Nucleate boiling of two and three-component mixtures

For three pure fluids and their two- and three-component mixtures, heat transfer coefficients were measured in nucleate pool boiling on the upward facing copper surface of 40 mm diameter. The more-, moderate- and less-volatile components in mixtures are refrigerants R-134a, R-142b and R-123, respectively. Heat transfer coefficients of mixtures were less than the interpolated heat transfer coefficients between pure components, with more reduction at higher heat flux. Two correlations originally developed for two-component mixtures by Thome and Shakir and by Fujita and Tsutsui reproduced well the measured heat transfer coefficients of three- as well as two-component mixtures. This result implies that the boiling range included in the correlations accounts for heat transfer reduction in mixture boiling.     

Particle composition and heat capacity of high‐temperature SF6 present at constant volume: Discussion on formula expressing relationship between constant‐pressure and constant‐volume heat capacities

Until now, the high‐temperature properties of SF₆ have been derived as a function of T for a given constant pressure P. This was based on the adoption of T and P as gas state parameters. In contrast, this paper adopts T and the gas volume V as the gas state parameters and then evaluates the particle composition and gas pressure for high‐temperature SF₆ present at a constant volume state. This evaluation is achieved by the minimization of Helmholtz free energy of the high‐temperature SF₆. A further derivation for the SF₆ gas at constant volume is performed to reveal the temperature dependence of the molar heat capacity C_Vm [J/(mol·K)] and the specific heat C_Vg [J/(kg·K)]. Use of the obtained C_Vm enabled us to discuss whether the formula C_Pm−C_Vm=R_m holds true for the high‐temperature SF₆ or not, where C_Pm and R_m are the molar heat capacity at constant pressure and the universal gas constant, respectively. Similar discussion is also performed on the formula indicating the relation between C_Pg and C_Vg, where C_Pg is the specific heat at constant pressure. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fundamental performance of superconducting fault current limiter with two air core coils

In this paper, we theoretically compared the fundamental characteristics of fault current limiter (FCL) with high‐Tc superconductor (HTS) and two coaxial air‐core coils based on steady‐state analysis. Two types of FCL are possible. One is parallel type and the other is transformer type. The parallel type can be divided into two types according to the combination of the winding direction of coils. That is, there are two cases that the coils are wound so that the magnetic fluxes induced by coils reduce and increase each other. In this paper, we called them parallel type 1 and 2, respectively. There is no significant difference in the HTS volume required to satisfy both the specified limiting impedance Z_FCL and initial current I_ini in limiting operation among those three FCLs although the HTS in each type of FCL has different length and cross‐sectional area. In the cases of those FCLs, we can improve the current limiting performance by arranging the HTS in the coils and applying the magnetic flux to the HTS in the limiting operation. The magnitudes of the magnetic flux density are almost the same. From the viewpoint of the FCL impedance in normal operation, parallel type 1 has the most desirable structure. On the other hand, transformer type is the best to eliminate the magnetic flux applied to the HTS in the normal operation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 29–36, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20477     

Fluctuation analysis of partial discharge pulse occurrence with an integral equation

This paper proposes an integral equation to describe the stochastic fluctuation of partial discharge (PD) occurrence under sinusoidal voltage stress based on a simple PD model. In the model, the stochastic behavior of PD fluctuation is assumed to arise from the fluctuation of the PD delay time after the inception voltage is built up across a discharge gap. For simplicity of calculation, the delay time is assumed to have an exponential distribution. Based on these assumptions, it is found that the proposed integral equation provides the basic characteristics such as the PD pulse distribution in the applied voltage phase angle domain. The authors have solved the equation numerically and demonstrate several ?–n distribution patterns with average delay times of 0.05 to 5 ms at low applied voltage. The solution is compared with PD characteristics obtained by Monte Carlo simulation based on the same PD model, and good agreement is found. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 16–28, 2001     

The simulated moving-bed reactor for production of bisphenol A

Bisphenol A was produced from acetone and phenol over an ion-exchange resin catalyst at 50–90°C. Phenol was used as solvent. The reaction proceeded under the excess phenol condition. The reaction rate was proportional to the acetone concentration in the initial period of the reaction. After the acetone conversion exceeded approximately 50%, the reaction rate became lower than expected by the first-order reaction rate. This was ascribed to water adsorption onto the resin. Batch adsorption and breakthrough experiments showed that water was adsorbed approximately seven times stronger than acetone and that bisphenol A was not adsorbed. Using the reaction rate equation for bisphenol A production, the adsorption isotherms and overall mass transfer coefficients of the components, the numerical simulation of the 3-zone-type simulated moving-bed reactor was carried out. High resin flow rate was required in order to remove water out of the reaction zone, and a high liquid flow rate was also required to desorb water from the resin in the recovery zone. As far as the flow rates were set appropriately, water was successfully removed to prevent the catalyst deactivation and the long-term stable production of BPA was allowed.     

Fast transmission power control using UPFC under output voltage saturation

This paper presents an electric power control scheme in the transmission line using a UPFC (Unified Power Flow Controller). From the practical application viewpoint, the simultaneous realization of fast power response and reduced power converter capacity are desired. The authors propose a new power control scheme of the UPFC with a current minor control loop. Using the proposed control, the fast power response can be realized and the necessary power converter capacity can be reduced considering the voltage saturation of the converter. The effectiveness of the proposed algorithm has been verified by experiments. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 66–74, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10220     

Mechanism of production of ultra-fine silicon carbide powder by arc plasma irradiation of silicon bulk in methane-based atmospheres

The mechanism of production of ultra-fine SiC powder from a silicon bulk by arc plasma irradiation in either an Ar + CH₄ + H₂ or an Ar + CH₄ atmosphere was studied. Layer and island phases were newly formed in the silicon bulk upon irradiation, and it was revealed from scanning electron and Auger electron spectroscopy that these phases were composed of SiC. The intensity of the X-ray diffraction peaks due to the SiC phase increased with irradiation time almost in parallel to the carbon content involved in the silicon bulk. It is proposed that CH₄ is dissociated in the arc plasma and dissolved in the molten silicon bulk to produce the SiC phase, the sublimation of which is mostly responsible for the production of ultra-fine SiC powder.     

Modulated structure and magnetic properties of age-hardenable Fe-Mn-Al-C alloys

Microstructural changes in the age-hardenable Fe-(30 to 34) wt pct Mn-(8 to 11) wt pct Al-(0.9 to 1.0) wt pct C alloys during aging in the temperature range between 773 and 823 K have been investigated by means of transmission electron microscopy (TEM) and X-ray diffraction. The wavelength of the modulated structure was found to be nearly constant for short aging times and then to increase on further aging, whereas the compositional modulation amplitude was found to increase rapidly from the beginning of aging. The growth of a spinodally modulated structure along the orthogonal «100» directions results in a periodic arrangement of the κ-carbide precipitates, (Fe, Mn)₃AlC_x, in the austenite matrix. The increases in hardness and residual and saturation inductions in the early stage of aging were in accord with the increase in the amplitude.