Chaotic Dynamics in a Percolation Model for Evaporation of a Solid Body: A Description of Solid/Gas Reactions with...

A nonlinear truncated model, concerning thermodiffusive chaos in gaseous media, has been employed to represent evaporation of a solid body on the basis of nonlinearity at the solid/gas interface. Solid/gas consumption has been described in the cell which is characterized by the wavenumber of the interfacial convective motion. The solid molecule/atom evaporates according to a Boltzmann law that is ruled by temperature profiles coming from the truncated model. This allows the interpretation of the evaporative mechanism as depending on a Poincaré map related to the interfacial dynamics and suggests a possible correspondence between kinetics and nonlinear cooperative regimes. Percolative properties (k-th moments, critical threshold and exponents, fractal dimension) of the evaporating solid path have been derived for different thermal levels (i.e., reactivity), namely, for different values of the reduced Rayleigh number (r), which in the model accounts for the temperature contribution. The achieved descriptions generally agree with microstructural and theoretical observations concerning gasification of reacting solid/fluid systems. Moreover, previously proposed kinetic data (i.e., gasification rate versus fractional conversion) of char/air reactions have been interpreted in terms of a percolation theory that involves the solid/gas reactivity and the order of the convective mode (i.e., wavenumber). This result resembles the so-called finite amplitude cellular convection in gaseous and liquid layers working in nonlinear regimes. Copyright 1999 Academic Press.