共查询到20条相似文献,搜索用时 31 毫秒
1.
Saint-Jalmes A Marze S Ritacco H Langevin D Bail S Dubail J Guingot L Roux G Sung P Tosini L 《Physical review letters》2007,98(5):058303
We report the results of fluid transport experiments in aqueous foams under microgravity. Using optical and electrical methods, the capillary motion of the foam fluid and the local liquid fractions are monitored. We show that foams can be continuously wetted up to high liquid fractions ( approximately 0.3), without any bubble motion instabilities. Data are compared to drainage models: For liquid fractions above 0.2, discrepancies are found and identified. These new results on foam hydrodynamics and structure can be useful for other poroelastic materials, such as plants and biological tissues. 相似文献
2.
A. A. Lobykin 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2009,3(1):154-160
It is shown that none of the domestic spacecrafts on which microgravity experiments can be performed satisfy the requirements for experiments on the physics of liquid and space materials science by the level of their onboard microgravity environment. The necessary level of microgravity environment for such experiments is ~10?7 g 0. Procedures for decreasing the microgravity onboard a prospective spacecraft intended for microgravity studies to a level necessary level are proposed. 相似文献
3.
We observed particles of different density ratio α = ρ
p
/ρ
f
in thermocapillary liquid bridges with steady and with time-dependent flow under normal- and under microgravity. Particle
accumulation structures (PAS) visualize some features of the hydrothermal wave in the liquid bridge. Relatively fast formation
of PAS from particles which are considerably less dense than the fluid (α = 0.42) in oscillatory thermocapillary flow of top-heated
liquid bridges was observed and explained by an additional buoyancy-assisted mechanism which brings the particles into the
surface flow. This PAS from particles with α = 0.42 will persist under normal gravity for infinite time. In contrast to these
less dense particles the heavier particles with α > 1 settle down under normal gravity on the lower end face of the liquid
bridge after some time and are no longer in suspension and PAS will fade out. On the other hand, particles with α = 0.42 will
be less suited for experiments under microgravity than particles with α > 1 because most of them will be trapped in the vortex
centre of the thermocapillary flow. The sedimented particles with α > 1 are a means to visualize some features of standing
hydrothermal waves which are visualzed and discussed for the first time. 相似文献
4.
O. S. Vaulina A. P. Nefedov O. F. Petrov V. E. Fortov 《Journal of Experimental and Theoretical Physics》2001,92(6):979-985
The paper deals with the results of experimental investigation of the dynamic behavior of macroparticles charged by way of photoemission, under conditions of microgravity. The experimental data have been obtained for bronze particles subjected to solar radiation in a buffer gas at a pressure of 40 Torr (Mir space station). Different procedures for determining the transport properties of macroparticles by analyzing video records of experiments are treated. The velocity distribution, the temperature, the charge, the friction coefficient, and the dust particle diffusion coefficients are found. The results of comparing the experimental and theoretical estimates demonstrate that the dynamic behavior of macroparticles under the conditions of investigations are defined by the process of their ambipolar diffusion. 相似文献
5.
6.
L. M. Krutyanskiy F. Zoueshtiagh P. Pernod P. Shirkovskiy A. P. Brysev 《Physics of Wave Phenomena》2017,25(2):151-155
Ultrasonic separation of two immiscible liquids under microgravity conditions has been demonstrated on example of liquid mixtures of FC-70 or FC-72 with silicone oils of 1.5 or 1.0 cSt viscosities, respectively. A 3-MHz focused ultrasound beam was utilized to form an emulsion from these liquid combinations, and a plane wave of the same frequency served to separate (demix) fluids. Droplet deformation under pulsed ultrasound in microgravity conditions is reported, and the observed singular behavior is discussed. 相似文献
7.
By and large the research communities today are not fully aware of the remarkable universality in the dynamic properties of many-body relaxation/diffusion processes manifested in experiments and simulations on condensed matter with diverse chemical compositions and physical structures. I shall demonstrate the universality first from the dynamic processes in glass-forming systems. This is reinforced by strikingly similar properties of different processes in contrasting interacting systems all having nothing to do with glass transition. The examples given here include glass-forming systems of diverse chemical compositions and physical structures, conductivity relaxation of ionic conductors(liquid, glassy, and crystalline),translation and orientation ordered phase of rigid molecule, and polymer chain dynamics. Universality is also found in the change of dynamics when dimension is reduced to nanometer size in widely different systems. The remarkable universality indicates that many-body relaxation/diffusion is governed by fundamental physics to be unveiled. One candidate is classical chaos on which the coupling model is based, Universal properties predicted by this model are in accord with diverse experiments and simulations. 相似文献
8.
Long-duration experiments with clouds of microparticles are planned for the ICAPS facility on board the International Space Station ISS. The scientific objectives of such experiments are widespread and are ranging from the simulation of aerosol behaviour in Earths atmosphere to the formation of planets in the early solar system. It is, however, even under microgravity conditions, impossible to sustain a cloud of free-floating, microscopic particles for an extended period of time, due to thermal diffusion and due to unavoidable external accelerations. Therefore, a trap for dust clouds is required which prevents the diffusion of the particles, which provides a source of relative velocities between the dust grains and which can also concentrate the dust to higher number densities that are otherwise not achievable. We are planning to use the photophoretic effect for such a particle trap. First short-duration microgravity experiments on the photophoretic motion of microscopic particles show that such an optical particle-cloud trap is feasible. First tests of a two-dimensional trap were performed in the Bremen drop tower. 相似文献
9.
This paper presents a precise numerical simulation of the transport processes in a rectangular cavity saturated with a binary liquid mixture. The full transient Navier-Stokes equations coupled with the mass and heat transfer equations are solved, numerically, using the finite-volume method. After validation against a proven commercial code comparing solutions on a benchmark natural convection problem, the newly developed code is used for a series of numerical experiments. Realistic thermal boundary conditions have been chosen, and the more drastic situation of power loss while conducting the experiment in microgravity is considered. The molecular and thermal diffusion coefficients are computed from theoretical models. Results reveal that, when vertical walls are held at constant but different temperatures, species separate in both the longitudinal and the transverse directions as radiation is allowed to take place along the horizontal walls. The numerical experiments performed clearly demonstrate that the kinetics of the mass transport in the mixture are conditioned by the ability to monitor the heat sources properly. Specifically, sudden temperature changes strongly disturb species separation in the experimental cells. This paper provides some trends for the accurate analysis of experiments involving mass transport inasmuch as the convective level is low enough to allow evaluation of the transport coefficients. 相似文献
10.
Ivlev AV Kretschmer M Zuzic M Morfill GE Rothermel H Thomas HM Fortov VE Molotkov VI Nefedov AP Lipaev AM Petrov OF Baturin YM Ivanov AI Goree J 《Physical review letters》2003,90(5):055003
The first experiment on the decharging of a complex plasma in microgravity conditions was conducted. After switching off the rf power, in the afterglow plasma, ions and electrons rapidly recombine and leave a cloud of charged microparticles. Because of microgravity, the particles remain suspended in the experimental chamber for a sufficiently long time, allowing precise measurements of the rest particle charge. A simple theoretical model for the decharging is proposed which agrees quite well with the experiment results and predicts the rest charge at lower gas pressures. 相似文献
11.
利用落塔的短时微重力条件, 实验研究了与容器连通的毛细管中的流体在微重力条件下的毛细流动过程, 并通过理论分析建立了相应的毛细管中弯月液面高度随时间变化的微分方程. 结果表明, 对于不同的接触角和不同的容器/毛细管参数, 由建立的理论公式得到的数值解结果都与实验结果在定量上较为一致. 此外, 实验中发现, 改变乙醇和去离子水混合液的比例可以明显地改变接触角参数, 但对毛细流动的影响很小, 建立的理论公式也对这一现象给出了合理的解释. 该研究对于预测和分析微流道及空间微重力条件下的毛细流动行为具有明显的应用价值. 相似文献
12.
Lipaev AM Khrapak SA Molotkov VI Morfill GE Fortov VE Ivlev AV Thomas HM Khrapak AG Naumkin VN Ivanov AI Tretschev SE Padalka GI 《Physical review letters》2007,98(26):265006
We describe the first observation of a void closure in complex plasma experiments under microgravity conditions performed with the Plasma-Kristall (PKE-Nefedov) facility on board the International Space Station. The void--a grain-free region in the central part of the discharge where the complex plasma is generated--has been formed under most of the plasma conditions and thought to be an inevitable effect. However, we demonstrate in this Letter that an appropriate tune of the discharge parameters allows the void to close. This experimental achievement along with its theoretical interpretation opens new perspectives in engineering new experiments with large quasi-isotropic void-free complex plasma clouds in microgravity conditions. 相似文献
13.
Armin Veshkini 《Combustion Theory and Modelling》2017,21(5):864-878
A numerical study is conducted of methane–air coflow diffusion flames at microgravity (μg) and normal gravity (1g), and comparisons are made with experimental data in the literature. The model employed uses a detailed gas phase chemical kinetic mechanism that includes PAH formation and growth, and is coupled to a sectional soot particle dynamics model. The model is able to accurately predict the trends observed experimentally with reduction of gravity without any tuning of the model for different flames. The microgravity sooting flames were found to have lower temperatures and higher volume fraction than their normal gravity counterparts. In the absence of gravity, the flame radii increase due to elimination of buoyance forces and reduction of flow velocity, which is consistent with experimental observations. Soot formation along the wings is seen to be surface growth dominated, while PAH condensation plays a more major role on centreline soot formation. Surface growth and PAH growth increase in microgravity primarily due to increases in the residence time inside the flame. The rate of increase of surface growth is more significant compared to PAH growth, which causes soot distribution to shift from the centreline of the flame to the wings in microgravity. 相似文献
14.
C. Lämmerzahl I. Ciufolini H. Dittus L. Iorio H. Müller A. Peters E. Samain S. Scheithauer S. Schiller 《General Relativity and Gravitation》2004,36(10):2373-2416
The mission OPTIS aims at improving tests of the foundations of Special and General Relativity by up to three orders of magnitude. The individual tests concern the isotropy and constancy of the speed of light, the time dilation (or Doppler effect), the universality of the gravitational redshift with various combinations of high precision clocks. Furthermore, laser tracking and a laser link allows a strongly improved measurement of the gravitomagnetic Lense–Thirring effect, of the gravitoelectric Einstein perigee advance, of the gravitational redshift, and a search for deviations from Newtonian gravity.For this mission, technologies are required which have been used recently to carry through the most precise tests of Special Relativity. The precision of these tests can be further increased under space conditions thanks to longer integration times, larger changes in the orbital velocity, and larger differences of the gravitational potential. Furthermore, very precise laser tracking and linking of satellites is a well established technique and will provide, in combination with the active drag–free control system, very accurate orbit data. The core technologies for OPTIS are optical cavities, highly stabilized lasers, capacitive gravitational reference sensors, drag–free control, ion clocks, frequency combs, and laser tracking systems. These technologies are also key technologies for other future missions. 相似文献
15.
Klindworth M Piel A Melzer A Konopka U Rothermel H Tarantik K Morfill GE 《Physical review letters》2004,93(19):195002
Dust-free regions around a Langmuir probe are studied in a complex plasma under microgravity. The dust particles settle in the presheath of the probe, where an equilibrium of the electric field force and the ion-drag force is established. The size and shape of the dust cloud are discussed with simple models. A more sophisticated presheath model is solved numerically to analyze the acting forces and the equilibrium position of the dust. The formation of distinct particle layers in the dust shell can be explained by the force gradients of the effective potential well. 相似文献
16.
D. Melnikov D. Pushkin V. Shevtsova 《The European physical journal. Special topics》2011,192(1):29-39
The study addresses the phenomenon of accumulation of rigid tracer particles suspended in a time-dependent thermocapillary
flow in a liquid bridge. We report the results of the three-dimensional numerical modeling of recent experiments [1,2] in
a non-isothermal liquid column. Exact physical properties of both liquids and particles are used for the modeling. Two liquids
are investigated: sodium nitrate (NaNO3) and n-decane (C10H22). The particles are modeled as perfect spheres suspended in already well developed time-dependent thermocapillary flow. The
particle dynamics is described by the Maxey-Riley equation. The results of our simulations are in excellent agreement with
the experimental observations. For the first time we reproduced numerically formation of the particle accumulation structure
(PAS) both under gravity and under weightlessness conditions. Our analysis confirms the experimental observations that the
existence of PAS depends on the strength of the flow field, on the ratio between liquid and particle density, and on the particle
size. 相似文献
17.
A detailed three-dimensional concurrent flame spread model is tested and compared with three sets of experiments. The parameters varied include: gravity, flow velocity, pressure, oxygen mole fraction, and sample width. In buoyant flows (normal and partial gravities), the computed steady spread rate and flame profiles agree favorably with experiment. The predicted extinction limits are lower but can be improved. Comparison in forced concurrent flow in microgravity shows correct trends. The predicted steady spread rates are lower than the experimental ones if the flames are short but higher than the experimental ones if the flames are long. It is believed that the experimental flames may not have fully reached steady state at the end of the 5-s microgravity drops. Longer duration microgravity experiments in future will be needed to substantiate this belief. 相似文献
18.
19.
Reed JA Cook A Halaas DJ Parazzoli P Robinson A Matula TJ Grieser F 《Ultrasonics sonochemistry》2003,10(4-5):285-289
A solution of gold chloride was reduced using ultrasound irradiation to prepare metallic gold nanoparticles under conditions of microgravity and normal gravity at sea level. Particle size distributions were measured using TEM analysis. A mean particle diameter of 10 nm was obtained in microgravity while a mean diameter of 80 nm was obtained in the laboratory. Absorbance measurements on the reacted solution found an enhanced reduction rate in the reduction of gold chloride in microgravity compared to that in the laboratory. 相似文献
20.
A. V. Filippov V. E. Fortov A. F. Pal’ A. N. Starostin 《Journal of Experimental and Theoretical Physics》2003,96(4):684-694
The decay of a dusty plasma in a photoemission cell under microgravity conditions is investigated on the basis of the method of nonlocal moments. It is founds that plasma decay in space experiments occurs in accordance with the mechanism of free electron diffusion followed by dust particle drift. An analytic solution is found for the evolution of radial distributions of the dust particle concentration and the electric field under the experimental conditions. The effect of abnormally high temperatures of dust particles is considered. The effect of axial magnetic fields on the decay of dusty plasma is investigated. It is shown that the plasma decay in a magnetic field is governed by the ambipolar diffusion mechanism, the decay being prolonged up to 103 s in a magnetic field on the order of 103–104 G in strength. 相似文献