Mixing efficiency and pressure drop analysis of liquid-liquid two phases flow in serpentine microchannels

Abstract

When fluids flow in microchannels, due to the relative low hydraulic diameter and low flow velocity, the flow is usually laminar flow, which hinders the effective mixing between two liquid-liquid phases. In this paper, the mixing efficiency at both droplet forming stage and droplet moving stage are investigated with the volume of fluid (VOF) method. The user defined scalar (UDS) is defined in the dispersed phase to analyze the mixing efficiency quantitatively. The droplet moves in the microchannel with the constant velocity, while serpentine microchannels are designed with different bend radius ranging. \( \overline{R} \) and ed are defined as the ratio of the bend radius to the width of the microchannel, and the ratio of the dispersed phase velocity to the droplet moving velocity, respectively. They are used for illustrating the effect of the bend radius and the dispersed phase fraction on the mixing efficiency in the droplet. Results indicate that the smaller dispersed phase fraction and smaller bend radius show the better mixing efficiency. However, the droplet production frequency changes in a parabolic trend with the variation of the dispersed phase fraction. The suitable dispersed phase fraction should be less than 0.5 in order to achieve a higher mixing efficiency and higher droplet formation frequency. In addition, the pressure drop in microchannel is increased with the decrease of the bend radius. The pressure drop observed in the micorchannel with square turn (\( \overline{R} \) = 0) and the microchannel with a bend radius of \( \overline{R} \) = 1 is nearly the same. This paper can be referred by someone dealing with the micromixer design and mass transfer in micro scale.