UCLA AOS145 Jan14

UCLA AOS145 Jan14 - Brownian D decreases. rrection which...

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orrection which increases as D p decreases. Brownian motion: random movement of particles in air - Difficulties in accurately modeling the billions of individual molecules results in using diffusion to describe the macroscopic scale movements - Mean velocity of molecules of a pure gas B = cB 8RTπMB = / cair 468 m s Viscosity: a measure of the resistance of a fluid under shear stress. For laminar flow (smooth, uniform) the sheer stress is: = τ μdudy Knudsen Number: defining the nature of air relative to the particle = Kn 2λDp Three regimes of particle-air interactions a. Continuum regime (Kn approaches 0) b. Free molecule, kinetic regime (Kn approaches infinity) c. Transition regime (Kn ~ 1) Diffusion of Gasses Fick’s First Law: the diffusive flux goes from high to low concentrations and is proportional to the concentration gradient = - J DdCdx Where J is the flux, D is the diffusion coefficient, C is the concentration, and x is distance. The (-) is used to denote the face that diffusion always occurs from high concentration to low. D
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This note was uploaded on 06/09/2010 for the course A&O SCI 145 taught by Professor Li during the Winter '10 term at UCLA.

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UCLA AOS145 Jan14 - Brownian D decreases. rrection which...

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