Modeling of Newtonian droplet formation in power-law non-Newtonian fluids in a flow-focusing device

• Published in: Heat and mass transfer Vol. 56; no. 9; pp. 2711 - 2723
• Main Authors: Chen, Qi, Li, Jingkun, Song, Yu, Christopher, David M, Li, Xuefang
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2020; Springer Nature B.V
• Subjects: Compressing; Computational fluid dynamics; Droplets; Engineering; Engineering Thermodynamics; Flow velocity; Fluid flow; Heat and Mass Transfer; Industrial Chemistry/Chemical Engineering; Microfluidic devices; Newtonian fluids; Non Newtonian fluids; Original; Power law; Rheological properties; Scaling laws; Thermodynamics; Two phase flow; Viscosity
• ISSN: 0947-7411; 1432-1181
• DOI: 10.1007/s00231-020-02899-6

Droplet formation in a flow-focusing device was modeled using the open source CFD package, OpenFOAM, with the VOF model for two-phase flow. Predictions using the interFoam solver and a power-law non-Newtonian model were first validated against experimental data in the literature. Then, the formation of Newtonian fluid droplets in power-law fluids was modeled during tubing, squeezing, dripping and jetting. The effects of the continuous phase rheological parameters on the droplet formation were investigated by changing the power law index ( n ) and the consistency coefficient ( K ). The results show that the droplet length and the spacing between two droplets decrease as n or K increase. However, the formation frequency and droplet velocity in the main channel increase as n or K increase. The results also show that n has a greater effect than K on the droplet formation. A method was developed to calculate the capillary number of the power-law continuous phase in the squeezing and dripping regimes including the influences of n and K . For a given dispersed phase flow rate, the formation frequency is inversely proportional to the droplet volume. A scaling law was also developed to predict the formation frequency since the droplet volume is found to vary linearly with the non-dimensional droplet length. The present work is useful for controlling droplet formation and designing microfluidic devices in areas where non-Newtonian fluids are used as the continuous phase.