Flow Properties of Microbubble Mixtures and Complex Fluids Passing through Micro-Apertures

Abstract

The pressure drops were measured for water, microbubble/water mixtures, and complex fluids (spherical micelle surfactant solution and polymer solution) in flows through micro-apertures (micro-orifices, circular pores, and hexagonal pores). For water, agreement between the resultant pressure drops and the predictions of the NavierStokes equation was obtained. For microbubble/water mixtures, drag reduction effect was suggested over a Reynolds number of about 1.0 × 10 1 in micro-orifice flows. Surfactant solutions exhibited the same results as microbubble/water mixtures. For polymer solutions, significant drag reduction was shown. Moreover, a drag reduction effect, which was independent of the used test fluids, was observed for Reynolds numbers over 1.0 × 10 1 in the flow through circular pores and hexagonal pores. To explain this phenomenon, the size effect, visco-elastic property, electric interaction, and interfacial tension are considered. The results suggest that electric interaction at the wall (interfacial tension) is a contributing factor. In addition, drag reduction rates were estimated. , who derived a mechanism for drag reduction by polymer additives based on elastic theory. Ogata et al. 19)have investigated the effect of surfactant solutions on the flow through a circular cylinder for Re ranging between 10 1 and 10 5 by measuring the drag coefficients and by flow visualizations.As summarized the above studies, channel flows (pipe flows, capillary flows, and rectangular channel flows) were investigated by using several types of fluids, and relationship between their rheological properties (elasticity and viscosity) and the drag reduction effect was reported for the complex fluids (dilute aqueous solutions of polymers and surfactants with wormlike micelles). Additionally, effects of volume fractions and particle diameters generated microbubbles were reported in microbubble drag reduction. However, the used characteristic length was more than 1 millimeter.Relative small size (< 1 mm) was limited. Moreover, spherical micelle surfactant solutions were not observed. On the other hand, drag reduction effect of microbubble mixtures, spherical micelle surfactant solutions, and polymer solutions in "capillary flows" was observed in our previous study 20) , which the diameter ranged from 110 μm to 0.75 mm. Also, it suggested pseudo-laminarization effect for the above test fluids. However, the flows through micron-sized apertures (example for orifice, slit, and pores) were limited. In this study, flows of water, microbubble/water mixtures, spherical micelle surfactant solution, and polymer solution passing through micron-sized apertures (micro-orifices, circular pores, and hexagonal pores) were investigated. Flow properties and the origin of drag reduction effects in the flows through microapertures are discussed by the results. EXPERIMENTAL PROCEDURE Test FluidsFour types of test fluids were used in this study. Deionized water (electric conductivity: 0.055 μS/cm; passed through a filter with pore size 5.0 μm befor...