Consistent temporal behaviors over a non-Newtonian/Newtonian two-phase flow

Abstract

The temporal behaviors of non-Newtonian/Newtonian two-phase flows are closely tied to flow pattern formation mechanisms, influenced significantly by the non-Newtonian index, and exhibiting nonlinear rheological characteristics. The nonlinear behavior of fluid flow cannot be directly inferred from the rheological models, making their temporal characteristics difficult to predict. This limitation hinders the development of a unified analytical approach and consistent results, confining researches to case-by-case studies. In this study, sets of digital microfluidics experiments, along with continuous-discrete phase-interchanging schemes, yielded 72 datasets under various non-Newtonian fluid solution configurations, micro-channel structures, and multiple Carreau-related models. Among these datasets, we identified consistent temporal behaviors featuring non-Newtonian flow patterns in digital microfluidics. Generally, selecting the most appropriate model to accurately represent the flow characteristics of non-Newtonian fluids is case-dependent. Nonetheless, there exists a generally applicable description of the flow behavior that is not affected by specific rheological model. This discovery is of significant importance for understanding the common behavioral characteristics of non-Newtonian fluids.