Interaction between convection and surface reactions in physical vapor transport in rectangular, horizontal enclosures

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The introduction of mixed boundary conditions on active surfaces allows us to introduce non-equilibrium interfacial surface kinetics together with its coupling to the convective motion of the bulk. The Navier-Stokes equations are used with both thermal and solutal source term in the momentum equation. The boundary conditions on the active surfaces are derived from the conservation equations for the specific properties of the interface. Based on these boundary conditions, a 1D description of diffusive transport in closed ampoules is given. Numerical solutions of the 2D non-steady transport equations were obtained by a finite difference method, carried out as a function of the chemical surface reaction rate, the diffusion coefficient and the gravity level values. It is found that: (a) the model with boundary conditions based on interfacial equilibrium is a zeroth order asymptotic description for infinite surface reaction rates of the present theory; (b) high diffusion coefficients lead to a uniform concentration field and vanishing solutal convection; (c) the concentration on the active surfaces may be affected by convection: it is quite uniform for low gravity level and is strongly disturbed for earth level gravity; (d) the surface concentration profile is the more coupled with convection the smaller the reaction rate is; (e) the concentration field, obtained for neither reaction nor diffusion-limited surface kinetics, exhibits quite new behaviours, compared with the ones previously obtained.