An optical fibre probe is a very useful device for practical bubble/droplet measurements of gas–liquid two-phase systems. To measure a sub-millimetre-size or micrometre-size bubble/droplet, one of the authors previously developed a single-tip optical fibre probe (S-TOP) and S-TOP micro-fabricated by a femtosecond pulse laser. The purpose of the present study was to enhance the measurement accuracy of the S-TOP. The most difficult problem to resolve in the S-TOP measurement is the detection of the position at which the S-TOP pierces a bubble/droplet. A pre-signal, which has normally been considered burdensome noise in signal analysis, can be effectively used to realize this important action. We analysed the properties of the pre-signal and discovered its hidden potential. Here we proposed a new method for effectively using the pre-signal for the practical detection of the penetrated position. We also demonstrated the effectiveness of the pre-signal method by using a bubbly flow. Finally, we conducted the uncertainty analyses of the S-TOP bubble measurement with the pre-signal method.

Our objective is to improve the accuracy of bubble measurement with Single-Tip Optical fiber Probe (S-TOP) in a bubbly flow. The STOP measures a point-wise void fraction and a velocity and diameter of a bubble simultaneously, by using only a single Mizushima, Sakamoto, and Saito CES 2 wedge-shaped tip. The STOP structure is very simple but raises an issue of an unclear touch position/angle between the STOP and a bubble. We propose a pre-signal threshold method in order to solve this issue. The pre-signal is one of the noisy optical signals from the STOP. First, the STOP signals are quantitatively analyzed with a newly developed 3D computational ray tracing method; the simulator can trace enormous ray segment trajectories in an optical fiber and render complicated optical boundary conditions. Moreover, in the simulator, evaluation of the complex output signals is achieved by computing the polarization and energy of every ray. We discovered that the intensity of the pre-signal indicates whether the STOP touches normally the center region of the bubble, or does not. We applied this characteristic to practical STOP measurement of a bubbly flow. As a result, the difference between the measured chord length via the STOP and the bubble minor axis from visualized images was significantly improved from 42 % (existing signal process) to 15 % (with processing through the method).

Bubble nucleation and growth following plasma channeling (filament) and white-light continuum in liquid irradiated by a single-shot fs-pulse were experimentally investigated with close observation of the time scale. Making full use of a new confocal system and time-resolved visualization techniques, we obtained evidence suggestive of a major/minor role of the non-linear/thermal effects during the fs-pulse-induced bubble's fountainhead (10−13 s) and growth (10−7 s), which was never observed with the use of the ns-pulse (i.e., optic cavitation). In this context, the fs-pulse-induced bubble is not an ordinary optic cavitation but rather is nonlinear-optic cavitation. We present the intrinsic differences in the dominant-time domain of the fs-pulse and ns-pulse excitation, and intriguingly, a mere hundred femtoseconds' excitation predetermines the size of the bubble appearing several microseconds after irradiation. That is, the nucleation happens temporally beyond a six-order-of-magnitude difference.

It is very difficult to remove extremely small particles from the surface of the wafer. Here, we proposed a new cleaning strategy using brush scrubbing, namely, nodule deformation induced fluid flow. Liquid absorption and desorption due to brush deformation enhance the mixing of liquids containing small particles. In this study, we developed a setup that reproduced the actual movement of PVA roller brushes on a rotating wafer and observed the contact surface of the brush nodule. We modeled the brush nodule deformation for each rotating condition. As a result, three types of nodule deformation were observed. In most cases, the nodule side face, rather than the bottom face was mainly in contact with the wafer surface. Moreover, we compared two types of roller brushes, normal cylindrical nodules, and edge treated nodules and found that the deformation can be significantly changed by chamfering nodule edge.

The adhesion force between two materials is a key factor in surface cleaning. In this study, we developed a method for measuring adhesion forces between polyvinyl acetal (PVA) brushes and several test surfaces to understand the brushes’ adhesion characteristics. We utilized both the viscoelastic properties of PVA brushes and a high-response load cell to evaluate the adhesion forces of the compressed brushes on a flat surface. The results of the study showed that the adhesion forces increased with increased contact time and amount of compression. Some materials strongly interacted with the PVA brushes. We also observed that the measured adhesion forces were due to the existence of a skin layer on the brush surface. Moreover, we compared the adhesion forces with torques generated from rotating PVA brushes. However, the results did not correlate with the adhesion forces, which suggests that the force in the quasi-static state differs from that in the sliding condition.

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Manuscript Mizushima, Nagami, Nakamura, and Saito-2-applicable to particles with diameters similar to a wave length of the irradiated ultrasound or with smaller diameters than that. Hence, particles which are larger than μm-order in diameter are difficult to be manipulated with MHz-band ultrasound. In the present study, to clarify an unknown flocculation mechanism of the particles in an ultrapure water under kHz-band ultrasound irradiation, we quantitatively discussed an interaction between the particle motion and the acoustic cavitation bubble motion based on the experimental results. First, we successfully captured the particle motion and acoustic-cavitation-oriented bubble motion simultaneously by using a high-speed video camera. Second, we measured the distribution of the sound pressure in the water phase and discussed the relationship between that of the sound pressure and the motion of the particle and the acoustic cavitation bubble. Finally, we investigated the effects of the gravity force, the acoustic radiation force and the spatial heterogeneity of the pressure acting on the particle. By combining the results, we found out that an acoustic-cavitation-oriented bubble adhered to the particle and the particles moved toward the [CES-D-12-01205] Manuscript Mizushima, Nagami, Nakamura, and Saito-3-pressure anti-nodes of the standing wave by the acoustic radiation force acting on the adhering acoustic-cavitation-oriented bubble.

Filling holes with liquid, or discharging gas from holes, is a fundamental process in both cleaning and painting. Discharging gas from small holes with closed end and high aspect ratio is extremely difficult due to surface tension. In this study, we developed a new gas discharge process from a hole by using acoustic wave irradiation. We irradiated two types of acoustic waves: waves with constant frequencies and those with variable frequencies in time i.e. sweep wave for test samples in a water pool. In addition, we observed gas discharge using high-speed video camera. As a result, we succeeded in completely discharging gas by using sweep frequency of the acoustic waves. From the observation results, we confirmed that gas discharge consists of three stages. The gas was discharged from the hole mainly at the first and third stage. In these stages, the natural frequency of the gas column in the hole was essential. In the second stage, the gas column in the hole breaks into multiple gas columns; then, the gas was hardly discharged even with the acoustic wave irradiation.