Modeling mass transfer in a Taylor flow regime through microchannels using a three-layer model

Abstract

The process of convection and diffusion in a Taylor regime of gas–liquid flow through microchannels is modeled based on a three-layer mass transfer model in the axisymmetric formulation. The circulation circuit of Taylor vortices is described in the form of outer and inner layers surrounded by a thin film that does not participate in circulation. Due to the assumption about the predominance of convection over radial diffusion in the inner layer (the Peclet number order of magnitude is nearly 10⁵) and a uniform concentration distribution over the cross sections of each layer, the problem is confined to a quasi-one-dimensional problem with boundary conditions of special type. The obtained numerical solutions allow us to determine the kinetics of mass transfer from a liquid to a channel wall in detail, calculate the average mass-transfer coefficient, and reveal optima in the dependences of the mass-transfer coefficient on the two-phase flow velocity and the capillary diameter; furthermore, there is also an optimum for the length of a liquid slug. The obtained results allow us to understand the pattern of Taylor convection and diffusion fluxes and to reveal the reasons for a decrease in mass fluxes under nonoptimal conditions. This enables the correction of selected geometric and process parameters during the design of microreactor equipment.