Improvement of flight hardware and isothermal Marangoni convection under micro-gravity conditions

During parabolic flights three different kinds of experiments were performed under reduced gravity conditions. The experiments were: I. A general learning process to work with hardware and fluid under micro-gravity conditions. II. The investigation of critical parts of hardware or critical moments in experiments. This can be a part in the preparation of future sounding rocket or Spacelab flights. III. The possibility to perform scientific experiments under micro-gravity conditions within 22 seconds. In the joined parabolic flights of march 1986 the main interest was to perform experiments with Marangoni convection due to concentration gradients along the gas-liquid interface under isothermal conditions. One experiment was performed with a horizontal surface tension gradient and the other observed Marangoni convection was due to the evaporation of a component from a solution under steady state conditions.     

Numerical simulation of 3D convective motion disturbing the soret separation of the two components of a binary fluid mixture

Buoyancy driven convection arising in a fluid mixture confined in a cylindrical container designed for a measurement of the Soret (thermal diffusion) coefficient of a binary mixture, has been investigated in the case of a cylinder submitted to an axial temperature gradient, in low but steady gravity conditions. These 3D convective motions and their effect on the Soret separation have been numerically simulated, using a 3D finite differences technique, for a wide range of the characteristic parameters. The results will allow to interpret any Soret experiment performed in micro-gravity conditions.     

Marangoni convection and mass transfer from the liquid to the gasphase

Marangoni convection can be introduced by instabilities in the evaporation of a component of a solution, under isotermal conditions. Three experiments were performed under micro-gravity conditions, to prevent density induced Rayleigh convections, during the D1-Spacelab flight. With a flat gas-liquid interface the system was stable, while a two-dimensional linear stability analysis predicts the system to be unstable. Deformation of the interface introduced concentration and thus surface tension gradients. The resulting Marangoni convection will enhance the mass transfer of the evaporation process.     

Marangoni convection when the surface tension increases with the temperature in normal and low gravity conditions

Thermocapillary convection has been studied in n-heptanol aqueous solutions whose surface tension is increasing with the temperature.

The fluid was confined in a parallelipipedic enclosure and a thermal gradient was imposed parallel to the free liquid/gas interface. The motions induced by the thermocapillary forces have been studied under low gravity conditions during Texus sounding rocket experiments and during the Spacelab D1 mission.

The combined thermocapillary and buoyancy convection have been extensively studied during ground based experiments.

The influence of the aspect ratio and of the alcohol concentration were investigated. Detailed velocity field was determined at the steady state under normal gravity conditions by Laser Doppler Anemometry (LDA).

The aspect ratio was of 0.3 and the temperatures imposed to the lateral sides of the cell were respectively 45°C and 60°C. With these experimental conditions, two superposed contrarotative cells were observed with rapid motions in the surface from the cold to the hot side. This convective pattern was also observed during the normal and high gravity periods of parabolic flights but during the low gravity period of the parabola the motions stopped everywhere in the fluid even in the surface and reappeared immediatly at the pull out of the parabola.     

EFFECTS OF CONVECTIVE FLUID MOTION UPON OXIDE CRYSTAL GROWTH IN HIGH TEMPERATURE SOLUTION

For understanding of the influence of convective flow on crystal growth, space high temperature in situ observation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystals in high temperature up to 1000°C. Model experiments using transparent liquids such as KNbO3 and a mix ture of Li2B4O7+KNbO3 were chosen to investigate effects on ground and in space.On the earth, an investigation of growth kinetics of KNbO3 crystal related to two different states of convection: diffusive-advective flow and diffusive-convective flow,has been performed. The per unit length of a step e is calculated from the exper imental data for two different states of convection. Analyses of these data show the effect of buoyancy convection is to enhance the sharpness of the interface. The growth of KNbO3 crystals from solution of KNbO3+Li2B4O7 was investigated in space. The streamlines of the steady thermocapillary convection in Li2B4O7 solvent was observed. Due to thermocapillary convection, KNbO3 crystal grains grew and filled the whole solution homogeneously. Earth-based quenching experiments are de signed in order to study polyhedral instability of KNbO3 crystal, which is controlled by diffusion mechanism limitation. In all cases, when the crystal was nucleated near air/solution surface, it lost its polyhedral stability and varied from polyhedrons to dedrites. The thickness of diffusion mechanism limitation layer is about 60μm.     

Collection of cometary dust

Rendezvous Missions to Comets lead to low velocities at the nucleus of the comet. The resulting impact velocity of the cometary dust on a target will range between 10 and 400 m/s. The dust particle which impacts on a target can be collected for a subsequent in-situ analysis.

The collection efficiency of a target depends in addition to obvious geometrical conditions upon the surface of the target. The surface characteristics can be divided into two groups:

• “dirty” surfaces, covered with silicate or hydrocarbon compounds (for example vacuum grease),

• “clean” surfaces, like gold (with additional sputtering).

This paper deals with the experimental and theoretical investigation of the collection efficiency of “clean” targets. Laboratory experiments are described which were conducted at the Technische Universität München, Lehrstuhl für Raumfahrttechnik, and the Max-Planck-Institut für Kernphysik, Heidelberg. In both experiments an electromagnetic accelerator is used to accelerate different types of dust in vacuum to velocities between 10 and 400 m/s.

The target is then examined under the microscope and a secondary ion mass spectrometer (which is a model of the laboratory carried on board of the spacecraft for “in situ” analysis). The adhesion of the dust grains at the target is evaluated experimentally in an ultracentrifuge.     

Physical parameters affecting living cells in space

The question is posed: Why does a living cell react to the absence of gravity? What sensors may it have? Does it note pressure, sedimentation, convection, or other parameters?

If somewhere in a liquid volume sodium ions are replaced by potassium ions, the density of the liquid changes locally: the heavier regions sink, the lighter regions rise. This may contribute to species transport, to the metabolism. Under microgravity this mechanism is strongly reduced. On the other hand, other reasons for convection like thermal and solutal interface convection are left. Do they affect species transport?

Another important effect of gravity is the hydrostatic pressure. On the macroscopic side, the pressure between our head and feet changes by 0.35 atmospheres. On the microscopic level the hydrostatic pressure on the upper half of a cell membrane is lower than on the lower half. This, by affecting the ion transport through the membrane, may change the surrounding electric potential. It has been suggested to be one of the reasons for graviperception.

Following the discussion of these and other effects possibly important in life sciences in space, an order of magnitude analysis of the residual accelerations tolerable during experiments in materials sciences is outlined. In the field of life sciences only rough estimates are available at present.     

天舟一号货运飞船空间实验装置蒸发相变地面实验

以天舟一号货运飞船为依托,开展空间蒸发相变传热规律的科学实验研究,探索重力对蒸发传热传质过程的影响规律.设计了一套地面蒸发实验平台,以蒸发相变液体FC-72为研究对象,通过红外热像仪测温、热流量计、差分热电偶等手段,观测FC-72液层在不同台面温度、注液量等情况下的相变界面变化、蒸发表面特性、流体物性及Marangoni对流涡胞的变化等,获取其蒸发两相流体的液层温度差、表面温度场、热流量值、蒸发速率和涡胞结构等.实验结果表明:在其他条件不变的情况下,FC-72液层与蒸发台面的温差越高,其蒸发速率越快;注液量越大,蒸发速率也越大;在蒸发过程中出现了浮力对流涡胞和Marangoni对流涡胞.此外,通过地面蒸发实验可以确定空间科学实验选用的实验介质和材料,进而优化确定空间科学实验的工况、参数及流程等,部分地面实验结果也将直接成为天地对比实验的科学成果.      

Modeling the radiation belts: what are the important physical processes to be taken into account in models?

During active periods, physical processes acting on particle dynamics are well known to have several origins and can play a role at different times, different locations, and with different time scales. As their effects can be opposite, it is necessary to identify them and their relative importance:

• the particle sources (plasmasheet or direct solar wind entry)

• the particle losses (precipitation or drift loss)

• the particle transport and acceleration (convection access, magnetic or electric pulse or variation and recirculation).

The various phenomena are explained and results are presented. In particular, we demonstrate that classical diffusion models like the Salammbo code can account for all these phenomena.     

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.      

Prediction of horizontal gas–solid flows under different gravitational fields

In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler–Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle–wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle–wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.     

火星表面热环境对航天器热控影响分析

火星大气对太阳辐射产生吸收和散射作用,同时还将与火星表面航天器发生对流换热.热设计时难以直接评估对流、辐射和导热三种换热对航天器的影响,从而确定主要的控温途径.在调研火星表面辐射、大气等热环境的基础上,从线性化传热系数和对流辐射比的角度对比分析了辐射、对流和导热对航天器的影响.器表辐射传热系数随光学属性和温度的变化范围...     

激光与热丝点火对多组分液滴着火及燃烧的影响

采用挂滴方法,实验研究多组分单液滴的着火和燃烧特性,考察激光和热丝两种点火方式对液滴燃烧速率、火焰形貌及着火延迟时间的影响.实验结果表明,随着热丝点火时间增加,燃烧速率因液滴周围自然对流增强而加快.常重力下液滴火焰为包覆型火焰,火焰高度与液滴初始直径之比的最大值约为18.当t/t_b>0.4时,尚处于热丝加热阶段的火焰高度比没有热丝加热的高约5D₀,比激光关闭后的火焰高度高5~10D₀.与热丝点火相比,激光点火响应迅速,对液滴附近气体干扰小,是地面上比较理想的点火方式.固定激光脉冲时间,随着激光强度的增加,单液滴的着火延迟时间缩短.      

Interaction of artificially injected plasma flows with ionospheric plasma

Results of rocket experiments on study of plasma flows (PF) artificially injected by sources separated from vehicles and their effect on medium parameters in ionosphere at altitudes 160:230 km are presented.PF were injected comprising lithium ions with velocities 1,2 x 10⁴ m/sec. and cesium-potassium ions with velocities (1,4–1,5)x10³ m/sec. Mass flow rate in case of lithium PS is 2 mg/sec, and in case of cesium-potassium PS is 0,2 g/sec. During experiments mass-spectrometer measurements of ion medium content in ranges of different ion masses were held, disturbancies of electric fields with frequencies up to 20 kHz and electron flows with energies 0,7keV, 4,6keV and over 40 keV were controlled at distancies from 150m to (500–600)m between plasma source and scientific equipment.     

Energetic ion emission for active spacecraft control

Future space missions aiming at the accurate measurement of cold plasmas and DC to very low frequency electric fields will require that the potential of their conductive surfaces be actively controlled to be near the ambient plasma potential. In the near-Earth space these spacecraft are usually solar-cell powered; consequently, parts of their surface are most of the time exposed to solar photons. Outside the plasmasphere, a positive surface potential due the dominance of surface-emitted photoelectrons over ambient plasma electrons is to be expected. Photo- and ambient electrons largely determine the potential and positive values between a few Volts up to 100 V have been observed. Active ion emission is the obvious solution of this problem. A liquid metal ion emitter and a saddle field ion emitter are nearing the stage of flight unit fabrication. We will attempt to clamp the spacecraft potential to values close to the plasma potential. We present first results from vacuum chamber tests and describe the emission behaviour and characteristics of emitters producing, respectively, In⁺ and N₂⁺ beams with an energy of ≥ 5 keV.     

超临界压力RP-3在竖直细圆管内混合对流研究

研究了超临界压力下碳氢燃料航空煤油RP-3在竖直细圆管内混合对流,分析了浮升力及热物性对碳氢燃料在垂直管中对流换热的影响。实验中控制热流密度从200~500 kW/m2变化,进口压力变化范围为3~5 MPa,进口雷诺数从5 000~10 500范围内变化。研究表明:在向上流动情况中进口段存在较为明显的入口效应,换热出现恶化现象,而在向下流动中未出现;对于向上和向下流动,由于热物性的综合影响,换热系数沿流动方向增大;在较低进口雷诺数(Re=5 700)时,对于向下流动,随着浮升力影响的增大,浮升力改变了流体径向速度分布,出现了换热强化;在较高进口雷诺数(Re=10 500)时,浮升力对换热的影响依然显著;判别式Bo*数小于5.6×10-7未能预测浮升力对碳氢燃料换热影响。      

Estimation of long-term cosmic ray intensity variation in near future and prediction of their contribution in expected global climate change

On the basis of results obtained in our paper [Dorman, L.I. Long-term cosmic ray intensity variation and part of global climate change, controlled by solar activity through cosmic rays, Paper D2.1/C2.2/E3.1-0097-04. Adv. Space Res., 2004 (accepted)], we determine: the dimension of the Heliosphere (modulation region), radial diffusion coefficient and other parameters of convection–diffusion; drift mechanisms of long-term variations of cosmic ray (CR) dependence on particle energy; level of solar activity (SA); and generally, the solar magnetic field. We obtain this important information on the basis of CR and SA data in the past, taking into account the theory of convection–diffusion and global drift modulation of galactic CR in the Heliosphere. By using these results and other regularly published predictions of expected SA variation in the near future, as well as predictions of the next SA cycle, we may make predictions of long-term cosmic ray intensity variation expected in the near future (up to 10–12 years). In [Dorman, L.I. Long-term cosmic ray intensity variation and part of global climate change, controlled by solar activity through cosmic rays, Paper D2.1/C2.2/E3.1-0097-04. Adv. Space Res., 2004 (accepted)], properties of connections between long-term variation in CR intensity and some part of a global climate change were estimated, controlled by solar activity through CR. We show that in this way we may make predictions of some part of a global climate change expected in the near future (up to 10–12 years and maybe more, depending upon the period during which definite predictions of SA can be made), controlled by solar activity through CR. In this case, estimations of expected long-term changes in the planetary distribution of cutoff rigidities, which also influence CR intensity, as well as CR-influenced effects on global climate variation, become important.     

Uncertainties in the production and propagation of cosmic rays in the Milky Way

We discuss the main sources of uncertainties in the calculation of the positron and antiproton top of the atmosphere spectra using models including diffusion and convection or reacceleration. We show that, even including uncertainties, the models that include diffusion and convection are more consistent with existing measurements. The next generation experiments like PAMELA will help to reduce the uncertainties in the values of the main free parameters of the models, thus improving our knowledge of the origin and propagation of cosmic rays.     

The magnitude of thermocapillary convection in larger melt volumes

Thermocapillary convection (TC) has been studied experimentally in a NaNO₃-melt of some cm³ volume. TC has been identified, its streamlines and flow velocities have been visualized and measured. TC dominated over natural convection in this ground based experiment and will be a very significant flow phenomenon in the relevant μ-g materials science experiments with melts with free surfaces. The sensitivity of TC to surface perturbations is pointed out. TC is very difficult to control.     

Studies of the configuration of the Venus ionospheric magnetic field

The dayside ionospheric magnetic field of Venus has been modelled from two different points of view. The Cloutier et al. electrodynamic model makes specific predictions about the behavior of the global magnetic field configuration that can be compared with those expected from the alternate diffusion/convection model. Although the diffusion/convection model is currently only one-dimensional, it is found that it is consistent with the observations in several areas where the 3-dimensional electrodynamic model is not.