共查询到20条相似文献,搜索用时 15 毫秒
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B. I. Renznikov Yu. P. Golovachov A. A. Schmidt M. S. Ivanov A. N. Kudryavtsev 《Technical Physics》2006,51(3):322-329
The flow of a thin liquid film over the nozzle wall under the action of tangential friction and pressure gradient is considered. For the slow flow of the film with constant thermal physical properties, analytical dependences of the film thickness and temperature at the interface on the coordinate along the nozzle edge are derived. The flow of the film over the variable-curvature nozzle edge when the gas expands into vacuum is considered. At the initial section of the curvilinear edge, the film thickness increases in inverse proportion to the root of the friction stress at the interface. Near the end point of the nozzle, the film thickens drastically because of a decrease in the friction and, consequently, the curvature of the interface diminishes. As a result, the deceleration of the liquid by the Laplace pressure gradient drops, which causes an additional sharp growth of the thickness of the film with the possibility of its dynamic and thermal disintegration and, eventually, contamination of the spacecraft surface. 相似文献
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《中国物理快报》2017,(8)
Deformation of water drops in shock-induced high-speed flows is investigated with a focus to the influence of primitive flow parameters on the rear-surface deformation features. Two typical deformation patterns are discovered through high-speed photography. A simple equation to evaluate the radial acceleration of the drop surface is derived. The combined use of this equation ancd outer flow siimulation makes it possible for us to reconstruct the profiles of the early deformed drops. The results agree well with the experiments. Further analysis shows that the duration of flow establishment with respect to the overall breakup time shapes the rear side profile of the drop. Thereby the ratio of the two times, expressed as the square root of the density ratio, appears to be an effective indicator of the deformation features. 相似文献
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在蒸汽爆炸的粗混合过程中,由于液体的快速蒸发,高温金属液滴的周围会产生一层很薄的蒸汽膜,此时液滴周围的边界层流动与没有液体蒸发时有很大的不同,因此,常温情况下的小球在连续液体中运动时的通用阻力模型在这种情况下是不适用的.本文通过受力分析,考虑了高温小球受力的分布和表面蒸发对小球周围力的影响,从阻力的基本机理上分析了蒸发状态下小球的运动阻力,分别提出了高温颗粒穿过自由表面时与其在液体中运动时的蒸发阻力模型.分析表明,当小球温度高于2500 K,特别是在靠近自由表面的区域,由于小球表面液体蒸发而产生的蒸发阻力作用非常明显.分析指出,小球的入水初速、小球表面的液体蒸发速率以及汽膜厚度都是影响小球运动阻力大小的重要因素. 相似文献
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《Revue Generale de Thermique》1997,36(9):672-681
The destabilization of a thin film by gravity is of central importance in many industrial devices, especially those involved in Thermics (film boiling, heat exchangers). In the simplest case of a liquid film hanging below a solid ceiling, spatial structures are forced by the destabilizing action of gravity (Rayleigh-Taylor instability): one observes regular lattices of pendant drops, that in turn become instable by coalescences and falling of the drops. When the film is supplied with liquid at a constant rate, other flow regimes are observed: periodic emission of drops, formation of regular arrays of liquid columns, liquid sheet. Liquid columns exhibit a collective dynamics that is typical of non-linear systems: modulations of their spatial periodicity, diffusion of the perturbations, self-sustained oscillations, propagation of solitary dilation waves, coalescences and nucleations of the columns, etc. 相似文献
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The preparation and evaluation of graded multilayer ta-C films deposited by FCVA method 总被引:1,自引:0,他引:1
Gui-Gen Wang Hua-Yu ZhangWen-Yan Li Fang-Xu YangLin Cui Hong-Bo ZuoJie-Cai Han 《Applied Surface Science》2011,257(11):5064-5069
In this study, a series of graded multilayer ta-C films were investigated by varying their sublayer thickness ratios, in which each film sublayer was prepared at different substrate bias by filtered cathode vacuum arc (FCVA) method. The experimental results show that the graded multilayer film structure can effectively decrease the internal stress level of deposited ta-C film, and meanwhile the graded multilayer ta-C films still have high sp3 fractions. The applied substrate bias voltage and sublayer thickness ratio can apparently influence the microstructure characteristics and internal stress of the graded multilayer ta-C films. The graded multilayer ta-C film has larger sp3 fraction when applying a larger negative substrate bias voltage and having a thicker outer sublayer during the film deposition process. However, the internal stress in the as-deposited film also increases with larger thickness of the outer sublayer, and the optimal ratio of sublayer thicknesses is 1:1:1:1 for graded ta-C film with four sublayers. 相似文献
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In a range of plastic deformation, the flow stress drop and the stress relaxation of Co and Fe single crystals are observed under an a.c. magnetic field. The magnitude of these drops is discussed on the basis of different deformation modes due to the crystal structure. 相似文献
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Z. Rozynek P. Dommersnes A. Mikkelsen L. Michels J. O. Fossum 《The European physical journal. Special topics》2014,223(9):1859-1867
Particles can adsorb strongly at liquid interfaces due to capillary forces, which in practice can confine the particles to the interface. Here we investigate the electrohydrodynamic flow driven packing and deformation of colloidal particle layers confined at the surface of liquid drops. The electrohydrodynamic flow has a stagnation point at the drop equator, leading to assembly of particles in a ribbon shaped film. The flow is entirely controlled by the electric field, and we demonstrate that AC fields can be used to induce hydrodynamic “shaking” of the colloidal particle film. We find that the mechanical properties of the film is highly dependent on the particles: monodisperse polystyrene beads form packed granular monolayers which “liquefies” upon shaking, whereas clay mineral particles form cohesive films that fracture upon shaking. The results are expected to be relevant for understanding the mechanics and rheology of particle stabilized emulsions. 相似文献
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针对含不溶性活性剂的垂直液膜排液过程,基于文献实验结果进一步完善了受活性剂浓度影响的分离压(disjoining pressure)模型,应用润滑理论建立了液膜厚度、活性剂浓度和液膜表面速度的演化方程组,通过数值计算分析了在不同分离压作用下含不溶性活性剂液膜的演化特征.结果表明,垂直液膜的排液过程通常经历两个阶段:首先是厚膜阶段,此时重力对排液过程起主导作用.在随后的薄膜阶段,毛细作用和分离压作用影响逐渐增大,其中分离压将控制液膜的演化历程.分离压对垂直液膜排液过程的影响与活性剂类型及活性剂浓度与静电作用力的关联强度密切相关.当分离压与活性剂浓度正相关时,随斥力关联系数α增大,液膜的排液和变薄过程得以减缓,由此增强了液膜稳定性;当分离压与活性剂浓度负相关时,随斥力关联系数α绝对值增大,液膜排液过程加速,由此加大液膜失稳的风险. 相似文献
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V. M. Korovin 《Technical Physics》2008,53(5):554-561
The subject of consideration is a film of a magnetic fluid applied on the surface of a thin magnetically soft cylinder. Quantities figuring in equations and boundary conditions describing the axisymmetric flow due to capillary and magnetic forces at capillary disintegration of the film are estimated in order of magnitude. The effect of magnetization on the capillary disintegration of the film is studied using simplified equations of ferrohydrodynamics. It is shown that magnetization shifts the range of Rayleigh capillary instability toward longer wave modes. As a result, drops arising at the final stage are larger than in the case of the nonmagnetic liquid. 相似文献
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We report on experimental measurements of the flow behavior of a wet, two-dimensional foam under conditions of slow, steady shear. The initial response of the foam is elastic. Above the yield strain, the foam begins to flow. The flow consists of irregular intervals of elastic stretch followed by sudden reductions of the stress, i.e., stress drops. We report on the distribution of the stress drops as a function of the applied shear rate. We also comment on our results in the context of various two-dimensional models of foams. 相似文献
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螺旋管内气液固三相流颗粒相分布规律 总被引:3,自引:0,他引:3
为了深入认识螺旋管多相流相分离现象,并为新型螺旋管除砂器设计提供指导,本文应用马尔文粒度仪,测量了螺旋管气水砂三相流底部水平段液膜中的颗粒浓度和粒度分布。研究表明:在泡状流和分层流条件下,螺旋管底部水平段可形成稳定的连续液膜流动;在宽广的气速范围内,液膜中的颗粒浓度分布规律均为内弯侧较低、外弯侧较高,说明螺旋管除砂器对于实际生产中流动工况的变化具有良好的适应性;泡状流中提高气速有利于分离;分层流中在中等气速条件下外弯侧颗粒浓度最大,中等气速是相分离的最佳操作工况。 相似文献
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Cylindrical liquid jets are inherently unstable and eventually break into drops due to the Rayleigh-Plateau instability, characterized by the growth of disturbances that are either convective or absolute in nature. Convective instabilities grow in amplitude as they are swept along by the flow, while absolute instabilities are disturbances that grow at a fixed spatial location. Liquid jets are nearly always convectively unstable. Here we show that two-phase jets can breakup due to an absolute instability that depends on the capillary number of the outer liquid, provided the Weber number of the inner liquid is >O(1). We verify our experimental observations with a linear stability analysis. 相似文献
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A high-resolution particle image velocimetry was used to characterize a low Reynolds number turbulent flow in a channel. Experiments were conducted over a sand grain-coated surface of large relative roughness, and the results were compared with measurements over a smooth surface. The roughness perturbation significantly modified the outer layer. Even though the streamwise Reynolds stress shows less sensitivity in the outer layer to the boundary condition, significant enhancements were observed in the wall-normal Reynolds stress and the Reynolds shear stress. These modifications were considered as footprints of the larger-scale eddies transporting intense wall-normal motions away from the rough wall. A quadrant decomposition shows that strong and more frequent ejections are responsible for the larger values of the mean Reynolds shear stress over the rough wall. The results also indicate that spanwise vortex cores with mean vorticity of the same sign as the mean shear are the dominant smaller-scale vortical structures over the smooth and rough walls. A linear stochastic estimation-based analysis shows that the average larger-scale structure associated with these vortices is a shear layer that strongly connects the outer layer flow to the near-wall flow. A proper orthogonal decomposition of the flow suggests that the large-scale eddy is more energetic for the rough wall, and contributes more significantly to the resolved turbulent kinetic energy and the Reynolds shear stress than the smooth wall. 相似文献
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Mietus WG Matar OK Seevaratnam G Wong A Briscoe BJ Lawrence CJ 《Physical review letters》2001,86(7):1211-1214
We describe the direct observation of deforming water drops in oil undergoing shear flow in a horizontal annular Couette cell. The drops assume a wide variety of highly reproducible structures depending on drop size, rotation speed, and flow history. These structures include toroidal rings of water around the rotating shaft and water sheaths, which, depending on experimental conditions, can either expand to press against the inner walls of the outer stationary cylinder or contract to hug the outside of the rotating shaft. 相似文献
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Results are reported on a combined experimental and numerical investigation of a free surface flow at small Reynolds numbers. The flow is driven by the rotation of the inner of two horizontal concentric cylinders, with an inner to outer radius ratio of 0.43. The outer cylinder is stationary. The annular gap is partially filled, from 0.5 to 0.95 full, with a viscous liquid leaving a free surface. When the fraction of the annular volume filled by liquid is 0.5, a thin liquid film covers the rotating inner cylinder and reenters the liquid pool. For relatively low rotation speeds, the evolution of the film thickness is consistent with the theory for a plate being withdrawn from an infinite liquid pool. The overall liquid flow pattern at this condition consists of two counter-rotating cells: one is around the inner cylinder and the other with weaker circulation rate is in the bottom part of the annulus and nearly symmetric about the vertical axis. With increasing rotation rate, the free surface becomes more deformed, and the dynamics of the stagnation line and the cusp line dividing the cells are tracked as quantitative measures of the interface shape. In addition, the recirculating flow cells lose symmetry and the cusp deforms the free surface severely. A comparison of numerically computed flow which describes the interface by a phase-field method confirms the dynamics of the two cells and the interface deformation. For filling fraction 0.75, the liquid level is slightly above the inner cylinder and a significant decrease in size of the bottom cell with increasing rotation rate is found. For filling fractions approaching unity, the liquid flow consists of one single cell and the surface deformation remains small. 相似文献