Journal of Japan Solar Energy Society
Online ISSN : 2433-5592
Print ISSN : 0388-9564
Volume 44 , Issue 2
Showing 1-4 articles out of 4 articles from the selected issue
Research paper
  • Part1- Investigation on Core Material with Structural Calculation and Heat Transfer Calculation and Trial Production of Vacuum Insulation Panels and Their Performance Evaluation
    Takao KATSURA, Zhang YANG, Masahiro AIHARA, Makoto NAKAMURA, Katsunori ...
    2018 Volume 44 Issue 2 Pages 49-57
    Published: March 31, 2018
    Released: April 20, 2018

    This study aims at developing the vacuum insulation panels (VIPs) with small thickness and light transmittance to contribute retrofitting insulation for existing buildings. The authors are focus on producing the slim and translucent VIPs with vacuum layer which hold by spacers. Firstly, the outlines of vacuum layer type VIPs were introduced. Next, the structural calculation was carried out as a mechanical analysis to determine the specific array of spacers to pillars supported type. Then, the heat transfer model applying the one-dimensional calculation was developed to predict the insulation performance of VIPs. After that, the authors conducted an experiment applying the guarded hot plate method in order to verify the apparent thermal conductivity of VIP according to the set pressure. The result showed that the apparent thermal conductivity was less than 0.1 W/(mK) and was enough low. Finally, the VIPs with different core materials were trial produced and the apparent thermal conductivity were evaluated by the heat flux method.

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  • Atsushi AKISAWA, Ryo KASHIIDE, Masayuki NAKAYAMA
    2018 Volume 44 Issue 2 Pages 59-64
    Published: March 31, 2018
    Released: April 20, 2018

    The objective of this study is to evaluate the performance of vertically mounted solar collector with a parabolic mirror for solar concentration to boost the energy density. A flat absorber is attached to the bottom of the parabolic mirror. Ray-tracing simulation was employed to estimate the recovery of solar irradiation and to find out the optimal settings of the geometrical parameters of parabola shape such as the focal length and the inclined angle. The system is assumed to be within the depth of 100 mm for being mounted on a wall. The objective function to be maximized was the energy intensity of solar irradiation captured on the absorber in winter season, i.e. from November until February. It was derived from the sensitivity analysis of the design parameters that the focal length of 95 mm and the angle of 25 degree would be optimal. The parabolic mirror effectively collects the sunlight so that the reflected sunlight contributes to 74-79 % of the solar intake every month. From the viewpoint of annual performance, it was predicted that the proposed system would provide quite high energy density in winter while very small one in summer, which is considered preferable because the behavior is in accordance with the change of heat load for residential buildings during a year.

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Technical paper
  • Masanori FUJIMOTO, Yoshiro TOCHITANI
    2018 Volume 44 Issue 2 Pages 65-71
    Published: March 31, 2018
    Released: April 20, 2018

    An experimental study is carried out to clarify the effect of the electric field on freezing initiation of supercooled water in a soft PVC (polyvinyl chloride) tube. It is selected for the reason that the hydrophobe of PVC is thought to maintain the supercooled state of water easily, in condition that the electric field is not applied. As water and silicone oil is filled in the tube, a triple-phase boundary is formed inside the tube. The electric field is applied from the outside of the tube by use of a pair of wire electrodes, which is set up in parallel to the axis of the tube. The experimental condition is -5 in temperature and 35kV DC in voltage. As a result, the PVC tube is, to some degree, effective to keep supercooled state of water steady. The electric field causes large amplitude oscillation of the triple-boundary in the tube. Application of the DC electric field is effective to initiate freezing of supercooled water, even if the water is filled in PVC tube of low wettability to water. Relative frequency of freezing initiation obtained is 1.0, and all samples began freezing within 10 seconds after the electric field had been applied.

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Short report