Jan 26 Growth velocity of droplets Use the Köhler equation to find a p sat for the edge of the particle, plug pressure into ideal gas law to obtain concentration c s Then use = ∞-cr c Rpr ( ∞-) c cs with ∞ c equal to ambient concentration to find concentration at surface of droplet Total flux to drop: = ( ∞-) J 4πRpDg c cs dependent on the radius, larger droplets have larger flux. Consider a mass balance: = ( ) MWJ ρWddt 43πRp3 = ( ∞-) dRpdt DgMWρpRp c cs Growth slows as droplet becomes larger. Cannot grow into raindrops by diffusion. At some point, R p is sufficiently large to reduce dR
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