伊藤 和宏

Three different salt crystals (K2SO4, KCl, and Na2SO4·10H2O) were produced via batch cooling and continuous crystallization using a bench-scale crystallization device, in order to elucidate the mechanism of inclusion of the mother liquor as a function of crystal size. The inclusion ratio of the mother liquor was higher at small sizes and decreased with crystal growth. All results were represented by the previously proposed model of core-aggregation and shell-growth processes for the three different salt crystals. Crystals with small Vickers hardness aggregated with each other, and the inclusion ratio of the mother liquor of aggregated grown crystals was high for all three salt crystals tested herein.

Continuous crystallization via indirect cooling of potassium aluminum sulfate dodecahydrate (KAl(SO4)(2)center dot 12H(2)O) was carried out using a draft tube-type crystallizer with a circulation flow path. The crystallizer was equipped with a newly designed system to monitor the degree of supersaturation in the circulation channel. The average degree of supercooling and growth rate were measured. The crystal growth rates calculated by the population balance model and the supersaturation monitor were different but close. The average supersaturation calculated from the supercooling degree and the solubility data in the literature was 0.19 g per 100 g H2O. This system is also expected to be applied to industrial crystallization where impurities are present.

To understand the inclusion of mother liquor in crystals at different sizes, the continuous crystallization of potassium sulfate was investigated. A bench-scale crystallizer of the draft-tube type was employed for both batch cooling and continuous crystallizations. A standard solution of potassium sulfate was employed as the saturated solution at 323 K. The batch cooling crystallization was first performed at 283 K at a rate of 5 K/h, after which the continuous crystallization was performed at 283 K at two different residence times. The crystal size distribution (CSD) of potassium sulfate crystals and the inclusion ratio of mother liquor in the crystals at different sizes were measured. The average size of the crystals was approximately 400-500 mu m, and the inclusion ratio was less than 1% for all sizes; however, the small and large crystals contained a considerable amount of mother liquor, and the specific crystals that exhibited the lowest inclusion ratios were investigated. Moreover, an impurity distribution model for the suspension crystals was proposed based on coreaggregation and shell-growth processes.

To improve energy production cost, it is necessary to operate bioreactors at a deeper depth to increase per unit area production; however, self-shading could be an inhibiting factor. Therefore, it is important to employ a variety of agitators so that microalgae in deep regions can be agitated, allowing sufficient aeration. We aimed to evaluate the effectiveness of a self-sufficient aerator in an open pond cultivation system for a microalga. Three experimental cases with different agitation velocities (high: Casehigh; low: Caselow; no agitation: Casezero) were evaluated. In Caselow, cells grew fastest in the early stage of cultivation due to reduced mechanical shear stress. However, the increased turbidity after 150 h reduced the cell density and increased chlorophyll a content, which could be attributed to low light intensity. The maximum TAG content was achieved in Casehigh. The findings suggest that strong agitation using an aerator can promote TAG accumulation.

The separation of the binary unsaturated fatty acids C18:1 + C18:2 system was examined by high-pressure crystallization at 298 K (25 °C). The binary fatty acid mixture containing 0.8 mol fraction of C18:1 was packed in the glass cell with a free piston, and then pressurized by an aqueous ethanol solution around the glass cell up to 200 MPa. The complete solid mixture was obtained after cooling at 253 K (- 20 °C) as a depressurized binary solid. The solid was divided into four parts, and the composition of C18:1 was analyzed at each part of the solid using a refractometer, which revealed there was a composition distribution throughout the solid with C18:1 crystallized one-directionally from the top to the bottom of the cell. High-pressure crystallization could be effective for the separation of binary fatty acids.

We evaluated the performance of a resorcinol–formaldehyde (RF) hydrogel as an adsorbent for removing aqueous cesium ions (Cs+), by synthesizing cylindrical pellets of RF gels under different molar ratios (R/C) between resorcinol (R) and sodium carbonate (C) as the catalyst for the sol–gel polycondensation in the range from 2.5 to 400. The RF gel prepared at R/C = 2.5, containing the greatest amount of sodium ion (Na+), had the greatest Cs+ adsorption amount (0.660 mmol g−1), because Cs+ could be adsorbed on the network structure in the gel through exchange with Na+ at an equal molar ratio, but with the smallest effective diffusion coefficient of Cs+ (1.45 × 10–12 m2 s−1). Kinetic analyses based on the Dryden–Kay and intra-particle diffusion models revealed that the diffusivity of Cs+ in the RF gel depended strongly on the density of the network structure, which can be controlled by varying the R/C ratio. Graphic abstract: [Figure not available: see fulltext.].

To evaluate biodiesel production from microalgae, a flotation experiment was conducted using the living cell culture fluid of the diatom Chaetoceros gracilis using a venturi tube type microbubble generator. We compared the separation performance of three different culture periods: 1, 2, and 3 weeks from the start of cultivation. After 1 week, the cells were in the logarithmic growth phase, while after 2 and 3 weeks, cell growth had reached the stationary phase. The amounts of triacylglycerol (TAG) in the foam on the surface of the fluid tank were measured. TAG increased during the first 20 min after the start of circulation without additional coagulants and pH adjustment. The disruption of cells was achieved simultaneously. The amounts of TAG in the culture fluids at weeks 2 and 3 were higher than those at week 1. C. gracilis cells in the stationary phase accumulated large amounts of TAG and were easy to disrupt by pressure fluctuation in the venturi tube. These results provide insight into the fracture strength and buoyance of cells for efficiently separating the cells from large volumes of culture fluid.

We examined the effect of high pressure on the sol–gel phase transition of a resorcinol–formaldehyde (RF) aqueous solution to a RF hydrogel, which was hold under a certain pressure varied in the range from the ambient pressure to 400 MPa. By employing the dynamic light scattering method, we analyzed the scattered intensity of a He–Ne laser which was irradiated to the RF solution to determine the hydrodynamic diameter of the structure formed during the phase transition. Before the completion of the phase transition, we measured the transient change in the size of colloidal particles, i.e. the unit of the porous structure formed in the RF hydrogel. It was revealed that the size of the colloidal particles increased with the increase in the pressure added to the RF solution. After the completion of the phase transition, we prepared a RF cryogel by removing solvent from a RF hydrogel by freeze-drying. The specific surface area of the RF cryogel was found to decrease with the increase in the added pressure, as a result of the increase in the size of the unit of the porous structure.

By employing an annular‐cylindrical‐type apparatus operated under a constant cooling rate, melt crystallization is studied to condense a saturated fatty acid (FA) from a binary mixture of the saturated FA with unsaturated FA. In the annular space between the stationary outer cylinder and the rotating inner cylinder, counter‐rotating toroidal vortices, that is, the Taylor vortices are observed. The vortices are found to play a unique role in the solidification of FAs to form a unique wavy layer on the inner cylinder. The mass and heat transfer analysis by numerical calculation reveals that both the velocity and temperature distributions change depending on the position in the annular space because of the centrifugal or centripetal radial flow caused by the Taylor vortices.

食品加工施設の排水は腐敗しやすく，槽底に滞った汚泥から臭気や硫化水素などが発生し，排水処理施設の能力を低下させる．これに対し，高流速で空気を注入する方式のエアレータを用いて攪拌し，好気性処理を安定させる方法を提案した．地下水槽（幅2m×水深1.75m）の底部にエアレータを設置し，曝気中の流速を3軸電磁流速計で測定した．3次元的な循環流が観察され，循環流量は約400 L/min と推定された．また，溶存酸素量（DO）の測定から，良好な酸素溶解効率（OTE）が得られた．さらに，実際の食品加工排水に適用した場合の処理状況について報告した．

We investigate the vapor bubble stability in liquid argon and water using a molecular dynamics simulation. The Lennard-Jones interparticle interaction potential is used to simulate the interaction forces between molecules. The Stillinger' s cluster criterion is employed to classify the vapor molecules evaporated from the bulk liquid. Using this criterion, the vapor molecules are determined to have no neighboring molecules within a 1.23 to 1.32σ radius, where σ is the interaction radius in the L-J potential. The pressure of vapor and liquid phase can be calculated from the virial equation of sate. The stability of bubble is disscussed applying the Young-Laplace equation. The spherical bubble shape is maintained, when the liquid pressure takes the negative value. The thickness of vapor-liquid interface and the number of molecules across vapor-liquid interface are not proportional to the size of bubbles.

We examined the degradation of aqueous phenol by ozonation in an aerated mixing vessel, which was combined with a fixed-bed reactor packed with high-silica zeolite (HSZ) pellets. Ozone-containing oxygen gas was introduced as fine bubbles through a sparger placed in the aerated mixing vessel, whereas the aqueous phenol solution was circulated between the vessel and the reactor. Measurements of transient changes in the concentration of both phenol and total organic carbon in the treated solution revealed that the degradation of phenol or total organic carbon by ozonation was enhanced by the presence of HSZ because both phenol and ozone could adsorb on the hydrophobic micropores. As a result of quantitative analysis of the treated solution, it was found that catechol, hydroquinone, humic acid, and maleic acid were the possible reaction intermediates during ozonation of aqueous phenol employing HSZ.

次世代バイオ燃料の資源として期待されている微細藻類（ツノケイソウ）の効率的な回収方法として，融液晶析を応用した凍結濃縮を検討した．ガラス製の冷却ジャケット付き晶析器を用いて壁面から中心部に向かって氷相を形成する操作を行った．操作条件として撹拌回転数，冷却温度，凍結率を変化させて，液中のツノケイソウ細胞の濃縮比および氷中のツノケイソウ細胞の希釈比を実測し，さらにツノケイソウ細胞の固液分配係数への影響を実験的に明らかにした．2種類の固液分配係数モデルによる実験データの相関性を比較した結果，分配が困難とされている高速凍結でもツノケイソウ細胞を濃縮できることを示唆した．

The biodiesel fuel ethyl oleate (fatty acid ethyl ester, FAEE) was produced using Novozym® 435 (immobilized lipase) by transesterification of a mixture of ethanol and triolein in a fixed-bed reactor operated in circulating batch mode. The miscibility of the mixtures during transesterification was predicted thermodynamically and the conversion ratio of triolein was studied as a function of reaction time. The yield of ethyl oleate increased when the feed molar composition of ethanol was increased. The glycerin by-product could be removed from the enzyme particles by the circulating feed mixture. The inactivation of Novozym® 435 by glycerin was also examined in the circulating batch mode experiments, and an effective reaction model was proposed to describe the inactivation of Novozym® 435 and ethanol effect during the transesterification reaction by using the modified Michaelis-Menten equation.

The present study evaluates the lipase (Novozym 435)-catalyzed transesterification of triolein and methanol mixtures to generate fatty acid methyl esters (FAMEs) using dimethyl ether (DME) in a batch reactor and a continuous pipe reactor. The addition of DME facilitated the preparation of homogeneous mixtures of triolein and methanol. The effect of the Novozym 435 and DME contents in the feed mixtures on the time-course of FAME production was analyzed. With increasing contents of Novozym 435 and DME in the feed mixtures, the FAME concentration increased more rapidly in the batch reactor than in the continuous reactor. The feed flow rate and DME content were varied, and the FAME concentration at the outlet of the pipe reactor was measured with variation of the residence time and DME content. Increasing the DME content in the feed mixtures and the residence time led to a more rapid increase in the FAME concentration for the batch reactor than that in the continuous pipe reactor.

This study investigated the use of pressure sensitive paint (PSP) as new measuring technique for measuring the pressure distribution of a gas bearing. An externally pressurized circular thrust gas bearing with single gas supply hole was used as the test bearing to investigate the suitability of this technique. The test bearing was 30 mm in diameter, with a gas supply hole of diameter 0.7 mm. A coat of PtTFPP, the substance used as the PSP, was applied to the bearing surface using an air-assisted spray. The PSP luminescence characteristics were calibrated before the tests because of their dependency on temperature and pressure. The pressure distribution was obtained by averaging 50 images captured by a 12-bit complementary metal-oxide semiconductor (CMOS) camera. These experimental results were compared with the results of a numerical analysis based on the divergence formulation method. There was good agreement between the experimental and analytical results, thus demonstrating the effectiveness of using PSP for pressure distribution measurements.

In application of micropumps to new fields in chemistry, biology, medical science and others, smaller sizes are supposed to be important rather than higher pump performance. In this study, considering from such a view point, micropumps using rotational and reciprocating motions of magnetic material balls were proposed and studied experimentally. The pump performance, i.e. the relation between flow rate and pump head are measured from liquid level changes in two containers connected to the inlet and outlet of the micropump. For the rotational motion micropump, while the maximum flow rate obtained, ~2 mL/min, is large enough as a micropump, the maximum pump head achieved, ~15 mm, is small even for a micropump. It is desirable to increase the pump head furthermore for this micropump. For the reciprocating motion micropump, the maximum flow rate obtained and the maximum pump head achieved are ~7.5 mL/min and ~625 mm, respectively. These values of the pump performance are sufficient as a micropump. Both the micropumps can be incorporated into microfluidic devices (tips) and can pump arbitrary kind of liquid.

In this study, we investigate the vapor bubble stability in liquid argon using a molecular dynamics simulation. The Lennard-Jones (L-J) interparticle interaction potential is used to simulate the interaction forces between argon molecules. The discrimination method based on Stillinger's cluster criterion is employed to classify the vapor molecules evaporated from the bulk liquid. In this criterion, the vapor molecules are determined to have no neighboring molecules within a 1.23 to 1320 sigma radius, where sigma is the interaction radius in the L-J potential. It is found that the spherical bubble shape is maintained and the Young-Laplace equation applies mainly as a result of the large negative pressure of the liquid. The 10-90 thickness of the vapor-liquid interface was approximately 30 to 90% of the bubble radius in the present simulation. A certain frequency of condensation and evaporation was maintained in the smaller bubble case, which is not proportional to the decrease in bubble surface area. (C) 2017 Elsevier B.V. All rights reserved.

To account for both the growth of solid layer and solute distribution in melt crystallization, we proposed empirical equations involving heat and mass transfer at the solid-liquid interface between the solid layer and melt. With the aim of separating saturated fatty acid as a solid phase from binary mixture of fatty acids as model biofuel, we performed melt crystallization by employing three different species of binary melts which contained triglyceride as unsaturated fatty acid, and myristic acid, palmitic acid, or stearic acid as saturated fatty acid, respectively. As a result, we confirmed the validity of the proposed equations under the varied crystallization conditions.

下水廃棄物の減容化とエネルギー回収の向上に対する基礎的検討を目的として，減圧脱気・蒸気処理法を試した．蒸気エジェクタを適用して消化汚泥を連続的に減圧槽に導き，これらの処理を施す装置を試作した．15 min間以上の連続処理が可能であり，処理した汚泥を発酵させた消化ガスのメタン成分が11ポイント増加することを示した．また本処理により，VTS, CODcr, BODの除去率が増加し，消化率も増加することを明らかにした．さらに，水エジェクタと蒸気エジェクタとを組み合わせて，脱気処理時の圧力を下げた実験を行い，可溶化が促進されることを示した

The present study investigates the charge–discharge processes of a Planté lead–acid battery performed under atmospheric pressure and 10 MPa. The ampere-hour efficiency of the lead electrodes was substantially increased by the secondary formation of the Planté electrode, and the ampere-hour efficiency under 10 MPa was slightly higher than that under atmospheric pressure. The active PbSO4 crystals on both electrodes were observed by SEM at different currents, and the morphology and crystal size distribution (CSD) were obtained. Active PbSO4 crystals nucleated and grew during discharging; whereas, they disappeared during charging. This is similar to the crystal behavior during continuous crystallization in a battery. Therefore, a simple population balance model was used to express the CSD of PbSO4 crystals on both electrodes. The CSD of both electrodes were similar at 10 MPa, but the CSD of the positive electrode was different from the CSD of the negative electrode. The current density on both electrodes was balanced under 10 MPa.

Anti-solvent crystallization from a ternary mixture was examined by an NpT ensemble molecular dynamics simulation. The co-solvent and anti-solvent effects were represented by the Lennard–Jones interaction energy parameter, εij. The homogeneous binary solution of the solute and solvent was achieved at a constant temperature and pressure. Anti-solvent crystallization was introduced by changing some co-solvent molecules to anti-solvent molecules, immediately. The configuration of solute molecules was investigated by using the radial distribution function, g(r), and the local composition, xL. The value of εij affected the configuration of the solute molecules significantly; the decrease in εij provided the localization and crystallization of the solute molecules. The composition of the anti-solvent molecules in the solution also affected the configuration of the solute molecules; the increase in the anti-solvent composition produced the crystal structure of the solute molecules more rapidly. These qualitative results corresponded well to anti-solvent crystallization. The radial distribution function represented the crystal structure for solute molecules, and the local composition of the solute was increased from the bulk composition as the effect of the anti-solvent increased. We proposed that the time variation of the local composition of the solute represents the temporal development of the crystal structure and the time to crystallization well.

The authors are developing a micropump which combines reciprocating motion of a magnetic material ball in a pumping channel and four passive check valves. An additional experiment has been performed for one combination of the ball outer diameter and the channel inner diameter, and results of this experiment are presented in this paper. Including the previous experiments performed by the authors, the maximum pump head of similar to 620 mm and the maximum flow rate of similar to 7.5 mL/min have been obtained in the present micropump. Also, in this study, model calculations have been performed in order to predict the pump performance, i.e. the relation between pump head and flow rate. Calculated flow rates agree well with experimental data for larger gaps between the ball outer diameter and the pumping-channel inner diameter; however, calculated flow rates are larger than the experimental data for smaller gaps. Therefore, it is necessary to improve the calculation models, in particular by calculating leak flow rate in the pumping channel as a flow through a nozzle instead of that through an orifice.

Air bubble injection and subcooled flow boiling experiments have been performed as part of the DOE Nuclear HUB project, Consortium for Advanced Simulation of Light Water Reactors (CASL). The main objective was to obtain a better understanding and detailed data needed to validate 3-D Interface Tracking Models and CFD models which can predict subcooled flow boiling phenomena in fuel assemblies of Pressurized Water Reactors. In both experiments, the flow channel was a vertical annulus of 4.8 mm gap width in which water at near atmospheric pressure flowed upward under a laminar or turbulent flow condition accompanied by air or vapor bubbles. The air bubble injection experiments yielded data on bubble formation and departure from a small hole on the inner tube, subsequent motion and deformation of the detached bubbles, and interactions with laminar or turbulent water flow. Instantaneous and ensemble-average liquid velocity profiles have been obtained using a Particle Image Velocimetry technique and a high speed video camera. Preliminary subcooled flow boiling experiments have been performed with subcooled water in the same annular channel geometry but with an electrically heated rod to generate the vapor bubbles. PIV measurements of turbulent velocity profiles in the presence of small vapor bubbles on the heated rod are presented. (C) 2013 Elsevier B.V. All rights reserved.

For the safety design of a Fast Breeder Reactor (FBR), if a Core Disruptive Accident (CDA) occurred hypothetically, it is required to suppress the rapid energy release due to a prompt criticality. Even if the rapid energy release does not occur, there is a possibility that a large amount of fuel melts. Therefore it is important to achieve Post Accident Heat Removal (PAHR). In order to achieve PAHR, it is strongly required that the molten material which is released from a core region gets cool and solidifies in the sodium coolant in a reactor vessel by breaking up. It is considered that the molten fuel is injected into the coolant like a jet. Furthermore, in the actual FBR, the interfacial temperature between the molten fuel jet and the coolant is considered to be lower than the melting point of the molten material. Thus for PAHR in CDA, it is important to understand the interaction between the jet and the coolant in such a condition and to estimate the molten jet behavior quantitatively. In order to estimate quantitatively the effects of the solidification on the molten jet behavior, we carried out the experiment in which a simulant material was injected into a simulant coolant. In the experiment, we used low melting point alloy (Bi -Sn) and water as the simulant molten material and the simulant coolant respectively. In the experiments, we chose the temperature range including the condition that the interfacial temperature was lower than the melting point of the molten material. The jet breakup and the fragmentation behavior of the molten material jet were observed with a high speed video camera. Then the jet breakup length is estimated form the results. We changed the initial interfacial temperature condition by adjusting temperature of the molten material and the coolant. We also changed the jet velocity by adjusting the height of the nozzle tip from the water surface. From the experiment, we found that the jet breakup behavior depends greatly on the interfacial temperature and the injection velocity and that the solidification of a molten material jet and the growth of unstable jet surface, which results from the relative velocity of the jet to the coolant, are in a competitive relation for the jet breakup. We also found that when the molten material jet breaks up into fragments, the breakup length is independent of the initial interfacial temperature and the initial injection velocity.

Experiments and numerical analyses have been performed on micropumps/minipumps using rotational motion of magnetic material balls. In the pumps, magnetic material balls and nonmagnetic materials balls rotate in a closed channel loop, and a part of the balls acts as a piston and the remaining part of the balls serves as a valve. Experiments have been carried out on two pumps, i.e. a smaller pump and a larger pump with channel cross-sections of similar to 1 mm and similar to 2 mm inner diameter, respectively. The maximum flow rate achieved and the maximum pump head obtained are similar to 500 mu l/min and similar to 70 Pa, respectively, for the smaller pump, and similar to 2000 mu l/min and similar to 150 Pa, respectively, for the larger pump. Numerical analyses have been performed by dividing the pumping loop into a piston channel and a valve channel. The numerical analyses overestimate the flow rate obtained in the experiments, except for the region of larger pump heads in the larger pump.

Flow through an air passage of ventilated automotive brake rotor affects the thermal energy dissipation from rotor into atmosphere. In the present work, a velocity profile around a ventilated brake disc was measured using a hot-wire anemometer in order to understand the statistical turbulent property of air passage flow. Three-dimensional velocity components were evaluated at 5 mm outside the disc edge by rotating X-type hot-wire probe. The probe was also tilted corresponding to rotational speed so that it could receive the maximum velocity from disc. The maximum value of both average and fluctuation velocity increased significantly than that of solid disc. The velocity fluctuation profile indicated asymmetric aspect in contrast to the average velocity profile. An empirical one-dimensional model was suggested for evaluation of flow through air passage. The predicted radius velocity agreed with the present experimental results by substituting local angular speed of disc into air circumferential velocity.

高速増殖炉（FBR）の炉心溶融事故（CDA）時に，溶融炉心の一部が冷却材中へジェット状に射出される可能性がある．本研究では, 実機と密度比が同程度の低融点合金と水を炉心溶融物と冷却材の模擬物質として用いた実験を行い, 両者の相互作用を理解し，固化に至るまでの詳細を把握することを目的とする．実験では, 溶融物を水中に自由落下させ, その挙動を高速度カメラで観測した. また, 固化物を回収, その形状, 質量および寸法を計測した. その結果, これまでに溶融物の温度により, 溶融物ジェットの流動の形態を溶融物と水の液-液接触および固-液接触条件に区分することができ, 更には固化物と可視化観測結果から, 界面凝固膜の材料強度を考慮した微粒化物径予測式が構築されている. そこで, 今回は溶融物ジェット界面挙動の詳細な可視化観測から界面凝固膜の材料強度を直接評価することで予測式の検証を試みた.

For the safety design of a Fast Breeder Reactor (FBR), Post Accident Heat Removal (PAHR) is required when a hypothetical Core Disruptive Accident (CDA) occurs. In PAHR, it is necessary to understand the interaction between molten core material and coolant m order to estimate whether the molten material jet is completely solidified by the coolant. The objective of the present study is to clarify the dominant factors of the fragmentation behavior on the jet breakup. In this study, we inject molten material and transparent fluid into coolant at free fall speed. The jet breakup and fragmentation behavior of the molten material and the transparent liquid are observed with a high speed video camera. In addition, we simulate liquid jet using the lattice Boltzmann method m order to investigate the jet breakup and the fragmentation behavior, which are difficult to be visualized or measured in the experiment.

The sensitivity of the gradient oscillatory number (CON), which is a potential hemodynamic indicator for cerebral aneurysm initiation, to flow input waveform shapes was examined by performing computational fluid dynamics (CFD) simulations of an anatomical model of a human internal carotid artery under three different waveform shape conditions. The local absolute variation (standard deviation) and relative variation (coefficient of variation) of the CON calculations for three waveform shapes were computed to quantify the variation in CON due to waveform shape changes. For all waveform shapes, an elevated CON was evident at a known aneurysm site, albeit occurring at additional sites. No significant differences were observed among the qualitative CON distributions derived using the three different waveform shapes. These results suggest that the CON is largely insensitive to the variability in flow input waveform shapes. The quantitative analysis revealed that CON displays an improved relative variation over a relatively high CON range. We therefore conclude that it is reasonable to use assumed flow input waveform shapes as a substitute for individual real waveform shapes for the detection of possible CON elevations of individual clinical cases in large-scale studies, where the higher values of CON are of primary interest. (c) 2012 Elsevier Ltd. All rights reserved.

When a hypothetical Core Disruptive Accident (CDA) occurs in Fast Breeder Reactor (FBR), it is strongly required that the molten core material can be solidified and cooled down by the sodium coolant in a reactor vessel. In order to estimate whether the molten material jet is completely solidified by sodium coolant, it is necessary to understand the interaction between the molten core material and the coolant. The objectives of the present study are to clarify the correlation of the jet breakup and fragmentation behavior and the dominant factors of both behaviors considering surface solidification. In order to investigate the influence of surface solidification on jet breakup and fragmentation behavior, experiments under surface solidification and liquid-liquid contact condition are conducted. Although the molten material jet is fragmented with each condition, jet breakup and fragmentation behaviors on each condition are different. In addition, when the surface solidification occurs, there is possibility that the material strength of solidified crust on the surface affects jet breakup and fragmentation behaviors. Then, numerical calculation based on hydrodynamics and material mechanics is conducted to evaluate the influence of the material strength on jet breakup and fragmentation behaviors. In comparison with the numerical estimation and mass median diameters obtained from experimental results, the effect of solidification on jet breakup and fragmentation behavior of molten material jet is discussed.

高速増殖炉（FBR）の炉心溶融事故（CDA）時に，溶融炉心の一部が冷却材中へジェット状に射出される可能性がある．本研究では, 実機と密度比が同程度の低融点合金と水を炉心溶融物と冷却材の模擬物質として用いた実験を行い, 両者の相互作用を理解し，固化に至るまでの詳細を把握することを目的とする．溶融物を水中に自由落下させ, 溶融物の挙動を高速度カメラで観測した. また, 実験後に固化物を回収し, その形状, 質量および寸法を計測した. その結果, 溶融物の温度により, 溶融物ジェットが異なる分散・微粒化挙動を示した. そこで流動の形態を溶融物と冷却水の液-液接触および固-液接触条件に区分し, 固化物と可視化観測結果から溶融物ジェットの流動構造の評価を試みた. 更に界面凝固膜の材料強度を考慮した微粒化物径予測式を構築し, 実験にて測定した固化物の質量メジアン径との比較を行い予測式の検証を行った.

Free surface fluctuations on a high-speed water jet were measured by a laser beam refraction technique. This method can be used to obtain quantitative time-series data on local surface fluctuations. The developed system employs two pulsed laser diodes, and it uses a high-speed optical sensor to detect the instantaneous positions of the laser beams that are refracted at the free surface. Fluctuations in the slope angle are measured at two locations separated by 1.27mm. The wave speed of each free surface wave, which is determined by the zero-upcrossing method, is experimentally evaluated by the cross-correlation method. A two-dimensional waveform is obtained by integrating the slope angle data. The local mean wavelength and mean wave steepness are evaluated for average jet velocities up to U=10 m/s. Streamwise waveforms of the high-speed water jet at several locations exhibit appreciable asymmetry and have steep profiles. Copyright © 2011 Kazuhiro Itoh et al.

The relation between the development of the wall boundary layer in a convergent nozzle and free surface waves on the emanated liquid jet has been investigated experimentally. In the convergent nozzle, which forms a water jet along a flat back wall, the velocity profiles of the wall boundary layer were measured using a laser Doppler velocimeter with jet average velocities of U0 = 5, 10 and 15 m/s. The property of free-surface waves and the intermittency factor of free surface fluctuations were also determined by photography and an optical measurement technique, using laser beam refraction on the jet surface. For the lowest velocity case U0 = 5 m/s, the mean velocity profiles of the boundary layer under the pressure gradient in the convergent nozzle indicated an inverse transition from turbulent to laminar boundary layer, so-called relaminarization. On the other hand, for the higher velocity case U0 ≥ 10 m/s, the relaminarization in the convergent section became incomplete. For these cases, the turbulent intensity near the wall increased significantly and the nozzle-exit boundary layer was restored quickly to a turbulent profile for a short parallel section immediately upstream of the nozzle exit plane. The increase in the velocity fluctuation near the wall promotes wave generation downstream of the nozzle exit plane. Therefore, the intermittence of the wave packet almost disappeared and the jet free surface was covered with continuous capillary waves when the turbulent boundary layer was separated from the nozzle exit.

Numerical analyses, both molecular dynamics (MD) analyses and continuous fluid analyses (by the finite difference method), have been performed on electric double layer and electroosmotic flow in nano-scale parallel plates. For a channel width of 8.2 nm, the MD analyses shows that the electric double layer covers whole channel while the continuous fluid analyses indicates that the electric double layer is formed only in the regions near the walls. For a channel width of 20.6 nm, both the MD analyses and the continuous fluid analyses show that the electric double layer appears only in the regions near the walls. It becomes obvious from the MD analyses that the thickness of electric double layer becomes large when the electric field is tilted from the direction of wall surface. By the continuous fluid analyses, the electroosmotic flow velocity is estimated to be 2.5 mm/s and 3.6 mm/s for channel widths of 8.2 nm and 20.6 nm, respectively. Copyright © 2011 by ASME.

For the safety design of the Fast Breeder Reactor (FBR), the Post Accident Heat Removal (PARR) is required when a hypothetical Core Disruptive Accident (CDA) occurs. In the PARR, it is strongly required that the molten core material can be cooled down and solidified by the sodium coolant in the reactor vessel. There is high possibility for molten material to be ejected as a liquid jet into sodium coolant in the reactor vessel. In order to estimate whether the molten material jet is completely solidified by sodium coolant or not, it is necessary to understand the interaction between molten core material and coolant such as jet breakup and fragmentation behavior in coolant. The jet breakup behavior is the phenomenon that the front of molten material breaks up in coolant. To clarify the mechanism of jet breakup and fragmentation during the CDA for the FBR, it is necessary to understand the correlation between jet breakup lengths and size distribution of fragments when molten material jet interacting with coolant. The objective of the present study is to clarify the dominant factor of the jet breakup length and the size distribution of fragments experimentally. Molten jet of U-alloy138 is injected into water as simulated core material and coolant by free-fall. The density ratio of core material and coolant is almost same as that of the real FBR system. The jet breakup behavior as interaction of molten material with coolant is observed with high speed video camera. Front velocity of the molten material jet is estimated by using the image processing technique. It suddenly decreases when the jet fall into the coolant. The jet breakup length estimated from observed images is compared with the breakup theories to understand the effect of experimental parameters for the jet breakup length. The solidified fragments are gathered and classified in size, and the mass in each size is measured. Median diameter is obtained from the mass distribution of the fragments. In comparison with interfacial instabilities, the median diameter of fragments shows the independent of relative velocity. The jet breakup lengths and median diameters compared with existing theories is discussed.

First, experiments have been conducted on separation of ferromagnetic particles from water-ferromagnetic particles dispersion flow by a magnetic field gradient. The test section, in which the magnetic field gradient is applied, is 0.05 m in height and 0.5 m in length. The experimental conditions are 0.1 m/s for inlet velocity, 0.0001 for inlet particles volume fraction and 0.0 T to 0.5 T for magnetic field (in the magnetic pole piece). The ferromagnetic particles are cobalt particles with an average diameter (at the test section inlet) of 8.4 μm. Secondly, numerical calculations have been performed in simulating the experimental test section and experimental conditions. In the calculations, increase in the particle diameter by the aggregation of magnetized particles has been considered in order to get better agreement between calculated and experimental results. It has become clear from experimental results that the larger the magnetic field becomes the smaller the particles volume fraction at the test section exit becomes and the volume fraction at the exit is nearly zero for a magnetic field of 0.5 T. It has also become clear from calculation results that the larger the magnetic field becomes the larger the particles volume fraction at the bottom of test section (meaning the particles accumulation in this region) and the smaller the volume fraction at the test section exit becomes.