Two-phase simulations of viscoplastic flow in superhydrophobic microchannels: interface stability, plug dynamics, and drag reduction

Superhydrophobic surfaces are widely investigated in microfluidics for drag reduction; however, their role in transporting viscoplastic biological fluids such as blood, mucus, and hydrogels remains poorly understood. Here, high-resolution two-phase simulations are performed to investigate pressure-driven viscoplastic flow in superhydrophobic grooved microchannels, focusing on three critical design indices: liquid/air interface pinning, central unyielded-plug breakage, and pressure-drop reduction. Groove geometry and flow inertia, represented by the Reynolds number, jointly determine whether the liquid/air interface remains pinned in the Cassie state or undergoes depinning, and a correlation is derived to predict this transition. For identical groove aspect ratios, the critical Reynolds number for depinning is markedly lower in thinner microchannels. Groove depth and width strongly influence plug deformation and breakage. Additional correlations quantify pressure drop and plug breakage, and the resulting predictive design map enables the optimization of superhydrophobic microchannels for lab-on-a-chip devices handling viscoplastic fluids.