Dynamic wetting / dewetting, which is characterized by the motion of the contact line (the triple phase line of the liquid-fluid interface and the solid surface), is ubiquitously-observed phenomenon in two- or three- phase flow field confined by solid walls. The behavior of the contact line and the contact angle is one of the major boundary conditions for the description of the behavior of the bulk interface, understanding of the behaviors are hence highly required. In this article, recent topics and future prospect on the interfacial flow and wetting are briefly introduced, with some personal histories of the authors’ studies on that field.
Drag reduction using bubbles are now in operation for marine vessels, and recorded significant fuel saving. Beside it, fluid mechanics inside high-speed bubbly turbulent boundary layer is highly complex. Efforts by scientists and engineers in Japan straggled in the last 30 years and recently reached the goal. They found further potential of technical improvement with recent experimental discovery on bubbles’ organizing behaviors.
Microbubbles are the bubbles of one to several hundred micrometers in diameter. Depending on the work field, their sizes are less than 100 μm for bioactivity. The microbubble technology has become more and more popular in many fields of science and engineering since its birth in “The Japan Kosen Association for College of Technology” in 1997. Recently, a considerable number of studies have been conducted on the effect of microbubbles on the environmental, industrial, food and medical fields. However, the basic characteristics and efficient application methods of microbubbles remain unclear. In this paper, the basic knowledge for the use of microbubbles in a variety of practical applications is indicated.
Increase in the consumption of electricity and in the heat dissipation density from semiconductors will become a serious problem also in space. To develop thermal management systems for space platforms, fundamental data for their design is to be obtained through boiling and Two-Phase Flow (TPF) experiments onboard international space station (ISS). In addition to the acquisition of data for heat transfer, the clarification of flow and heating conditions, where gravity effects disappear, become an important objective of the experiment. An experimental setup was developed thorough the long-term discussion and design among JAXA, researchers and manufactures supporting the project, and was already transported to ISS. Objectives and situation of the present research and a desired direction of future experiments are described with reference to the existing data obtained from short-term microgravity experiments for flow boiling.
This paper, first of all, explains a two-dimensional depth-integrated tsunami flow model, which is often used in practice. The validity and utility of the model were examined by applying the model to tsunami induced by The 2011 Tohoku Earthquake. Furthermore, this study expounds a three-dimensional fluid analysis model “DOLPHIN” that can calculate solid-gas-liquid multiphase flow, as well as a visualization system of tsunami simulation using a three-dimensional numerical tool “OpenFOAM”, which provides dynamic information so as to enable to intuitively understand the characteristics and risks of the disaster.
Thinking over the series of Japan-US two-phase flow seminars, the necessity and meanings of the multi-phase flow research are mentioned over the research conducted concerning the accident at Fukushima Daiichi Nuclear Power Station. There could be found the heavy concerns on the difficulty of elucidating the complex phenomena at the accident; none-the-less, there surely exist not a few places in which the multiphase flow research could play the important and active roles, repeatedly conducting and accumulating research on the steady road to fulfill the elucidation of the accident and recover the trust, after the fact of which I would believe that we could draw a future image of new nuclear powers.
The applications of Artificial Intelligence ie AI show diversity in any fields. On the other hand, research of the predicting heat transfer regardless of single-phase or two-phase flow is still untouched. Therefore, we have confirmed usefulness using AI’s deep learning function on horizontal flow boiling heat transfer in flowing mini-channel that is actively researched. The effect of the surface tension in the mini-channel is large compared with conventional large tubes, and then the heat transfer mechanism is very complicated. For this reason, the numerical correlations of many existing researchers the prediction result is not good. However, the mechanistic correlation based on the visualization experiment, which the authors' research group published several years ago has very high precision. Therefore, in this research paper, we confirmed the effectiveness of using deep learning for predicting of the boiling heat transfer in mini-channel while comparing our correlation.
Fine bubbles are used for cleaning system, separating process, food industry and so on. However, commercially available devices for fine bubble generation cannot be applied for particle dispersion liquid because they need liquid pumps and particles are accumulated on their systems. Moreover, the bubble diameter cannot be controlled in those devices. The uniformed and controlled bubble diameter is important for a reasonable industrial device design. Therefore, in this study, a novel method for fine bubble generation without liquid circulation was developed. A horizontally oscillating micro-nozzle was used to make bubbles small. The effect of the gas flow rate, the oscillating frequency, and the oscillation amplitude on the average bubble diameter was investigated experimentally. Moreover, visualization and quantification of liquid motion around the oscillating nozzle was carried out in this study. It was clarified that the liquid viscous force due to the relative velocity of the nozzle motion to the liquid motion enhances the bubble detachment from the nozzle in this method.
The fact that the spray characteristics of automotive fuel injectors of direct injection type are substantially influenced by cavitation in the nozzles is widely known. Many researchers have been engaged in understanding the relation between a cavitating flow and characteristics of fuel spray using a numerical simulation till now. In a free surface flow analysis and a multiphase flow analysis, advantages of using a particle-based meshless method are utilized. However, particle-based meshless methods have not been used to simulate cavitation. In this study, the cavitation in a two-dimensional nozzle and the water jet were simulated using Moving Particle Semi-implicit (MPS) method employing a cavitation model. The simulation results are relatively close to experimental data.