W/(m•K). For the probe of optimized nozzle angle and heat conductivity, the dilution ratio can be quantified by two easy-to-use empirical expressions in terms of the critical pressure drop as well as the linear relation between the dilution ratio and the operation pressure drop. Subsequently, a realistic probe is fabricated according to the rational design and then calibrated through a well-established setup and procedure, as thus an appropriate range of dilution ratio (about 70 ~ 350) is obtained. Combined with a commercial rotating disk thermodiluter (RTD) and a scanning mobility particle sizer (SMPS), the online monitoring system is set up to follow the spatially-resolved PSDs of TiO2 nanoparticles in a co-flow CH4/O2 diffusion flame. The PSDs measured agree well with the thermophoretic sampling results as benchmark (Xu and Zhao 2015), which demonstrates the customized dilution sampler combined with the commercial SMPS possesses excellent performance and effectiveness for monitoring detailed nanoparticle evolution and spatiotemporal distribution in aerosol flames. And more broadly, it is expected that other aerosol flames, e.g., sooting flame, spray-pyrolysis flame, can be on-line diagnosed using this sample probe they have a lot in common.
References Goudeli, E., Gröhn, A.J., and Pratsinis, S.E. (2016). Sampling and dilution of nanoparticles at high temperature. Aerosol Sci. Technol., 50: 591-604. Xu, Z., and Zhao, H. (2015). Simultaneous measurement of internal and external properties of nanoparticles in flame based on thermophoresis. Combust. Flame, 162: 2200-2213. Zhao, B., Yang, Z., Wang, J., Johnston, M.V., and Wang, H. (2003). Analysis of Soot Nanoparticles in a Laminar Premixed Ethylene Flame by Scanning Mobility Particle Sizer. Aerosol Sci. Technol., 37: 611-620.