Effect of acid–base interaction on the sorption characteristics of liquids in poly(vinylidene fluoride)

The sorption characteristics of various liquids in poly(vinylidene fluoride) (PVDF) were investigated in relation to the Lewis acid–base interaction between the liquids and the polymer. The sorption amount of various liquids and the sorption selectivity of binary mixtures in PVDF were measured and their characteristics were found to be significantly affected by acid–base interaction. The acid–base interaction was evaluated from the Drago constants of PVDF, which were obtained by extending the Fowkes' method observing the shift of stretching frequency of the carbonyl bond of ethylacetate sorbed in PVDF. The partial molar enthalpy change of mixing at infinite dilution was estimated using the Drago constants of PVDF and used as a parameter explaining the sorption characteristics of liquids in PVDF. © 1992 John Wiley & Sons, Inc.     

Application of signal processing techniques to the detection of tip vortex cavitation noise in marine propeller

The tip vortex cavitation and its relevant noise has been the subject of extensive researches up to now. In most cases of experimental approaches, the accurate and objective decision of cavitation inception is primary, which is the main topic of this paper. Although the conventional power spectrum is normally adopted as a signal processing tool for the analysis of cavitation noise, a faithful exploration cannot be made especially for the cavitation inception. Alternatively, the periodic occurrence of bursting noise induced from tip vortex cavitation gives a diagnostic proof that the repeating frequency of the bursting contents can be exploited as an indication of the inception. This study, hence, employed the Short-Time Fourier Transform (STFT) analysis and the Detection of Envelope Modulation On Noise (DEMON) spectrum analysis, both which are appropriate for finding such a repeating frequency. Through the acoustical measurement in a water tunnel, the two signal processing techniques show a satisfactory result in detecting the inception of tip vortex cavitation.     

EXPERIMENTAL ESTIMATION OF A SCALING EXPONENT FOR TIP VORTEX CAVITATION VIA ITS INCEPTION TEST IN FULL- ANDMODEL-SHIP

Tip vortex cavitation noise of marine propeller became primary concerns to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model-and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full-and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.     

Numerical analysis of pulsating heat pipe based on separated flow model

The examination on the operating mechanism of a pulsating heat pipe (PHP) using visualization revealed that the working fluid in the PHP oscillated to the axial direction by the contraction and expansion of vapor plugs. This contraction and expansion is due to the formation and extinction of bubbles in the evaporating and condensing section, respectively. In this paper, a theoretical model of PHP was presented. The theoretical model was based on the separated flow model with two liquid slugs and three vapor plugs. The results show that the diameter, surface tension and charge ratio of working fluid have significant effects on the performance of the PHP. The following conclusions were obtained. The periodic oscillations of liquid slugs and vapor plugs were obtained under specified parameters. When the hydraulic diameter of the PHP was increased to d=3mm, the frequency of oscillation decreased. By increasing the charging ratio from 40 to 60 by volume ratio, the pressure difference between the evaporating section and condensing section increased, the amplitude of oscillation reduced, and the oscillation frequency decreased. The working fluid with higher surface tension resulted in an increase in the amplitude and frequency of oscillation. Also the average temperature of vapor plugs decreased.     

Dynamic impact characteristics of KN-18 SNF transport cask – Part 2: Sensitivity analysis of modeling and design parameters

In Part 1 of this study, an advanced numerical simulation method was proposed to investigate the impact characteristics of the KN-18 spent nuclear fuel (SNF) transport cask recently developed in Korea and verified against the experimental results.     

CO oxidation from syngas (CO and H<Subscript>2</Subscript>) using nanoporous Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The concept of “waste-to-wealth” is spreading awareness to prevent global warming and recycle the restrictive resources. To contribute towards sustainable development, hydrogen energy is obtained from syngas (CO and H₂) generated from waste gasification, followed by CO oxidation and CO₂ removal. In H₂ generation, it is key to produce more purified H₂ from syngas using heterogeneous catalysts. In this respect, we prepared Pt/Al₂O₃ catalyst with nanoporous structure using precipitation method, and compared its catalytic activity with commercial alumina (Degussa). Based on the results of XRD and TEM, it was found that metal particles did not aggregate on the alumina surface and showed high dispersion. Optimum condition for CO conversion was 1.5 wt% Pt loaded on Al₂O₃ support, and pure hydrogen was obtained after removal of CO₂ gas.     

Battery performance of PMMA-grafted PE separators prepared by pre-irradiation grafting technique

Poly(methyl methacrylate)-grafted polyethylene (PE-g-PMMA) separators were prepared by pre-irradiation grafting technique of methyl methacrylate onto a commercial polyethylene separator. The prepared separators were characterized by using charge/discharge (C/D) cycling test, AC impedance, and thermal stability analyses. Thermal shrinkage (TS) of the PE-g-PMMA separators decreased with an increasing degree of grafting up to 70% above which it was saturated. The PE-g-PMMA separators showed a better oxidation stability on the anode up to 5 V and a better cycle life performance than the original PE separator. These characteristics make the prepared separators suitable for applications in high voltage secondary lithium batteries.     

Synthesis and dispersion of polypyrrole nanoparticles in polyvinylpyrrolidone emulsion

Monodisperse particles of conducting polypyrrole (PPy) were directly synthesized in large quantities by emulsion polymerization with FeCl₃ in organic solvents in the presence of polyvinylpyrrolidone (PVP). The particles were almost spherical form capped with PVP and their sizes ranged from 30 to 60 nm with a narrow size distribution when molecular weight of PVP was 3700k. The particle sizes were decreased with an increase in molecular weight of PVP: as molecular weight is increased from 40k to 3600k, the size is decreased from 90–110 to 60–80 nm, respectively. These PPy particles are easily dispersed in organic solvents such as water, methanol, butanol isopropanol and these solutions can also be blended with organic binder polymers by casting for film formation. The conductivity of pelletized PPy particles was 10–15 S/cm.     

Miniaturized inertia Generators as power supplies for small-caliber fuzes

This paper describes miniaturized inertia generators for converting mechanical energy into electrical energy for military applications, especially as power supplies for electrical fuzes. In order to minimize the volume of the generators, our design adopted a ring-shaped magnet enclosing a coil assembly. The inertia generators are intended not to ignite an electrical detonator but to charge a capacitor that drives the electric circuit of fuze. A mechanical safety system, a shear plate, is used as a release mechanism for the inertia generators to prevent them from operating accidentally. We designed the inertia generators by using the simulation results of an electromagnetic analysis tool. In an experimental study, we performed safety tests on the shear plate and firing tests of the fabricated inertia generators. The present inertia generators show that a voltage of 14.2 V was charged on a capacitor of 30 /spl mu/F within the charging time of 0.68 ms and the critical acceleration for safety was 5000 G, verifying that the inertia generators can be used as power supplies for small-caliber electrical fuzes.