機械工学

Turbo-pumps have recently been utilized in various industrial fields for reasons of high efficiency and easy maintenance, in place of positive displacement pumps. A pump head degradation due to a two-phase flow comes up as an important engineering problem with the diversification of applications and operating fluids. The objectives of this paper, consisting of this report and the other, are first to review the past research on gas-liquid two-phase flow pump performance, secondly to discuss two-phase flow dynamics in the rotating flow passages and to describe a conceptual view and the present situation for designing two-phase flow pumps. In this report, the transition of two-phase flow problems in pumps are briefly reviewed and the head degradations, associated with various gas phase behaviors in a centrifugal pump, are illustrated to deepen the reader's understanding. Then, the existing methods based on some analytical models for predicting pump performance are described.

A gas-liquid two-phase flow problem in turbo-pumps has lately become of interest to pump designers and engineers. The final goal in tackling this problem is to develop a pump which does not lose its pumping function even in a two-phase flow with high void fraction. In this report the transition from a bubbly flow to gas accumulation in the centrifugal pump impeller with inlet void fraction increasing is discussed after showing qualitatively that the gas accumlation in the impeller causes the pump head degradation. Next, effects of pump geometries on the head degradation are made clear from the review of past experimental results. Finally, a conceptual view for designing this kind of pump is described in the present situation of two-phase flow pump research.

For the past two decades, Water Jet Technology has been studied and developed in order to facilitate the mechanical and material improvement of high pressure pumps. In particular, for nearly ten years, the practical use of this technology has been widely expanded from civil engineering to medical tools. YBM has been developing and distributing mud pumps together with boring/drilling machines for mine drilling, ground water development and civil construction. The YBM high pressure triplex plunger pump (Jet Pump), developed according to accumulated technology, is utilized for jet cutter piling and jet grouting jobs in civil construction works, fracturing and water circulation works in the test of Hot Dry Rock (HDR) electric power generation systems, and the Oyster-shell Crushing and Tilling Systems used in fishery farms. Several example of Jet Pump utilization are introduced in this technical note.

This paper presents a review on the current researches for the multiphase flow problems in turbomachinery, except for those caused by cavitation. Air-water two-phase flows are discussed from the aspects to define pump head and related characteristics, to predict the performance change using one-dimensional two-fluids models, to deepen our understanding of scale effect and unsteady flow phenomena, and to precisely simulate multidimensional flows inside the rotating impellers using turbulent and two fluids models. Solid-water two-phase flow problems are described from the viewpoints of precise prediction of erosion due to impingement of the solid particles entrained.

In the past, a serious railroad accident had occurred in Japan. In that accident, it had taken a long time to rescue the confined passengers within the crushed trains, because of the danger of the ignition to combustible vapor of leaked gasoline. Through the repeated occurrence of such fire accidents, the Fire and Disaster Management Agency (FDMA) in Japan was strongly demanding the development of the rescue apparatus that could be used in the combustible vapor and deployed the water jet cutter system all over the rescue parties. Under these circumstances, the Water Jet Technology Society of Japan (WJTSJ) was received the consignment of the research supported by the science and technology promotion system for fire fighting and disaster prevention of FDMA in Japan. The WJTSJ has started up the fire fighting project team to research the water jet cutter system from various contents. On this project, seven research workings were organized and these researches and developments have achieved respectively. In this paper, the outlines of this project and short summery of these workings research and development are reported.

The numerical procedure for hydroplaning was developed by considering the following three important factors; fluid/structure interaction, tire rolling, and practical tread pattern. The tire is analyzed by FEM with Lagrangian formulation and the fluid is analyzed by FVM with Eulerian formulation. Since the tire and the fluid are modeled separately and their coupling is automatically computed by the coupling element, the fluid/structure interaction of the complex geometry such as the tire with the tread pattern can be analyzed practically. The predictability was validated by comparing the hydroplaning simulation with the experiment on the subjects such as the water flow, the velocity dependence of hydroplaning, and the effect of the tread pattern on hydroplaning. In order to predict the streamline in the contact patch, the procedure of the global-local analysis was developed. The predicted streamline enabled us to develop the new tire pattern in a short period based on the principle; “make the stream line smooth”.

In order to extend the HCCI high load operational limit, the effects of the distributions of temperature and fuel concentration on pressure rise rate were investigated through theoretical and experimental methods. The Blowdown Supercharge (BDSC) system and the EGR guide parts are employed simultaneously to enhance thermal stratification inside the cylinder. Also, direct fuel injection system was also used to control the distribution of fuel concentration. As a result, pressure rise rate during high load HCCI operation was successfully reduced with the thermal stratification enhanced by the EGR guide. It is also found that the uniformed fuel concentration distribution generated by a direct fuel injection had less effective to reduce pressure rise rate. Because directly injected fuel into hot EGR gas decreased EGR gas temperature leading to reduce thermal stratification generated by the EGR guide.

Ecotype water turbines can be utilized small and distributed water resources with little civil engineering works and without environmental burdens. In Japan, network of agricultural waterway extends 400 thousands kilometers, this abundance of waterpower has a high expectations for electric power generation. The turbines will promote local production for local consumption of electricity. Waterfall type turbine and undershot turbine are investigated and demonstrated in some field tests. These are opened type which has no casing and any water pipes. We summarize our results of the investigation of eco-friendly water turbines.

The authors are aiming at the development of a low power two-fluid-type atomizing system which can generate a large flow rate of fine liquid droplets, i.e., mists. In the present paper, the outline and the performance of the system studied to date in Kumamoto University are described together with its application to the mist cooling in a greenhouse and the reduction of smoke and harmful gas, say CO2, by the adsorption by the mists.

Well-established recommendations exist for the sizing of safety valves and the connected inlet and outlet lines for steady-state, single-phase gas/vapor or liquid flow. However, in the case of a two-phase vapor/liquid flow, the required relieving area to protect a system from overpressure is larger than that required for single-phase flow. This report includes a widely usable engineering tool for the sizing of the typical safety valves. It is based on the omega parameter method, which is extended by a thermodynamic non-equilibrium parameter. The recommended sizing procedure starts with the definition of the sizing case and includes a method for the prediction of the mass flow rate required to be discharged and the dischargeable mass flux through a safety valve.

In high speed turbopumps for rocket engines, the cavitation occurs and often causes the flow instabilities such as the cavitation surge and the rotating cavitation. The flow instability due to the cavitation is called “cavitation instability” and has been a severe problem in the development of liquid fuel rockets. The mechanism of the occurrence of the cavitation instability in turbopump inducers, the suppression method of the instability, and the current state of the numerical simulation of cavitating flow in turbopumps are discussed.

The authors invented a multi-fluids mixer with multifunction, which can generate microbubble, mist (i.e., tiny liquid droplet), and emulsion of immiscible liquids. In the present paper, the outline and the hydraulic performance of the mixer studied to date in Kumamoto University are described especially for its usage as the microbubble generator, with its application to water purification and healthcare.

We have developed special spray nozzle systems, which can be applied to dispersion, mixing, and atomization of fluids. Through the specially made spray nozzle, high speed swirling gas flow is generated, where liquid phase can be easily dispersed and atomized due to its strong shear stress, resulting in a good performance in various industrial processes. In this article we introduce the basic feature of our spray nozzle system, and its various applications to dispersion, mixing and atomization, including nanoparticle generation technology.

Physical cleaning based on underwater ultrasound is widely used in industry and its cleaning efficiency is known, from recent studies, to be augmented by promoting the mechanical activity of cavitation bubbles. As a side effect, ultrasound cleaning may give rise to material damage from violent collapse of cavitation bubbles. Traditionally, degassed water is favored as cleaning solution in order to reduce the probability of having cavitation (and the resulting erosion); however, there is no chance to promote cleaning efficiency with this approach. In this review, we introduce our recent effort toward the development of an erosion-free ultrasonic cleaning technique using aerated water. Under dissolved gas supersaturation in aerated water, bubbles can be created easily with low-intensity ultrasound and the resulting bubble dynamics are expected to be mild enough to avoid erosive collapse. To demonstrate this conjecture, we run a series of ultrasound cleaning tests with glass samples on which submicron SiO2 particles are spin-coated; we use a transparent cleaning bath for visualization of acoustic phenomena by a high-speed camera. Dissolved oxygen (DO) supersaturation in water (aerated by oxygen microbubbles) and ultrasound frequency (at 28 kHz or 200 kHz) are varied as parameters, while the input power to drive the ultrasound transducer is fixed and the ultrasound amplitude at the pressure antinode is set at Pe=1.0 atm (root-mean-square value) for the case of degassed water. Particle removal efficiency (PRE) is defined based on image analysis of light scattering from the residual particles (i.e., the so-called Haze method). We see that there exists an optimal DO supersaturation to maximize the PRE. We also see that the PRE is higher in the case of lower frequency (28 kHz), for its cavitation inception threshold is reduced and the number of activated bubbles is thus increased.

We carried out molecular dynamics simulations of water infiltration into a slit pore for the understanding of the rinsing process of semiconductors, whose minimum length scale seemingly reached the continuum limit. The possibility of water infiltration strongly depended on the wettability, i.e., the sign of the cosine of contact angle due to the large Laplace pressure. The time needed for the infiltration was small due to the high meniscus velocity, and the gas molecules remaining in the slit did not have remarkable effects on this process. Macroscopic relations gave reasonable estimates for these static and dynamic processes even at the nanoscale.

PVA brushes are widely used for cleaning semiconductor device surfaces. PVA brushes are a soft porous polymer which can be absorb much amount of water. In this review, we briefly introduce the proposed cleaning mechanism. Then some results of frictional analysis of PVA brushes are described. In the frictional analysis, viscoelastic behavior of the brush, surface wettability of a plate, and brush deformation during scrubbing were important. In addition, we introduce a visualization result of real contact area between PVA brush and contact surface.

Chemical solvents used for industrial washing process have a negative impact on the environment and the health of their users, and they are high-cost cleaning. In order to reduce the amount of chemical solvent used in the washing process, the non-chemical washing technology with microbubble is expected. We focus on the microbubble generator with a Venturi tube. This generator can generate the bubbles of hundred-micrometer diameter in high void fraction. And it is maintenance-free because of its simple structure. In this paper, authors introduce capability of oil washing with microbubbles generated using a Venturi tube and photoresist removal with Ozone microbubbles, which is friendly for the environment and no harm to the product.

PVA roller brushes are widely used for cleaning after the CMP process, one of the semiconductor manufacturing processes. The PVA roller brush features protrusions called nodules and rotates on the semiconductor wafer in cleaning. This article introduces a cleaning model that uses that PVA roller brush to remove nanoscale impurities. The evanescent fields on a prism enable us to observe the contact behavior of the brush nodules and clarify that there is little brush volume near the surface during sliding. We classified brush deformation into three types depending on the relative velocity of the wafer and nodule. A stamped contact occurs at a negative relative velocity, i.e., when the wafer overtakes the nodule, and this contact is related to cross-contamination from the brush. Finally, we present a model where water absorption and desorption associated with nodule volume deformation plays an important role in nanoscale impurities removal.

In the semiconductor device manufacturing process, wet cleaning is an important process that determines product yield. In this paper, spray cleaning in the wet process of semiconductor device manufacturing is described from the perspective of macroscopic fluid dynamics. When micrometer-order particles adhere to the substrate, the van der Waals force, as discussed in DLVO theory, is dominant. When these particles are removed by spraying, the fluid drag force on the particles is a major factor. In addition, in semiconductor device cleaning, it is not enough to simply increase the fluid drag; as a trade-off, increasing the fluid drag also increases the probability of pattern collapse and electrostatic damage. Thus, as semiconductor device miniaturization progresses, cleaning methods with even higher selectivity are needed.