In recent years, it has been defined by the International Organization for Standardization (ISO) that fine bubble of 100 μm or less be referred to as fine bubble. Fine bubbles will have specific properties different from bubbles that are seen in everyday life such as millimeter size and centimeter size by refining the gas. For example, the total surface area of a plurality of fine bubbles having the same volume as a single bubble of centimeter size is significantly large, and the chemical reaction, physical adsorption and mass transport at the gas-liquid interface are dramatically improved. Moreover, the fine bubbles have such property that dissolution efficiency of internal gas is improved from a huge total surface area acquired. In this study, cleaning and purification were performed utilizing the specific properties of these fine bubbles. In cleaning, the research was conducted on the removal of oils adhered to polypropylene and the removal of salt fixed to aluminum foil. Regarding the oil removal, the removal effect that relies on the total surface area of fine bubbles was verified. Regarding the removal of fixed salt, the result that by efficiency improvement of the removal of fixed salts is attained from phenomena such as fine bubble dissolution and bubble formation again. On the other hand, in the purification, fine bubbles were supplied to a river model tank containing the actual river sediment, and the changes in the water quality were investigated. As a result, the oxide layer of the sediment was formed from the high dissolution efficiency of the fine bubbles, and the suppression of elution of phosphorus from the sediment was verified.

Ultrafine bubbles (UFB, Nanobubbles), which are fine bubbles with a bubble diameter of 1 μm or less, have been studied in many fields and become to be practically used. UFB suspended water can be applied for cleaning technology also. Urinary calculus, which is a kind of scale, is produced in pipe, heat exchanger and others, with decomposition of urea. It is a problem in toilets because it promotes the propagation of bacteria when it adheres, clogging water distribution pipes. In this research, the effect of UFB onto the adhesion (production) of urinary calculus is studied and its properties are investigated. It suggests that UFB existence would take the structure of urinary calculus to be brittle on the basis of urinary calculus adhesion during 3 month. Its effect would take scale adhered to be easily removal, while the inhibition of accumulation of urinary calculus could not observed by the existing of UFB.

Transport of fine bubbles (FBs) in porous media has drawn increasing attention, as a promising technology for soil and groundwater remediation. Understanding the transport characteristics of FBs in soils is essential to optimize FB-based remediation techniques. FB transport is highly influenced by flow rate, gas species, chemical properties of FB water such as pH and ionic strength. Transport models for colloidal particles including colloid filtration theory are applicable for characterizing FB transport in the porous media. In addition, DLVO theory representing interaction energy between colloidal particles and collector was helpful for understanding attachment mechanism of FBs in the porous media.

Non-aqueous phase liquids (NAPL) are immiscible materials and their flow behavior in the soil is multi-phase flow. In general, NAPL is categorized as contaminant fluid in the ground so it is important to study the contamination and remediation mechanism of NAPL in the ground. Micro focused X-ray computed tomography (CT) scanner is a powerful tool to observe inner condition of soil. The objective of this study was to understand the flow behavior of NAPL in soil. In this paper, experimental study was introduced to visualize the behavior of NAPL. In particular, it was explained that the study using X-ray CT to visualize the pore structure of sandy soil contaminated by light-NAPL (LNAPL) and remediated by flushing water and air. The result suggested that increase of the air flow rate did not attribute to reduce the volume of LNAPL blob in the range of capillary number which was defined as fingering phenomenon. However，different conditions of residual LNAPL blobs were found out significantly with increase of injection rates. The result of further image analysis, which could determine the number and size of blobs, indicated that it was caused by interaction of entrapment by wetting phase liquid and small pore.

The wettability of liquid film flowing on an inclined plate is extremely deteriorated if there is a vertical wall on the channel side. In this study, an experimental study was conducted to investigate the influence of the side wall on the dryout of liquid film flow. The film surface forms a meniscus having a minimum film thickness near the side wall. The thin film thickness causes the dryout of film flow at lower flow rate. To avoid the appearance of the minimum thickness, the test channels of SUS-304 plate having circular side walls with various curvature radii R_S were manufactured and the surface profiles of liquid film were measured experimentally for three kinds of test liquids. The meniscus profile was flattened at appropriate radius of curvature, i.e., R_S.~6 mm for θ_R=20～30°(θ_R : receding contact angle) in this experiment. The critical Weber number at which dryout disappears is lowered remarkably and is recovered to the value those experienced for the flat plate without side walls.

We investigate the vapor bubble stability in liquid argon and water using a molecular dynamics simulation. The Lennard-Jones interparticle interaction potential is used to simulate the interaction forces between molecules. The Stillinger' s cluster criterion is employed to classify the vapor molecules evaporated from the bulk liquid. Using this criterion, the vapor molecules are determined to have no neighboring molecules within a 1.23 to 1.32σ radius, where σ is the interaction radius in the L-J potential. The pressure of vapor and liquid phase can be calculated from the virial equation of sate. The stability of bubble is disscussed applying the Young-Laplace equation. The spherical bubble shape is maintained, when the liquid pressure takes the negative value. The thickness of vapor-liquid interface and the number of molecules across vapor-liquid interface are not proportional to the size of bubbles.

The growth of a cavitation bubble cloud and the corresponding pressure near the tip of the cavitation bubble cloud formed by the backscattering of the focused ultrasound from a laser-induced bubble have been analyzed experimentally. The laser-induced bubble which is generated near the geometrical focus of the focused ultrasound is used as a reflector of the incident wave to yield strong negative pressure which leads to the cavitation inception and following cavitation bubble cloud formation. In the present study, optical observation by a high-speed video camera with frame rate up to 1.25 Mfps and the pressure measurement by the fiber optic prove hydrophone (FOPH) are carried out simultaneously to estimate the cavitation inception pressure. It is shown that the cavitation bubble cloud grows conically along with the propagation axis of the incident wave. The distance between the top interface of the cavitation bubble cloud and the geometrical focus of the focused ultrasound becomes a limited value even though the focused ultrasound keeps on irradiating, which indicates that the cavitation bubble cloud grows within the focal region with sufficient negative pressure due to backscattering. The pressure measurement reveals that the negative pressure amplitude backscattered from a free surface is larger than that of the focused ultrasound itself. Negative peaks in the pressure waveform have a long term fluctuation whose increments correspond the sudden growth of the cavitation bubble cloud. Cavitation inception pressure was measured defining it as the negative pressure at the top interface of the cavitation bubble cloud just before the FOPH was covered with cavitation bubbles. The measured cavitation inception pressure was -24 MPa in the present study.

When the focused ultrasound of sufficient acoustic intensity in liquid interacts an air-liquid interface, atomization of the liquid occurs. This atomization process is well known that droplets are generated from the apexes of standing capillary waves with a wavelength that can be related to ultrasonic frequencies. In addition, there is a hypothesis that cavitation bubble oscillations can play a significant role in the pinch-off of droplets from capillary wave. The aim of this study is to clarify the influence of bubbles on the atomization of liquid. In this paper, we used the focused ultrasound with a frequency of 1 MHz; then, we observed the atomization process by using a high-speed photography. Also, we added the microbubbles to enhance the atomization of liquid. We found that threshold acoustic intensity of generating fine droplets becomes smaller. This result indicates that bubbles contribute significantly to the atomization of the liquid.

In this paper, mechanism of interaction between shock wave and particles is investigated using CFD-DEM model. In CFD-DEM model, the limit of the grid resolution depends on the particle size. The particle-grid is introduced to solve this problem, and investigate the effect of it in the gas-particle shock tube. From the result of no particle grid case, large pressure oscillations appear because the grid size is almost the same as the particle size. On the other hand, the results of pressure fluctuations are good agreement with the experiment results using particle-grid. Hence, the particle-grid contributes to maintain calculation accuracy.

Chest drainage is frequently used in medical practice as an important treatment for respiratory diseases. For the purpose of quantifying air leak flow rate in a thoracic drainage unit, we will develop a gas flow rate measurement technique at low flow rate range. A test apparatus simulating a thoracic drainage unit is used to grasp and evaluate the process of bubble formation, which is evident from visualization results of exhaust gas, and evaluate the validity of the gas flow rate obtained from image processing. As a result, the correlation between the characteristic frequency of the pressure fluctuation and the bubble diameter was confirmed. Moreover, strong correlation between the bubble generation frequency and pressure changing was confirmed. There are suggested that the gas flow rate could be obtained from pressure measurement.

For a bubble approaching a flat plate, the Marangoni effect on the drainage suppression of a liquid film and the wall repulsive force are numerically studied. We investigated the driving force of gas-liquid interface. We carry out direct numerical simulation using a boundary-fitted grid conforming to the interfacial deformation. Spatiotemporal development of Marangoni stress and liquid film drainage are quantitatively investigated for various Marangoni numbers. The simulated results reveal that the repulsive force on the wall increases with increasing of the Marangoni number, indicating the suppression of the bubble-wall coalescence owing to the surfactant-driven Marangoni effect. For the sufficiently high Marangoni number, the repulsive force reaches at plateau. Such a saturated force is attributed to an excessive addition of the surfactant, which is likely to make the gas-liquid interface non-slip. The inertial force due to the flow in the liquid film and the Marangoni effect are significant for the deformation of the gas-liquid interface to the dimple shape. The dominant driving force of the interface deformation is not the Laplace pressure but the flow pressure.

Compulsive sedimentation of soil particles using coagulant is one of the solution for long-term turbid water in dams that has a bad effect on the environment of downstream rivers. We focus on allophane as a coagulant. The purpose of this study is to develop an atomization and transportation technique for allophane with a Venturi tube. We utilized the microbubble generator with a Venturi tube to atomize allophane. First, we visualized internal flow of the tube and measured diameter distribution of allophane after passing through the tube. As a result, allophane was atomized as small as that stirred for 10 minutes by ultrasonic, and it is suggested that allophane diameter hardly depends on liquid flow rate in the tube. Second, we throw allophane after passing through the tube into turbid water. As a result, the sedimentation of soil particles was promoted, and the turbidity of water was improved with the passage of time. The speed of sedimentation of soil particles is found to dependent on liquid and gas flow rate and presence of a Venturi tube. Third, we did transportation experiment of allophane. It is found that allophane is transported greatest under conditions of microbubble generation. Furthermore, we measured zeta potential of particles, and tried to reveal the mechanisms of turbid water treatment and transportation.

Ionic liquid is a molten salt composed of only anion and cation. The melting point of ionic liquid can be decreased to around room temperature by the combination of anion and cation. Because of the unique properties of ionic liquid such as high ionic conductivity, very low vapor pressure, electrochemical and thermal stability, solubility and absorbability, ionic liquid is applied to various energy and environmental technologies. In this study, the droplet formation process and spray characteristics in ionic liquid electrospray have been investigated by axisymmetric two dimensional multi-phase numerical simulation using surface tracking method. The formation of Taylor cone and droplet ejection resulting from electrostatic force acting on the interface with applied voltage was successfully demonstrated by numerical simulation. The spray mode transition with discontinuous decrease of droplet diameter occurs between 400 and 500 V in this operation conditions. After transition, the break-up location becomes almost independent of applied voltage and the droplet ejection frequency increases. It was found that the relationship between Bond number, Bo and Weber number, We with elongation velocity of liquid thread as representative velocity shows that spray is initiated at Bo ~ 0.7 and We ~ 50, and the spray mode transition occurs at around Bo~4 regardless of supply flow rate.

Microbubbles (MB) are widely used as contrast agents in ultrasound diagnostic imaging because of its surpassing responsiveness to several MHz band. Recently, many researchers are trying to apply MB and ultrasound to drug delivery system (DDS) using MB as drug carrier or gene transfer. For clinical application of MB-DDS, it is crucial to manipulate microbubbles contactlessly, capture in a desired place, and destruct them near the target. In this research, we developed a promising method to capture and manipulate Sonazoid using a concave transducer which radiates focused ultrasound. We used concave transducers, witch calibers were 40 mm and focal distances were 40 mm. The center of the transducers was made a 20-mm diameter hole in to allow observation light to pass through. We found that MB in focused ultrasound field can manipulate moving ultrasound focus mechanically, it is mainly the effect of primary Bjerknes force. The accuracy of the two-dimensional manipulation was 10 μm order. The manipulation force by primary Bjerknes force was 6 pN in 5.46 MHz, 4 kPa ultrasound conditions. The accuracy of the manipulation is sufficiently better compared to the focal width radiated by the concave transducer. When estimating trapping force near a bubble cluster formed at the focal region, secondary Bjerknes force is mainly acting on MBs in 10 μm order distance.

Viscosity of liquids is an important property determining flow characteristics such as shear stress caused by a flow, and elongation and dripping of films and drops. Conventional techniques determine liquid viscosity from shear stress acting in a capillary tube, on a vibrating plate, or on a rotating cylinder. The disadvantages of the methods are its relatively long measurement time and large amount of samples required, and more importantly, its inapplicability for coagulating liquids whose viscosity increases with time. Here we develop an original liquid viscosity measurement technique that employs a drop impact on a solid surface. The measurement principle is based on the energy budget: An impacting drop spreads on a solid surface due to kinetic energy which is on the surface converted to the viscous dissipation and the surface tension energy. We can therefore deduce the viscosity from the inertial, the surface tension force and the maximum spreading diameter. The simplicity of the present technique enables us to overcome the problems of the conventional methods. In experiments, we measured the viscosity of glycerol aqueous solution drops using a high-speed camera and a laser sensor. In conclusion, we revealed the uncertainty of the present technique is approximately 10 %, which was evaluated both by uncertainty analysis and by experimentally comparing the viscosity with the ones obtained with an Ostwald viscometer.

To clarify the spatial structure of number density distribution of bubbles in stout beer poured into a container, we investigated local time development of the void fraction and velocity of bubbles. The propagation velocity of the texture, i.e. the number density distribution, appearing near the inclined wall of the container is measured by the images analysis. We measured the local void fraction using brightness of images while the velocity of bubbles by means of Particle Tracking Velocimetry. As the result of measurements, we found the local void fraction and the bubbles advection velocity increase and decrease repeatedly with a time delay. We conclude the pattern of the number density distribution of bubbles is composed of fluid blobs which contain less bubbles; extruding and suction flows respectively toward and from the interior of the container form respectively in front and back of the blobs.

Inhaled drug delivery is the most common treatment for respiratory disease today. The inhaled particles deposit mostly in upper respiratory even if they are aim to deposit in lower regions such as lung. Many previous studies have revealed that the Stokes number, which is the ratio of a characteristic time of the flow field T_f to the relaxation time of the particle T_p, well describes the deposition in upper respiratory tracts. However, most of the previous studies defined T_f as the ratio of the inlet diameter to the inlet velocity. This assumption oversimplifies a realistic flow field in an upper respiratory where the characteristic length and velocity greatly depends on the region. Here we propose a Stokes number, St_wall, in which T_f employs the inverse velocity gradient on the respiratory tract surface. As a result of our numerical simulation studies, we revealed that we can estimate the local deposition position with St_wall which can be calculated with the CFD of the airflows only. We also found that even the deposition fraction by the inertial impaction of particles of sinusoidal inflow rates can be well described with the impaction factor if it is weighted with the air inflow rate.

An aerosol particle collection by liquid droplets has been applied in many industries. One example of this is the radioactive aerosol removal system in the safety system of the nuclear reactor. In this study, to clarify the capturing behavior of aerosol particles by liquid droplet, the velocity distribution of aerosol particles around the droplet was measured by the particle image velocimetry (PIV). Moreover, the capturing behavior of the aerosol particles near the droplet interface was observed by using a high-speed and high-resolution video camera. The experimental results showed that aerosol particles flowing near the cross-sectional center of the droplet were captured at the droplet interface after the velocity of the aerosol particles decreases near the droplet. However, aerosol particles that came to positions out of the center did not reach the droplet interface and were not captured at the interface. In addition, there were four behaviors of aerosol particles near the upstream interface of the droplet. The capturing behaviors were categorized into two types, capture at the droplet interface and that inside the droplet. The capture inside the droplet was observed more than the capture at the interface. In the case that particles were not captured, we observed that particles moved along the droplet interface and followed the stream. In the captured case, the diameter of the aerosol particles was larger and the Stokes number was about 1 or more. The result indicated that the main aerosol-particle capturing-mechanism at the upstream side of the droplet was due to inertial collision.

Experiments for gas-liquid two-phase flow in a horizontal rectangular micro-channel were conducted. The channel with rectangular cross-section of 1.0 mm height × 1.0 mm width was used as the test channel. In order to understand the effects of wettability on the two-phase flows in the micro-channel, the channel wall near gas and liquid mixer was coated by a hydrophobic agent. The contact angles were approximately 80°for the non-coating surface (hydrophilic) and 127° for the coating one (hydrophobic). In the experiments, flow pattern, bubble length, bubble velocity, void fraction and pressure drop were measured. From the comparison of the measured parameters between coating and non-coating cases, the hydrophobic surface (coating surface) makes bubble length longer. Then, the longer bubble reduces pressure drop.