Droplet behaviour influences significantly the quality of emulsions and the performance of microfluidics applications. Despite the numerous studies on droplet behaviour, the interactions between the suspended droplet and its surrounding walls, especially for non-Newtonian fluids, are not yet fully understood. Here, we investigate the behaviour of isolated droplets subjected to a simple shear in a wide range of capillary numbers, confinement ratios and viscosity relations between the droplet and the carrier fluid. Simulations are performed using the colour-gradient lattice Boltzmann method (LBM), which is also adapted to handle power-law fluids. Findings on the Newtonian droplets in a Newtonian carrier fluid show that droplet deformation and orientation to the flow, i.e. tumbling, are enhanced with increasing confinement. Even more, with a larger viscosity ratio the rate of the deformation increases more significantly while the rate of tumbling becomes smaller. Noteworthy, the largest deformation is presented by droplets of the same viscosity as the matrix fluid. We also find that in a shear-thickening carrier fluid droplet deformation and tumbling are enhanced while they are reduced in a shear-thinning fluid. Additionally, with increasing confinement, the lowest capillary number a droplet breaks increases in the low viscosity ratio cases, contrary to the high viscosity ratio ones. At unity viscosity ratio this critical capillary number is slightly affected while droplets are found to break at a lower capillary number in a power-law carrier fluid. Simulations are performed to examine the behaviour of power-law droplets sheared in a Newtonian carrier fluid. The results are correlated well with the ones of the Newtonian droplets when the droplets obtain ellipsoidal shapes. However, upon slight deviation from the ellipsoidal shape the behaviour of power-law droplets differs substantially from their Newtonian counterparts.
|Date of Award||1 Jun 2016|
- University Of Strathclyde
|Supervisor||Yonghao Zhang (Supervisor) & Jason Reese (Supervisor)|