Recovery characteristics of optical hydrogen sensor using Pd thin film: Behaviour of three-stage hydrogen desorption

The recovery behaviour of optical hydrogen sensor using Pd film has been investigated. The change in reflectance with hydrogen desorption indicated distinctive characteristics with three-stage curve which depended on thickness of the Pd film. Moreover, the distinction became clearer with increasing number of absorption-desorption cycles. These behaviours were related to the change in pressure concentration isotherm.     

Estimation of power outage size based on the dominating differential equation

This paper describes a method to estimate how much power will drop after severe generation outage. When a large generation outage occurs, system frequency plummets to an unacceptable frequency level. Frequency drop affects both customers and generation systems. Thus adequate and quick load-shedding must be done to prevent problems. To institute any load-shedding policy effectively, the size of the generation outage must be precisely estimated in a very short time. So far, several methods have been proposed to estimate the power outage amount by measuring the decaying frequency variations that are obtained at each local bus. These methods are easily applied, but cannot be expected to provide good results in real power system operations because of the noises that are a part of decaying frequency variations. To cope with this problem, a new estimation method based on one that uses the dominating differential equation is proposed in this paper. The most precise estimation at this point is obtained by using additional factors, such as the sine wave included in the decaying frequency fluctuations and considered as a part of the equation. Simulation studies on a model power system consisting of five generating stations and four load points show that the newer method is encouraging. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (3): 39–49, 1997     

Operating principles of pin diodes

Analytical models of the pin diode in a small‐current operation are not known yet. This article presents a simple analytical model of the pin diode operation with its confirmation by a numerical simulation. At the onset, carrier recombinations are not included for the sake of simplicity. The exact J_F?V_F characteristic could have been induced only by accounting for the Boltzmann distribution of each carrier across the junctions and the diffusion current of each minority carrier in a p‐anode or n‐cathode. Based on this new model, the modifications of hole–electron densities product (n_en_h) across junctions, a rough estimation of the large operational current, its carrier distributions, and the effect of carrier recombination on the carrier distribution are plainly estimated and are also compared with the simulation results. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(4): 47–56, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20844     

Burnett Method with Absolute Pressure Transducer and Measurements for PVT Properties of Nitrogen and Hydrogen up to 473 K and 100?MPa

A measurement method for PVT properties of high-temperature and high-pressure gases was developed by simplifying the Burnett method and revising the data acquisition procedure. Instead of a differential pressure transducer, which is traditionally used, an absolute pressure transducer is used in the present method, and the measurement of pressure becomes easier. However, the absolute pressure transducer is placed outside the constant temperature bath because of the difficulty of its use in high-temperature surroundings, and some parts with different temperatures from the sample vessels exist as dead space. The present method takes into account the effect of the dead space in the data acquisition procedure. Nitrogen was measured in the temperature range from 353 K to 473 K and at pressures up to 100 MPa to determine the apparatus constants, and then, hydrogen was measured at 473 K and up to 100 MPa. The determined densities are in agreement within uncertainties of 0.07% to 0.24% (k = 2), both with the latest equation of state and existing measured data.     

Dynamic simulation for optimal hydrogen refueling method to Fuel Cell Vehicle tanks

A dynamic simulation approach to investigate an optimal hydrogen refueling method is proposed. The proposed approach simulates a transient temperature, pressure and mass flow rate of hydrogen flowing inside filling equipment in an actual station during the refueling process to an Fuel Cell Vehicle (FCV) tank. The simulation model is the same as in an actual hydrogen refueling station (HRS), and consists of a Break-Away, a hose, a nozzle, pipes and an FCV tank. Therefore, we can set actual configurations and thermal properties to the simulation model, and then simulate the temperature, pressure and mass flow rate of hydrogen passing through each position based on the supply conditions (temperature and pressure) at the Break-Away. In this study, the simulated temperature, pressure and mass flow rate are compared with the corresponding experimental data. Therefore, we show that the dynamic simulation approach can accurately obtain those values at each position during the refueling process and is an effective step in proposing the optimal refueling method.     

Crystallography and Interphase Boundary of Martensite and Bainite in Steels

Grain refinements in lath martensite and bainite structures are crucial for strengthening and toughening of high-strength structural steels. Clearly, crystallography of transformation plays an important role in determining the “grain” sizes in these structures. In the present study, crystallography and intrinsic boundary structure of martensite and bainite are described. Furthermore, various extrinsic factors affecting variant selection and growth kinetics, such as elastic/plastic strain and alloying effects on interphase boundary migration, are discussed.     

Excess Carbon Enrichment in Austenite During Intercritical Annealing

Carbon enrichment in the austenite transformed from martensite during intercritical annealing was measured by electron probe microanalyzer and three-dimensional atom probe microscopy in Fe-2Mn-0.3C and Fe-0.35C alloys. At early stages of the transformation, negligible Mn partitioning occurs, and carbon content in austenite is higher than orthoequilibrium and paraequilibrium predictions. This is presumably attributed to finite intrinsic interface mobility and/or solute drag effect. The resultant free energy dissipation at interface was estimated.