Pressure changes through a sudden expansion in rectangular microchannels for laminar and turbulent flows

This study experimentally investigates the relationship between the pressure change (ΔPe) at a sudden expansion and the Reynolds number for liquid flows in rectangular microchannels with different expansion ratios. In the experiments, water and an aqueous glycerol solution with various mass concentrations were used as test liquids, and detailed pressure distributions near the sudden expansion section were measured to determine the ΔPe under laminar to turbulent flow conditions. The experimental results showed that ΔPe increases with Reynolds number; however, the increasing trend is affected by the flow conditions both upstream and downstream of the expansion as well as by the reattachment length of the recirculation region formed downstream of the expansion. The Borda–Carnot equation was found to underestimate ΔPe, particularly in the laminar flow regime. To address this, a prediction model for ΔPe was developed by considering both the velocity distribution and the reattachment length effects. The model parameters were determined by applying the least-squares method, with supporting findings from previous studies for the momentum correction factor, Darcy friction factor, and the reattachment length. The proposed model successfully predicted ΔPe within ±12% on average over a wide Reynolds number range from laminar to turbulent flow regimes. These results demonstrate that the model provides a reliable basis for evaluating expansion losses in microchannels and has potential applicability to the design of microfluidic and microreactor systems.