Hiroaki Kobayashi

<p>A loading system plays a role of loading and unloading liquid hydrogen between a carrier ship and a ground storage facility in hydrogen supply chain in which hydrogen in the form of liquid phase is transported by the carrier ship from a resource-rich country to a consuming country. An emergency release system (ERS), which is one of components of the loading system, is installed in the middle of transfer pipe of the loading system, and has function of separating and plugging the pipe at an abnormality during loading so as to prevent a large amount of cryogenic fluid from scattering. We have conducted R & D study of the ERS for liquid hydrogen based on an existing one for liquid natural gas (LNG). Whole system function of the ERS including separation behavior was verified conducting a field experiment with the ERS test model and liquid hydrogen. Through several tests, the separation mechanism and behavior were verified, and also, soundness of the seal mechanism was evaluated. While, auto-ignition phenomena were observed on the separation surface of the ERS after the separation, of which causes have not been identified yet. Characteristics of dispersion behavior of hydrogen that was released at the separation could be investigated measuring distribution of temperature and hydrogen concentration around the ERS test model.</p>

<p>To improve safety regulations for fuel cell vehicles and hydrogen infrastructure, experiments of cryo-compressed hydrogen leakage diffusion were conducted. The experimental apparatus can supply 90 MPa hydrogen of various temperature conditions. Measurement items were hydrogen concentration distribution, blast pressure, flame length, and radiant heat. In addition, high speed camera observation was carried out to investigate the near-field of cryogenic hydrogen jet at supercritical pressure. The experimental apparatus can supply 90 MPa hydrogen at various temperature conditions (50 K–300 K) at a maximum flow rate of 100 kg/h. The hydrogen leakage flow rate was measured using pinhole nozzles with different outlet diameters (0.2 mm, 0.4 mm, 0.7 mm, and 1 mm). It was confirmed that the hydrogen leakage flow rate increases as the supply temperature decreases. The hydrogen concentration distribution was measured by injecting high-pressure hydrogen from the 0.2-mm pinhole for 10 min under a constant pressure/temperature condition. As the hydrogen injection temperature decreased, it was found that the hydrogen concentration increased, and an empirical formula of the 1% concentration distance for the cryogenic hydrogen system was newly presented.</p>

<p>JAXA has constructed an experimental facility to pressurize and supply liquid hydrogen at a maximum pressure of 90 MPa to conduct experimental research on the injection of high pressure liquid hydrogen into the atmosphere. Liquid hydrogen has a property that its density greatly changes depending on pressure despite being a liquid phase. In addition, the high pressure hydrogen gas is in a supercritical state and has an intermediate property between a gas and a liquid. Therefore, it is a difficult question whether to treat the injection of high pressure liquid hydrogen as a gas phase phenomena or as a liquid phase phenomena. As a result of the experiment, it was found good to apply the liquid orifice equation to predict the discharge flow rate of high pressure liquid hydrogen.</p>

<p>The payload capacity of launch vehicles must be increased in order to allow the exploration and development of space to be extended from low-Earth orbit into the solar system. A propellant system using a cryogenic fluid must reduce the amount of unusable propellant due to evaporation and boiling. However, in space exploration and development, where safety and reliability of missions are critical, predictions of the boiling heat transfer of current technology are not sufficiently reliable for thermal management design due to a lack of knowledge and relevant research. Therefore, the objective of this research is to understand and accurately predict boiling heat transfer by developing numerical simulation tools for two-phase flows that consider phase change. In this paper, recent research activity toward the development of chill-down process simulation technology is presented.</p>

In this paper is presented a microgravity experiment system utilizing a high altitude balloon. The feature is a double shell structure of a vehicle that is dropped off from the balloon and a microgravity experiment section that is attached to the inside of the vehicle with a liner slider. Control with cold gas jet thrusters of relative position of the experiment section to the vehicle and attitude of the vehicle maintains fine microgravity environment. The design strategy of the vehicle is explained, mainly referring to differences from the authors' previous design. The result of the flight experiment is also shown to evaluate the characteristics of the presented system.

Capacitance type void fraction sensors for cryogenic fluid has been developed by our research group. The sensors are roughly categorized into three types; arc type, small-sized arc type, and asymmetric type. In this paper, the three type sensors are compared, and each sensor's merits and demerits are indicated. The arc type sensor was first developed. The sensor is simple, but S/N ration is low and influence of "temperature drift" is large. The small-sized arc type sensor was developed for the sounding rocket S310 test No.43, so the sensor was needed to make as small as possible. The sensor succeeded to measure the void fraction of the liquid nitrogen flow even under microgravity. The asymmetric type sensor was deviced to improve the measurement accuracy. Inaccuracy of the sensor between true void fraction and measured void fraction was only 3% for stratified flow, whereas that of the arc type sensor 30%.

大気球シンポジウム 平成26年度（2014年11月6-7日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県著者人数: 18名資料番号: SA6000021014

液体水素移送に関して、常電導かご型誘導モータがポンプ駆動用として試作されたが、多大な損失が発生した。一方、かご型回転子巻線の超電導化により、損失の大幅な低減が実験的に確認されている。更に固定子巻線の超電導化することで、更なる損失低減が可能となる。本研究では、MgB₂超電導線材を用いた固定子巻線構造を検討した。従来構造ではMgB₂線による製作が困難なため、レーストラック型要素コイルの組合せによる巻線構造を提案した。またギャップ磁束分布の数値解析の後、MgB₂線を用いて要素コイルを製作し、その健全性を確認した。次に12個の要素コイルを結線した3相4極の固定子巻線を構成し、MgB₂回転子を用いた無負荷試験、負荷試験を行った。

An electric pump composed of an MgB₂ motor is combined with superconducting level sensors using thin CuNisheathed MgB₂ wires to transfer liquid hydrogen. An impeller is attached to the lower end of a rotating shaft on the MgB₂ motor and covered with an outer casing to form a centrifugal pump. Then, the MgB₂ motor and impeller are placed vertically inside a cryostat with an infill of liquid hydrogen. A glass Dewar vessel is prepared to receive the liquid hydrogen transferred from the cryostat containing the MgB₂ motor. The MgB₂ sensors are used not only to detect the level of liquid hydrogen but also to control the electric pump on the basis of their pre-estimated calibration curves. By using the assembled pump system, the liquid hydrogen is successfully transferred from the cryostat to the glass Dewar vessel via a transfer tube. (Translation of the article originally published in Cryogenics 52 (2012) 615-619)

現在、液体水素の残量を外部から高精度、高信頼度を持って判断できる技術は確立されていない。そこで、我々のグループでは、超電導線と非超電導線を用いた新構造液体水素用液面計を提案している。この液面計は従来構造液面計に非超電導線を回路的に直列に配置したもので、超電導の発生電圧と非超電導線の差分を取ることで、高精度に液面を計測することが可能である。非超電導線は線引き加工後の未熱処理線を用いた。そして、SUSシースMgB₂線とこの未熱処理線を用いて液面計を試作し、液体水素中で動作模擬試験を行った。また、数値解析により実験結果の再現を試みた。