Numerical simulations of bubble formation in viscoelastic fluids within focusing microchannels using OpenFOAM

The comprehension of bubble formation mechanisms in viscoelastic fluids within microchannels is crucial for the optimization of gas–liquid microreactions and microfluidic processes. In this study, a three-dimensional numerical investigation of bubble formation in viscoelastic fluids within a focusing microchannel was conducted using OpenFOAM. The volume of fluid method was employed to track the gas–liquid interface, while the Oldroyd-B model was utilized to describe the complex rheological behavior of the viscoelastic fluids. The effects of two-phase flow velocity ratio, relaxation time, and liquid viscosity on the evolution of the bubble neck width, bubble size, and channel pressure were observed. A model was proposed to characterize the evolution of the bubble neck width. Furthermore, an empirical correlation for predicting bubble size was proposed, with the relaxation time as a critical parameter based on dimensional analysis. The results revealed four flow patterns, including bubble flow, slug flow, tip-streaming, and annular flow. A flow pattern map was constructed based on two-phase velocities. Notably, the pressure drop within the main channel was significantly reduced by the viscoelastic property of the fluids, offering novel insights into the fluid dynamics of viscoelastic fluids at the microscale.