The multi-fluids mixer patented by Sadatomi & Kawahara (2012) can be utilized as a twin-fluid atomizer, in which liquid atomization is implemented by supplying compressed gas into a mixing chamber, and water is sucked automatically due to a vacuum pressure induced by an orifice. A series of experiments were conducted to study the effects of the geometries (i.e., size of atomizer, orifice shape) on spray performance. From a comparative analysis of the experiments, the effects of the geometrical parameters on spray characteristics, such as mist generation rate, atomization efficiency, Sauter mean diameter of atomized water droplets, etc., were clarified. Finally, the CO₂ elimination capacity of the mist sprayed by the atomizer with the optimum specification was tested in a closed room with different spray time and different methods. The results showed that, the maximum capacity of CO₂ elimination was obtained by spraying mist for 5 minutes with a PET propeller, and the CO₂ concentration could be reduced from 1000 ppm to 800 ppm.

抄録全体を表示

In order to investigate the modifications of spatial-temporal developing flows by adding microbubbles in O(10 μm) diameter, flow structures appearing in shear flows of a horizontal mixing layer are visualized from velocity distributions obtained by (I) image analysis combining particle tracking velocimetry (PTV) and laser induced fluorescence (LIF), and (II) ultrasound velocity profiling (UVP). As the result of measurement, Reynolds shear stress is increased by introducing microbubbles at the early stage of the mixing-layer. In the developing region, however, Reynolds shear stress is flattened at the center of mixing layer and is reduced in bulk. Energy spectra of the velocity fluctuations show that energy of flow structures, whose length scale is as equivalent to the initial vortex layer thickness, is partially reduced. The size of vortex layer thickness is enlarged due to the local modification of the flow structures appearing in the early stage of mixing-layer.

抄録全体を表示

A micro-bubble generator with a venturi tube generates many micro-bubbles and pressure waves with bubble breakup phenomena. However, physical characteristics of the pressure wave in the venturi tube are not clarified. In the present study, a propagation speed and a pressure value of the pressure wave in the venturi tube were measured by an observation with a high speed video camera and a pressure transducer. In addition, an effect of void fraction on the pressure wave was investigated with the observation, the pressure measurement and a void fraction measurement with a constant electric current method. From these measurements, it was confirmed that the propagation speed decreased with an increase of the void fraction. Besides, the speed followed a sonic speed of a homogeneous model for gas-liquid two-phase flow. Therefore the pressure wave propagation was affected by the gas volume of bubbly flow.

抄録全体を表示

Snow characteristics are changed by climate or region. For the efficient development of a snow blower, stable and quantitative performance evaluation method is required. We try to reproduce the snow removal work using Discrete Element Method (DEM) in this study. In addition to conventional DEM, we developed potential model for reproducing the compaction of snow and air drag model to consider the characteristics of actual snow. And we found that simulation result is qualitatively consistent with the experimental result.

抄録全体を表示

The understanding of two-phase flow dynamics under microgravity is necessary to design a two-phase flow loop type thermal control system for space structures. Experiments at Japanese experiment module “KIBO” in the international space station are planned in 2015. In the ISS experiments, interface structures of gas-liquid two-phase flows at the just downstream of the heating section will be recorded by a high speed rate camera. One of the objects is to clarify the relationship between void fraction and flow pattern. In this paper, void fractions were measured by capacitance method to clarify two-phase flow characteristics of FC-72 which is used as the working fluid in the ISS experiment. Measured results of average void fraction agreed well with the correlations based on drift-flux model. On the other hand, flow pattern transitions agreed well with those by Mishima-Ishii' s equation. Moreover, from the mean square deviation in the probability distribution of measured void fraction, it is possible to classify flow patterns.

抄録全体を表示

In a solid spallation target of an accelerator driven system, high energy particles and high density heat are generated in the target material by irradiating a proton beam. Therefore, it is essential to establish a heat removal technique in the high energy radiation field. In addition, although heat transfer characteristics, especially boiling phenomena, are affected by the surface wettability, there is no research on the relation between the proton beam irradiation and the surface wettability. Thus, in this study, the effect of the proton beam irradiation on the surface wettability was investigated by comparing with those of ultraviolet and gamma ray irradiations with a titanium dioxide (TiO₂) sample. On the other hand, a photoelectric effect of TiO₂ on the wettability has not been studied in the past. Therefore, the photocurrent was detected when TiO₂ was irradiated by ultraviolet. And then, its effect on the surface wettability was investigated by measuring water contact angle on the sample surface. Furthermore, in order to study the photoelectric reaction due to the radiations, the photocurrents were also measured when TiO₂ samples were irradiated by gamma ray and proton beam. As a result, it was shown that the photocurrent behaviors in the radiations were much different from well-known photoelectric reaction of TiO₂.

抄録全体を表示

Container-less processing could prevent the heterogeneous nucleation and contamination due to the container wall. Acoustic levitation is expected to be used in the field of the analytical chemistry and manufacturing new materials. Thus, it is important to understand the non-linear behavior of an acoustically levitated droplet. The purpose of the study is to experimentally investigate the interfacial behavior and translational motion of an acoustically levitated droplet. In this study, translation of the droplet with the different reflectors was recorded by high speed video camera and estimated quantitatively. As a result, it is shown that translational amplitude of droplet with concave reflector was drastically smaller than that with flat type because of the lower sound pressure gradient around the levitated droplet.

抄録全体を表示

Critical Heat Flux(CHF) is one of the most important factors in the designing of the water tube in boiling two-phase flow equipment, such as a conventional boiler, a nuclear power plant and so on. However, the CHF has quite different mechanism on each flow pattern, i.e. bubbly flow, slug flow and annular flow. In this investigation, in order to understand the influence of the flow pattern on CHF, the axial stepwise heating tube along the axial direction was used. As the experimental results, the location of the temperature excursion was correlated with the flow regime, and the influence of the mass flux on the heat flux characteristic at a heating section was also reported. The results have suggested the conditions where the CHF induced by the large bubble could be able to occur.

抄録全体を表示

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 micro-bubble is expected. In the present study, we focus on the microbubble generator with a venturi tube. This generator can generate the bubbles of several-hundred-micrometer diameter in high void fraction. And it is maintenance-free because of its simple structure. The object of the present study is to develop the washing technology with micro-bubbles generated by using a venturi tube. First, the mechanism of washing technology is clarified. The generations of micro-bubbles from bubble collapses were observed in the venturi tube through a high speed video camera. Also, separating dirt from a washing target by a micro-bubble could be observed. The behavior of bubbles separating from the washing target with oil was observed. Furthermore, the pressure on a washing surface, the pressure fluctuations with high amplitude were measured in the flow condition with the bubble collapse phenomena. In washing experiments with oil paint, it was confirmed that washing effect was improved in the condition with the bubble collapse and the pressure fluctuation. Consequently, it is proposed that bubbly jet flow, micro-bubbles and the pressure fluctuation are the advantage of this washing technology.

抄録全体を表示

Thermocapillary convection is known that flow affects the quality of grown crystal by a Floating Zone (FZ) method. Half zone system is often employed to understand a nature of flow behavior as a simplified model. Two-dimensional steady flow transits to three dimensional oscillatory one at critical temperature difference ΔT_c between supporting disks. This transition condition is organized using critical Marangoni number. The objective of this study is to investigate influence of size on the onset condition of oscillatory flow by comparing experimental results both under terrestrial condition and microgravity aboard the International Space Station. Consequently, it is found that ΔT_c depends on liquid bridge size and linearly decreases with a growing number of liquid bridge length.

抄録全体を表示

Droplets of slug flow made on micro channel T-junction is used for emulsion, solid beads and so on as the applications. It is necessary to control a size of slugs for these applications and also needed to understand the mechanism of formation process of slug flow. In the present study, relationship between the formation behavior of slug flow at the T-junction and length of droplet of two-phase slug flow has been studied experimentally and numerically. We observed formation behavior of two phase slug flow at the T-junction in detail by using silicon-glass micro channel which width and depth are 100 μm respectively and measured length of the droplet of slug flow by the observation. We also simulated two-phase slug flow in a micro channel to examine the mechanism of formation process of slug flow by using phase-field model lattice Boltzmann method. We confirmed that length of droplet which is formed by same flow rate of continuous and dispersed phase became shorter with increasing of Weber number by experimental results and numerical simulation. In addition, it is also confirmed that interface shape has influence on slug length. By numerical simulation, it is suggested that interface shape can change as a competition between shear-stress and interface-tension forces.

抄録全体を表示

A number of authors have investigated the chemical processing due to fission of collapsing bubbles. In the present study, we focus on a venturi type microbubble generator. In this generator, rapid shrinkage and the collapse of bubble are generated. The purpose of the present study is to clarify the possibility of the chemical reaction in the venturi type microbubble generator. The chemical reaction was examined from pH, electric conductivity and gas concentration measurement because CO₂ gas which changes pH, electric conductivity and CO₂ gas concentration of solvent is expected to generate in the present chemical reaction. In order to identify the bubble breakup, we observed bubbly flow behavior in the venturi tube. Consequently, the difference of change of pH value, electric conductivity and CO₂ gas concentration were obtained by rapid bubble breakup.

抄録全体を表示

Numerical simulation of gas-liquid-solid interaction is one of the most challenging themes in CFD (Computational Fluid Dynamics). In order to understand the detail of the interface deformation and separation, it is necessary to carry out high-order accurate and large-scale CFD simulations. We have developed a CFD code based on a novel interface capture method, AMG-BiCGSTAB solver, 5th-order WENO scheme, and immersed boundary method (IBM). The code is written in CUDA, and the GPU kernel function is tuned to achieve high performance and good scalability on the TSUBAME supercomputer. It has become possible to carry out large-scale multiphase flow simulations. In a violent air-water flow, small splashes by collision of a particle are described clearly, and good performance scalability is also shown for multi-GPU computing.

抄録全体を表示

A nitrogen gas-lead bismuth two-phase flow was experimentally studied as a two-phase flow with large liquid-to-gas density ratio. Experiments were performed to understand turbulent structure in a liquid-metal two-phase flow by using a miniature electro-magnetic probe. Radial profiles of axial liquid velocity and turbulence intensity were measured by using the electro-magnetic probe. Turbulence is induced mainly by rising bubbles in the liquid-metal. Measurement results show that the turbulence intensity at the tube center was proportional to the void fraction to the power of 0.8 for higher void fraction at the present experimental conditions.

抄録全体を表示

Variable inlet guide vanes (IGVs), which are a type of swirling flow generator, are installed at the inlet of the centrifugal compressors to reduce the inlet Mach number of the rotor blades. However, flow instabilities are known to occur downstream of the IGVs. In this study, circular cylinders with tangential blowing were applied as guide vanes to generate swirling flow, and the flow instabilities downstream of the IGVs or circulation cylinders with tangential blowing were investigated experimentally and numerically. The unsteady flow characteristics downstream of each swirling flow generator are discussed here.

抄録全体を表示

The critical heat flux (the CHF) in a saturated pool boiling of water was investigated experimentally under the attachment of a honeycomb porous plate on the heated surface. In the previous study, the CHF was shown experimentally to be enhanced to more than double that of a plain surface. According to the proposed capillary limit model, the CHF can be increased by decreasing the thickness of the honeycomb porous plate. However, the CHF could not be greatly enhanced under the condition that the thickness of the honeycomb porous plate was comparable to the thickness of the macrolayer formed beneath vapor masses. As a result, it was found that honeycomb porous plates should be composed by the superposition of two kinds of porous materials and each of the honeycomb porous plates must fulfill the following conditions for CHF enhancement in a saturated pool boiling. First, a honeycomb porous plate, installed just on the heated surface, has very fine pores to supply water to the heated surface by strong capillary action, and the thickness of it should be as thin as possible to decrease the pressure drop caused by water flow inside the honeycomb porous plate. Second, the other honeycomb porous plate , placed just on the honeycomb porous plate stated above , is structured to hold a sufficient amount of water in order to prevent the inside of the honeycomb porous plate from drying out during a coalescent vapor bubble staying on a honeycomb porous plate .

抄録全体を表示

Two-dimensional, simultaneous measurement of the liquid interface profile is highly desired for understanding the time evolution of the interface behavior near the moving contact line. In this study, we examine the applicability of Color Coding Method, originally developed for the measurement of interface wave, to the measurement of the shape of interface near the contact line. The gradient profile of a sessile drop reconstructed with the proposed method shows good agreement with that obtained from the backlighted photograph with the deviation in the contact angle less than 6 degrees. The dynamic contact angle distribution on the finger developed on an advancing front of a liquid film flowing down an inclined solid surface is investigated and found to take a maximum around the tip of the finger.

抄録全体を表示

SubChannel Void Sensor (SCVS) consisting of electrodes with 6-wire by 6-wire and 5-rod by 5-rod electrodes has been developed to acquire boiling two-phase flow dynamics in 5×5 rod bundle geometry. The SCVS can acquire a local void fraction in 32 points (=6×6-4) of central subchannel regions and 100 points (=4×25) of near rod surface regions. The temporal resolution is up to 5000 frames (cross sections) per second. The devised sensors are installed every 500mm in the heated rod bundle and exhibits the quasi three-dimensional boiling two-phase flow structures, i.e. void fraction distribution.

抄録全体を表示