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1.
A numerical study on the interaction of two spherical drops in the thermocapillary migration is presented in the microgravity environment. Finite-difference methods are adopted. The interfaces of the drops are captured by the front-tracking technique. It is found that the arrangement of the drops directly influences their migration and interaction, and the motion of one drop is mainly determined by the disturbed temperature field because of the existence of the other drop. 相似文献
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The unsteady double diffusion of the boundary layer with the nanofluid flow near a three-dimensional(3 D) stagnation point body is studied under a microgravity environment. The effects of g-jitter and thermal radiation exist under the microgravity environment, where there is a gravitational field with fluctuations. The flow problem is mathematically formulated into a system of equations derived from the physical laws and principles under the no-slip boundary condition. With the semi-similar tran... 相似文献
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束继祖 《Acta Mechanica Sinica》2003,19(2):127-133
In the present paper, the experimental studies on thermocapillary convection are reviewed. The author‘s interest is mainly focused on the onset of oscillatory thermocapillary convection,the features of oscillatory flow pattern, and the critical Marangoni number related with temperature and free surface oscillation. The coordinated measurement in a microgravity environment of a drops haft is also addressed. 相似文献
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Researches on two-phase flow and pool boiling heat transfer in microgravity, which included ground-based tests, flight experiments, and theoretical analyses, were conducted in the National Microgravity Laboratory/CAS. A semi-theoretical Weber number model was proposed to predict the slug-to-annular flow transition of two-phase gas–liquid flows in microgravity, while the influence of the initial bubble size on the bubble-to-slug flow transition was investigated numerically using the Monte Carlo method. Two-phase flow pattern maps in microgravity were obtained in the experiments both aboard the Russian space station Mir and aboard IL-76 reduced gravity airplane. Mini-scale modeling was also used to simulate the behavior of microgravity two-phase flow on the ground. Pressure drops of two-phase flow in microgravity were also measured experimentally and correlated successfully based on its characteristics. Two space experiments on pool boiling phenomena in microgravity were performed aboard the Chinese recoverable satellites. Steady pool boiling of R113 on a thin wire with a temperature-controlled heating method was studied aboard RS-22, while quasi-steady pool boiling of FC-72 on a plate was studied aboard SJ-8. Ground-based experiments were also performed both in normal gravity and in short-term microgravity in the drop tower Beijing. Only slight enhancement of heat transfer was observed in the wire case, while enhancement in low heat flux and deterioration in high heat flux were observed in the plate case. Lateral motions of vapor bubbles were observed before their departure in microgravity. The relationship between bubble behavior and heat transfer on plate was analyzed. A semi-theoretical model was also proposed for predicting the bubble departure diameter during pool boiling on wires. The results obtained here are intended to become a powerful aid for further investigation in the present discipline and development of two-phase systems for space applications. 相似文献
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微重力气液两相流动与池沸腾传热 总被引:1,自引:0,他引:1
综述了近年来中国科学院微重力重点实验室(国家微重力实验室)完成的一系列微重力气液两相流动与池沸腾传热方面的地基实验、飞行实验和理论研究等方面获得的主要成果.在微重力气液两相流动方面,提出了半理论Weber数模型用于预测微重力条件下气液两相弹-环状流转换,并采用Monte Carlo方法,针对气泡初始尺寸对泡-弹状流转换的影响进行数值研究.通过俄罗斯"和平号"空间站与IL-76失重飞机实验,获得了微重力下的气液两相流型图,与此同时在地面利用小尺度毛细管模型模拟了微重力气液两相流动特征.实验测量了微重力气液两相流压降,并基于微重力流动特性建立了一个泡状流压降关联模型.在微重力池沸腾传热方面,利用我国返回式卫星完成了两次空间实验,其中,第22颗返回式卫星搭载铂丝表面R113池沸腾实验采用控制温度的稳态加热方式,而实践8号育种卫星搭载平面FC-72池沸腾实验则采用控制加热电压的准稳态加热方式.同时,还进行了地面常重力和落塔短时微重力条件下的对比实验研究.观察到丝状加热表面微重力时轻微的传热强化现象,而平板加热表面微重力核态池沸腾低热流时传热强化、高热流时传热恶化.微重力实验中观察到气泡脱落前存在横向运动现象,据此分析了气泡行为与传热之间关系,并提出了一个预测丝状加热表面气泡脱落直径的半理论模型.旨在对相关领域的进一步发展和空间两相流系统的应用提供数据及理论支持. 相似文献
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B. Scheid J. Margerit C. S. Iorio L. Joannes M. Heraud P. Queeckers P. C. Dauby P. Colinet 《Experiments in fluids》2012,52(5):1107-1119
The dynamics of thermal ripples at the interface of a volatile pure liquid (C2H5OH) is studied experimentally and numerically. Liquid evaporates under a flow of inert gas (N2) circulating along the interface. The evaporation rate is varied by regulating both the gas flow rate and the gas pressure.
Experiments in microgravity environment allowed to identify a transition to “interfacial turbulence,” along which some particular
events such as nearly periodic and possible intermittent behaviors. Direct numerical simulations have been performed, and
compare qualitatively well with experimental results, offering new insights into the physical mechanisms involved. Small-scale
ripples appear to arise from a secondary instability of large-scale convection cells and their motion seems to follow the
corresponding large-scale surface flow. The relative role of surface tension and buoyancy in triggering these flows is assessed
by comparing experiments and simulations in both microgravity and ground conditions. Qualitative features compare satisfactorily
well such as typical speed and orientation of the thermal ripples, as well as spiral flow in the bulk. 相似文献
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The microporosity formation in a vertical unidirectionally solidifying Al–4.1%Cu alloy casting is modeled in both microgravity
and standard gravity as well as in the conditions of decreased (Moon, Mars) and increased (Jupiter) gravity. Due to the unique
opportunities offered by a low-gravity environment (absence of metallostatic pressure and of natural convection in the solidifying
alloy) future microgravity experiments will significantly contribute to attaining a better physical understanding of the mechanisms
of microporosity formation. One of the aims of the present theoretical investigation is to predict what microporosity patterns
will look like in microgravity in order to help plan a future microgravity experiment. To perform these simulations, the authors
suggest a novel three-phase model of solidification that accounts for the solid, liquid, and gas phases in the mushy zone.
This model accounts for heat transfer, fluid flow, macrosegregation, and microporosity formation in the solidifying alloy.
Special attention is given to the investigation of the influence of microporosity formation on the inverse segregation. Parametric
analyses for different initial hydrogen concentrations and different gravity conditions are carried out.
Received on 14 April 2000 相似文献
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水平井开采石油遇到的几个流体力学问题 总被引:1,自引:0,他引:1
本文从渗流力学和流体动力学方面讨论了利用水平井技术开采石油时在油藏工程和采油工程中遇到的几个力学问题,如水平井产量的计算,水平井非稳态试井及流场分析,水平井井筒内压力降及其对产量的影响、水平井近井油藏和井筒内流体流动耦合等,半提出水平井开采机理仍存在很多基础理论需要研究解决。 相似文献
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The d2-law validity during n-decane droplet vaporization in microgravity environment is examined experimentally. Two sets of experiments are performed, under normal and microgravity, in stagnant hot atmospheric environment. The environment temperature is varied in the range up to 967 K. The droplet is suspended onto the cross point of two micro-fibers of 14 μm in diameter. This technique enables to greatly minimize the effect of fiber on droplet heat and mass transfer. The results show that, for ambient temperatures below approximately 950 K, departure from the d2-law is observed during droplet vaporization in microgravity environment. In addition, the droplet lifetime is longer in microgravity than in normal gravity under the same ambient test conditions. However, for temperatures exceeding approximately 950 K, the experimental results demonstrate that the d2-law holds throughout the entire droplet lifetime, and the mass transfer rate is identical in both microgravity and normal gravity environments. 相似文献
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The mathematical formulation of the Dewar container sloshing dynamics for a partially filled liquid of cryogenic superfluid
helium II driven by the gravity gradient or jitter accelerations associated with slew motion in a microgravity environment
are studied. The numerical computation of sloshing dynamics is based on the non-inertia container bounded frame and the solution
of time-dependent, three-dimensional partial differential equations subjected to the initial and boundary conditions. This
study discloses that the capillary effect of sloshing dynamics governs the liquid-vapor interface fluctuations driven by the
gravity gradient or jitter accelerations associated with slew motion in a microgravity environment. The peculiar behavior
of superfluid helium in response to sloshing dynamics is also investigated. 相似文献
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At liquid–gas or liquid–liquid interfaces thermocapillary or Marangoni convection develops in the presence of a temperature
or concentration gradient along the interface. This convection was not paid much attention up to now, because under terrestrial
conditions it is superimposed by the strong buoyancy convection. In a microgravity environment, however, it is the remaining
mode of natural convection. During boiling in microgravity it was observed at subcooled conditions. Therefore the question
arises about its contribution to the heat transfer. Thus the thermocapillary convection was intensively studied at single
gas bubbles in various liquids both experimentally and numerically. Inside a temperature gradient chamber, the overall heat
transfer around single bubbles of different volume was measured with calorimetry and the liquid flow with PIV and LDV. In
parallel to the experiment, a 2-dimensional mathematical model was worked out and the coupled heat transfer and fluid flow
was simulated with a CV-FEM method both under earth gravity level and under microgravity. The results are described in terms
of the dimensionless Nusselt-, Peclet-, Marangoni-, Bond- and Prandtl-number.
Received on 23 August 1999 相似文献
16.
Mario Minale 《Rheologica Acta》2010,49(8):789-806
Dilute polymer blends and immiscible liquid emulsions are characterized by a globular morphology. The dynamics of a single
drop subjected to an imposed flow field has been considered to be a valuable model system to get information on dilute blends.
This problem has been studied either theoretically by developing exact theories for small drop deformations or by developing
simplified models often based on phenomenological assumptions. In this paper, a critical overview of the available models
for the dynamics of a single drop is presented, discussing four different systems, namely the Newtonian system, where a single
Newtonian drop is immersed in an infinite Newtonian matrix; the non-Newtonian system, where at least one of the components,
the drop fluid or the matrix one, is non-Newtonian; the confined Newtonian system, where the matrix is confined and wall effects
alter the drop dynamics; and the confined non-Newtonian system. 相似文献
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This paper discusses the behavior of g-jitter induced free convection in microgravity under the influence of a transverse
magnetic field and in the presence of heat generation or absorption effects for a simple system consisting of two parallel
impermeable infinite plates held at four different thermal boundary conditions. The governing equations for this problem are
derived on the basis of the balance laws of mass, linear momentum, and energy modified to include the effects of thermal buoyancy,
magnetic field and heat generation or absorption as well as Maxwell's equations. The fluid is assumed to be viscous, Newtonian
and have constant properties except the density in the body force of the balance of linear momentum equation. The governing
equations are solved analytically for the induced velocity and temperature distributions as well as for the electric field
and total current for electrically-conducting and insulating walls. This is done for isothermal–isothermal, isoflux–isothermal,
isothermal–isoflux and isoflux–isoflux thermal boundary conditions. Graphical results for the velocity amplitude and distribution
are presented and discussed for various parametric physical conditions. 相似文献
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液滴热毛细迁移是微重力流体科学中的典型科学问题, 微重力液滴动力学研究不仅具有流体力学的理论意义, 而且具有重要的实际应用价值. 建立了二维轴对称激光驱动液滴迁移模型, 通过仿真计算研究微重力环境下激光驱动液滴迁移的过程, 研究了液滴直径、母液参数等对液滴迁移速度及行为的影响. 首先研究了母液和液滴对激光系数均较小, 液滴初始位置不同时液滴的迁移行为; 然后研究了母液对激光吸收系数较小, 液滴对激光吸收系数较大时, 不同液滴直径与母液宽度比条件下液滴的迁移行为. 仿真结果表明: 当母液和液滴对激光的吸收系数都很小时, 液滴迁移的方向主要受到液滴初始位置的影响; 当母液对激光的吸收系数较小, 液滴对激光的吸收系数较大时, 液滴会朝激光方向迁移, 液滴初始位置对迁移方向影响较小, 但液滴直径与母液宽度之比会影响液滴迁移行为. 将模拟结果与YGB理论对比, 仿真结果与理论结果趋势一致. 研究激光驱动液滴迁移的物理机制, 探索界面张力作用机理, 得到激光驱动液滴迁移的规律, 探索对液滴的驱动控制方法. 相似文献
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The effects of magnetic field on the microgravity combustion characteristics of a single methanol droplet in homogeneous flow
are numerically investigated to develop an effective magnetic control method for microgravity droplet combustion and spray
combustion systems. First, governing equations of microgravity single methanol droplet combustion under a homogeneous magnetic
field based on an unsteady two-dimensional, spherically symmetric model including single-step chemistry are presented. Employing
numerical modeling, several combustion behaviors are calculated taking into account the effect of the unsteady magnetic field
profiles at the flame front. It is found that the flame front becomes deformed and is elongated in the direction of the magnetic
field due to the inhomogeneous magnetic pressure distribution at the interface between the fuel vapor phase and the oxidizer
phase. This nonuniformity of magnetic pressure is caused by the transient deformation of the magnetic field with refraction
of magnetic flux at the flame front due to the difference of magnetic susceptibility between the diamagnetic fuel vapor phase
and the paramagnetic oxidizer phase. 相似文献
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The surface tension driven flow in the liquid vicinity of gas bubbles on a heated solid wall has been investigated both, in
a reduced gravity environment aboard a sounding rocket, and in an earth-bound experiment. Both experiments deal with temperature
gradients within the liquid surrounding of a bubble which cause variations of the surface tension. These, in turn, lead to
a liquid flow around the bubble periphery termed thermocapillary or thermal Marangoni-convection. On Earth, this phenomenon
is widely masked by buoyancy. We therefore carried out an experiment under reduced gravitational acceleration. In order to
simultaneously observe and record the flow field and the temperature field liquid crystal tracers have been applied. These
particles offer the feature of selectively reflecting certain wavelengths of incident white light depending on the crystals
temperature. Although the bubble injection system did not perform nominally during the flight experiment, some interesting
flow characteristics could be observed. Comparison of results obtained in microgravity to data measured on Earth reveal that
due to the interaction of thermocapillarity and buoyancy a very compact vortex flow results on ground, while in microgravity
the influence on the surface tension driven flow penetrates much deeper into the bulk. This result is of special interest
regarding the production of materials in space.
Dedicated to Professor Dr. Julius Siekmann on the occasion of his 70th birthday
The work described herein was supported by the German space agency DARA (Deutsche Agentur für Raumfahrtangelegenheiten GmbH)
through DARA Grant 50 WM 9434. The authors thank the European Space Agency (ESA) for the opportunity to conduct the TEXUS
33 sounding rocket experiment. The flight hardware has been partly built by Daimler-Benz-Aerospace which is gratefully acknowledged.
Also, the authors are indebted to Mr. H.-H. Wolf for his careful evaluation of the particle images 相似文献