Tatsuro Wakimoto

Removal of Fine Particles on a Wall by High-Frequency Turbulence Added Air Flow

A cleaning technique to remove particles of several micro-meter diameter from a surface under dry environmental conditions is greatly needed in the manufacturing processes of LCDs. However, it is usually difficult to remove the fine particles by simple airflow because the particles adhere to the surface by strong forces. For this reason, a cleaning device equipped with a special nozzle is used in the actual industrial process. The nozzle has triangular cavities to add strong high-frequency fluctuations to the airflow. To clarify the effect of this fluctuation on particle removal quantitatively, we measured the airflow velocity, pressure fluctuation on a surface, and removal ratio for four types of nozzles: two varieties cavity nozzles and two straight nozzles with different lengths. The correlation between the intensity of pressure or velocity fluctuation and removal ratio for the cavity nozzles suggests that the turbulent fluctuation added by the cavity contributes to particle removing.

Residual bubble volume formed behind a sphere plunging into liquid bath (meniscus breakdown with finite velocity of sphere penetration)

The residual bubble formed from spherical particles plunging into a liquid bath has an important effect on the performance of CaO particles used for the desulfurization of melted iron. Previous work has theoretically estimated the residual bubble volume resulting from quasi-static sphere immersion by applying the energy minimization principle to the gas–liquid interface meniscus at its rupture [Katoh et al., “Residual bubble formed behind a sphere plunging into liquid bath (in Japanese),” Jpn. J. Multiphase Flow 28, 547–553 (2015)]. Here, we propose a method to theoretically estimate the residual bubble volume for sphere penetration with a finite velocity from 0.05 to 30 mm/s into a liquid bath. To do so, the meniscus rupture at the sphere’s critical depth was calculated via a dynamic equation in which the energy gradient along the sphere surface was considered as the driving force to move the triple-phase contact line. The bubble volume was then estimated by calculating the system energy at the meniscus breakpoint and by using the principle of minimum energy. The model results were verified experimentally for a variety of liquids, showing that the proposed model can be used for estimation of the residual bubble volume.The residual bubble formed from spherical particles plunging into a liquid bath has an important effect on the performance of CaO particles used for the desulfurization of melted iron. Previous work has theoretically estimated the residual bubble volume resulting from quasi-static sphere immersion by applying the energy minimization principle to the gas–liquid interface meniscus at its rupture [Katoh et al., “Residual bubble formed behind a sphere plunging into liquid bath (in Japanese),” Jpn. J. Multiphase Flow 28, 547–553 (2015)]. Here, we propose a method to theoretically estimate the residual bubble volume for sphere penetration with a finite velocity from 0.05 to 30 mm/s into a liquid bath. To do so, the meniscus rupture at the sphere’s critical depth was calculated via a dynamic equation in which the energy gradient along the sphere surface was considered as the driving force to move the triple-phase contact line. The bubble volume was then estimated by calculating the system energy at the meniscus ...

Simultaneous determination of micellar structure and drag reduction in a surfactant solution flow using the fluorescence probe method

As widely known, the addition of a specific type of surfactant to water reduces drag in a pipe flow. This effect is considered to be a result of the suppression of turbulent transition caused by the ordered structure of rod-like micelles that is referred to as a shear-induced structure (SIS). However, it is typically difficult to determine the SIS since it is necessary to noninvasively detect the SIS with several hundred nanometers in the actual moving flow. In this study, we used the fluorescence probe method to locally determine the SIS in a pipe flow. When hydrophobic fluorescence molecules are added to the surfactant solution, the fluorescence molecules are trapped in micelles. Thus, fluorescence intensity varies based on the change in the micellar structure. We verified the applicability of the fluorescence probe method to the SIS detection and determined the relationship between the micellar structure and the drag reduction in the pipe flow by simultaneously measuring the fluorescence intensity and ...