Numerical study of conjugate mass transfer from a spherical droplet at moderate Reynolds number
Résumé
Hydrodynamics and conjugate mass transfer from a spherical droplet at low to moderate Reynolds num- ber have been investigated by direct numerical simulation. The study particularly focuses on the coupling between the internal and external flows, and their respective effects on the resulting mass transfer of a solute under 2D axi-symmetric configuration. The influence of the viscosity, density, and diffusivity ratios (μ∗, ρ∗and D∗ respectively) between the two phases, as well as that of the equilibrium constant k (or Henry’s number) characterizing thermodynamic equilibrium at the interface, has been studied in a range of flow Reynolds numbers relevant for solvent extraction processes (up to Reynolds number 100). The temporal evolution of the Sherwood number has been analyzed and a general correlation is proposed for its steady state regime. Interestingly, simulation results show that correlations available in the literature in the limiting cases k√D∗<<1 and k√D∗>>11 , referred to as internal and external mass transfer regimes, are not always appropriate in the context of conjugate mass transfer. This limits the use of the addition rule of transfer resistances, which reflects the flux continuity in the double stagnant film model. Indeed, a significant discrepancy is observed under specific configurations, especially at low Péclet number (Pe≤500) where non uniform interface concentration prevails.
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