2026/07/21 by Nader Afshar, N. Afshar, Yuri S. Muzychka +2
Engineering · #Heat Transfer and Boiling Studies #Innovative Microfluidic and Catalytic Techniques Innovation #Microfluidic and Capillary Electrophoresis Applications
paper · doi:10.1016/j.expthermflusci.2026.111814
openalex publication_date 2026/07/21 · openalex created_date 2026/07/22 · openalex updated_date 2026/07/28
This study investigates gas–liquid two-phase flow in wide rectangular microchannels with constant microscale depth and different widths, with emphasis on extending the operating window of slug flow to higher volumetric flow rates. Experiments were performed in acrylic microchannels with an average depth of approximately 0.66 mm and widths of 5, 10, and 15 mm using air with distilled water and silicone oils of 1, 3, and 5 cSt. Flow regime maps were constructed from visual observations, and the liquid phase velocity field in slug flow was measured using Micro-PIV. For the fully wetting air-silicone oil systems, six regimes were identified: bubble, bubble-slug, slug, unstable slug, annular, and churn flow. In contrast, only unstable slug, annular, and churn regimes were observed for air–water, due to partial wetting of the acrylic walls, gas-wall contact, and the absence of a continuous liquid film around the gas plugs. Increasing channel width shifted the slug-family regimes toward higher total flow rates and extended the unstable slug operating window for all silicone-oil systems. Stable slug flow was also extended for the 1 cSt and 3 cSt oils, whereas the 5 cSt oil showed earlier transition to unstable slug flow in the widest channel because of stronger viscous resistance to lateral gas plug expansion. Existing maps which are defined based on hydraulic diameter showed poor agreement with the present high aspect ratio data. Therefore, force based empirical transition maps were developed using an area-based characteristic length, ( L c = A ). A ( Γ - θ ) map classified the four main regime families with 92 % accuracy, while a ( Γ - ψ ) map separated bubble-slug, slug, and unstable slug regimes with 88.8 % accuracy. Micro-PIV measurements revealed plug slip, transverse interfacial motion, and back tail circulation within the liquid film. A continuity-based analysis showed that local reverse flow must occur near the minimum film thickness location, supporting the experimentally observed circulation.