Journal of The Japan Society of Microgravity Application
Print ISSN : 0915-3616
Volume 24 , Issue 3
Showing 1-22 articles out of 22 articles from the selected issue
  • Odawara Osamu, Fujita Osamu
    2007 Volume 24 Issue 3 Pages 205-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    Download PDF (128K)
  • P. HALDENWANG, C. NICOLI
    2007 Volume 24 Issue 3 Pages 207-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    We analytically and numerically analyse the stability of a spray-flame propagating through a homogeneous three-component lean premixture composed of fuel droplets (typically a heavy alkane with low vapour pressure), a second gaseous fuel (typically a light alkane “stimulating” combustion) and air in excess. The fuel vapour evaporating from the droplets has a Lewis number larger than one ( i.e. fuel-1 with Le1>1), while the light gaseous fuel-2 has a Lewis number smaller than one ( Le2<1 ). The initial mass fraction of fuel-1 (under liquid phase),(Yl1)u , expresses the spray liquid loading, while(Yg2)u is the initial mass fraction of gaseous fuel-2, the overall fuel amount in fresh mixture therefore being (Yl1)u+(Yg2)u . For relative liquid loading ,δ=(Yl1)u /{(Yl1)u+(Yg2)u} higher than 50%, an excellent agreement between both numerical and analytical predictions on the intrinsic spray-flame instability is found. Conversely, poor agreement between numeric and asymptotic is found for the predicted threshold of diffusional-thermal pulsating instabilities in fully gaseous premixed flames at large Lewis number. This difference comes from the fact that the mechanism leading to spray-flame oscillations is intrinsic, and not based on differential diffusional effects. When increasing (Yl1)u , spray-flame instability threshold decreases and for vanishing (Yg2)u pulsations are found to occur for conditions that can easily be met in experiments on large carbon number fuel sprays.
    Download PDF (1498K)
  • C. EIGENBROD, J. C. DITTMER, O. ESSMANN, H. J. RATH
    2007 Volume 24 Issue 3 Pages 213-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    A new approach for spray ignition simulation is presented. Since the numerical effort of simulating an evolving spray within a hot and pressurized ambient from shortly after inj ection until ignition is interminable, the problem is tackled by splitting the simulation into two tasks. A CFD package is used to calculate a two phase flow through a simulation domain based on a configuration model. From this two phase flow droplet track data and gas phase values are extracted to serve as variable boundary conditions for the second task, the one dimensional single droplet ignition simulations, which are fully transient and based on detailed chemistry, named spraylet. The obtained ignition delay times can be transformed into spatial distributions of ignition probability. While the CFD part is handling spray formation, turbulence, temperature, pressure and global vaporization within the confinements, the spraylet calculations take care of droplet related physics and chemistry. The reworked model is able to reproduce single and multistage ignition and simulation can be performed beyond the limit of complete evaporation. The software framework for this approach has been implemented using a dummy function as substitute for the spraylet calculations still under development. The dummy function, which is intended for testing purpose only, comprises a very simple ignition criterion based on a threshold temperature.
    Download PDF (1833K)
  • H. ITO, Y. NAKADE, T. UCHIYAMA, O. FUJITA
    2007 Volume 24 Issue 3 Pages 220-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    The effects of a direct-current electric field on carbon nanotube(CNT) synthesis in a flame method utilizing a planar siffusion flame were investigated under microgravity and atmospheric pressure. Ethylene and oxidizer(75vol%O2-25vol%Ar) are supplied to the parallel rectangular burner to form the planar diffusion flame above it. 100%Ar is ventilated around the flame. ferrocene was used as a metal catalyst for CNT formation. Carbonaceous compounds generated in the flame were collected on biased TEM grids and analyzed by TEM. The results showed that electric bias strongly affects the CNT formation. One new finding of the study is the existence of a specific condition to generate large amounts of CNT with aid of DC bias, where no CNT was formed without the DC bias.
    Download PDF (3638K)
  • S. TAKAHASHI, S. B. JEE, T. IHARA
    2007 Volume 24 Issue 3 Pages 225-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    The flame spread rate over a PMMA film was measured with varying ambient balance gas, N2, CO2, He and Ar, in normal gravity and microgravity. A scale analysis was also conducted to discuss how ambient flow velocity, Vg, and gas properties affect the flame behavior. With decreasing the Vg, the flame behavior moves to the microgravity-regime. However, the Vg at which the regime switches is different according to the ambient gas properties. In Ar and CO2 balances, the flame is robust even with very low Vg because of their small preheat-zone length, Lg is so large that the range of Vg where the thermal-regime is held is very narrow, which results in weak flame both in normal gravity and microgravity. This result implies that not only the Vg but also the gas properties must be taken into account to discuss the flame spread in microgravity. The dimensionless hest loss number proposed by the present scale analysis gives good help to estimate the ‘‘critical flow velocity’’ below which the flame cannot spread. Keyword(s)
    Download PDF (1997K)
  • K. YAMAMOTO, Y. YAMAUCHI, T. KUWAHARA, M. TANABE
    2007 Volume 24 Issue 3 Pages 231-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    ``Thermo-acoustic streaming'' is a newly-found thermal convection. When heat is released locally in standing sound waves, it is generated toward a node. The driving force of this streaming is considered to be a kind of acoustic radiation force. To clarify the characteristics of this convection, the authors made visualization experiments and numerical simulations. Experiments were done in microgravity to remove the effects of buoyancy. In the simulations, FDTD (Finite Difference Time Domain method) and time-averaged model (ARF model) were used. The heat-source was placed at a node, an anti-node and the middle of the node and the anti-node. The node case, the simulations’ results agree with experimental results well. The anti-node and the middle case, however, the ARF results do not agree with the others. Two-dimensional effect, i.e. a flow whose direction is perpendicular to the thermo-acoustic streaming is found. The Rayleigh streaming, the radiation force of 2-D standing sound waves and that of 2-D flow oscillating caused by local heating in the 1-D standing wave were examined as the causes of two-dimensional effect. Analyzing the FDTD, it is concluded that the cause of the flow is the result of the 2-D oscillating flow that occurs near the heat-source.
    Download PDF (1525K)
  • X. ZHANG
    2007 Volume 24 Issue 3 Pages 235-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    Apparatus to simulate microgravity combustion under normal gravity is important for the safety of manned spaceflight. The narrow channel is such an apparatus in still an open question. In present paper, the opposed-flow flame spread over thin solid fuel in finite space under different gravities was compared experimentally and numerically. The comparison of flame appearances and flame spread rates under various gravities suggest that the horizontal channel of 1 cm height can suppress natural convection effectively. Such apparatus can simulate the microgravity flame spread in the channel of same geometrical size. Therefore, using the horizontal narrow channel on the ground to simulate the microgravity flame spread in the same environment, then considering the effect of channel size on flow field and heat loss to get the characteristics of microgravity flame spread in space of other size may be a feasible method. Keywords: microgravity, flame spread, thin solid fuel, finite space, numerical simulation, experiment
    Download PDF (1991K)
  • M. KIKUCHI, S. YAMAMOTO, S. YODA, M. MIKAMI
    2007 Volume 24 Issue 3 Pages 241-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    Flame spread phenomena of linear n-decane droplet array are investigated by microgravity experiments and numerical analysis. Especially, pre-evaporation effects of droplets on flame spread process are examined in this study. In microgravity experiments, each droplet which consists of the array is formed and sustained at intersections of fine, X-shaped SiC fibers of 14 micrometer diameter. Activation delay time of the igniter wire after insert of the array into the combustion chamber, tw, is employed as primary experimental parameter to control the degree of pre-evaporation of the array. Experiments are performed with some different droplet diameter (d0) and droplet interval (S) at ambient air with T = 600 K. Experimental results showed development of blue flame at spreading flame front with enhancement of pre-evaporation. Also, OH radical emission showed characteristic shape at flame front region when pre-evaporation of droplets are developed. Flame spread rate Vf increased with increase in the degree of pre-evaporation. However, Vf appears to approach some value with further pre-evaporation. In addition, numerical results showed similar characteristic flame structure at flame front as experimental results. It was suggested the flame front has a structure like a triple flame.
    Download PDF (2303K)
  • O. IMAMURA, K. YAMASHITA, J. OSAKA, M. TSUE, M. KONO
    2007 Volume 24 Issue 3 Pages 246-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    Combustion experiments of two droplets combustion were carried out in the DC electric field under microgravity. Two ethanol droplets are arrayed in the direction of electric field between two plate electrodes. As a result, flame deformations of anode-side flame and cathode-side flame are different from each other, but increases in burning rate constants are comparable level for two flames. This indicates different mechanism of effect of electric field for each flame. The convective effect is considered to be the main reason for cathode-side flame, on the other hand electron injection from the cathode-side flame is considered as the reason for anode-side flame. In order to discuss this phenomenon, droplets combustion in non-uniform electric field was also performed using a needle and a plate electrode, because electron emission will be expected when the needle electrode is negative. As a result, effects of electric field on flame deformations depend on polarity of electrode, however, effects on burning rate constant is comparable level in spite of polarity. From this experimental result, effect of electron injection is expected to appear as effect of local flow through negative ions. This effect of electron can be applied to anode-side flame in two droplets combustion and observed combustion behavior can be explained qualitatively.
    Download PDF (1697K)
  • O. MORIUE, K. MATSUO, E. MURASE, S. SCHNAUBELT, C. EIGENBROD
    2007 Volume 24 Issue 3 Pages 251-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    A fully transient numerical model of spontaneous ignition of single fuel droplets was developed. A physical part of the model is one-dimensional, and therefore it can easily employ a detailed chemical reaction model, which is necessary to reproduce complicated spontaneous ignition process of hydrocarbon fuels. The model simulates an isolated droplet in an open ambient at constant pressure. It was verified through microgravity experiments for relatively large (~0.7 mm) droplets, and was successful in quantitative reproduction of ignition delays of cool and hot flames. With the verified numerical model, ignition of relatively small (< 100 μm) droplets can be numerically observed. However, an isolated droplet in an open ambient that is smaller than a certain initial diameter does not ignite unlike droplets in a spray. The model was modified to handle a droplet in a closed cell so that single droplets could be compared to sprays. Two-stage ignition behavior (cool- and hot-flame ignitions) was observed even for such fine droplets. There was transition from heterogeneous ignition to homogeneous ignition with decreasing initial droplet diameter. The effect of ambient temperature on two-stage ignition was examined in terms of ignition delays, total heat release and cool flame temperature.
    Download PDF (996K)
  • T. NISHIDA, O. KAWANAMI, I. HONDA, Y. KAWASHIMA, H. OHTA
    2007 Volume 24 Issue 3 Pages 255-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    We investigated the heat transfer during tube quenching for developing an on-orbit cryogenic fluid management system. This paper describes the experimental results of tube quenching for two flow directions (up flow and downflow) under terrestrial conditions. Liquid nitrogen (LN2) is used as the test fluid, and it is injected into a transparent heated tube at a mass velocity of 100-600 kg/m2s. The tube is made of pyrex glass, and it has an inner diameter of 13.6 mm and a wall thickness of 1.2 mm. The thermal data reveals that the quenching time during which the inner wall temperature became equal to the LN2 boiling temperature (77.3 K) under up flow condition is less than that under downflow condition. The flow visualization data reveals the existence of a filamentary flow only under the downflow condition, and this flow pattern leads to a decrease in the cooling rate of the tube wall.
    Download PDF (3025K)
  • M. ANDO, H. OHTA, A. OKAMOTO, H. KAWASAKI
    2007 Volume 24 Issue 3 Pages 261-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    In recent years, feasibility of Space Solar Power System (SSPS) was examined from various aspects. Thermal management of SSPS is one of the most serious problems because of the generation of a great amount of waste heat at high heat flux density for both systems of microwave SSPS and laser SSPS. Removal and transportation of such waste heat can be realized by using two-phase fluid flow for thermal management system of SSPS. Two-phase fluid flow is a promising method to transport a large amount of thermal energy because it accompanies the transportation of latent heat of vaporization. To realize the cooling of the laser medium, heat flux at the cooling surface should be lower than the critical heat flux determined by the fluid and flow conditions. Also, temperature of the system should be maintained at allowable level. The paper studies the feasibility for thermal management system of bulk laser type SSPS simulating the cooling process by two-phase fluid flow of water and FC72. To increase the critical heat flux on a large heat transfer surface, a new structure of narrow channel is devised and its performance is tested.
    Download PDF (1459K)
  • C. WANG, S. XU, Z. SUN, W. HU
    2007 Volume 24 Issue 3 Pages 267-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    In this study, a series of experiments were conducted, respectively, in the drop tower-which provides 3.5 seconds of microgravity and on the ground base (g=1) to test the effect of gravity on the contact angle of drops setting on the solid surface. The results show that the volume of the droplet has little influence on the measured contact angle in the microgravity condition. For small sized droplets, the measured contact angle on the ground is almost the same as in microgravity condition, while for large sized droplets, the measured contact angle on the ground is about 4° larger than the value of the microgravity.
    Download PDF (3506K)
  • C. WANG, S. XU, Z. SUN, W. HU
    2007 Volume 24 Issue 3 Pages 271-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    When the Concurs-Finn condition is fitted, there will be no equilibrium configuration in the interior corner under microgravity, and the fluid will move to the walls and can rise arbitrarily high along a part of the wall. In this study, we utilize the climb of the liquid in interior corner when the Concurs-Finn condition is fitted to study the dynamic contact angle under microgravity condition in drop tower. The advancing of the fluid along the edge and the receding of the fluid along the bottom side are recorded by CCD camera. The dynamic contact angle and related velocity can be obtained by analysis. This method overcomes the difficulties in controlling the velocity of the contact lines in the small time duration of microgravity condition in drop tower. And the dynamic contact angles for different velocities of silicone oil on PMMA are measured in drop tower experiments.
    Download PDF (4615K)
  • S. XU, C. WANG, Z. SUN, W. HU
    2007 Volume 24 Issue 3 Pages 275-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    In this study, we try to investigate the capillary flow in interior corner under microgravity condition in drop tower experiments. Especially, the effect of liquid volume on the capillary flow in the container of same size is discussed. The experiments show that the reorientation of the liquid-gas surface is different for the different liquid volumes. The influence of viscosity is also studied. The experimental results show that the climbing speed is larger when the volume is larger. By measuring the angles of contact line with the edge of the container, the time range that tip location is linear with time can be determined properly. For 0.5ml and 0.12ml silicone oil, the tip location is linear with time in the final stage of the microgravity condition in drop tower experiments, and the larger viscosity will make the climbing speed smaller.
    Download PDF (2815K)
  • H. INARI, T. WAKATSUKI, Y. KONISHI, Y. FUKUNAKA, R. C. ALKIRE
    2007 Volume 24 Issue 3 Pages 279-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    Copper was electrodeposited potentiostatically in 0.05 M CuSO4 - 0.05 M H2SO4 aqueous solutions onto a TaN film sputtered on a silicon substrate. Two different electrolytic cell configurations were designed in order to discuss quantitatively the effect of gravitational level on the nucleation and growth of metal electrodeposition in detail: (a) a horizontal cathode surface facing downward over an anode (C/A) and (b) an anode over cathode (A/C). FE-SEM image demonstrates the progressive nucleation model on TaN substrate. A/C configuration introduces more number of nuclei than the case of C/A at a constant applied potential. Moreover, the comparison of nearest-neighbor distance distribution among precipitated particles with Poisson random distribution confirms the existence of ``exclusion zone'' The growth rate of the exclusion zone is surely influenced by the gravitarional level. Then, the potentiostatic electrodeposition was engaged in A/C configuration inside a centrifugal field. The nucleus number densty becames slightly insreasing the gravitational level. It is saturated above 100 G.
    Download PDF (2002K)
  • H. OSAKI, T. WAKATSUKI, Y. FUKUNAKA
    2007 Volume 24 Issue 3 Pages 285-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    ZnO films were potentiostatically electrodeposited in 0.1 M Zn(NO3)2 aqueous solution on to ITO/FTO substrate. Two types of electrode configurations were employed in order to discuss quantitatively the effect of gravitational strength on nucleation and growth of ZnO in detail: (a) a horizontal cathode surface facing downward over an anode (C/A) and (b) an anode over a cathode (A/C). Current transients were generally derived into four stages: the increased measured current quickly drops in the first stages, records a minimum current in the 2nd and then starts to increase in the 3rd followed by the 4th. The measured transient in the 4th stage is surely influenced by gravitational field vector: it slightly declines in C/A while continues to increase with time in A/C. SEM pictures show that the A/C configuration introduces more number of nuclei than the case of C/A configuration. The present research is provided for the preliminary terrestrial experiment before the electrochemical processing in microgravity environment.
    Download PDF (1729K)
  • T. I WAKAMI, M. NOKURA
    2007 Volume 24 Issue 3 Pages 290-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    The Micro-Gravity Laboratory of Japan has been providing high-quality 4.5 s microgravity environment for many researchers. In addition, we are attempting to provide microgravity environment /drop experiments for the younger generation who will produce scientific results in the future. This paper describes the facility and several examples of educational experiments.
    Download PDF (3102K)
  • Y. INATOMI, T. ISHIKAWA, T. HASHIMOTO, S. SAWAI, Y. SAITO, T. YOSHIMIT ...
    2007 Volume 24 Issue 3 Pages 296-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    The first microgravity experiment using a new free-fall capsule released from 40 km altitude was performed on May, 2006 based on a drag-free technique. The fundamental data for analyzing the drag-free control, the flight sequence, and the wireless communication between the capsule and a control room were successfully obtained in the flight.
    Download PDF (2224K)
  • D. AKITA, K. YAMADA, N. IZUTSU, H. FUKE, M. TORIUMI, Y. MATSUZAKA, S. ...
    2007 Volume 24 Issue 3 Pages 301-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    Scientific balloon flights can provide excellent opportunities for microgravity experiments. A balloon-drop microgravity experiment system, which is aiming for the experiment duration longer than 30 sec, is currently under development in ISAS/JAXA. The first flight of the microgravity experiment system was successfully performed in spring 2006. In this paper, the system configuration and the operation sequence of this system are reviewed. In addition to that, preliminary feasibility of a tethered balloon system for simplified short-term microgravity experiments is also studied. By using the tethered balloon, in exchange for the relatively short experiment duration, the operation cost for an experiment becomes drastically lower than that of a normal scientific balloon flight. The experiment system by using the scientific balloon is very promising for the microgravity experiments in terms of the reasonable cost and the experiment duration.
    Download PDF (2638K)
  • R. AKIBA, I. EGAMI, S. YANO, T. KOREKI, M. YAMASHITA, D. AKITA, T. YAM ...
    2007 Volume 24 Issue 3 Pages 307-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    Conceptual design of a new convenient free fall capsule was developed for conducting animal experiment. In order to provide microgravity environment for at least 20 sec, technical feasibility of an atmospheric balloon borne system was examined. An experiment capsule is hung up by a balloon up to 3,000 m height. Free fall down to 1,000 m creates 20 sec microgravity environment inside the capsule. The terminal velocity of 196m/s, reaching after the fall, should be safely decelerated by deploying a parachute or any other appropriate way. The landing velocity is managed to be suppressed to around 1m/s. In order to cancel fluid dynamical drag during the free fall, use ofa thruster system is one of the candidates. Our design goal is to develop the capsule that could be repetitively operated at affordable expenses. Safe recovery of the system after free fall might be the key for such concept. We hope our system would cradle many seeds of application by providing convenient access to microgravity.
    Download PDF (918K)
  • R. AKIBA, I. EGAMI, T. KOREKI, O. FUJITA, M. YAMASHITA
    2007 Volume 24 Issue 3 Pages 312-
    Published: 2007
    Released: January 21, 2021
    JOURNALS OPEN ACCESS
    The reduced gravity devices were developed based on the yoyo principle. Their performance was examined, and found useful to conduct experiments for scientific and educational purposes. The operation of this yoyo device was improved by governor mechanism attached to the pulley. The governor optimized the profile of momentum of inertia of the pulley assembly. Another option tested was the double-capsule configuration, which enabled to generate microgravity in the inner test section.
    Download PDF (1796K)
feedback
Top