不同重力条件下单气泡池沸腾现象的数值研究

对不同重力条件下常压饱和水中单气泡池沸腾现象的气泡生长过程及传热特性进行了数值模拟. 采用简化的润滑流模型计算生长气泡底部微液膜的贡献, 而其他宏观区域的气液两相介质则用连续界面模型统一处理. 气液界面形状和加热面上接触线的运动分别采用Level Set方法和固定的表观接触角来近似刻画. 计算结果表明, 气泡生长过程中, 当量直径近似与生长时间的1/3～1/2次方成正比, 重力对相关趋势的影响不大, 但强烈影响着气泡脱落直径和生长时间, 其中脱落直径反比于重力的1/3次方, 生长时间反比于重力的4/5次方. 在固定的核化点数密度条件下, 加热面平均热流密度近似与壁面过热度的3/2次方成正比, 该趋势并不随重力的减弱而改变.      

基于流动沸腾气泡脱落行为的重力无关性分析

在流动沸腾现象中，气液两相密度差异导致重力对流动和传热性能产生很大影响，因此重力效应研究对于流动沸腾的航天应用具有重要意义.在对Bower-Klausner-Sathyanarayan重力无关准则（BKS准则）分析的基础上，提出其判据存在理论缺陷，不能正确反映重力效应.采用与BKS准则相同的气泡脱落模型，但忽略气泡沿加热管壁的滑动效应，重新计算常重力条件下不同流动方向起始沸腾阶段单气泡的脱落尺寸，归纳得到一个新的基于Fr（Froude数）的重力无关准则.该准则与实验结果符合更好，且与主导作用力准则基本相符.      

Analysis of gravity-wave induced instabilities and turbulence viscosity parameters from optical emissions

The effects of gravity waves on OH and 5577 0I emissions have been used to investigate (1) the possible production of “secondary” waves or “ripples” by a “primary” wave; (2) the possible application of such observed optical emissions for computing atmospheric parameters such as turbulence viscosity in the mesospheric regions.     

Drop motion in a rotating immiscible liquid body

The interaction of liquids is an important part of many processes and is often used for such purposes as causing a separation of solution components by mass transfer between phases, allowing a chemical reaction between liquids or their components, providing direct contact heating or cooling, or creating emulsions. Containerless space processing may well involve the interaction of liquids in the form of drops. For example it may be desirable to form an alloy in space by merger of two or more drops. Encapsulation of a volatile liquid by a second less volatile and immiscible liquid might be a means for avoiding volatilization. Rotation of such systems would enhance mixing where desirable and/or provide means for drop management. In this study, single drop behavior in rotating liquid bodies is studied experimentally.     

池沸腾现象中热毛细对流的成因

针对微重力条件下单组份液体池沸腾现象,探讨了有关热毛细效应作用及其成因的不同观点,指出正确描述气液相变界面两侧的温度关系是解决争议的关键.详细评述了现有的气液相变界面温度模型,发现气液相变的非平衡特征会导致气液界面上产生温度梯度,引起表面张力的显著差异,从而驱动热毛细对流的形成.但现有气液相变界面温度模型机理差异迥然,预测结果也差别很大,因此,需要更深入研究.      

Interaction of gravity with other environmental factors in growth and development: an introduction.

The life of plants and other organisms is governed by the constant force of gravity on earth. The mechanism of graviperception, signal transduction, and gravireaction is one of the major themes in space biology. When gravity controls each step of the life cycle such as growth and development, it does not work alone but operates with the interaction of other environmental factors. In order to understand the role of gravity in regulation of the life cycle, such interactions also should be clarified. Under microgravity conditions in space, various changes are brought about in the process of growth and development. Some changes would be advantageous to organisms, but others would be unfavorable. For overcoming such disadvantages, it may be required to exploit some other environmental factors which substitute for gravity in some properties. In terrestrial plants, gravity can be replaced by light under certain conditions. The gravity-substituting factors may play a principal role in future space development.     

过冷核态池沸腾中的Marangoni效应

分析了过冷核态池沸腾过程中气泡横向运动现象,指出其成因在于相邻气泡界面温度差引起的Mara-ngoni对流对周围液体的吸引.通过对该流动的尺度分析,得到了气泡横向运动特征速度及其可观测度的估算公式,其预测结果与实验观测相一致.特别是对极细小的初始核化气泡,该公式预测了强烈的横向Marangoni对流会导致气泡顶端微射流的形成.该效应在加热面水平向下或微重力沸腾等气泡脱落频率较低的情形中尤为重要.      

Evaluating the robustness of the enantioselective stationary phases on the Rosetta mission against space vacuum vaporization

The European Space Agency’s Rosetta mission was launched in March 2004 in order to reach comet 67P/Churyumov–Gerasimenko by August 2014. The Cometary Sampling and Composition experiment (COSAC) onboard the Rosetta mission’s lander “Philae” has been designed for the cometary in situ detection and quantification of organic molecules using gas chromatography coupled to mass spectrometry (GC–MS). The GC unit of COSAC is equipped with eight capillary columns that will each provide a specific stationary phase for molecular separation. Three of these stationary phases will be used to chromatographically resolve enantiomers, as they are composed of liquid polymers of polydimethylsiloxane (PDMS) to which chiral valine or cyclodextrin units are attached. Throughout the ten years of Rosetta’s journey through space to reach comet 67P, these liquid stationary phases have been exposed to space vacuum, as the capillary columns within the COSAC unit were not sealed or filled with carrier gas. Long term exposures to space vacuum can cause damage to such liquid stationary phases as key monomers, volatiles, and chiral selectors can be vaporized and lost in transit. We have therefore exposed identical spare units of COSAC’s chiral stationary phases over eight years to vacuum conditions mimicking those experienced in space and we have now investigated their resolution capabilities towards different enantiomers both before and after exposure to space vacuum environments. We have observed that enantiomeric resolution capabilities of these chiral liquid enantioselective stationary phases has not been affected by exposure to space vacuum conditions. Thus we conclude that the three chiral stationary phases of the COSAC experiment onboard the Rosetta mission lander “Philae” can be considered to have maintained their resolution capacities throughout their journey prior to cometary landing in November 2014.     

Hydrodynamical evolution of AGN driven by radiation from circumnuclear starbursts

We explore the hydrodynamical evolution of dusty gas around active galactic nuclei (AGN) driven by the radiation from circumnuclear starbursts. For this purpose, we calculate the temporal equilibrium states between the radiation force by starburst regions and the gravity in galactic nuclei. As a result, we find that the equilibrium patterns between the radiation force and the gravity are roughly characterized by three types. The first is the situation where the starburst luminosity is larger than the Eddington luminosity. In this case, the dusty gas is blown out like a wind. We may detect intense infrared (IR) radiation from the starburst regions screened by blown-out dusty gas. The second is the situation when the radiation force is comparable to the gravity. In this case, the equilibrium surface surrounds the nuclear regions as well as starburst regions. Since the dusty gas absorbs UV or soft X-rays from the center and re-emits IR radiation, we may recognize it as a Seyfert 2 galaxy. The last is the situation where the starburst luminosity is small. In this case, the dusty wall of equilibrium would be built up only in the vicinity of starburst regions. The radiation from central regions is rarely obscured, because the dusty regions have only small angular extension. So, it would look like a Seyfert 1 galaxy which is characterized by intense soft X-rays. When we consider the stellar evolution in starburst regions, the starburst luminosity decreases with time. Therefore, we can recognize the above three types as time evolution; a starburst galaxy (first stage), a Seyfert 2 galaxy (second stage), and a Seyfert 1 galaxy (third stage). Note that we present here an alternative scenario for explaining the relation between Sy 1's and Sy 2's to the standard “Unified Scheme”.     

重力对单气泡生长特性的影响

采用VOF (Volume of Fluid)多相流模型, 通过用户自定义函数UDF (User Defined Function)实现相变过程中质量和能量的输运, 对微重力条件下尺寸为10mm × 10mm × 25mm的矩形通道的池沸腾现象进行数值模拟, 得到了微重力及常重力作用下单个气泡生长特性的差异. 模拟结果表明, 微重力条件下气泡周围的流线与温度场的分布有显著差异; 由于表面张力作用, 微重力下的气泡脱离特性与常重力下不同; 在微重力条件下, 气泡直径的变化比较复杂, 并与重力加速度的大小有关; Marangoni流对微重力下的流动影响很大, 使换热系数波动, 而且波动的幅度随重力加速度的减小而增大.      

孤立气泡生长过程的短时微重力落塔实验研究

利用中国科学院国家微重力实验室北京落塔提供的3.6s微重力时间开展了短时微重力条件下的池沸腾实验研究, 分析了微重力条件下孤立的单个气泡生长过程特征. 实验中采用掺杂磷的N型光滑硅片作为加热面(加热片尺寸10mm×10mm×0.5mm), 以含气率0.0046 (气液摩尔分数比)的FC-72作为工质, 利用恒流源对加热片通电加热. 通过对实验观测到的单个气泡生长图像及相应传热数据分析可知, 经典传热机制控制的气泡生长模型可以描述其早期特征. 相关模型中经验参数的拟合结果在文献报道的数值范围内, 表明重力对气泡生长早期影响较小, 但较大的气泡尺寸可以提供更准确的数值结果.      

Middle atmosphere electrical structure,dynamics and coupling

The ram current to ion traps and the insensitivity of ion conductivity to compressibility provide the basis of robust techniques for middle atmosphere measurements. Gerdien condensers are more difficult to implement but provide more information. Mesospheric electrical conductivity shows many orders of magnitude variability, with depressions below gas phase model values indicating dominance by aerosol particles. The mobility of these ions has been directly measured and indicates particles of thousands of AMU. Large mesospheric fields have come into question, and diagnostic measurements show that many such measurements may be artifacts. However, some measurements of V/m fields with symmetrical and redundant sensors appear to be real. These fields complicate the “mapping” picture of electrical coupling and may also modulate the transport of aerosol particles. They are probably related to neutral atmosphere dynamics and/or the aerosol particles. Lightning couples much more energy to the middle atmosphere and above than previously suspected, primarily in the ELF-ULF range. There are many important unanswered questions in this relatively unexplored frontier area which may be answered with low cost balloon and sounding rocket experiments.     

Influence of different natural physical fields on biological processes.

In space flight conditions gravity, magnetic, and electrical fields as well as ionizing radiation change both in size, and in direction. This causes disruptions in the conduct of some physical processes, chemical reactions, and metabolism in living organisms. In these conditions organisms of different phylogenetic level change their metabolic reactions undergo changes such as disturbances in ionic exchange both in lower and in higher plants, changes in cell morphology for example, gyrosity in Proteus (Proteus vulgaris), spatial disorientation in coleoptiles of Wheat (Triticum aestivum) and Pea (Pisum sativum) seedlings, mutational changes in Crepis (Crepis capillaris) and Arabidopsis (Arabidopsis thaliana) seedling. It has been found that even in the absence of gravity, gravireceptors determining spatial orientation in higher plants under terrestrial conditions are formed in the course of ontogenesis. Under weightlessness this system does not function and spatial orientation is determined by the light flux gradient or by the action of some other factors. Peculiarities of the formation of the gravireceptor apparatus in higher plants, amphibians, fish, and birds under space flight conditions have been observed. It has been found that the system in which responses were accompanied by phase transition have proven to be gravity-sensitive under microgravity conditions. Such reactions include also the process of photosynthesis which is the main energy production process in plants. In view of the established effects of microgravity and different natural physical fields on biological processes, it has been shown that these processes change due to the absence of initially rigid determination. The established biological effect of physical fields influence on biological processes in organisms is the starting point for elucidating the role of gravity and evolutionary development of various organisms on Earth.     

The role of gravity in the evolutionary emergence of multicellular complexity: Microgravity effects on arthropod development and aging

While experiments carried out in Space with isolated cells have shown that eucaryotic cells are able to sense and respond to the absence of gravity by modifying their reactions, experiments in which more complex processes have been investigated, such as Biological Systems undergoing development under Microgravity, have been surprisingly unaffected by the space environment. This can be considered a curious result since all organisms are evolutionarily adapted to the current level of the gravity force in our planet and should eventually change if this parameter will vary in a permanent manner. In fact, the small effects of the modifications in gravity on development in short term experiments may be equivalent to the difficulties in detecting the involvement of other basic physical processes such as diffusion-controled auto-organizative reactions in currently developing biological systems. An apparent exception to this lack of effect is experiments where brine shrimp dormant gastrulae directly exposed to the space environment accumulate developmental defects as a consequence of cosmic irradiation. In this article we discuss the idea that at a certain stage during the evolutionary emergence of multicellular organisms the cues laid by generic forces such as gravity were involved in the evolutionary organization of these primitive organisms. As evolution proceed, these early mechanisms may have been obscured and/or made redundant by the appearance of new internal, environment-independent biological regulatory mechanisms. On the other hand, behavioral responses that may be important, for example, in setting the life-spans of organisms may still be more readily susceptible to manipulation by external cues as experiments carried out by our group in Space and on the ground with Drosophila melanogaster indicate.     

Equatorial ionosphere–thermosphere system: Electrodynamics and irregularities

The equatorial ionosphere and thermosphere constitute a coupled system, with its electro dynamical and plasma physical processes being responsible for a variety of ionospheric phenomena peculiar to the equatorial region. The most important of these phenomena are: the equatorial electrojet (EEJ) current system and its instabilities, the equatorial ionization anomaly (EIA), and the plasma instabilities/irregularities of the night ionosphere (associated with the plasma bubble events – ESF). They constitute the major topics of investigations having both scientific and practical objectives. The tidal wind interaction with the geomagnetic field is responsible for the atmospheric dynamo electric fields, that together with the wind system, drives the major phenomena, under quiet conditions. Drastic modifications of these phenomena can occur due to magnetospheric forcing under solar-, interplanetary- and magnetospheric disturbances. They can also undergo significant modifications due to forcing by atmospheric waves (such as planetary- and atmospheric gravity waves) propagating upward or from extra tropics. This article will focus on the ambient conditions of the ionosphere–thermosphere system and the electro dynamics and plasma instability processes that govern the plasma irregularity generation. Major emphasis is given to problems related to the structuring of the equatorial night ionosphere through plasma bubble/ESF irregularity processes. Specific topics to be covered will include: equatorial electric fields, thermospheric winds, sunset electrodynamic processes, plasma drifts, EEJ plasma instability/irregularity generation, nighttime/post sunset plasma bubble irregularity generation, and very briefly, disturbance electric fields and winds and their effect on the ionization anomaly, the TEC and ESF/plasma bubble irregularities.     

微重力下三角形微通道内冷凝换热分析

采用VOF模型和自定义函数的方法对三角形微通道内冷凝换热特性进行了数值模拟研究.为验证模型的合理性,将计算得到的传热系数与文献中经验关联式的结果进行对比.分析了重力和表面张力对气液界面分布和传热性能的影响.结果表明,重力对微通道内气液界面分布和截面平均传热系数的影响很小.表面张力在非圆形微通道内的冷凝过程中发挥主导作用.在表面张力作用下,更多的冷凝液流向尖角,使壁面附近液膜厚度变薄,传热阻力减小,传热系数增强.      

微重力池沸腾中的气泡和传热行为数值模拟

基于标准动量传输方程、连续性方程以及能量方程,建立了单个气泡的二维数值模型,考察了微重力过冷核态池内沸腾中的气泡动力学和传热行为.在动量传输方程中耦合了表面张力和Marangoni力,连续性方程和能量方程中耦合了相变效应,考虑了加热面上过热液体层的影响,并引入相场函数捕捉气液界面的动态变化.结果表明:气泡在生长过程中,形状由最初的半球形变为椭球形,最后变为脱附时的梨形;气泡在加热面上自由迁移,呈非轴对称结构,并且气泡上部的温度场呈现为蘑菇云状;气泡的脱附直径正比于g-0.488,脱附周期正比于g-1.113,加热面上的平均热通量正比于g0.229.      

Studies of the interaction of gravity with biological membranes using alamethicin doped planar lipid bilayers as a model system.

Gravity interacts with biological systems on different levels of complexity. For the understanding of the action of gravity on such systems at higher degrees of organisation, the investigation of interactions on the membrane and even on the molecular level is crucial. To do such studies, planar lipid bilayers with incorporated transport mediating molecules, i.e. membranes of defined biochemical composition, are close to perfect model systems. In our experiments we have used painted planar lipid bilayers doped with alamethicin. Alamethicin is especially suitable for such studies because of its high sensitivity to applied external forces, which is a result of its special pore forming mechanism. Additional, different to most other transport mediating molecules, a big amount of data from the literature is available about the dependency of alamethicin pores on physical and chemical membrane parameters. We found that the conductance of alamethicin doped bilayers is dependent on the angle of the bilayer with the gravitational vector and that it furthermore can be reduced significantly under hyper gravity conditions in a centrifuge. The effect of gravity here is not an effect on the pore conductance or the membrane-aqueous solution interface, but it is due to an interaction of gravity with the pore forming mechanism, as can be shown by investigating the dependency of the alamethicin pore kinetics on the applied forces.     

Flare build-up study — Homologous flares group — Part I

According to the definition of the homology (optical) kept in reference, the homologous flares (HFl) may be observed wherever flares occur. The supposed supplementary preflaring conditions to have HFl may be either that the preflaring conditions have not been destroyed by the first flare (and then what mechanism has stopped the first and triggered the second ?) or that the preflaring conditions have been destroyed and rebuilt (and then, how ?). The analysis of data related to some selected active regions AR by the members of the working group, and the earlier works on HFl, may be used simultaneously to investigate the differences between one set of HFl and the others, the location of their sites and the evolution of HFl productive AR. This study brings the appearance of new footpoints from one flare to the following, the behaviour of cool arches (surging arches) leading to information on the changes of the magnetic configuration, and to peculiar characteristics of HFl, oif 2nd, 3rd in the time order concerning the chromospheric transition zone or coronal regions. The time delay between two consecutive homologous flares appears very quickly as an essential parameter to study homology. It was found that every set of flares (same type of site) is able to produce “rafales” of homologous flares, i.e. two, three, four, oir more flares with Δt in the range of one hour or less. The observations show no great chantes in macroscopic photospheric patterns (B, V) during this H flaring period. They lead to compare their temporal variation curves of flare brightness. A quantitative brightness parameter of homology relation has been defined. Some scale changes have also been detected in the dynamic spectrum of the site, and it is in good agreement with a very interesting theoretical suggestion made by P. Sturrock to produce such “rafales”. It may be shown that the closely consecutive time-homologous flares (CCHF) or “rafales” represent a good tool to analyse the critical conditions related to the origin and the amount of energy, mechanism of storage and release, necessary and, perhaps, sufficient conditions. New statistical results, applied to the different selected homologous flare active regions are presented and show the existence in homologous flaring areas of a “pivot” of previous filaments interpreted as a signature of an anomaly in the Solar rotation.     

Time-dependent dynamical behavior of surface tension on rotating fluids under microgravity environment

Time dependent evolutions of the profile of free surface (bubble shapes) for a cylindrical container partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry, have been studied. Numerical computations of the dynamics of bubble shapes have been carried out with the following situations: (1) linear functions of spin-up and spin-down in low and microgravity environments, (2) step functions of spin-up and spin-down in a low gravity environment, and (3) sinusoidal function oscillation of gravity environment in high and low rotating cylinder speeds. The initial condition of bubble profiles was adopted from the steady-state formulations in which the computer algorithms have been developed by Hung and Leslie/1/, and Hung et al./2/