Production and Visualization of Vivid Streakline with the Self-Assembly of Surfactant Molecules

Abstract

Aims: Streakline and its visualization and production techniques are one of important indices for fluid dynamics, civil engineering, material engineering, and so on. In chaotic or turbulent flow field where global mixing occurs, fluid trajectory exponentially expands in particular directions. Consequently, it is quite difficult to visualize streak as a “line” because experimental streak behaves as a “sheet” that has rounded surface. In the present study, to product and visualize a vivid and distinct streakline, a non-ionic surfactant was utilized. Study Design: Experimental study containing simulation. Place and Duration of Study: Division of Chemical Engineering, Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, between December 2010 and October 2011. Methodology: The novel production and visualization technique for vivid streakline in three-dimensional (3D) flow field was developed. The innovative characteristic of visualization technique is that the expansion of streak can be suppressed by the surface tension with the self-assembly of surfactant molecules in the tracer fluid. The impeller-agitated tank was adopted as an unsteady 3D flow system. A non-ionic surfactant, "Emulgen  (Kao Co., Ltd., polyoxyethylenelaurylether) was adopted, whose concentration was optimized at about 9 mass% in advance. Results: The obtained streakline could keep the linear form for a long time not to expand, and there was little leakage of colored component due to the effect of molecular diffusion. The streakline could circulate freely in the tank; nevertheless its linear structure was maintained for a long time even if the streakline collided with the tank wall and impeller blades. The periodical consistency of streakline structure could be confirmed, which was one of necessary and sufficient conditions for the movement of streakline with flow field. Conclusion: This study clearly demonstrates the production method of vivid streakline with the help of surfactant. While this technique has a little room for additional refinement, the present technique may be used and developed for future science and practical applications.