Influence of randomly distributed wall roughness on the flow behaviors of liquid-liquid slug flow in a co-flowing microchannel

Abstract

In present study, the influence of randomly distributed wall roughness on the flow behaviors of liquid-liquid slug flow in a co-flowing microchannel has been numerically investigated, as the manufacturing tolerance of microfluidic device in engineering application is unavoidable. A circular axisymmetric microchannel model is adopted to study the effect of roughness height and correlation length on the wall roughness generation and internal laminar flow characteristics in the microchannel. The wall roughness is modeled by well-known Gaussian distribution method. The prediction of slug velocity and liquid film thickness from numerical simulations has been well validated with the empirical and analytical correlations and experimental data in the literature. The obtained results show that the rough wall condition significantly affected the internal flow behaviors, such as slug moving velocity and slug breaking-off. According to the quantitative comparison of normalized surface areas between high (larger than 0.4 m/s) and low (smaller than 0.69 m/s) velocity region, the surface area of low velocity region under rough wall condition (wall roughness: D/l=3.333 and σ/D = 0.018) is 46 % larger than smooth wall condition, which means effective flow area of microchannel is reduced. The surface area of high velocity region under rough wall condition increases around 66 % compared with smooth wall condition. This study could be used as a promising reference and provide more understanding for roughness control in industrial microfluidic device.