원형관 코팅장치에서 연소 입자의 응축성장에 미치는 2차원 열 및 물질전달의 영향
Effects of Two‐dimensional Heat and Mass Transports on Condensational Growth of Soot Particles in a Tubular Coater
0
조회
0
다운로드
0
인용
0
참고문헌
키워드
초록
Soot particles emitted from combustion processes are often coated by non‐absorbing organic materials, which enhance the global warming effect of soot particles. It is of importance to study the condensation characteristics of soot particles experimentally and theoretically to reduce the uncertainty of the climate impact of soot particles. In this study, the condensational growth of soot particles in a tubular coater was modeled by a one‐dimensional (1D) plug flow model and a two‐dimensional (2D) laminar flow model. The effects of 2D heat and mass transports on the predicted particle growth were investigated. The temperature and coating material vapor concentration distributions in radial direction, which the 1D model could not accounted for, affected substantially the particle growth in the coater. Under the simulated conditions, the differences between the temperatures and vapor concentrations near the wall and at the tube center were large. The neglect of these variations by the 1D model resulted in a large error in modeling the mass transfer and aerosol dynamics occurring in the coater. The 1D model predicted the average temperature and vapor concentration quite accurately but overestimated the average diameter of the growing particles considerably. At the outermost grid, at which condensation begins earliest due to the lowest temperature and saturation vapor concentration, condensing vapor was exhausted rapidly because of the competition between condensations on the wall and on the particle surface, decreasing the growth rate. At the center of the tube, on the other hand, the growth rate was low due to high temperature and saturation vapor concentration. The effects of Brownian diffusion and thermophoresis were not high enough to transport the coating material vapor quickly from the tube center to the wall. The 1D model based on perfect radial mixing could not take into account this phenomenon, resulting in a much higher growth rate than what the 2D model predicted. The result of this study indicates that contrary to a previous report for a thermodenuder, 2D heat and mass transports must be taken into account to model accurately the condensational particle growth in a coater.
Abstract
Soot particles emitted from combustion processes are often coated by non‐absorbing organic materials, which enhance the global warming effect of soot particles. It is of importance to study the condensation characteristics of soot particles experimentally and theoretically to reduce the uncertainty of the climate impact of soot particles. In this study, the condensational growth of soot particles in a tubular coater was modeled by a one‐dimensional (1D) plug flow model and a two‐dimensional (2D) laminar flow model. The effects of 2D heat and mass transports on the predicted particle growth were investigated. The temperature and coating material vapor concentration distributions in radial direction, which the 1D model could not accounted for, affected substantially the particle growth in the coater. Under the simulated conditions, the differences between the temperatures and vapor concentrations near the wall and at the tube center were large. The neglect of these variations by the 1D model resulted in a large error in modeling the mass transfer and aerosol dynamics occurring in the coater. The 1D model predicted the average temperature and vapor concentration quite accurately but overestimated the average diameter of the growing particles considerably. At the outermost grid, at which condensation begins earliest due to the lowest temperature and saturation vapor concentration, condensing vapor was exhausted rapidly because of the competition between condensations on the wall and on the particle surface, decreasing the growth rate. At the center of the tube, on the other hand, the growth rate was low due to high temperature and saturation vapor concentration. The effects of Brownian diffusion and thermophoresis were not high enough to transport the coating material vapor quickly from the tube center to the wall. The 1D model based on perfect radial mixing could not take into account this phenomenon, resulting in a much higher growth rate than what the 2D model predicted. The result of this study indicates that contrary to a previous report for a thermodenuder, 2D heat and mass transports must be taken into account to model accurately the condensational particle growth in a coater.
참고문헌 (17)
- Elliott, R. W., "Regularities in the diffusion coefficients of a homologous series", Nature Physical Science, 234, pp.98~99 (1971)
- Fuchs, N. A., "High‐dispersed aerosols, In Topics in Current Aerosol Research", pp.1~60 (1971), Pergamon Press
- Jacobson, M. Z., "Examining feedbacks of aerosols to urban climate with a model that treats 3‐D clouds with aerosol inclusions", Journal of Geophysical Research, 112, pp.D24205~ (2007)
- Otto, E., "The log‐normal size distribution theory of Brownian aerosol coagulation for the entire particle size range: Part II. Analytical solution using Dahneke’s coagulation kernel", Journal of Aerosol Science, 30, pp.17~34 (1999)
- Park, S. H., "Particle‐size‐dependent aging time scale of atmospheric black carbon", Particle and Aerosol Research, 5, pp.45~52 (2009)
- Park, S. H., "The log‐normal size distribution theory of Brownian aerosol coagulation for the entire particle size range: Part I: Analytical solution using the harmonic mean coagulation kernel", Journal of Aerosol Science, 30, pp.3~16 (1999)
- Park, S. H., "Change in particle size distribution of aerosol undergoing condensational growth: alternative analytical solution for the low Knudsen number regime", Journal of Aerosol Science, 33, pp.1297~1307 (2002)
- Park, S. H., "A two‐dimensional laminar flow model for thermodenuders applied to vapor pressure measurements", Aerosol Science and Technology, 47, pp.283~293 (2013)
- Ramanathan, V., "Global and regional climate changes due to black carbon", Nature Geoscience, 1, pp.221~227 (2008)
- Riipinen, I., "Equilibration time scales of organic aerosol inside thermodenuders: Evaporation kinetics versus thermodynamics", Atmospheric Environment, 44, pp.597~607 (2010)
- Rosner, D. E., "“Heavy” species Ludwig‐Soret transport effects in air‐breathing combustion", Combustion and Flame, 123, pp.547~560 (2000)
- Saleh, R., "Hygroscopic growth and evaporation in an aerosol with boundary heat and mass transfer", Journal of Aerosol Science, 38, pp.1~16 (2007)
- Saleh, R., "On transport phenomena and equilibration time scales in thermodenuders", Atmospheric Measurement Techniques, 4, pp.571~581 (2011)
- Seinfeld, J. H., "Atmospheric Chemistry and Physics: From Air Pollution to Climate Change" (1998), John Wiley & Sons, Inc
- Soewono, A., "Morphology and Optical Properties of Coated Aggregates", 박사, pp.2013
- Tjong, H., "Measurement of Soot with Organic Coatings by Laser‐Induced Incandescence", 석사, pp.2012
- Tsantilis, S., "Population balance modeling of flame synthesis of titania nanoparticles", Chemical Engineering Science, 57, pp.2139~2156 (2002)