Recent progress in the applications of fine bubble technology to agriculture and marin is presented. Fine bubbles were examined in vitro to find whether antibacterial activities would be exhibited against Saccharomyces cerevisiae, Escherichia coli, Salumonella typhimulium, Staphylococcus aureus and Bacillus subtilis. Among them, Saccharomyces cerevisiae cells tended to grow well under both aerobic and anaerobic conditions by the action of microbubbles. Furthermore, the application of fine bubble technology has made it possible to give the high harvests of shrimps, seaweeds, strawberries, eggplants, tomatoes and pears. To clarify the underlying mechanism, interaction of microbubbles with a model protein, bovine serum albumin (BSA), was studied using fluorescence spectroscopy.

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One of the mysteries in ultrafine bubbles is their long lifetime in spite of the fact that the gas diffusion theory predicts the very short lifetime of 20 μs － 80 μs for ultrafine bubbles of 100 nm － 200 nm in diameter in liquid water saturated with air. In the present review, 8 proposed models for the stability of ultrafine bubbles are discussed. In addition, we propose the dynamic equilibrium model of an ultrafine bubble partly covered with hydrophobic material.

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It can be emphasized that miniaturization of bubble‐size is one of the superiority with regard to the non‐uniform creation of reaction fields within liquid phase. Owing to the combination of energy supply such as ultrasonic or electromagnetic waves with reaction fields, physicochemical phenomena occurring in these reaction fields are significantly observed. In this paper, the classification of the reaction field presented in the gas‐liquid‐solid system under fine‐bubble supply was carried out. Then, the engineering applications for environmental conservation and material manufacturing were described.

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In order to synthesize methane hydrate at high formation rate, finebubbles were utilized. The finebubble generator consisted of a liquid pump and a special line mixer. Finebubbles shortened an induction time of hydrate formation because the nucleation of hydrate was enhanced. With increasing liquid circulation flow rate, the induction time of hydrate formation shortened and the formation rate of hydrate increased because the number of finebubbles increased. The induced air flotation of oil droplets was conducted by the finebubble generator for oil-in-water emulsion separation. Compared with millibubbles, the dispersion of finebubbles effectively separated oil droplets. This was because finebubbles had high efficiency of collision with droplets and it was difficult to detach droplets because of the low rising velocity of finebubbles. The oil separation was largely enhanced at the solution pH below 4.5 because the electrostatic attraction between oil droplets and finebubbles was generated.

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Scientific knowledge about ultrafine bubbles obtained so far has been explained for supporting the promotion of international standardization of fine bubble technology (ISO/TC281). The mechanism of the ultrafine bubble generation, the long-time duration of its existence, various useful effects has been explained based on the obtained scientific experimental and analytical results, which would not be enough so far. The expected industrial applications and the important fundamental research topics of ultrafine bubbles have been described based on the several characteristic features of ultrafine bubbles.

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A gas-liquid separation cycle is one of the technologies that can improve the cooling capacity. In this study, the availability of a conventional gas-liquid separator for the room air conditioner of 7.1 kW class was evaluated and an improved gas-liquid separator that has an inflow pipe with a bottom hole and some side holes was proposed. The proposed gas-liquid separator was further improved for easy manufacturing and the gas separation efficiency and the cooling capacity when the gas-liquid separation cycle was applied to the room air conditioner of 7.1 kW class were investigated. As a result, approximately complete gas-liquid separation was realized and the cooling capacity was improved by about 3%.

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This paper reports consideration of the transmission laser energy estimating method for an efficient underwater processing with support form a CO₂ laser-induced bubble column. To calculate the transmission laser energy through the laser induced bubble column in water, the experiment of pulsed CO₂ laser-induced bubble column formation visualization and laser energy measurement though the CO₂ laser-induced bubble column in water was performed. The process of the CO₂ laser-induced bubble generation was observed by high-speed video camera. Pulsed 50W CO₂ laser beam of 10.6 μm in wavelength was irradiated onto the water surface, and then bubble is generated near the water surface. With further transmission of laser beams through the growing the bubble, local vaporization was continued and the bubble length was elongated. The transmitted energy though the bubble column was estimated by time rate of bubble growth time and was corrected for absorption loss and reflectance loss, and compared with the measured transmitted energy by power meter.

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Serious damages are possibly caused by high-speed Liquid Droplet Impingement (LDI) on the material surface. In particular, the wear by LDI in piping system of nuclear power plant is becoming great problem in recent years because of high aging operation. Therefore, it is important for the safety of piping systems in nuclear power plant to evaluate accurately effect of high speed LDI on the inner pipe wall. In this study, by using our in-house fluid/material two-way coupled numerical method which considers reflection and transmission on the fluid/material interface, high-speed LDI on material surface is simulated. The algorithm of two-way coupled method at fluid/material interface is applied as follows: fluid pressure on material surface and normal stress of vertical direction of material surface are obtained by considering reflection and transmission of pressure and stress waves based on acoustic impedance. Nonslip condition is adopted on fluid/material surface, where the vertical velocity has the values obtained by considering reflection and transmission and the tangential velocity of fluid has the same velocity of material which is calculated by material analysis. From the numerical results, it is shown that variation of impingement velocity has an effect of linear for maximum pressure and equivalent stress but variation of droplet diameter has little an effect of these values.

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Experiments were carried out to explore the mechanisms of bubble lift-off from a vertical heated surface in subcooled pool boiling. The experiments were conducted at atmospheric pressure and distilled water was used as the test fluid. A high speed camera was used for observation of bubble behavior. The main experimental parameters were the static contact angle of the heated surface, the liquid subcooling, and the wall heat flux. The time variation of bubble size was measured through image analysis. The growth force acting on the bubble was calculated using the measured time-evolution of the bubble size. The bubble growing on the vertical heated surface started to be extended in the horizontal direction when the sign of the growth force turned from negative to positive. It was hence considered that the growth force is one of the main causes of the bubble lift-off from a vertical heated surface. Furthermore, a correlation was developed for the bubble lift-off diameter considering the distribution of heat transfer rate around the bubble.

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