Experimental study on bouncing and coalescence of a pair of bubbles rising side by side in a quiescent liquid has been performed. A novel bubble generator has been developed to generate pairs of bubbles precisely. High-speed imaging technique has been employed to investigate the trajectory and shape of bubbles in detail. We observed that the trajectory of rising bubble varies with Reynolds number. When the Reynolds number is over the critical region, a pair of bubbles approaches each other and then collides. After the collision, two types of motion are observed: coalescence and bouncing. We investigate the critical Reynolds number and Weber number, based on the rising velocity, over which bubbles bounce. As a result, we clarify that the critical Weber number is around 2 regardless of Morton number. The critical Reynolds number decreases with increasing Morton number. In addition, we have found that the bouncing of a pair of bubbles differs from that of single bubbles at a wall; the two bubbles perform attracting and bouncing motion continuously with a rising velocity being kept almost constant, and the amplitude of bouncing motion of bubbles is seven to eight times larger than that of a single bubble at a wall.
It is known that, in upward pipe or channel flow, bubbles migrate toward the wall and the distribution of the local void fraction has saddle shape. In our experiment, 1mm mono-dispersed bubbles were generated in the vertical channel by the addition of surfactant. In the case with a small amount of 3-Pentanol in the liquid-phase, the bubbles accumulated near the wall and formed bubble clusters. On the other hand, in the case with Triton X-100 which has much higher molecular weight, the bubbles did not migrate toward the wall. The surfactants cause Marangoni effect and change the boundary condition of the bubble surface. One of the factors of the bubble migration is thought to be the shear-induced lift force. It is indicated that the shear-induce lift force is strongly influenced by the change of the boundary condition due to the presence of surfactants.
This paper proposes a new measurement technique for multi-phase flow using correlation and multi-wave method. The authors developed a unique ultrasonic transducer named as multi-wave TDX. The TDX consists of a special ultrasonic element having two basic ultrasonic frequencies. The central 3 mm diameter area has a basic frequency of 8 MHz and the outer area has a basic frequency of 2 MHz. The TDX can emit the two ultrasonic frequencies independently. Using the two ultrasonic wave lengths, signals of two basic frequencies can be obtained at the same time. Comparing with the each echo signal, the signal combination can be classified into 3 groups. Hence, applying ultrasonic correlation method (UTDC) and the signal comparison method for multi-wave method, bubble rising velocity and liquid velocity distribution can be obtained simultaneously.
Micro-bubble technology has been recognized to be a useful tool to purify water in lake or sea under pollution and to promote the growth of marine and agricultural products. In this study, the performance of Sadatomi's micro-bubble generator has been experimentally investigated in order to estimate the pump power required in the use at deep water level. In addition, an analytical model has been proposed to predict hydraulic performance of micro-bubble generator under any water depths and its validity has been confirmed.
We recently proposed a new method for generating monodispersed nanobubbles from porous glass membranes with uniform pores, in a system consisting of a gaseous phase and a continuous water phase containing a surfactant. In this study, the effect of the surface wettability of the membrane on monodispersed nanobubble formation, using various surface-modified membranes, was examined. The bubbles were generated by forcing air through a surface-modified membrane with mean pore diameters of 72, 210 and 530 nm into distilled water containing 0.3 wt.% of sodium dodecyl sulfate. The membranes were chemically modified with different silane coupler reagents and their surface wettability was evaluated from the contact angle between the membrane surface and the water phase. The contact angle, θ, could be controlled by the number of carbon atoms of the alkyl group in the reagent and/or the concentration of the reagent. Nanobubbles with a narrow diameter distribution were generated from a membrane with θ < 45°. Bubble diameter was determined by the pore diameter and was independent of the contact angle. In contrast, relatively large bubbles with a broad diameter distribution were generated from a membrane with θ > 45°. In this case, an increased contact angle brought about an increase in the mean bubble diameter and a decrease in the monodispersity of the bubbles.
The bubble column with draft tube installed with perforated plates was proposed as the reactor for the production of biodiesel from vegetable oil and superheated vapor of ethanol without catalyst. The effects of conditions of perforated plate on the flow characteristics were examined. The bubble column was made from transparent acrylic resin. The diameter was 200 mm and the height was 2000 mm. A perforated tube gas sparger was set at the bottom of the column. The draft tube with 140 mm in diameter was concentrically inserted in the column. The perforated plates were installed in the draft tube at the equal interval. The number, the hole diameter and the fraction of opening area of the perforated plate were changed. As the gas and liquid phases, air and water were used. The flow pattern was observed, and the liquid circulation flow rate and the gas holdups in the riser and downcomer were measured. By installing the perforated plate in the draft tube, the coalesced bubbles were subdivided and the liquid circulation flow rate became lower. With increasing number of the perforated plate, the gas holdup in the riser increased but that in the downcomer decreased. On the basis of energy balance, the liquid circulation flow rate was analyzed, and the empirical equation for the energy loss coefficient of perforated plate was expressed as a function of the opening fraction. From the value of rising velocity of bubble swarm in the riser, the degree of bubble subdivision by the perforated plate was evaluated. In the present experimental conditions, the degree of bubble subdivision was scarcely affected by the hole diameter and the opening fraction. It became unchanged when the number of perforated plate was more than 7, i. e. the length between plates was less than about 200 mm
The flow structure induced by the droplet impacting on liquid surface in a liquid tank was studied. This study focuses properties inside the tank induced by the two-phase jet flow during the aeration process. As an underlying process of the flow phenomena whereby the two-phase jet flow falls to the free surface and produces a circulating flow in the tank, we chose to examine the phenomena just after a droplet falls into the gas-liquid interface. This was done in practice by observations using high speed video, experimental modeling, and also by numerical analysis. Subsequently, we could gain insights into the influence of a drop or two drops impacting on the gas-liquid surface. This basic data can clarify the mechanism of the flow in the tank.
The impact of single water drop on a plane water surface was observed visually using a high-speed video camera to investigate the influences of impact angle and drop shape on the outcome of collision. In annular two-phase flow, the amount of secondary drops produced after the impact of a primary drop is important because of its contribution to the entrainment rate of drops and consequently the heat flux at the dryout of liquid film. In the present experiments, the primary drop diameter, impact velocity and impact angle were within 0.19-1.23 mm, 1.4-11.1 m/s and 36-89°, respectively; the film thickness was set at 2 mm. Within the experimental ranges tested, the minimum Weber number for the formation of secondary drops was approximately 200 and almost insensitive to the impact angle and drop shape, provided the absolute velocity of primary drop was used in evaluating the impact Weber number. However, the size of secondary drops was much larger and consequently much larger amount of secondary drops was produced at oblique impacts than at the normal impacts.
Though many experimental data have indicated that cavitation in a nozzle of pressure atomizer might affect liquid jet atomization, our knowledge on the effects of cavitation and Reynolds numbers, σ and Re, on cavitating flow and discharged jet is still rudimentary. Flow visualization under various values of σ and Re was, therefore, carried out by making use of a transparent two-dimensional nozzle. Tap water at atmospheric pressure was used in the experiments. Water temperature and flow rate were varied to adjust σ and Re to desired values. As a result, we confirmed that (1) cavitating flow and jet are not affected by the Reynolds number, but by the cavitation number, and (2) cavitation plays an important role in the liquid jet behavior just downstream of the nozzle exit.
Fine atomization of the liquid jet from a fuel injector in an automobile engine lowers engine emissions and improves fuel efficiency. Simulation of liquid-film breakup near the injector outlet is useful for predicting the atomization. However, grid methods and particle methods require a large amount of computation time in the practical engineering aspect because fine meshes smaller than liquid films or a large number of particles are needed. In this study, we have tried to simulate the breakup of liquid films by using groups of particles in the particle method. In the simulation, the particle method was applied only to the liquid film and the grid method was used in other areas to shorten the computation time. We then simulated the breakup of a liquid film near the outlet of a fuel injector used for automobile engines, and found that our hybrid method could simulate the breakup of the liquid film into ligaments.
Unsteady motion of a finitely stretched liquid column suspended in another quiescent fluid is studied numerically for the flow where both inertia and viscosity are dominant. A Front-Tracking / Finite Difference method is used to simulate the interfacial motion of the liquid column. The end of the column retracts and forms into a bulb due to non-uniform capillary force. Three different modes of the motion are identified: (I) the bulb pinches off and the rest of the column also breaks up into daughter drops, (II) the bulb moves toward the midsection of the column and the column becomes a spherical drop, and (III) the bulb pinches off due to end-pinching. These modes can be classified by the Ohnesorge number and the viscosity ratio.
Generally, particles used in industrial fluidized beds have size distribution. When the size distributed particles are fluidized, they tend to segregate with each other. The segregation is caused by difference of drag force between larger and smaller particles. In the present paper, we focus on the drag force for a binary mixture of particles differing in diameter, and propose some drag force models for fluidized beds with the size distributed particle. An experiment under the same condition as the numerical simulation is performed to validate the proposed drag force models. We examine pressure drop property of the particle bed and how the segregation progresses as fluidizing time goes on both numerically and experimentally. The calculation results for each drag force model are compared with the experimental result.
Particle dynamics of nuclear fuel material has not been considered in conventional nuclear criticality evaluations. However, the particle motion influences nuclear criticality significantly. In the present study, the criticality calculation is combined with the discrete element method to investigate the effects of the particle behavior on nuclear criticality. Particle motion is analyzed in a rotating drum by the discrete element method and then the nuclear calculation is carried out. We focus on particle size distribution, size segregation and change of surface area of the particle bed. The particle size distribution has an important influence on the nuclear criticality evaluation, because it affects not only the particle movement but also the atomic number densities in the bed. The surface area of the particle bed shows a close correlation with the multiplication factor. On the other hand, the size segregation does not have a significant effect on nuclear criticality.
In order to enhance nucleate boiling heat transfer it is efficient to increase nucleation site density. This study deals with heat transfer enhancement surface manufactured by thermal spraying. Two thermal spraying methods using copper as a coating material, wire flame spraying (WFS) and vacuum plasma spraying (VPS), were applied to the outside of copper cylinder with 20 mm OD. The surface structure by WFS was denser than that by VPS. The heat transfer performance around the horizontal tubes under microgravity was evaluated in pool boiling experiments using HCFC123 for heat fluxes between 1.0 and 160 kW/m2 and saturation temperature of 30 °C. The microgravity experiments were carried out during a parabolic flight of an airplane. As a result, the surface by VPS produced higher heat transfer coefficient and lower superheat at boiling incipiency under microgravity. For the smooth surface, the effect of gravity on boiling heat transfer coefficient was small. For the coated surface, a large difference in heat transfer characteristics by gravity was observed in the moderate heat flux range. The heat transfer was deteriorated by the change from the normal gravity to hyper-gravity, while it was improved by the transition from the hyper-gravity to microgravity. The difference in heat transfer coefficient was a little between the normal gravity and microgravity. The effect of the coatings on the CHF was not observed.
The helically coiled tube of heat exchanger is used for the evaporator of prototype fast breeder reactor “Monju”. This paper aims at the grasp of two-phase flow phenomena of forced convective boiling of water inside helical coiled tube, especially focusing on oscillation phenomena of dryout point. A glass-made helically coiled tube was used to observe the inside water boiling behavior flowing upward, which was heated by high temperature oil outside the tube. This oil was also circulated through a glass made tank to provide the heat source for water evaporation. The criterion for oscillation of dryout point was found to be a function of inlet liquid velocity and hot oil temperature. The observation results suggest the mechanism of dryout point oscillation mainly consists of intensive nucleate boiling near the dryout point and evaporation of thin liquid film flowing along the helical tube. In addition, the oscillation characteristics were experimentally confirmed. As inlet liquid velocity increases, oscillation amplitude also increases but oscillation cycle does not change so much. As hot oil temperature increases, oscillation amplitude and cycle gradually decreases.
Adiabatic vertically downward air-water two-phase flows in a single channel commercial plate heat exchanger were visualized by a neutron radiography method to clarify the flow characteristics and the differences in liquid distribution from those of vertically upward flows. From the visualized results, it was shown that water fell down without a spreading at a lower gas volumetric flux and tended to flow in the left-side of the shortest pass between the inlet and exit. The liquid distribution was opposite to that of the upward flows in which liquid fraction was higher along the both side of the single channel. In the case of a higher gas volumetric flux above 7 m/s, liquid spread at the enlarged section and the liquid distribution in the main part of the heat exchanger seemed to be homogenous. Measured average void fractions for the air-water downward flows showed almost the same tendency as those for the upward flows, and those were well correlated based on Drift flux model. On the other hand, the frictional pressure loss of the downward flows showed lower values than those of the upward flows at the lower gas volumetric flux less than 13 m/s. The difference was might be caused by the difference in flow pattern. For the higher gas volumetric flux over 13 m/s, the difference in frictional pressure loss was a little. Frictional pressure loss was well correlated by L-M method.
Heat transfer characteristics were experimentally examined in the field where a volatile liquid pool of per-fluorocarbon PF5050 (boiling point 306 K) was directly in contact with an immiscible hot water pool. Heat was supplied to a horizontal continuous liquid-liquid (LL) interface by downward hot water jet flow. Bubble incipience occurred with a thin PF5050 liquid film atop growing bubbles. Characteristics of bubble departure from the droplets were discussed based on comparison with Mersmann's formula. On heat transfer, curvature of the liquid-liquid interface controlling the bubble departure sizes had a predominant effect in both droplet and LL cases. Heat transfer characteristics could be explained based on this result, by using Weber number and buoyancy-interfacial tension ratio.
Recently, the development of the high-performance heat exchanger is desired from the view point of saving energy and resources. The application to the heat exchanger of dropwise condensation phenomenon which shows high heat transfer performance is desired. However, the relationship between the behavior of the condensate droplet and the heat transfer on the wide condensing surface in dropwise condensation has been not clarified. In this study, the heat transfer characteristics under dropwise condensation are investigated by the calculation and the experiment when the vertical condensing surface is vibrated in gravitational direction. As a result, we found that the heat transfer coefficient was enhanced by the vibration.
The volcanic eruption is categorized into non-explosive eruption with static magma flow and explosive eruption with shock wave. Volcanic eruption is a phenomenon of sudden eruption of high-pressure magma by the sudden decompression after pressure release. In the present study, it is experimentally investigated by using the simulant material what is the dominant mechanism which divides the explosive eruption and non-explosive eruption. The effects of volatile substance and viscosity of the material on the phase change behavior under the sudden decompression are investigated with transparent visible shock tube apparatus which simulate the volcanic sudden decompression with two-fluids component system of silicone oil as high viscosity fluid and acetone as volatile substance. In the experiment, it is observed that simulant material suddenly erupts upward after sudden decompression. It is experimentally confirmed from the experimental results that the flow pattern is changed when eruption speed changes. It is suggested that the nonlinear change of the eruption behavior is caused by the interaction between volatile substance vaporization and viscosity resistance.
We have developed a numerical method to evaluate behaviors of the cavitating bubbles based on the recent CFD (computational fluid dynamics) techniques. The method employs a finite-volume method combined with the high order and flexible interpolation scheme, CIVA. Two kinds of fluid behaviors, liquid (incompressible) and gas (compressible), are simultaneously computed by the unified scheme, CUP, which can handle the large density ratio (especially in case of mercury) associated with cavitation. By combining it with a new numerical cavitation model, which takes into account of compressibility of gas, good numerical results of water and mercury can be obtained._
A hybrid CMFD (computational multi-fluid dynamics) method is proposed for the prediction of gas-liquid and/or liquid-liquid dispersed two-phase flows including large-scale interface, poly-dispersed bubbles and drops. The method is the hybrid integration of an interface tracking method (ITM), three kinds of particle tracking methods (PTM) and an averaging method based on a multi-fluid model (MFM). The integration enables us to cover a wide range of d*=d/Δx, where d is the particle diameter and Δx the grid size, and to perform various kinds of multiphase CFD such as standard interface tracking, particle tracking and multi-fluid simulations, and hybrid simulations by making an arbitrary combination of ITM, PTM and MFM. The field equations and numerical solution procedure of the proposed method are described in detail. To demonstrate its potential, a poly-dispersed air-water bubbly flow in a vertical square duct and an air-water bubble plume in an open vessel are computed using the combination of ITM, PTM and MFM.
For interface-tracking simulation of two-phase flows with a high density ratio, a computational method, NS-PFM, combining Navier-Stokes (NS) equations with a phase-field model (PFM) is proposed in this study. In accordance with the free energy theory, PFM describes an interface as a finite volumetric zone across which physical properties vary continuously. Surface tension is defined as an excessive free energy per unit area induced by the density gradient in the interface zone. The Cahn-Hilliard (CH) equation is used for predicting interface configuration. PFM therefore does not require any elaborating interface-tracking algorithms for predicting interface motion. The proposed NS-PFM is applied to several problems of incompressible, isothermal two-phase flow with the same density ratio as that of an air-water system. Numerical simulations demonstrate that, (1) the volume flux driven by local chemical potential gradient in the CH equation plays an important role in interfacial advection and reconstruction, (2) the NS-PFM gives good predictions for pressure increase inside a bubble caused by the surface tension, (3) predicted collapse of two-dimensional liquid column in a gas under gravity agrees well with available data, and (4) coalescence of free-fall single drop into a liquid film is successfully simulated in three dimensions, without using conventional interface-capturing/tracking techniques.
An advanced VOF (volume of fluid) method with sophisticated interface evaluation is proposed for two-dimensional and three-dimensional two-phase flows on the incompressible viscous fluid. In the improved VOF method, the stabilized bubble function finite element method with numerical stability and acceptable accuracy is employed. The interface expression suited to the finite element analysis is derived to estimate the interface of the gas-liquid based on the digitizer method.
The effects of surface tension on flow characteristics of two-phase annular flow in vertical pipes of 16 to 5 mm i.d. have been studied experimentally and analytically. In the adiabatic experiments, three kinds of liquids mainly with different surface tension were used as the test liquids while air as the test gas. The data obtained were instantaneous and mean void fraction, pressure drop and flow regime, etc. at near atmospheric pressure. The effects of surface tension on each flow parameter were studied by comparing the data for the different liquids. In the analysis, the above data were compared with calculations by various correlations in literatures. Regarding the void fraction, the calculations were conducted mainly by the well-known two-phase two-fluid model. The constitutive equations of the interfacial friction force were tested against the data. The results of the above experiments and comparisons are reported in this paper.
In order to know the effects of gas-liquid inlet and mixing conditions on two-phase flows in microchannels, adiabatic experiments were conducted with changing a combination of inner diameters for the mixer and the microchannels. In the experiments, horizontal circular microchannels of 100, 176 and 251 μm diameter were used as the test channel, and water and nitrogen gas as the working fluids. It was observed that both “quasi-homogenous flow” and “quasi-separated flow” occurred if the area ratio of the microchannel to the mixer was below a certain value. Furthermore, void fraction and two-phase frictional multiplier were found to be smaller in the quasi-homogeneous flow than the quasi-separated one.
A simple design micro-heat pipe was proposed. It was composed of 20.0 × 20.0 mm square flow circuit which had two adjacent narrow-sides (1.0 × 1.0 mm2 or 0.5 × 1.0 mm2) and two adjacent wide-sides (5.0 × 1.0 mm2 or 2.5 × 1.0 mm2). A heating spot was at the narrow side and a cooling spot was at the wide side. Working fluid was ethanol. The flow circuit was placed horizontally. Bubbles generated at the heating spot migrated toward the wide side, the bubbles coalesced there to form a large bubble, and then the large bubble moved to the cooling spot. Finally, the large bubble was condensed at the cooling spot. This cycle repeated continuously. As a result of it, heat transport from the heating spot to the cooling spot was produced in the micro heat pipe. An analysis of a flow mechanism was performed by solving a simple flow equation based on the flow resistance. It was proved that one-way circulation flow could be formed in the flow circuit. Predicted flow velocities were close to measured velocities. The growth rate of generated bubble in the present micro heat pipe was in agreement with the conventional prediction for heat-transfer-controlled period. The heat transport efficiency per unit mass of the proposed micro heat pipe was much better than the heat conduction of any metallic plate.
Numerical simulation of gas-liquid two-phase flow is important for design of nuclear power systems. Conventional codes require experiments from laboratory scale to mock-up to obtain database for constitutive equations and verification. The aim of this study is to provide new simulation technique to substitute for a part of costly experiments. The extended two-fluid model developed by Hitachi, Ltd. was employed to treat inhomogeneous and intermittent two-phase flow behavior, which had been considered through constitutive equations. Validity of the new simulation code for complex two-phase flow was proved by comparison between calculated and experimental void fraction signals from two-phase flows in circular tubes, CCFL of a thick plate, and natural circulation of aerated pool in double cylinders. For measurement of instantaneous, multi-dimensional void fraction distributions, wire-mesh sensor techniques were employed for all test setups. It was found that the two-phase flow has higher orders of dynamics than initially expected, leading to development of robust analysis methods. The comparison was successful for well-structured flow patterns as slug flow, since the large diameter bubbles show low dimensional dynamics. It is also noted that an optimal delay time reconstruction method and a point correlation dimension method together were useful to increase the reliability of the analysis.
A steam injector has been investigated as one of the most important component of the next-generation reactor. It has a function of a passive pump without large motor or turbo-machinery and its performance as a pump depends on direct contact condensation phenomena between a supersonic steam and a sub-cooled water jet. However the turbulent heat transfer under large shear stress is not enough investigated. Furthermore although it well known that non-condensable gases affect the condensation heat transfer, the effect of the non-condensable gas on the condensation of supersonic steam on high-speed water jet has been not cleared. In the present study the operating characteristic of the steam injector is examined in detail, based on the observation results and measurement results of the temperature and the pressure distribution in the steam injector with non-condensable gas in steam. From experimental results, it is experimentally clearly the flow transient phenomena exist at SI start up period. It is also clarified that discharge pressure is depended on the inlet steam pressure, the inlet water flow rate, the throat diameter and non-condensable flow rate. Finally a heat transfer coefficient is estimated about 0.96 to 1.06 MW/K · m2 without non-condensable gas condition in steam.
Experimental studies on the flow behavior of gas-liquid annular two-phase flow passing through a nozzle section were carried out. This study is concerned with the central steam jet injector for a next generation nuclear reactor. In the central steam jet injector, steam/water annular two-phase flow is formed at the mixing nozzle. To make an appropriate design and to establish the high-performance steam injector system, it is very important to accumulate the fundamental data of the thermo-hydro dynamic characteristics of annular flow passing through a nozzle section. On the other hand, the transient behavior of multiphase flow, in which the interactions between two-phases occur, is one of the most interesting scientific issues and has attracted research attention. In this study, the transient gas-phase turbulence modification in annular flow due to the gas-liquid phase interaction is experimentally investigated. The annular flow passing through a throat section is under the transient state due to the changing cross sectional area of the channel and resultantly the superficial velocities of both phases are changed compared with a fully developed flow in a straight pipe. The measurements for the gas-phase turbulence were precisely performed by using a constant temperature hot-wire anemometer, and made clear the turbulence structure such as velocity profiles, fluctuation velocity profiles. The behavior of the interfacial waves in the liquid film flow such as the ripple or disturbance waves was also observed. The measurements for the liquid film thickness by the electrode needle method were also performed to measure the base film thickness, mean film thickness, maximum film thickness and wave height of the ripple or the disturbance waves.
The characteristics and the performance limit of a steam injector have been investigated. The disruption of a 5 mm diameter water jet that flowed coaxially into a pipe of 7, 10 or 20 mm diameter where vapor flow existed and the heat transfer of vapor condensation on the jet surface were examined. The heat transport to the radial direction in the jet was stronger than that of the turbulent flow in a pipe. The condensation heat transfer was mainly dominated by the heat transport in the water jet since the vapor condensation heat transfer efficiency was quite high. If the Kelvin-Helmholtz instability wave length was used as the jet disruption criterion, it predicted the jet disruption conservatively. It was proved that the steam injector tested could elevate the delivery pressure to five times higher than the suction-side water pressure in the present experimental condition.
A new concept of a two-phase MHD power generation system using a cavitating flow of an Electrically Conducting Magnetic Fluid (ECMF) is proposed, and the driving and power generation performance of the system is numerically predicted. A typical computational model for cavitating flow of a mercury-based magnetic fluid is proposed and several flow characteristics, taking into account the strong nonuniform magnetic field, are numerically investigated to realize the further development and high performance of the proposed new type of two-phase fluid driving system using magnetic fluids. Based on numerical results, the two-dimensional structure of the cavitating flows as well as the cloud cavity formation of the ECMF through a vertical converging-diverging channel are shown in detail. The numerical results demonstrate that an effective two-phase electromagnetic driving force and fluid acceleration, and high power density can be obtained by the practical use of magnetization of the working fluid of ECMF. Also clarified is the cavitation number of ECMF in the case of a strong magnetic field with a larger value than that in the case of a nonmagnetic fluid. Further clarified is the precise control of the cavitating flow in ECMF that is possible by effective use of the magnetic body force that acts on cavitation bubbles.
This paper describes a new measuring technique of void fraction using a magnetic fluid. The proposed measurement utilizes the electromagnetic induction so that the measurement can be realized with simple experimental devices. The present study consists of two kinds of experiments; one is “static experiment (calibration test)” and another is “flow experiment (actual flow test)”. In the present study, the experiments have been performed with fully diluted magnetic fluid for the purpose of applying to the ordinary two-phase flows such as water-air two-phase flow. Results of the experiments have verified that the proposed measuring technique of void fraction is very effective to measure the void fraction in the two-phase flow by adding a small amount of the magnetic fluid to objective fluid.
This paper reports the experimental research on micro-visualization of the growth process of cluster formation of ferromagnetic nano-particles in a water-based magnetic fluid on micro capillary flow. The purpose of this research is to observe the characteristics of primary clusters in micro capillary flow. The thermal behaviour of ferromagnetic nano-particles in micro capillary flow was observed through micro-visualization using the optical dark-field microscope system and particle tracking velocimetry (PTV) data processing system. Real-time visualization of primary clusters in a water-based magnetic fluid on micro capillary flow was carried out. Furthermore, the effect of magnetic field on the mixing process of using a water-based magnetic fluid in micro capillary flow was investigated.
Water purification of lower layer in a lake of dam was investigated using micro bubble technology. A device for generating pure oxygen micro bubbles in the lower layer of the lake of dam was developed. Almost all micro bubbles formed by the micro bubble generator shrank and changed to micro-nano bubbles in tap water. The rising velocity of micro bubbles obeyed Stokes' law. The dissolved oxygen concentration of the lower layer in the wide area of the lake increased rapidly after providing pure oxygen micro bubbles. In addition, the turbidity increased temporarily by the supply of the bubbles, but the increasing area of the turbidity stayed only in the lower layer of the lake.
Japan Meteorological Agency performs 7-day sea ice forecasting in Southern Okhotsk Sea with numerical dynamic and thermodynamic models. The current JMA computation uses a continuum model for the ice dynamic process. In this paper, The Distributed Mass/Discrete Floe Model, which considers the discrete characteristic of sea-ice and well simulates the ice edge location in short computational time, was introduced and the thermal mixing process of sea water was improved. In addition, for a higher accuracy forecasting, the current grid size of 12.5×12.5km was reduced down to 5×5km and improvement of sea-surface current data was discussed.
The removal performance of chlorinated organic compound from the porous material under ultrasonic irradiation was experimentally investigated. As the model PCB, o-dichlorobenzene was used. The solvent was hexane or dodecane. Wood chips impregnated with o-dichlorobenzene were used as the sample. The ultrasonic and solvent conditions were changed, and the removal ratio of o-dichlorobenzene from sample was measured. In order to examine the removal behavior of chlorinated organic compound from pore, the Stefan tube injected with o-dichlorobenzene was used as the sample. The pore and solvent conditions were changed, the interface position between o-dichlorobenzene and solvent in Stefan tube was measured and the penetration depth of solvent in Stefan tube was determined. By the ultrasonic irradiation, the removal ratio rapidly increased and became almost unity after 120 minutes for the sample with 10 mm in length. The removal rate for the ultrasonic irradiation was much higher than that for the shaking. The difference in removal ratio between the ultrasonic irradiation and the shaking became larger as the sample was bigger. The removal ratio increased with increasing sound pressure amplitude and became constant beyond a certain sound pressure amplitude. At the fixed sound pressure amplitude, the removal ratio at 28 kHz was nearly equal to that at 45 kHz. The removal ratio hardly depended on the solvent temperature. The removal ratio for degassed solvent was larger than that for non-degassed solvent. The penetration depth in Stefan tube had a maximum value against location of Stefan tube in solvent, but had no significant influence on size and depth of pore in Stefan tube. When the saturation degree of dissolved oxygen in solvent was 0.65, the penetration depth in Stefan tube was largest.
Murotokaiyoshinnsousui Co. Ltd. located in the east of Kochi Prefecture produces salt and mineral liquid by the solar evaporation process with Muroto Deep Sea Water. This method has an advantage of making high quality salt and mineral to meet the demand of customers. But on the other hand, this has some problem for intentional production and mass production under the influence of the weather. Therefore, this study are aimed to develop a significant industrial production process of salt and mineral to get a equal quality of existing ones produced by the solar evaporation process with Deep Sea Water, which shall be realized to be able to make a intentional and mass production with more low cost. Particularly, this paper presents the multiple-effective Vacuum-evaporator which is one of the concentrators. We define this multiple-effective Vacuum-evaporator as a process device to extract gypsum from concentrated deep sea water, and make decision for density of concentrated water. And also, we have practical inspection for automatic concentration operation. The results are summarized as follows: (1) Acceptable production tolerance was controlled by less than 10% as a result of practical inspection for concentrated Deep Seawater waste at the boiling point of multiple-effective Vacuum-evaporator based on the target of Baume's value 10. (2) When we studied about concentrated control using by the conductivity meter, we got the result in error value by less than ±0.2 and in tolerance ratio by less than 2% against target of Baume's value 10. It means to be possible to produce salt and mineral using by Deep Seawater Waste to meet precisely with target concentration density.