Time filter

Source Type

Sato R.,Tohoku University | Tajima I.,Nasu Denki Tekko Corporation | Nakagawa T.,Tokai University | Uchida H.,Tokai University
Journal of Alloys and Compounds

This paper reports kinetic properties of H2 absorption of TiCr2 and a Ti-Cr based alloy: Ti0.44Zr 0.56Cr0.86Fe0.68Ni0.21Mn 0.25Cu0.03. In this study, the influence of surface oxidation of these alloys on the H2 absorption rate was investigated from a viewpoint of practical application to a metal hydride (MH) freezer system. The changes of reaction mechanisms of hydrogen absorption by various surface conditions were elucidated by measurements of the pressure and temperature dependences of the reaction rate of these alloys. © 2013 Elsevier B.V. All rights reserved. Source

Koizumi T.,Obayashi Corporation | Kanda M.,Nihon University | Nishi M.,Nasu Denki Tekko Corporation | Tanaka H.,Shimizu Corporation | Kubota R.,Nihon University
Journal of Structural and Construction Engineering

This paper describes characteristics of air pressure variation field on the surface of the 3-dimentional square prism under aerodynamic vibration. The analysis is conducted by means of Complex Proper Orthogonal Decomposition, which is referred as CPOD. The improved hybrid aerodynamic vibration technique is applied to measure the air pressure. As a result, two typical modes, which are symmetrical mode and inversely symmetrical mode, are included in the CPOD mode. It is found out that the inversely symmetrical mode is a governing mode to generate the aerodynamic vibration, and in the case of generating Vortex Induced Vibration or Galloping Vibration, we can distinguish these phenomena from the information of phase angle distribution of inversely symmetrical mode. Source

Abe M.,Nasu Denki Tekko Corporation | Honjo T.,Tokai University | Kuji T.,Tokai University
Keikinzoku/Journal of Japan Institute of Light Metals

The structure and hydrogenation properties of Ti-Mg alloy synthesized by ball-milling have been investigated. In this study, α-Ti powder (HCP) was successfully transformed into β-Ti (BCC) powder by ball-milling for 216 ks. This composition was obtained to mix elemental powder of each Ti (HCP or BCC) and Mg by ball-milling with the ratio of 12.5, 25, 37.5, and 50 at% Mg. The structure and thermal stability of these samples were analyzed by means of X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). In this results, Ti-Mg alloy with β-Ti maintained BCC phase as much as the ratio of 37.5 at% Mg, and it was the steady state until 573 K. Furthermore, from the comparison of hydride properties of Ti 75Mg 25 alloy with BCC phase synthesized from β-Ti and a-Ti, alloy with β-Ti easily absorbed hydrogen at the room temperature, while alloy with a-Ti hardly reacted with hydrogen. In addition, the lattice parameter of Ti-Mg with β-Ti was 0.326 nm, and the strain was lower than alloy with α-Ti. However, Ti 75Mg 25 after hydrogenation was transformed into TiH 2. Source

Watanabe F.,Ashikaga Institute of Technology | Watanabe F.,Hitachi Engineering and Service Co. | Takahashi T.,Nasu Denki Tekko Corporation | Tokuyama H.,Nasu Denki Tekko Corporation | And 2 more authors.
Wind Engineering

A large number of small wind turbines are installed in an urban area or on a rooftop where they experience sudden changes of wind speed and wind direction. For small wind turbines, the yawing load is one of the important design drivers because of its severity. Typically, a passive yaw system using a tail fin is employed for these small wind turbines. IEC61400-2 ed.2 provides a simplified equation for the maximum yaw angular velocity, or yaw rate, for use in estimating the yawing load. However, it is unclear whether this yaw rate considers the sudden change of wind direction. Furthermore, this simplified equation of yaw rate is only function of a rotor radius.In this paper, in order to consider the sudden change of wind direction, the authors derived the theoretical equation of the yawing motion to calculate yaw rate up to yaw angle of 180 degrees. This equation embraces the design variables including rotor radius, design tip speed ratio, tail fin area, and moment of inertia about the yaw axis. This theoretical equation was verified by comparing with wind tunnel test results. A number of theoretical calculations were undertaken varying all the design variables to find the relationship between the design variables and the yaw rate. Then, a new simplified equation, to calculate the yaw rate for a small wind turbine with a passive yaw system, is derived. This simplified equation is more practical than the existing IEC standard because it includes all design variables. This new equation enables to the yawing load to be estimated even for large change of wind direction. Source

Tajima I.,Nasu Denki Tekko Corporation | Abe M.,Nasu Denki Tekko Corporation | Uchida H.,Tokai University | Hattori M.,Tokai University | And 2 more authors.
Journal of Alloys and Compounds

This paper aims to elucidate the mechanisms of the initial activation of the FeTi alloy with nano-structured surface layers (n-FeTi) by the kinetic measurement of hydrogen absorption of the alloy. The alloy sample was prepared by mechanical grinding. The n-FeTi exhibits much higher initial rate of hydrogen absorption than an untreated FeTi alloy. From the measurements of pressure and temperature dependences of the initial rate of hydrogen absorption, the rate controlling step was found to shift from the dissociation of H2 molecules on the surface to the permeation of H atoms through grown surface oxide layers with the growth of surface oxide layers. From the measurement of work function, the n-FeTi surface was found to exhibit a much lower value for the work function of 4.73 eV than an untreated surface. These results suggest that the nano-structured surface layers easily exchange electrons with the H2 molecules, which promote the H2 dissociation, and hence, results in an enhanced hydrogen absorption rate. © 2013 Elsevier B.V. All rights reserved. Source

Discover hidden collaborations