Numerical investigation on the effect of surface wetting properties on gas – Liquid two-phase flow in microchannel using level set method

Over the past decade, the potential of two-phase flows at the microscale has gained increasing attention and provided an impetus for the development of multiphase microfluidic systems for a variety of applications. In microscale two-phase flow, dimensional scaling dictates the dominant role of the surface interactions due to the increasing surface-to-volume ratio. Within a confined microchannel, these surface interactions include not only the interfacial interaction between the two phases, but also the interaction of each fluid with the channel walls. In this paper, we investigate the influence of surface wetting properties on air–water two phase flows in rectangular microchannels. Specifically, we varied the hydrophobicity of the microchannels and injected air and water in parallel to generate air–water two-phase flows in a horizontal rectangular microchannel that is 300 µm in width, 100 µm in height and 1 cm in length. A CFD simulation is carried out with COMSOL Multiphysics, using the Two-Phase Flow, Laminar, Level Set application mode. This application mode uses the Navier-Stokes equations to describe the momentum transport, including the surface tension and the conservation of mass, and also a reinitialized level set method to represent a discrete fluid interface between the air and water. Our work demonstrates that different wetting properties of a microchannel give rise to dramatic changes in the morphological characteristics of two-phase fluid flows at the microscale. We identified five flow regimes in microchannels with hydrophobic walls, whereas only two flow patterns were observed in hydrophilic microchannels. The results are compared with experimental results for micro-channels and showed good agreement, comparisons between the numerical results and experimental findings are also presented and discussed.