Yuki Mizushima

Detection method of a position pierced by a single-tip optical fibre probe in bubble measurement

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.

A novel particle separation technique using 20-kHz-order ultrasound irradiation in water

Ultrasound techniques such as washing, fine-particle manipulation and mixing have been investigated. MHz-band ultrasound was usually used in the previous work, and studies of kHz-order ultrasound are very rare. In the usual manipulation technique, μm- order particles are targeted due to wavelength limitations. We discovered an interesting phenomenon that holds promise for a novel particle separation technique using kHz-order ultrasound. Here, particles with sub-mm- or mm-order diameters were flocculated into a swarm in water irradiated by 20-kHz ultrasound. To develop a practical separation process, we investigated the stationary position and dia. of the particle swarms and the sound- pressure profiles in a vessel, as well as the flocculation mechanism, by varying the irradiation frequency, water level, particle diameter and particle amount. The primary stationary position corresponded to the wavelength calculated from the resonant frequency regardless of the particle diameter. Subtle changes in the frequency and water level resulted in a significant change in the stationary position. Based on these results, we propose a new separation process based on the particle diameter for sub-mm- or mm-order particles.

A newly developed method for detecting a pierced position/angle by using a pre-signal in bubble measurement via a single-tip optical-fiber probe

The Optical Fiber Probe (OFP) has been widely applied for measurement of gas-liquid two phase flows. One of the authors already developed an S-TOP (Single-Tip Optical-fiber Probe with a wedge-shape tip), and reported its satisfactory performance of bubble/droplet measurements only by using the single tip. The purpose of this study is to improve the accuracy of the S-TOP in bubble measurements. To detect a touch position of the S-TOP on the bubble surface is very important. We propose a pre-signal threshold method. The pre-signal appears when the S-TOP tip is approaching to the bubble frontal-surface. It appears intensively and sharply, only when the tip touches the center region of the bubble, vertically. Utilizing this useful characteristic of the pre-signal, we can extract only the signals possessing particular conditions that the S-TOP almost perpendicularly pierces the near center region of a bubble. Firstly, the details of the pre-signal threshold method are described. Secondly, the effectiveness of ...

A Newly Developed Technique for Detection of a Contact Position in Bubble Measurements by a Single-Tip Optical Fiber Probe

An optical fiber probe has been frequently employed to measure bubble diameters, velocities, and local void fractions simultaneously in gas-liquid two-phase systems. For the application of the probe to tiny-bubble measurement, one of the authors already developed a Single-Tip Optical fiber Probe (STOP). The purpose of this study is to rapidly improve the measurement accuracy of the S-TOP. A bubble chord length pierced by the S-TOP is obtained. Consequently, the chord length depends on the pierced position. The chord lengths measured by the S-TOP include an error owing to the random positions pierced by the S-TOP; i.e. the measured chord length becomes shorter than the bubble minor axis, with a shift of the contact position towards the outer edge of the bubble. The S-TOP axis crosses the direction of the bubble motion at a random angle. This also causes a miscalculation of the chord lengths. In order to correct these errors in the S-TOP measurement, we need to detect the contact position and the intersection angles. To realize this, using a pre-signal is quite effective. The pre-signal is generated clearly and intensively, only when the S-TOP sensing tip is ground in a wedge shape and the tip touches vertically the center region of the bubble frontal surface. The pre-signal becomes weak and indistinct under the other contact conditions. Making the smart use of these phenomena, we are able to solve the above defects of the S-TOP. First, the relationship between the intensity of the pre-signal and the pierced positions/angles is systematically quantified. Second, a signal processing to detect the pierced positions/angles, based on the relationship, is established. Third, we discuss a mechanism of the pre-signal. We determine the most suitable S-TOP size, tip diameter and wedge-angle, for the most accurate measurement. Finally, we demonstrate the effectiveness of our newly proposed method.Copyright