Interlaboratory comparison can be effective to obtain consistent findings on ultrafine bubbles (UFBs). In this study, the stability of UFBs during international transportation was reported for the first time. We conducted stability tests in cooperation with German and Canadian institutions. UFBs were measured using two laser-based characterization techniques: particle tracking analysis (PTA) and dynamic light scattering (DLS). Acceleration and temperature during transportation were also measured. The results showed that regardless of transportation, the number concentration of UFBs decreased, while the size of UFBs increased with time. By filling the glass vial with UFB dispersion and minimizing the liquid flow in the vial, the effects of transportation were virtually eliminated. It was also suggested that the liquid flow caused by vibration during transportation may have enhanced the aggregation of UFBs. We report the results of an inter-instrumental comparison among PTA and DLS instruments using the transported UFB dispersions.
Bubbles with a diameter of 1 to 100 μm are defined as microbubbles (hereinafter, this is called "MB"), and are used for floatation separation because of their adhesion to suspended substances. However, there are few research reports on floatation separation, and standardization for device design has not been performed, so improving the efficiency of floatation separation devices has become an issue. Therefore, in this study, the experiments were carried out to clarify the floatation separation characteristics by microbubbles as a basic research of floatation separation by microbubbles. In the experiment, the soft flour was used as a suspended substance, and as basic characteristics, the state of adhesion with microbubbles, the relationship with bubble diameter, and the rising velocity rate were measured. In addition, as the actual floating separation performance, the concentration time with each initial concentration was investigated. The conclusions are as follows: About 60% of the adhered form of the microbubbles and the soft flour was observed as a form in which a single microbubble adhered to the soft flour. The number of microbubbles with a bubble diameter of 80-90 μm was attached in the case of single microbubble attachment to flour is large. In the floating separation characteristics, floatation the soft flour concentration in the tank decreases sharply at the short time, and then gradually decreases. The higher the initial concentration, the longer the processing time required to reach the target concentration, but the tendency of the concentration decrease was the same. The final concentration remains around 20 ppm in all experimental conditions. These results are important for standardization of floatation separation characteristics in the future.
We develop a novel equipment that levitates giant drops, size of which is larger than the capillary length, over a moving wall. Generally, the levitation of giant drops is challenging since a drop larger than capillary length deforms and breaks up easily. We overcome this difficulty by equipping a special-shaped glass hollow cylinder. The novel equipment successfully levitates a drop of 5 ml in volume, which is more than 500 times larger than volumes of levitating drops reported in previous works. Remarkably, the giant drop levitates more than 24 hours for the special-shaped cylinder and a liquid film over the cylinder surface. This containerless manipulation of giant drops may open a new door for new method of material science and high-precision chemical analysis. In addition, we investigate the levitation mechanism of a giant drop over a moving wall. We adopt interferometry to observe the bottom shape of the drop which is complex because of the air flow between the drop and the moving wall. It is found that, when the drop size is large enough, the bottom shape of the drop shows surface waves, which has not been reported by any previous researches. Phase speed and wavelength of the surface wave vary with experimental parameters (i.e. wall velocity and drop diameter). Interestingly, both phase speed and wavelength have a linear relationship to the product of wall velocity and drop diameter.
The external power supply of Fukushima nuclear power plant was lost by the Great East Japan earthquake, which might have resulted in shortage of water in the spent fuel pool. Many researchers are developing cooling system of spent fuel pool (SFP) by loop heat pipe without power supply. However, thermal stratification in SFP was not considered to predict the cooling performance. The purpose of this study is to develop the solving system for thermal stratification without power supply by injecting air to SFP. Simulated test using thermosensitive self-operated valve was done. The flow visualization test and the solving test for thermal stratification have been done by using three kinds of air injection structure. The following conclusions are obtained. ①Air injection method can solve the thermal stratification. ②Using the thermosensitive self-operated valve, the air can be injected without power supply. ③Elbow type was suitable structure as air injection structure.
Experiments on countercurrent flows of air and water in a 3×3 rod bundle were carried out, and countercurrent flow limitation (CCFL), pressure gradients dP/dz and void fractions α were measured under flooding conditions. Flooding with smooth and thin liquid film occurred at the top when the gas volume flux JG was small, whereas flooding with rough and thick liquid film took place at the bottom for medium and large JG. This behavior was similar to flooding in a vertical pipe. CCFL characteristics were expressed by Kutateladze parameters and agreed with those for the upper tie plates in BWR fuel bundles. The volume flux JL of falling water in the bundle was larger than JL in a vertical pipe, but it was smaller than JL through horizontal perforated plates without rods. α under flooding conditions were lower than α under stagnant water (JL = 0) conditions in the region of JG > 4 m/s. The wall friction and interfacial friction factors were obtained from the data and discussed.