Flow Properties of Mixed Ultra-Fine Bubble Micellar Solutions Passing through Small Slits

The effect of ultra-fine bubble (UFB) mixtures on the flow properties of micellar solutions passing through small slits was investigated. Steady-shear viscosity and dynamic viscoelasticity were measured because their rheological properties were evaluated. The resultant steady-shear viscosity (complex viscosity) and relaxation time were changed by mixed UFB. Pressure drops for ultrapure water (UPW), silicone oil, and mixed UFB water agreed with the predictions. On the other hand, worm-like micellar solutions showed higher pressure drops than those of UPW alone. Interestingly, pressure drops of micellar solutions mixed with UFB were lower than those of micellar solution alone. Furthermore, the experimental results arranged in dimensionless forms based on the hydraulic diameter showed the difference between with and without UFB in the range of slit-width ≥ 84 µm. For discussing these experimental results, elastic properties and flow-induced birefringence were observed. Mean elastic stresses and first normal stress difference were measured by jet thrust method. Those of micellar solutions were higher than those of micellar solutions without UFB. The magnitude of Weissenberg number was greater than the order of 103. Thus, the strong elastic properties exhibited an increase in pressure drop. Additionally, flow-induced birefringence was changed by mixed UFB. Flow properties were altered due to the change in the orientation of the worm-like micelles (flow-induced structure).