A lattice-gas study of dispersion in alveolated channels

Abstract

Axial dispersion in alveolated channels was studied via lattice-gas automata (LGA), for both slug and step-change inlet conditions. There was good agreement between the effective diffusion coefficient ( D ∗ ) calculated by the LGA method, and the D ∗ predicted by the ‘stagnant pocket’ formalism developed by Aris, Turner, and Tsuda et al. The enhancement of D ∗ was dependent on the ratio of alveolar volume to central channel volume and the Peclet number. For Pe ≥ 5, D ∗ was substantially greater than the Taylor-Aris prediction for flow between parallel flat plates. For Pe < 3, D ∗ was less than the molecular diffusion coefficient, D m . In the absence of buoyancy, inlet conditions (pulse vs step-change) had little effect on the calculated D ∗ (≤ 3%). The effect of buoyancy, however, depends on the inlet condition; for an LGA corresponding to 1 mol% SF 6 tracer gas in air, D ∗ was increased up to 20% for the step-change, and decreased up to 6% for the slug.