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Articles by H. Asano
Total Records ( 4 ) for H. Asano
  H. Murakawa , T. Ueda , T. Yoshida , K. Sugimoto , H. Asano , N. Takenaka , K. Mochiki , H. Iikura , R. Yasuda and M. Matsubayashi
 

In order to clarify the effects of water on performances of a Polymer Electrolyte Fuel Cell (PEFC), measurements of water distribution in a Japan Automobile Research Institute (JARI) standard PEFC were carried out by means of neutron radiography. Furthermore, the cell voltage and the pressure drop between inlet and outlet of the air were simultaneously measured. The effects of channel geometry, i.e. single-serpentine and three-serpentine, and relative humidity of air were investigated. The experimental conditions were current density of 200 mA/cm2, hydrogen utilization of 9.5% and oxygen utilization of 40%. The membrane electrode assembly (MEA) area was 5×5 cm2. The pictures were taken every 15 s with an exposure time of 12 s. The spatial resolution was 108 μm. From the measurements, the relation between cell voltage, pressure drop and movement of the water plug in the channel was confirmed. The PEFC performances were recovered as the water plug evacuated. Condensed water in the channel decreased with the relative humidity of air. However, it may affect the MEA permanence. Therefore, the most appropriate operating conditions should be decided for taking into account both the cell performances and the permanencies.

  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.

  T. Baba , S. Harada , H. Asano , K. Sugimoto , N. Takenaka and K. Mochiki
 

Boiling two-phase flows in a single-channel commercial brazing plate heat exchanger were visualized by thermal neutron radiography method, and the effect of flow direction, such as vertically upward or downward, on liquid distribution in the channel and boiling heat transfer performance was considered. The experiments had been carried out using thermal neutron radiography facility of JRR-3 of JAEA in Japan. The relationship between heat transfer coefficients and flow behaviors for three kinds of inlet condition, such as subcooled liquid, saturated liquid, and wet vapor, was investigated. Though vertically upward flow is generally selected for boiling flow to remove vapor bubble from heating surface by buoyancy force, it was shown from the result that downward boiling flow produced higher heat transfer performance than upward flow. Especially, the tendency was remarkable at low-quality condition. From the visualization results, it could be clearly observed that there was a large difference between upward and downward in-flow pattern around the inlet. The results show that the lowering of heat transfer performance was caused by the difference of flow pattern.

  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.

 
 
 
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