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A new shape of the mixer in supercritical hydrothermal flow-type reactors was proposed and evaluated by neutron radiography and nanoparticle synthesis.

Direct numerical simulations were carried out to investigate three-dimensional, unsteady magnetohydrodynamic (MHD) convection in a spherical electromagnetically levitated molten Cu-Co droplet with a diameter of 5 mm under different strengths of the static magnetic field. The strength of the static magnetic field ranged from 0 to 3 T. MHD convection under lower static magnetic fields presented turbulent flow. The velocities in the levitated droplet decreased with increasing strength of the static magnetic field. At more than 1.5 T, the convective flow pattern became axisymmetric and the turbulent energy reached almost zero, i.e., MHD convection presented laminar flow. Comparisons of the present numerical results with past experimental results demonstrated that the marked change in phase separation structures in undercooled Cu-Co alloys at 1.0 to 1.5 T was closely related to the laminar-turbulent transition of MHD convection in the levitated droplet.

The compositional dependence of the thermal conductivity of a molten copper-iron (Cu-Fe) alloy at low Fe contents was measured herein by combining a periodic laser heating method and an electromagnetic levitator (EML) with a static magnetic field that can suppress the melt convection in the molten sample. The measured thermal conductivities markedly decreased with the composition of Fe up to 20 at. pct.

Graphical abstract, Highlights • Temperature-responsive copolymer was synthesized using ultrasound. • The responsive temperature of the copolymer was controlled by reaction conditions. • Time course of the molar fraction of poly(N-isopropylacrylamide) was measured. • Lower critical solution temperature (LCST) increased with ultrasonic irradiation time. • LCST can be controlled by ultrasonic irradiation condition., Poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (poly(NIPAM-co-HEMA)) is a temperature-responsive copolymer that is expected to be applicable as an advanced functional polymeric material in various fields. In this study, a novel method was developed to control the responsive temperature of poly(NIPAM-co-HEMA) using an ultrasonic polymerization technique. Initially, the behavior of the reaction was investigated using NIPAM and HEMA monomers under ultrasonic irradiation. A high ultrasonic power was found to produce a high reaction rate and low number average molecular weight of the copolymer. The polydispersity of the synthesized copolymer was approximately 1.5 for all ultrasonic powers examined. In the early stage of the reaction, the molar fraction of NIPAM in the copolymer was lower than the initial molar fraction of the monomers. It was concluded that ultrasonic irradiation affected the initiation reaction and polymer degradation, but did not affect the propagation reaction. Furthermore, the effect of the ultrasonic irradiation conditions on the temperature responsiveness of the copolymer was investigated. The lower critical solution temperature (LCST) of the copolymer was found to increase with increasing ultrasonic irradiation time. In addition, in the early stages of the reaction, the measured values of the LCST were higher than the estimated values using copolymer composition. This can be attributed to some parts of the copolymer chain possessing a higher NIPAM fraction than the overall fraction due to different reactivities of the monomers and terminated radicals. This hypothesis was indirectly verified by the synthesis of a block copolymer from the PNIPAM homopolymer and HEMA monomer.

Wetting is a fundamental and important phenomenon that is encountered in various engineering processes, and particularly, the understanding of mesoscopic dynamic wetting of not only pure liquids but also suspensions with nanoparticles is required with the recent miniaturization of devices. Therefore, it is important to establish a technique to precisely measure the dynamic behavior of liquid thin films near the three-phase contact line. In the present study, the mesoscopic wetting behavior of nonvolatile polydimethylsiloxane (PDMS, 20 cSt) and a PDMS suspension containing PDMS-modified SiO2 nanoparticles at a concentration of 1 wt% is measured using a phase-shifting imaging ellipsometer (PSIE) developed in our previous study, although the aggregates of nanoparticles are formed in the suspension. The PSIE can measure the two-dimensional thickness profile of liquid thin films from nanometer to micrometer scales. From the measured thickness profiles, we investigate the effect of the suspended nanoparticles on the apparent contact angle θa and precursor film length Lp. The dependence of θa and Lp on the velocity of contact line U ranging from 10–8 to 10–6 m/s is characterized. The contact angles of both fluids reflect the Cox–Voinov law, i.e., the θa is proportional to U1/3. At the same U, the θa of the suspension is higher than that of pure PDMS. The Lp of both fluids is proportional to U−1 and is the same at the same U. Furthermore, the Lp and thickness profiles at the nanometer scale are consistent with adiabatic precursor film theory.

The effect of melt convection on the phase separation structures in undercooled Cu Co alloys was investigated using the electromagnetic levitation technique, where the melt convection was controlled by applying a static magnetic field. The three-dimensional phase separation structures of the solidified Cu Co alloys were first observed using neutron computed tomography. A large number of small spherical Co-rich phases were dispersed in the Cu-rich phase matrix when the static magnetic field was relatively small. In contrast, several coalesced Co-rich phases, which were elongated along the direction of the static magnetic field, appeared in the higher strength of static magnetic field.

Normal spectral emissivity of molten Cu-Fe alloy with different compositions was measured at the wavelength of 807 nm using an electromagnetic levitator superimposed with a static magnetic field, which is capable of producing accurate normal spectral emissivity data because the applied static magnetic field suppresses translational and surface oscillations of a levitated sample to consequently reduce measurement uncertainties. Cu-Fe alloy samples used in this study were Cu97Fe3, Cu93Fe7, Cu92Fe8, Cu90Fe10, Cu80Fe20, and Cu70Fe30. The strength of the static magnetic field and temperature ranged from 3.0 to 3.5 T and 1350 to 1750 K, respectively. The measured normal spectral emissivity indicated negligible temperature dependence in a wide temperature range. In contrast, the compositional dependence indicated a distinct tendency in which the emissivity increased markedly with the composition of Fe up to 10 at pct.

The objective of this work was to investigate diffusion phenomena in methane clathrate hydrates during depressurization that lead to their dissociation. A thermodynamic mass transfer model is proposed that considers cage occupancy in structure I clathrate hydrates and methane diffusion from both S-cages (dodecahedron: 12 pentagons) and M-cages (tetradecahedron: 12 pentagons, 2 hexagons). Methane occupancies during dissociation were measured in situ with Raman spectroscopy with a newly-constructed optical system and data were estimated with Langmuir constants calculated by assuming a spherically symmetric cell potential. Model results were in agreement with experimentally-measured changes in average occupancy with time, so that dissociation kinetics at the interface were concluded to be strongly related to both methane diffusion and cage occupancy. Dissociation kinetics of methane hydrate can be reliably estimated with the proposed model. The proposed model is applicable to the study of methane hydrate dissociation-limited mechanisms or to larger-scale geological systems being used to estimate gas production rates.

A series of three-dimensional numerical simulations was conducted to investigate the convection inside an electromagnetically levitated silicon droplet under vertical, horizontal and rotational magnetic fields, respectively. The results show that the flow is totally axisymmetric and two counter-circulating vortexes appear in the droplet with an inner-outer distribution under vertical magnetic fields. The inner vortex brings fluids from the top area to bottom area directly, which is potentially responsible for the requirement of quite strong vertical magnetic fields in the experimental measurement of thermal conductivity of molten silicon. With horizontal magnetic fields, the vortexes inside the droplet turn to an up-down distribution, which is more beneficial in the thermal conductivity measurement since it prevents the direct convective heat transfer effectively. However, the horizontal magnetic field fails to suppress the convection effectively and the flow is intense and spatially imbalanced, leading to a less stable flow state. The rotational magnetic field combines the advantages of the formers, suppresses the convection along z-axis apparently and creates an up-down distribution of vortexes simultaneously. It suggests that the rotational magnetic field shows potential interest in the measurement of thermal conductivity of melts. Besides, the rotational magnetic field would evoke forced convection in azimuthal direction, which can be better controlled by varying magnetic intensity and rotating frequency. The azimuthal flow is expected to balance the rotation of melts induced by helicity of coils in experiments and shows potential advantages in melt stirring and solidification from undercooled melts.

Neutron radiography can visualize heavy oil flows in metallic reactors used to upgrade heavy oils. Thus, we visualized heavy oil flows in a packed bed using real-time neutron radiography to support its capability and to offer basic experimental data necessary for verification and validation of numerical simulations. Atmospheric residue was used as the heavy oil sample and heavy oil and N2 gas were concurrently supplied into a packed bed from above a reactor simulating a trickle bed reactor. Reactor temperatures were set at either 100°C or 250°C to change heavy oil viscosity. The heavy oil flow rate was kept constant at 2.5 mL/min and the N2 gas flow rate was set at either 1 L/min or 3 L/min at 25°C. A series of neutron radiography experiments was conducted at the B-4 neutron imaging facility in the Kyoto University Research Reactor (KUR) with a thermal neutron flux of 5 × 107 n/cm2⋅s. We performed image processing for the neutron radiographs to calculate neutron beam attenuation and clarify flow behavior. Visualization results show differences in flow behavior depending on operating factors. Temperature had a particularly substantial effect on flow behavior because heavy oil viscosity depends strongly on temperature. The flows also showed different behaviors for 1 mm and 3 mm packed particle sizes because the void ratios in the packed bed, which were preliminarily observed by X-ray computational tomography (CT), change with particle size. Channeling flow was observed with 3 mm particles and a temperature of 250°C. Furthermore, this work suggests that neutron radiography can be used to investigate heavy oil flows in metallic reactors.

A nanofluid is a colloidal suspension of nanoparticles, and its properties depend on the structures of nanoparticles in a base fluid. In this study, numerical simulations of the dispersion and aggregation behavior of surface-modified Al2O3 nanoparticles in toluene under shear flow are performed. The motion of nanoparticles is calculated based on Newton's equation of motion. Then, the flow of the solvent is determined by solving the Landau–LifshitzNavier–Stokes equation, and both calculations are coupled using the immersed boundary method. The effects of various factors on the dispersion and aggregation behavior of surface-modified nanoparticles are investigated numerically. For nanoparticles modified with oleic acid, which has a high affinity for toluene, the nanoparticles tend to be dispersed in toluene. For decanoic acid, which has a low affinity for toluene, the nanoparticles are dispersed in a limited shear rate range depending on the surface density of the modifier. Such dispersion and aggregation behavior of surface-modified nanoparticles is explained by considering the aggregation due to the high shear flow, which causes the potential energy barrier to vanish, as well as the dispersion of nanoparticles caused by shear stress.

Three-step phase-shifting imaging ellipsometry is proposed for the dynamic measurement of a nanofilm's thickness profile in two dimensions. The designed apparatus consists of an ellipsometric optical configuration and an image-processing unit to perform phase-shifting imaging ellipsometry measurements, a key technique used to achieve dynamic and two-dimensional measurements. The uncertainties of the ellipsometric parameters ψ and Δ were evaluated based on the developed optical system and the proposed three-step phase-shifting technique. The thickness profile of a SiO2 nanofilm on a silicon substrate was measured to calibrate the proposed apparatus; results were comparable to those obtained by a commercial spectroscopic ellipsometer. The measured thickness profiles are almost flat over the area of 1.10 mm × 2.21 mm with the spatial resolutions of 1.58 and 4.62 μm in the horizontal and vertical directions, respectively. The differences of average thickness between the proposed apparatus and a commercial spectroscopic ellipsometer were less than 3 nm. Furthermore, measurement precision was validated by obtaining a standard deviation of less than 2.5 nm.

A Si1–xGex (x ∼ 0.5) crystal measuring 10 mm in diameter was grown by the traveling liquidus zone method using the Gradient Heating Furnace aboard the International Space Station. We quantitatively...

The thermal conductivity of molten Cu-Co alloy with different compositions around the liquidus line temperature was measured by the periodic laser-heating method using an electromagnetic levitator superimposed with a static magnetic field to suppress convection in a levitated droplet sample. During the measurement, a static magnetic field of 10 T was applied to the levitated droplet. To confirm that the strength of the static magnetic field was sufficient to suppress convection in the droplet, numerical simulations were performed for the flow and thermal fields in an electromagnetically levitated droplet under a static magnetic field, and moreover, for the periodic laser-heating method to determine the thermal conductivity. It was found that the thermal conductivity of molten Cu-Co alloy increased gradually with increasing Cu composition up to 80 at. pct, beyond which it increased markedly and reached that of pure Cu. In addition, it was found that the composition dependence of the thermal conductivity can be explainable by the Wiedemann–Franz law.

The second and third microgravity experiments on SiGe crystal growth by the traveling liquidus-zone (TLZ) method were carried out aboard the Japanese Experiment Module (JEM) “Kibo” in the International Space Station (ISS) in July 2013 and February 2014. In this study, we numerically investigated the details of transport phenomena and solidification in these two experiments. We found that the deformation of the melt/SiGe crystal interface shape increased with time, and that the growth rate near the crystal edge was much larger than that near the central axis. Comparing the numerical and experimental results of the concentration distribution of Ge, the numerical concentration distributions are reasonably coincident with the experimental ones in both the axial and radial directions. In addition, both numerical and experimental results show that the radial distributions of the Ge concentration remain relatively uniform throughout the entire crystal, although the mean values depend on the growth length.

Advancing the practical applications of surface-modified nanoparticles requires that their dispersion in solvents can be controlled. The degree of dispersion depends on the affinity between surface-modified nanoparticles and solvents, which can be quantified using the work of adhesion at the interface. Herein, the affinity between a surface-modified inorganic solid and an organic solvent was evaluated by calculating the work of adhesion at the interface. The phantom-wall method, which is a thermodynamic route for evaluating the work of adhesion at an interface using molecular dynamics simulations, was applied to the decanoic acid-modified Al2O3/hexane interface. Molecular dynamics simulations were performed for flat interface systems to focus on the interactions between substances that affect the affinity on the surface. As a result, the surface coverage of decanoic acid was found to affect the work of adhesion, with a maximum value of 45.66 ± 0.75 mJ/m2 at a surface coverage of 75%. An analysis of the mass density profiles of Al2O3, decanoic acid, and hexane in the vicinity of the interface showed that the increase in the work of adhesion with the surface coverage was due to the penetration of hexane molecules into the decanoic acid layer on the Al2O3 surface. At a surface coverage of 75%, some hexane molecules were trapped in the layer of oriented decanoic acid molecules. These results suggested that the interfacial affinity can be enhanced by controlling the surface modification so that the solvent can penetrate the layer of the modifier.

Accepted: 2016-09-12, 資料番号: SA1160350000

In this work, CeO2 nanoparticles were synthesized hydrothermally with supercritical water using a tubular flow reactor with three different configurations and various flow rates of the feed solution and supercritical water, and the effects of the reactor configuration and the flow rates of the two streams on the size distributions of the synthesized nanoparticles were investigated. In addition, the flow and thermal fields in the reactors were calculated numerically under the experimental conditions using FLUENT software, where the numerical results for the flow and thermal fields were also verified by neutron radiography. Comparing the experimental results of nanoparticle synthesis with the numerical results, it was revealed that the size distributions of the synthesized nanoparticles could be explained well on the basis of the flow patterns and temperature distributions in the reactor, which depended on the reactor configuration and process conditions.

Supercritical water upgrading of heavy oil has attracted considerable attention, as the upgrading process can reduce the sulfur content and decrease the average molecular weight of the oil. Understanding the flow and mixing behavior of heavy oil in supercritical water is important to improve the process efficiency. We performed neutron radiography experiments to directly visualize the behavior of heavy oil in supercritical water. Atmospheric residue was used as a heavy oil sample, and the heavy oil and supercritical water were supplied countercurrently to a 1/2-inch tube reactor packed with Al2O3 particles with a diameter of 3 mm; the pressure and temperature were set to 25 MPa and 400°C. The behavior of the heavy oil in the supercritical water depended on the oil and water flow rates. This study demonstrates that neutron radiography is a feasible visualization technique for the investigation of heavy oil behavior in supercritical water.

The spatial structures of polystyrene (PS) nanocomposite thin films containing oleic acid-modified nanoparticles were investigated. A layer of the nanoparticles was formed at the surface of the thin film under all conditions in this work. Aggregates of the nanoparticles were formed simultaneously in the film when the concentration of the nanoparticles was relatively high. The effects of the evaporation rate and the molecular weight of PS on the spatial structures of the nanoparticles in the thin films were discussed using the ratio of the time constants for phase separation (diffusion) of the nanoparticles, gravitational sedimentation of the aggregates and drying. As the ratio of the diffusion time to the drying time increased, the thickness of the nanoparticle layer and the diameter of the nanoparticle aggregates decreased, and then reached a constant value. When the ratio of the sedimentation time to the drying time was high, the relatively small aggregates were dispersed throughout the thin film since the effect of gravitational sedimentation was small.

Poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) having low polydispersity was synthesized in mixed solvent of ethanol and water using ultrasonic irradiation without any chemical polymerization initiator. The effects of the volume fraction of ethanol in the solvent, the molar ratio of two monomers, the monomer concentration and the ultrasonic power intensity on the time courses of the conversion to the polymer, the number average molecular weight, and the polydispersity of synthesized polymer were investigated in order to determine the optimal conditions to synthesize the copolymers with a narrow molecular weight distribution (i.e. low polydispersity). The optimum volume fraction of ethanol in the solvent was 60 vol% to synthesize the copolymers with a low polydispersity. A higher ultrasonic power intensity resulted in a faster polymerization rate and a lower number average molecular weight. The polydispersity was less than 1.5 for all ultrasonic power intensities up to 450 W/dm3 applied in this work. A higher monomer concentration gave a faster polymerization rate and a higher number average molecular weight. The polydispersity was less than 1.5 when the monomer concentration was lower than 0.4 mol/dm3. A higher molar ratio of N-isopropylacrylamide resulted in a higher polymerization rate and a lower number average molecular weight. The copolymers with polydispersity less than 1.5 can be obtained regardless of the molar ratio of N-isopropylacrylamide. The copolymers synthesized by the ultrasonic polymerization method had a high temperature responsibility.

The compressive deformation characteristics of a single aggregate of polystyrene particles were studied both experimentally and theoretically. Experimental apparatus to measure the mechanical characteristics of a single aggregate with in situ observation of the compression behavior of the aggregate was constructed. Then, the time variations of the compressive force and deformation behavior of the aggregate during simple compression were investigated. In addition, discrete element method (DEM) simulations were carried out to numerically demonstrate the compression behavior of an aggregate between two planes, where the time variation of the compressive force of the aggregate as well as the area strain of each particle in the aggregate can be predicted. The largest spike-like peak of the compressive force appeared at the stage where an aggregate with a hexagonal bilayer structure was formed, as observed experimentally. The compressive force of the aggregate increased as the number of particles in the aggregate increased or the diameter of the primary particles decreased. An increase in the frictional coefficient between primary particles caused an increase in the compressive force of the aggregate for the entire period of compression, but the frictional coefficient between a particle and a wall did not affect the compressive deformation behavior of the aggregate.

The recalescence events of phase-separated Co-rich phases in undercooled molten CuCo droplets electromagnetically levitated under various static magnetic fields were observed directly using a high-speed camera, and also the surface velocities on the levitated droplets were measured by tracing the trajectories of the phase-separated Co-rich phases as tracer particles. In addition, numerical simulations of melt convection in a spherical electromagnetically levitated CuCo droplet exposed to a static magnetic field were performed assuming laminar flow. We observed the emergence of many intermittent bright spots due to recalescence on the entire surface of the levitated droplet, and the frequency of the bright spots decreased markedly as the static magnetic field increased, with no bright spots observed at fields larger than 1.5 T. Also, the Reynolds numbers were evaluated from the measured and calculated velocities in the droplet for various static magnetic fields and compared with the critical Reynolds number of approximately 600, at which the laminar–turbulent transition of a magnetohydrodynamic (MHD) flow in an electromagnetically levitated droplet occurs, as proposed by Hyers et al. The above results clearly revealed that the marked change in the phase separation structures in undercooled molten CuCo droplets at approximately 1.5 T is due to a convective transition from turbulent flow to laminar flow in the levitated droplets, as speculated in our previous work.

The drag and lift forces acting on an inviscid bubble moving near a plane wall in a quiescent liquid were numerically investigated using a three-dimensional direct numerical simulation (DNS) based on the marker and cell (MAC) method. The numerical results showed that the presence of the wall causes an increase in the drag force. The direction of the lift force acting on a bubble near the wall changed depending on the Reynolds number and the distance between the bubble and the wall. At low Reynolds numbers, the wall-induced lift coefficient of a bubble was positive, causing the bubble to move away from the wall. In contrast, at high Reynolds numbers, the negative wall-induced lift force appeared at a position away from the wall, although the wall-induced lift force became positive in the immediate vicinity of the wall. It seems that this direction change in the lift force causes the bouncing motion of the bubble, as reported by Takemura and Magnaudet (2003).

A silicon germanium mixed crystal Si1−xGex (x~0.5) 10 mm in diameter and 9.2 mm in length was grown by the traveling liquidus-zone (TLZ) method in microgravity by suppressing convection in a melt. Ge concentration of 49.8±2.5 at% has been established for the whole of the grown crystal. Compared with the former space experiment, concentration variation in the axial direction increased from ±1.5 at% to ±2.5 at% although average Ge concentration reached to nearly 50 at%. Excellent radial Ge compositional uniformity 52±0.5 at% was established in the region of 7–9 mm growth length, where axial compositional uniformity was also excellent. The single crystalline region is about 5 mm in length. The interface shape change from convex to concave is implied from both experimental results and numerical analysis. The possible cause of increase in concentration variation and interface shape change and its relation to the two-dimensional growth model are discussed.

In this study, a global model of heat transfer for the Czochralski crystal growth of oxides is developed by integrating the conventional model and the improved radiation element method by the ray emission model (REM2) in which radiative heat transfer in semitransparent crystals with a specular surface, that is, reflection and refraction at the crystal surface, is considered. The validity of the present model is verified by comparing it with the conventional model. Then, the effects of the optical thickness and the refractive index of the crystal on the temperature distribution in the furnace and on the melt/crystal interface shape are numerically investigated.

We have synthesized metal oxide nanoparticles through hydrothermal reaction at around 400 °C and 25 MPa by mixing the stream of metal ion solution at room temperature with another stream of supercritical water in a continuous flow-type reactor. In order to visualize the mixing behavior of the two streams, we performed neutron tomography measurements. By performing tomography measurements while rotating the mixing piece with supplying supercritical water and room temperature water, we succeeded in obtaining the three dimensional distribution of neutron attenuation. The results clearly showed how the two streams mix, which serves as a reference for numerical simulation.

Accepted: 2014-05-12, 資料番号: SA1005064000

The thermal dewetting of polystyrene composite thin films with oleic acid-modified CeO2 nanoparticles prepared by the supercritical hydrothermal synthesis method was investigated, varying the nanoparticle concentration (0-30 wt %), film thickness (approximately 50 and 100 nm), and surface energy of silanized silicon substrates on which the composite films were coated. The dewetting behavior of the composite thin films during thermal annealing was observed by an optical microscope. The presence of nanoparticles in the films affected the morphology of dewetting holes, and moreover suppressed the dewetting itself when the concentration was relatively high. It was revealed that there was a critical value of the surface energy of the substrate at which the dewetting occurred. In addition, the spatial distributions of nanoparticles in the composite thin films before thermal annealing were investigated using AFM and TEM. As a result, we found that most of nanoparticles segregated to the surface of the film, and that such distributions of nanoparticles contribute to the stabilization of the films, by calculating the interfacial potential of the films with nanoparticles.

We studied the effect of melt convection on phase separation structures in undercooled Cu80Co20 alloys by using an electromagnetic levitator, where a static magnetic field was applied to control convection in the molten alloys. It was found that, when the static magnetic field was relatively small, dispersed structures with relatively fine Co-rich spheres distributed in the matrix of the Cu-rich phase were observed. However, a few large, coalesced Co-rich phases appeared in the Cu-rich matrix when the magnetic field exceeded a certain value, i.e., approximately 1.5 T in this study. The mean diameter of the droplet-shaped Co-rich phases distributed in the matrix of the Cu-rich phase increased gradually with the magnetic field and increased rapidly at approximately 1.5 T. Moreover, it was speculated from the result of periodic laser heating that the marked change in the phase separation structures at approximately 1.5 T might be due to a convective transition from turbulent flow to laminar flow in the molten sample, where the time variation of temperature in the lower part of the electromagnetically levitated molten sample was measured when the upper part of the sample was periodically heated.

An alloy semiconductor Si 1− x Ge x ( x ~0.5) crystal was grown by the TLZ method in microgravity. Ge concentration was 48.5±1.5 at% for the whole region of 10 mm diameter and 17.2 mm long crystal. Compositional uniformity was established but the average concentration was a little deviated from the expected 50 at%. For further improving compositional uniformity and for obtaining Si 0.5 Ge 0.5 crystals in microgravity, growth conditions were refined based on the measured axial compositional profile. In determining new growth conditions, difference in temperature gradient in a melt, difference in freezing interface curvature, and difference in melt back length of a seed between microgravity and terrestrial growth were taken into consideration.

We have visualized the distributions of temperature and water density in a tubular flow reactor for supercritical hydrothermal synthesis of nanoparticles by neutron radiography, and investigated the effect of reactor configuration on the mixing behavior in the reactor. Here, three types of reactors were used, and the mixing behaviors of supercritical water and room-temperature water at a T-junction in the reactors were observed. As a result, it was revealed that the distributions of temperature and water density in the tubular flow reactors strongly depend on their configurations by neutron radiography. In addition, numerical simulations have been carried out to investigate the flow patterns and temperature distributions in the reactor in detail using the commercial software FLUENT, and it was demonstrated that the numerical results can explain the experimental results obtained by neutron radiography well. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1168–1175, 2014

Densities and thermal conductivities are reported for a series of N-alkylpyridinium tetrafluoroborate compounds with butyl (N-butylpyridinium tetrafluoroborate), hexyl (N-hexylpyridinium tetrafluoroborate) and octyl (N-octylpyridinium tetrafluoroborate) groups. The densities were measured with a vibrating tube densimeter over the temperature range 293–353 K at pressures ≤20.0 MPa. The transient short hot wire method was used to measure thermal conductivity over the temperature range 294–335 K at pressures ≤20 MPa. It was found that the effect of alkyl chain length on thermal conductivities in N-alkylpyridinium tetrafluoroborates is the same degree as 1-alkyl-3-methylimidazolium tetrafluoroborates. The experimental values at 293 K and 0.1 MPa were consistent with the predicted values proposed by Froba et al.