Flow of Dilute Colloidal Dispersions in Water through a Small Orifice

Abstract

Fluctuation of flows through a small orifice has been measured for water and two kinds of colloidal dispersions including fine particles about 100 nm in diameter with 1 % volume fraction in water. In this volume fraction, a surface potential of the particles is composed of an electrostatic repulsion and a van der Waals attraction and it affects flow properties. Experiments clarify that a specific flow instability occurs for water at the Reynolds number about 60, and the dispersion of polystyrene particles having strong repulsion increases the specific flow instability in low salt concentrations(LSC) but makes it disappear in high salt concentrations(HSC). Meanwhile, it is found that the dispersion of silica particles having strong attraction is stable in flows except the specific flow instability in LSC but it suppresses the specific flow instability in HSC as in the case of polystyrene particles. Criterion whether the orifice flow is stable or not is predicted by comparison of the second minimum location of the surface potential and the mean surfaces distance of the particles.