One-dimensional model and solutions for creeping gas flows in the approximation of uniform pressure

A model, along with analytical and numerical solutions, is presented to describe a wide variety of one-dimensional slow flows of compressible heat-conductive fluids. The model is based on the approximation of uniform pressure valid for the flows, in which the sound propagation time is much shorter than the duration of any meaningful density variation in the system. The energy balance is described by the heat equation that is solved independently. This approach enables the explicit solution for the fluid velocity to be obtained. Interfacial and volumetric heat and mass sources as well as boundary motion are considered as possible sources of density variation in the fluid. A set of particular tasks is analyzed for different motion sources in planar, axial, and central symmetries in the quasistationary limit of heat conduction (i.e. for large Fourier number). The analytical solutions are in excellent agreement with corresponding numerical solutions of the whole system of the Navier-Stokes equations. This work deals with the ideal gas. The approach is also valid for other equations of state.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

On the way of detecting the negative thermophoresis: results of microgravity experiments and gas-kinetic analysis

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Experimental study of thermophoresis of aerosol particles under microgravity conditions

Experimental estimations of thermophoretic velocity of spherical copper particles in nitrogen measured in microgravity conditions at the Bremen drop tower (Germany) at very low values of the Knudsen number (Kn ≈ 0.002) and very high thermal-conductivity parameter Λ ≈ 20 500 are presented. Comparison of the obtained data with the gas-kinetic theory, taking into account both thermal-creep flow and thermal-stress slip flow mechanisms of thermophoresis is carried out. The obtained results demonstrate indirectly the action of the thermal stress slip flow mechanism, however, negative thermophoretic velocities have not been recorded. The important role of energy accommodation coefficient for gas molecules on the particle surface for explanation of the obtained results is discussed. An additional analysis of experimental data is necessary, aiming at the increase of reliability of thermophoretic velocity estimates.info:eu-repo/semantics/publishe

Micro-vélocimétrie 3D par holographie digitale

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Use of inert immiscible liquid for crystal separation out of its feeding solution in weightlessness

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Cloud manipulation system: Thermal characterization and drop tower experiment

Cloud Manipulation System is developed in the framework of the scientific program Interaction in Cosmic and Atmospheric Particle Systems (ICAPS) of the European Space Agency. The project is aimed at investigation of dust agglomeration in the conditions related to astrophysical processes. The cloud manipulation system should provide 1) high enough particle collision rate to get extended clusters and to observe cluster-cluster agglomeration, 2) possibility to deliver a chosen clusters to the observation volume of high resolution optics for the in situ detailed analysis, 3) varying in time and space forces for the investigation of particle transport phenomena and dust cloud dynamics in microgravity conditions. Thermophoresis have been chosen as the main driving force. Development of thermophoretic Cloud Manipulation System required considerable advancement in realization of thermoelectric temperature variators, modeling of thermophoretic dynamic balance, characterization of system thermal parameters. Tests in short duration microgravity conditions of the Bremen drop tower successfully demonstrated main functions, i.e. cloud squeezing and positioning, and proved feasibility of the system development for long duration microgravity missions. Copyright © (2012) by the International Astronautical Federation.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Dust in space

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Viscous fingering in miscible liquids under Microgravity conditions

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Results and perspectives of the investigation of traditional and thermal stress induced thermophoresis of particles in gas in microgravity

Thermophoretic motion of particles suspended in a gas has been a subject of extensive theoretical and experimental investigations for many years because of its wide spread in nature, significance for fundamental and applied aerosol physic. Negative thermophoresis, i.e. solid particle motion towards hotter region in a gas and not as usually from hotter region, was predicted more than 40 years ago and remains an unsolved problem for a choice between different models treating main driving mechanisms -- thermal slip and thermal stress induced gas motion. For a problem of negative thermophoresis, we present experimental evidences in favor of the latter mechanism based on direct observation of particle motion at microgravity; Knudsen particle number 2\cdot 10(-3) (Kn being the ratio of the molecular mean free path to the particle size); particle-to-gas heat conductivity ratios 2\cdot 10(4) for copper solid particles and 1.8 for glass bubbles. For both types of particles the experimental results fit well the gas kinetic model of Beresnev and Chernyak [1]. We present characteristics of a set-up and procedures that are able to provide sufficient accuracy and volume of experimental data for testing any model of particle thermophoresis. High quality microgravity is a necessity for such investigations. The short duration microgravity of drop towers suits well this requirement. The sign and value of the thermophoretic force strongly depends on the Knudsen number, particle-to-gas heat conductivity ratio and accommodation coefficients, all of which vary within several decimal orders of magnitude. In order to make crucial conclusions on the choice of the adequate model, there should be hundreds of short duration microgravity experiments. The European Space Agency scientific project Interaction in Cosmic and Atmospheric Particle Systems (ICAPS) [2] planned for the International Space Station, provides complementary opportunities for the investigation of thermophoresis at large and very large Knudsen numbers for single particles and large clusters of particles under wide range of experimental parameters, i.e. different particle sizes, shapes, materials; different properties of gases; several types of additional forces and their time-space variation. ESA PRODEX Program, Belgian Federal Science Policy Office and Bremen Drop Tower Operation and Service Company ZARM FABmbH (Germany) are greatly acknowledged for their support. [1] Beresnev S. Chernyak V. Thermophoresis of a spherical particle in a rarefied gas: Numerical analysis based on the model kinetic equations // Phys. Fluids. 1995. V.7. P.1743. [2] Blum, J. et al. "Dust in Space", Europhysicsnews, Vol. 39, pp. 27-29, 2008.info:eu-repo/semantics/nonPublishe

Observation of macroscopic aerosol motion due to thermal creep on chamber walls at low Knudsen number in microgravity

In a rarefied gas the temperature field and the gas motion are closely related, and the temperature field can cause, in a confined flow geometry, a steady flow without the help of external forces. This is due to the creep of the fluid along the walls induced by a wall temperature gradient, as a consequence of the molecular transfer of momentum to the wall. Experiments performed in microgravity conditions in two small cells, with mono- and bi-atomic carrier gases (Ar, N2), and a thermal gradient between upper and bottom horizontal plates, allowed the measurement of the width of the thermal creep and the induced velocity of the gas near the vertical cell wall, due to thermal gradient. In addition, experiments demonstrated the existence of the thermal creep flow in the cells, even with Knudsen number as low as 10-5. The work evidences experimentally, and for the first time, the thermal creep flow in small cells, due to wall temperature gradient, with Knudsen number as low as 10-5. In view of these results, the no-slip boundary conditions of the Navier-Stokes law in the "continuum" regime can be inadequate in non-isothermal flow geometry and in microgravity conditions. © 2014 Elsevier Inc.SCOPUS: ar.jinfo:eu-repo/semantics/publishe