Improvement of solidification model and analysis of 3D channel blockage with MPS method

In a severe accident of a nuclear power reactor, coolant channel blockage by solidified molten core debris may significantly influence the core degradations that follow. The moving particle semi-implicit (MPS) method is one of the Lagrangian-based particle methods for analyzing incompressible flows. In the study described in this paper, a novel solidification model for analyzing melt flowing channel blockage with the MPS method has been developed, which is suitable to attain a sufficient numerical accuracy with a reasonable calculation cost. The prompt velocity diffusion by viscosity is prioritized over the prompt velocity correction by the pressure term (for assuring incompressibility) within each time step over the “mushy zone” (between the solidus and liquidus temperature) for accurate modeling of solidification before fixing the coordinates of the completely solidified particles. To sustain the numerical accuracy and stability, the corrective matrix and particle shifting techniques have been applied to correct the discretization errors from irregular particle arrangements and to recover the regular particle arrangements, respectively. To validate the newly developed algorithm, 2-D benchmark analyses are conducted for steady-state freezing of the water in a laminar flow between two parallel plates. Furthermore, 3-D channel blockage analyses of a boiling water reactor (BWR) fuel support piece have been performed. The results show that a partial channel blockage develops from the vicinity of the speed limiter, which does not fully develop into a complete channel blockage, but still diverts the incoming melt flow that follows to the orifice region.     

Coherent Electron Transport in Air-Stable,Printed Single-Crystal Organic Semiconductor and Application to Megahertz Transistors

Organic semiconductors (OSCs) have attracted growing attention for optoelectronic applications such as field-effect transistors (FETs), and coherent (or band-like) carrier transport properties in OSC single crystals (SCs) have been of interest as they can lead to high carrier mobilities. Recently, such p-type OSC SCs compatible with a printing technology have been used to achieve high-speed FETs; therefore, developments of n-type counterparts may be promising for realizing high-speed complementary organic circuits. Herein, coherent electron transport properties in a printed SC of a state-of-the-art, air-stable n-type OSC, PhC₂−BQQDI, by means of variable-temperature gated Hall effect measurements and X-ray single-crystal diffraction analyses in conjunction with band structure calculations, are reported. Furthermore, the SC FET is tested for high-speed operations, which obtains a cutoff frequency of 4.3 MHz at an operation voltage of 20 V in air. Thus, PhC₂−BQQDI is shown as a new candidate for practical applications of SC-based, organic complementary devices.     

Nonlinear resistivity in epoxy composites containing Mn-based ferrite magnetic particles

In this study, magnetic particles were employed as nonlinear resistive materials in electric stress grading composites. Epoxy resin films containing either manganese-based ferrite magnetic (Mn-FM) particles or manganese-magnesium-based ferrite magnetic particles were prepared, and the threshold voltages required for these films to exhibit nonlinear resistivity were determined. The sample containing Mn-FM particles having irregular shapes [Mn-FM(i)] at 20 vol % showed the highest nonlinear resistivity. Assessments of the magnetic characteristics of these materials demonstrated a relationship between magnetic flux density and nonlinear resistivity. The magnetic flux density of the Mn-FM(i) composite was the highest among the various specimens, indicating that magnetic flux density may affect nonlinear resistivity. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48229.     

Thermal and chemical recycle of waste polymers

Catalytic degradations of polyethylene into fuel oils and of polystyrene into styrene monomer have been studied using solid acids and bases as catalysts. Solid acids such as silica-aluminas and ZSM-5 zeolite were found to be effective to degrade waste polyethylene into fuel oils, and solid bases such as BaO and K₂O were concluded to be effective to convert waste polystyrene into styrene monomer. A design of recyclable polystyrene films will be briefly mentioned.     

Synergistic catalysis of carbon black oxidation by Pt with MoO3 or V2O5

A series of SiO₂-supported MoO₃, V₂O₅, and Pt catalysts were prepared for the study of model soot oxidation with simulated diesel exhaust gas. Composite samples of Pt with the metal oxides demonstrated higher oxidation activities than the single-component SiO₂-supported MoO₃, V₂O₅ or Pt catalysts in the absence of SO₂ in the reactant gas. Based on the effects of NO₂ on carbon oxidation, a synergistic reaction mechanism was suggested to explain the effects of combining Pt with the oxides: Pt catalyzes the oxidation of NO with gas phase O₂ to NO₂, while MoO₃ and V₂O₅ catalyze the oxidation of carbon with NO₂. Finally, the effects of SO₂ on the carbon oxidation reaction were examined and discussed.     

Performance evaluation of squirrel‐cage damper structure for superconducting generators

Superconducting generators have many advantages such as increasing generation efficiency and improving power system stability. In Japan, 70‐MW‐class superconducting generators have been developed through the national project “Electric Power Application of Superconducting Technologies (1988–1999).” In this paper, performance evaluation of the rotor damper structure for the 70‐MW‐class model generator is discussed. Double‐layered damper structure, which consists of a squirrel‐cage warm damper and a single‐layered cold damper, was set as the target. As the first step, basic electromagnetic and thermal performances were obtained. Consequently, it was proven that the damper structure had the performances to satisfy the requirements of the superconducting generators. Performances obtained from the experimental model, design of the 70‐MW model rotor, and evaluation by the verification tests are described in this paper. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 19–33, 2005; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20025     

Performance evaluation of 6000‐A‐class superconducting field windings for 600‐MW‐class superconducting generators

Superconducting generators have many advantages such as increasing generator efficiency and improving power system stability. In Japan, a national project has been conducted since 2000 which is aimed at the development of fundamental technologies required for high‐output‐density and large‐capacity superconducting generators. This paper describes the results of this project, focusing on 6000‐A‐class field winding development. Copyright © 2004 Wiley Periodicals, Inc. A superconducting generator with a high output density and a large capacity has inherent factors that decrease superconducting stability. These are: (1) increase in the magnetic field in the winding which is caused by the increase in winding current density and (2) difficulty in fabricating windings which increases as a conductor diameter becomes larger. To secure the stability, we adopted a higher‐copper‐content conductor and a design that increases winding fixing pressure, along with devising a winding method that accommodates larger conductor diameter. These improvements were applied to a partial model of a 600‐MW field winding. Test results of the model showed good stability, indicating that design and fabrication technique for a 6000‐A‐class superconducting field winding has been successfully evaluated. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 7– 18, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20332     

Measurement and numerical analysis of flammability limits of halogenated hydrocarbons

Flammability limits measurement was made for a number of halogenated compounds by the ASHRAE method. Most of compounds measured are the ones for which discrepancy was noted between the literature values and predicted values of flammability limits. As a result, it has been found that most of the newly obtained values of flammability limits are not in accordance with the literature values. Numerical analysis was carried out for a set of flammability limits data including the newly obtained ones using a modified analytical method based on F-number scheme. In this method, fitting procedure was done directly to flammability limits themselves instead of fitting to F-number. After the fitting process, the average relative deviation between the observed and calculated values is 9.3% for the lower limits and 14.6% for the upper limits.     

RF number as a new index for assessing combustion hazard of flammable gases

A new index called RF number has been proposed for assessing the combustion hazard of all sorts of flammable gases and their mixtures. RF number represents the total expectancy of combustion hazard in terms of flammability limits and heat of combustion for each known and unknown compounds. The advantage of RF number over others such as R-index and F-number for classification of combustion hazard has been highlighted.     

Crystallization of amorphous carbon at high static pressure and high temperature

Amorphous carbons prepared from furfuryl alcohol resin have been studied in a high-pressure apparatus of octahedral anvil type at pressures up to 18 GPa and at temperatures up to 2000° C. The amorphous carbons, when heated under pressure, crystallized first into graphite at 450 to 600°C and then into diamond at 1120 to 2000° C. The temperatures for the onset of these crystallizations,T ₉ andT _d, were determined by a simple technique. As the temperature for the preparation of the amorphous carbons was raised from 700 to 1000° C,T ₉ at 15 GPa increased slightly whereasT _d at the same pressure turned from a decrease into an increase beyond 750° C for the preparation temperature. For amorphous carbon prepared at 850° C,T _g increased a little whileT _d decreased markedly with increasing pressure.