On the mathematical model simplification using constant Lewis number – Impact assessment on heterogeneous char conversion process

Reactive systems in a thermochemical conversion domain are modelled considering N-specie, 1-energy and 2-mass conservation equations assuming negligible pressure gradient resulting N+3 non-linear coupled PDE system with dependency on thermodynamic transport properties. Typically, simplistic temperature-dependent polynomials chosen for estimating thermal conductivity specific heat, however, the estimation of mass diffusion coefficient ( D i;mix ) follows complicated procedure involving kinetic theory culminating Chapman-Enskog equation. This renders solution computationally intensive. The complexity is simplified by constant Lewis (Le) number, standard practice analytical conventional reactive systems. In fixing Le, equated to diffusivity (a ratio properties) specie energy equation yielding similar collapse simultaneous 3 equations. current article explores validity limitation Le simulation char process air steam. Results compared fixed estimated Chapman{Enskog expresion. analysis suggests that remains invariant only under severely restricted set conditions. Fixing influences, either over-/under-predicting time scales product gas composition.