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Articles by N. Takenaka
Total Records ( 3 ) for N. Takenaka
  I. Sakata , T. Ueda , H. Murakawa , K. Sugimoto , H. Asano , N. Takenaka , R. Yasuda , T. Tomura and M. Shiozawa
 

A polymer electrolyte fuel cell (PEFC) consists of a membrane electrode assembly (MEA), gas diffusion layers (GDL), hydrogen and oxygen supply channels. At the anode, protons and electrons are generated, while at the cathode the protons and electrons combine to form water. The condensed water may affect the fuel cell performance. In order to clarify the effect of water distribution on the PEFC performance, three-dimensional water distribution in the PEFC was visualized by using a neutron radiography facility at JRR-3 in JAEA. For observing the detailed water distribution, a small sized PEFC was designed. Size of the gas channel is 1 mm width and 0.5 mm depth. Thickness of the MEA and the GDL are about 50 and 200 μm. The electrode area is 0.35×3.5 cm2. The PEFC was set on an automatic rotating stage, and a picture was taken every 2.25° by using a cooled CCD camera with grey scale of 16 bit. The exposure time was set at 15 s. Using the 80 pictures which correspond to 180°, a computed tomography (CT) was carried out. In order to observe water distribution with high spatial resolution, the LiF scintillator with a thickness of 50 μm was used. From the water distributions parallel and perpendicular to the MEA, existence of water around O-ring can be confirmed. However, the detailed distribution in the PEFC is difficult to obtain from the two-dimensional pictures. On the other hand, CT pictures make possible to obtain the three-dimensional water distribution. In this study, the spatial resolution of 76.5 μm was achieved, and existence of water in the PEFC could be confirmed.

  K. Sugimoto , Y. Kamata , T. Yoshida , H. Asano , H. Murakawa , N. Takenaka and K. Mochiki
 

Heat generation density of electric elements increases close to the limit of forced air-cooling. New cooling technology is required and a self-vibration heat pipe is proposed for the electric elements cooling. The self-vibration heat pipe, which has a meandering capillary channel, can operate for vertical and horizontal heat removal without gravity effects. However, the behaviors of the working fluid in the pipe have not been well studied. The purpose of this study is to clarify the working fluid phenomena in the heat pipe. The working fluid in the pipe was visualized by neutron radiography system at JRR-3 in Japan Atomic Energy Agency. The liquid columns in the meandering channel of the heat pipe were recorded by a high-speed camera. The obtained images were segmented and the meandering capillary channel was uncoiled by image processing methods to show the temporal vibration of the liquid columns in the stretched channel. Periods of the column oscillation were about 0.5–1.5 s. The oscillation of the columns was analyzed by a mass-spring model. The periods of the oscillation were obtained and compared with the experiment results. It was shown that the analytical values agreed fairly with the experimental ones.

  M. Nakamura , K. Sugimoto , H. Asano , H. Murakawa , N. Takenaka and K. Mochiki
 

Neutron radiography is suitable for the visualization of liquid behavior in a metallic machine. Observation of oil behavior in a small 4-cycle engine on operating was carried out by using the neutron radiography facility at JRR-3 in JAEA. The engine was not fired but operated by an electrical motor. Movies were taken by a neutron image intensifier with a color CCD camera of 8-bit resolution, 30 frames/s and 640×480 pixels developed by Toshiba Corp. The engine was placed on a turn table and was rotated, so the movie could be taken from any angle. Numbers of revolution of the engine were changed from 260 to 1200 rpm. Visualized images of the mechanism and the oil behavior in the engine were obtained.

 
 
 
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