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We have been studying impurity atoms in superfluid helium (He II) using laser spectroscopic method. It is known that a depletion called “atomic-bubble” is formed when atoms are immersed into He II. Laser ablation is one of the effective methods to introduce atoms in He II, however, this process also causes vaporization of liquid helium due to the sudden transition of solid sample to high-temperature and high-pressure vapor. It is considered that it takes some time for atoms to form bubble states. Thus, we expect to observe time delay of atoms to get into He II.As the first step of the study above described, in this work, we aim to investigate dynamics of atoms optically by observing laser-induced fluorescence from atoms generated by laser ablation method in air, vacuum and liquid nitrogen.

This research monitored the ease and simplicity in the observation of the magnetic properties of liquid oxygen and the subsequent development of education materials for use in the science class. Through the research, we found the method by which we can observe magnetic properties of liquid oxygen with ease. Because of the difference between the boiling point of liquid oxygen and liquid nitrogen, the liquid oxygen was procured from the condensation on the surface of aluminum can containing liquid nitrogen. This method of acquisition of liquid oxygen without using oxygen gas makes it safer and more efficient to collect it as well as to observe its magnetic properties. When a drop of liquid oxygen is brought in close proximity to the magnetic qualities of liquid oxygen can be observed., 液体酸素の磁気的性質の観察が安全で容易にできる理科教材を開発した。液体窒素の沸点と液体酸素の沸点の相違から，アルミ缶に液体酸素を凝結させ，その液滴を磁石に近づけることにより液体酸素の磁気的性質が観察できる。

地球軌道上の宇宙構造物あるいは宇宙船に衝突の可能性のある物体として、流星体およびスペースデブリがある。近年、宇宙環境利用の頻度が高まるにつれ、スペースデブリの数も年々増加し、その衝突が宇宙環境利用に支障をきたすようになってきている。高速衝突現象の重要な現象にデブリクラウドがある。スペースデブリが宇宙構造物主壁に与える損傷は、デブリクラウドの形成過程とデブリの微少破片の分布に依存する。従って、デブリクラウドを詳細に可視化することは重要である。またこれまでの高速衝突試験は、そのほとんどが常温下におけるものであり、地球低周回軌道などのスペースデブリが衝突する実際の温度環境下での研究は、まだ十分には行われてきていない状況である。そこで本研究では、極低温環境下におけるWhippleバンパーシールドヘの高速衝突現象を解明するために、地球低周回軌道上の日陰温度(約-150度C)に近い極低温環境下におけるアルミニウム材への高速衝突現象について、衝撃解析ソフトウェアAUTODYNを用いて数値シミュレーションを行った結果、および2段式軽ガス銃を用いた極低温に冷却した試験板への高速衝突実験結果との比較を示す。, 資料番号: AA0049122138

In cryogenic fluid, such as rocket propellants, thermal effect has to be properly treated, which is usually neglected in common fluids. In the present study, a cavitating flow solver, which is based on bubble two-phase flow model including energy equation, was constructed and flow calculation was carried out around 2D NACA0015 airfoil. Comparison between water and liquid nitrogen reveals that cavitating pattern between these two fluids are completely different and this difference was raised from thermal effect of cryogenic fluid. The effect of numerical dissipation was also discussed to reveal that excess numerical dissipation affected the cavitation very much, consequently, cavitation performance became completely different from that due to the higher-order calculation., 資料番号: AA0045948032, レポート番号: NAL SP-57

Flashing of liquid nitrogen in a pressure vessel (cryostat) was observed at depressurization rates from 0.01 to 4.0 MPa/s. The explosive boiling behavior was observed by using a video camera. Pressure and temperature changes in the pressure vessel were measured. In the case of high depressurization rates, mist formation was observed in the vapor phase near the vapor-liquid surface at the early stage of the depressurization rocess. This mist layer becomes more dense as the depressurization rate increases. Observations of mist formation and the calculated temperature drop of the vapor under an adiabatic expansion process show that mist formation depends on the vapor expansion and boiling near the vapor-liquid surface. Mist formation in flashing phenomena play an important role in which the thermal nonequilibrium states between the supercooled vapor and the superheate liquid are relaxed due to depressurization.

In a natural circulation loop，flow instability，such as density wave oscillation, occurs under a certain operating condition，while the influence of flow oscillation on the heat transfer is not well understood so far. Experiment was conducted by using a natural circulation loop of liquid nitrogen with test tubes of dimensions of 3.0mm/5.0mm I.D.，and 900mm heated length. It was indicated that the heat transfer correlation of Schrock-Grossman was in good agreement with experimental results in the saturated boiling region even under oscillatory flow condition，and that the correlation of Roko was in good agreement with the experimental results of post-dryout heat transfer even under oscillatory flow condition. On the other hand，the CHF was well predicted using the lumped-parameter model，taking account of the circulation rate, oscillation frequency and amplitude of mass flux in the natural circulation loop.

The aim of this study is to clarify the fundamental features of the flashing phenomenon of cryogenic liquid nitrogen under rapid depressurization. Liquid nitrogen flashing experiments have been carried out using a cryostat with windows. From these experimental results, it is shown that a pressure recovery process after rapid depressurization occurs when bubbles generated in the lowtemperature region grow and rise in liquid nitrogen. Furthermore, local minimum pressure and pressure recovery within the vessel are predicted by saturated pressure corresponding to initial liquid temperature. The local minimum pressure depends strongly on initial temperature rather than on the rate of depressurization.

Circulation characteristics and flow instabilities are investigated in a natural circulation loop of liquid nitrogen. The circulation velocity increases with the increase in the heat flux and decreases with the increase in the flow restriction. Beyond a certain limit of heat flux, so called "density wave oscillation"occurs. By applying a lumped-parameter model and homogeneous two-phase flow model to the present natural circulation system, the numerical simulation is conducted. The simulation well represents the transient behavior of the system and the estimated threshold conditions of the flow oscillation agree well with the experimental results.

In the present study, we focused on the length of the tip cavitation as a cavitation parameter for experimental investigations of the thermodynamic effect on a cavitating inducer. Comparison of the length of tip cavity in liquid nitrogen (76 K and 80 K) with that in cold water (296 K) allowed us to estimate the strength of the thermodynamic effect. In addition, unstable cavitation phenomena occur when the cavity length develops over the throat. Sub-synchronous rotating cavitation appears both in liquid nitrogen and in cold water. In contrast, cavitation surge appears only in cold water at a lower cavitation number. From these experimental results, thermodynamic effects on cavitation performance and instabilities were discussed., 資料番号: AA0063226000, レポート番号: JAXA-RM-06-003

The Cryogenic Inducer Test Facility (CITF) was constructed in the JAXA Kakuda Space Center and has been in operation since 2003. Liquid nitrogen and liquid hydrogen are used as working fluids for experiments on rocket engine turbopump inducers, enabling the thermodynamic effects on cavitation to be examined. The performance of CITF was verified from the elemental tests and inducer running tests. In this article, the verification test results and future programs are presented., 資料番号: AA0049203000, レポート番号: JAXA-RR-05-042

第27回宇宙利用シンポジウム (2011年1月24日-25日, 宇宙航空研究開発機構宇宙科学研究所相模原キャンパス), 相模原市, 神奈川県, The Twenty-seventh Space Utilization Symposium (January 24-25, 2011. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, This paper describes the activity of collaboration research among Korean Advanced Institute of Science and Technology (KAIST), Konkuk University, Seoul National University and Tohoku University. We are focusing on the behavior of cryogenic fluid under microgravity environment. The surface tension and wettability of cryogenic fluid become dominant factors for the estimation of fluid shape and its dynamic behavior under microgravity condition. By considering these thermophysical properties, we are planning to conduct microgravity experiment generated by parabolic flight of small aircraft. In this paper, the activities of the cryogenic research working group are briefly introduced and our final goals are explained., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: AA0065129033

Experiments injecting liquid nitrogen into the water jet, which focused on their differences between both of boiling temperatures, were carried out to improve the thrust from nozzle water flow. Effects of jet acceleration were evaluated by means of the measurements of thrust loads added on the convergent-divergent nozzle connecting with or without the parallel pipe submerged into the water tank. The characteristics of liquid-vapor two-phase nozzle flow appeared to be somewhat compressible fluid because of the explosive vaporization of liquid nitrogen, so that considerable increment of water acceleration at the part of divergent region of nozzle resulted in apparently higher thrust by exhaust jet from the nozzle.

We introduce an attractive demonstration experiment, ""Levitation of a ping-pong ball"", by cold liquid nitrogen. Liquid nitrogen in a PET (PolyEthylene Terephthalate) plastic bottle evaporates rapidly by being heated from the tap water around the bottle, and the nitrogen gas flows from a pipe which is attached to the bottle cap. A ping-pong ball floats above the pipe when the ball is put into the nitrogen-gas stream, due to the Bernoulli principle. We give some tips and important points for this demonstration, based on the experiences of scientific outreaches.