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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 1:54 |
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Conference: Bucharest University Faculty of Physics 2001 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
PRECIPITATION SCAVENGING OF GASES
Authors:
Sabina Stefan, Laura Ciocan
Affiliation:
University of Bucharest, Faculty of Physics, P.O.Box MG-11
E-mail
Keywords:
Abstract:
In the precipitation scavenging of gases, the rate of transfer of gas molecules to the surface of a stationary or falling drop can be very accurately predicted; difficulties in predicting gas scavenging rates arise when the scavenged gas has an appreciable vapor pressure over the surface of the drop and thus the composition, of the drop must be known in order to predict the net rate of transfer of material to the drop.
Gas flux to a cloud or raindrop can be expressed as kg(c - cs), where kg is the gas-phase mass transfer coefficient (cm sec-1), c is the bulk gas-phase concentration in the air and cs is the gas concentration in the drop.
The convective - diffusive mass transfer coefficient is given by Frossling (1938) equation,by using
Dg -the diffusivity coefficient of the gas in air (cm2 s-1), the cinematic viscosity (cm2 s-1), u the drop falling terminal velocity (cm s-1) and the drop equivalent diameter.
The dependence of kg upon D0 is related to the terminal velocity of the raindrop, u, which in turn, is a function of the equivalent drop diameter (Pruppacher and Klett, 1978):
u= 958?1-exp (- (D0/0.1710)1.147)? (cm s-1)
The aim of this paper is to calculate the mass transfer coefficient and the falling velocity for CO2, CS2, SO2 and to evaluate the coefficient scavenging to raindrop-size distribution.
The results show that the velocity depends almost linearly to radius and the mass transfer coefficient decreases with the increasing of the droplet size.
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