Subsea minerals, such as seafloor massive sulfides, rare earth elements in deep-sea mud, are found in deep sea within the exclusive economic zone of Japan. However, the development of subsea resources has not reached the commercialization stage because many technical issues still need to be addressed. Then, efforts for solving these issues are conducted in Japan and other countries. Air-lift pumping systems are one of the promising methods for subsea mineral resource productions. In developing air-lift pumping systems, one of the technical issues is flow assurance for gas-liquid-solid three-phase flow. We reviewed the correlations of volume fractions and frictional pressure drops in gas-liquid and liquid-solid two-phase flows and proposed correlations for three-phase flows. We carried out some experiments of air-lift pumping systems and obtained data of volume fractions of each phase and frictional pressure drops. To validate the proposed correlation, we compared calculated results by the proposed correlations with experimental data. The comparison suggested that the volume fraction of gas-phase and the frictional pressure drops could be calculated by the proposed correlations. Meanwhile, deviations between experimental data of solid-phase and calculated results of that was large and new methods were needed for calculated them.

In this paper, the study on the performance of a 200 m airlift pump for water and highly-viscous shear-thinning slurry is introduced, mainly following the published paper [1]. The experiment was conducted using the facility in Advanced Institute of Science and Technology, Tsukuba, which had been used for the project of polymetallic nodule about 30 years ago. Here, in the present study, we investigate the airlift performance for the shear-thinning slurry which imitates the rare-earth mud water in the deep ocean. The experimental results showed that the airlift pump can work properly not only for water but also highly viscous slurry. It was confirmed that actual airlift performance obtained with the experiments does not show the reduction of the lifted liquid with increasing the gas flow rate, which the numerical results show the some deviation of the predicted value for high gas flow rate.

Air-lift two-phase and particulate three-phase flow in a vertical pipe has been measured by ultrasound with the aim of revealing the transient dynamics of the air-lift performance. Changing the gas flow rate and mass loading of solid particles, we measured the void fraction and liquid flow rate in the slug-flow regime at 55 Hz in sampling rate. We found that mixing the liquid phase with solid particles reduced the mean axial length of the bubbles and the void fraction was reduced because of the long slug destabilized by the particles.

The displacement of more viscous fluids by less viscous fluids in porous media provides not only an industrial application for enhanced oil recovery (EOR) from reservoirs, but also a fundamental study of the phase transition phenomena of fluids, combining fluid mechanics and thermodynamics. Recent studies have shown that the coupling of thermodynamic and hydrodynamic instabilities results in the formation of self-driven active fluid that significantly affects EOR. In this paper, we discuss the phase transition phenomena of the fluid in a porous medium simulating EOR from both hydrodynamic and thermodynamic aspects.

Venturi tube is a microbubbles generator with simple and robust design. Air was injected into the liquid flow, transported through the throat of the Venturi tube and break up as microbubbles in the diverging area. In high-speed liquid, cavitation occurred along with the air transported to the throat of the Venturi tube. One of the factors that affected cavitation existence is dissolved gas level in the liquid. Therefore, this study aims to compare the microbubble collapse phenomena under different dissolved gas level to further understand the effect of cavitation to microbubbles formation. In this experiment, two different dissolved oxygen level (DO) were used to represent the dissolved gas level in the liquid. The result showed that although breakup mechanism was generally the same for both DO level, higher DO at high liquid speed had more wrinkles on its bubbles surfaces during the bubbles breakup process. Pressure measurement results at higher liquid speed demonstrated that DO 8.5 mg/L had slightly higher inlet pressure than DO 6.5 mg/L for the same gas flow condition. Calculation on bulk cavitation number and pressure loss coefficient suggested cavitation occurrence at higher liquid speed and higher air flow ratio. Higher DO have slightly higher pressure loss coefficient under the same bulk cavitation number. On the other hand, bubbles number distribution results showed that higher DO condition produced more bubbles than lower DO specifically at higher liquid speed with low and medium air flow ratio. Calculation of SMD for different DO at high liquid speed resulted in a slightly smaller bubbles diameter at low and medium air flow ratio of higher DO while the value is almost the same for high air flow ratio. At low liquid speed, higher DO have smaller SMD value for all air flow ratio cases.

Predicting the dynamics of an electrically charged drop impacting a solid surface is of great importance in various industrial applications such as spray coating and painting. An impacting drop decelerates immediately before the touch-down by the lubrication pressure of the intervening air. The pressure build-up forms a dimple resulting in the entrapment of bubbles under the drop. We measured and visualized the dimple and bubble formations using high-speed interferometry and back-light imaging techniques by focusing on the effect of the electrostatic charge on the surface deformation. We clarified that the dimple size decreased, and the kink of the dimple became more flattened with increasing the charge, which resulted in forming a micro-bubble band around a central bubble. By comparing the dimple profile obtained with interferometry and bubble images, we revealed that an air layer, thinner than 266 nm, raptures into small pieces forming a microbubble band while a thicker air layer collapses into a bubble. Replacing a substrate from conductive to dielectric hinders the decrease in dimple volume, confirming Maxwell stress acting between the drop bottom surface and the substrate plays a crucial role in determining the bubble entrapment.