Anisotropic flow physics in diamond microchannels: Design implications for microfluidic rectifiers handling Newtonian fluids

The study explores anisotropic flow behavior in microchannels, which is crucial for advancing microfluidic rectifiers. Specifically, the investigation focuses on the directional flow behavior of Newtonian fluids within diamond-shaped microchannels, a topology holding significant promise across various disciplines. Unlike non-Newtonian fluids, Newtonian fluids lack inherent directional traits, needing high Reynolds numbers for inertial effects necessary for effective rectification in asymmetric flow structures. High Reynolds numbers in microchannels are challenging, but diamond microchannels uniquely exhibit inertial effects even at low Reynolds numbers, yet their potential for designing rectifiers is largely unexplored. The study presents two unique asymmetric diamond microchannel designs and conducts thorough three-dimensional numerical analyses to assess fluid flow across different design parameters. Rectification is quantified through fluid diodicity, demonstrating that configurations with higher width and aspect ratios and shorter lengths produce significant rectification effects. Examining velocity profiles and flow resistances in both directions illustrates irreversible flow physics. Notably, the observed maximum diodicity for the proposed design reaches 1.61 for Newtonian fluids, surpassing most previous designs by 11%–40%. Quantitative relationships between flow resistances in both directions and design variables through regression analysis allow determining flow resistances within ±8% and fluid diodicity within ±7% and ±10%, respectively, based on constant flow rate and pressure drop. These correlations provide valuable insights for the initial design of microfluidic rectifiers using these configurations. The results offer essential guidance for effectively designing microfluidic rectifiers using diamond microchannels in various scientific applications.