Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

KINETICS OF SURFACE IRREVERSIBLE REACTIONSIN TURBULENT FLOW IN THE LONG TIME LIMITE.G. ObrazovskiiPP-I-31OOO Khimpolitech, Zelenay Gorka, 1, 630060, Novosibirsk, Russia, fax:(383)3320049,Novosibirsk State University, 630090, Novosibirsk, Russia,e-mail: e_obrazovskii@ngs.ruSurface reaction play an important role in many physical and chemical processes. Someof numerous applications of the surface reactions include catalytical reactions, several typesof electrode reactions, dissolution processes. The overall decay rate of reactants is determinednot only by the transport of reactants to the surface but also by the rate of chemical reactionconstants. For well-developed turbulence when mixing in turbulent flow considerablyenhance transport of reactants to the surface, finiteness of rate of chemical reaction can limitthe overall decay rate of reactants.The evolution of chemical reactants concentration in turbulent flow is described by meansof passive scalar theory, when a feedback of reactants to the flow is negligible. In nonstationaryproblems, as it was shown in [1,2], after short intermediate stage theinhomogeneities of the passive scalar are localized near the wall where the advective mixingis not so efficient as in bulk. These results were generalized on the case of bulk chemicalreactions in [3]. In [4] the effect of advective diffusion on the decay rate of the chemicals bythe first-order surface fast reaction for well-developed turbulence was analyzed.Here we analyze decay of chemicals due to an irreversible m-order reaction taking placeon a flat surface with finite rate constant in turbulent flow in closed vessel and in the casewhen a chemicals are contained near the wall by an external field, for example, electric, highgradientmagnetic and centrifugal force fields. Since the reactants are rapidly mixed byturbulent flow, their inhomogeneous distribution must be localized in narrow boundary layernear the reaction surface. So in the limit of well-developed turbulence the surface can beconsidered approximately as a plane and problem can be treated as one-dimensional. Thedecay of the concentration n of reactant in closed vessel averaged over velocity fluctuations ofthe turbulent flow is described by the equation [1]:Δ t n = Δ x [(k + D adv (x)) Δ x n ], (1)where k is molecular diffusion coefficient, D adv = μ x 4 is eddy diffusion coefficient, x is thedistance from the wall. The parameter μ is estimated as μ = V 4 L /Re ν 3 , where V L is thecharacteristic scale of velocity fluctuations, ν is kinematic viscosity, Re = V L L/ ν is the267