Unsteady absorption of sulfur dioxide by an atmospheric water droplet with internal circulation |
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| Institution: | 1. Department of Climatology and Atmosphere Protection, University of Wroclaw, 8 A. Kosiby St., Wroclaw, PL 51670, Poland;2. Department of Analytical Chemistry, Gdansk University of Technology, 11/12 G. Narutowicza St., Gdansk, PL 80233, Poland;1. Department of Colloid Chemistry, St. Petersburg State University, Universitetsky pr. 26, 198504, St. Petersburg, Russia;2. Max-Planck-Institute for Colloid and Interface Science, D-14476, Golm, Germany;3. Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria;4. CNR − Istituto per l''Energetica e le Interfasi, Genova, Italy;5. Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore, West Bengal, India;1. School of Chemistry and Chemical Engineering, Southwest University, Chongqing, 400715, China;2. School of Chemistry and Chemical Engineering, Chongqing University, Chongqing, 401331, China;1. School of Automation, Guangdong University of Technology, Guangzhou 510006, China;2. Guangdong Key Laboratory of Precision Equipment and Manufacturing Technology, School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China;3. School of Computer, Guangdong University of Technology, Guangzhou 510006, China;4. Guangdong Construction Polytechnic, Guangzhou 510440, China;5. Engineering Research Center for Optoelectronics of Guangdong Province, School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510640, China |
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| Abstract: | Unsteady absorption characteristics of sulfur dioxide by an atmospheric water droplet in motion are predicted numerically and analyzed theoretically to recognize the physical mass transport processes inside an aerosol droplet, which is frequently encountered in the atmosphere. Considering the absorption of sulfur dioxide by a droplet in cloud or fog with various velocities, three different Reynolds numbers, viz., Reg=0.643, 1.287, and 12.87 are studied and compared with each other. The results indicate that for the Reynolds number of 0.643, sulfur dioxide always penetrates toward the droplet centerline throughout the entire absorption period. This is due to the mass transfer dominated by diffusion along the radial direction. In contrast, when the Reynolds number is 12.87, the strength of the vortex motion inside the droplet is strong enough. It results in that, most of the time the concentration contours parallel the streamlines and the lowest SO2 concentration is located at the vortex center. As a consequence, the diffusion distance is reduced by a factor of three and the absorption time for the droplet reaching the saturated state is shortened in a significant way. With regard to an intermediate Reynolds number such as 1.287, a two-stage mass transfer process can be clearly identified. In the first stage, it is dominated by one-dimensional diffusion, in which over 50% sulfur dioxide is absorbed before the saturated state is reached. In the second stage, the vortex motion mainly controls the mass transfer. However, the contour core is inconsistent with the vortex center. This is because the characteristic time of mass diffusion is in a comparable state with that of droplet internal circulation. The present study elucidates that the strength of a droplet's internal motion plays a vital role in determining SO2 absorption process. |
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