共查询到20条相似文献,搜索用时 15 毫秒
1.
T. A. Yakhno O. A. Sanina M. G. Volovik A. G. Sanin V. G. Yakhno 《Technical Physics》2012,57(7):915-922
The temperature field distribution at the liquid-air interface in drops of water and water solutions drying on a glass substrate is studied with thermal imaging means. It is shown that irrespective of the liquid composition, the circumferential temperature of the drops (along the boundary line) is always higher than the temperature on the top. The temperature field on the surface of the drops is nonstationary and varies chaotically during water evaporation. It is found that the dynamics of histograms for albumin-containing and albumin-free liquids differ. Mechanisms behind the origination of thermocapillary liquid flows and their directivity in the drying drops are discussed. 相似文献
2.
The flow of drops suspended on an inclined surface, are studied by numerical simulations at finite Reynolds numbers. The flow is driven by the acceleration due to gravity, and there is no pressure gradient in the flow direction. The effect of the Reynolds number, the Capillary number and density ratio on the distribution of drops and the fluctuation energy across the channel are investigated. It is found that drops tend to stay away from the channel floor, which is consistent with the behavior observed in the granular flow regime. Drops that are less deformable will stay further away from the channel floor. Also, drops appear at a larger distance from the floor as the Reynolds number increases. Simulations at large density ratios show that results are more compatible with computer simulations of granular flows. The behavior observed here resembles more the granular flow regime when the restitution coefficient is low. 相似文献
3.
It is widely accepted that the frictional pressure drop is impossible to be negative for pipe flow. However, the negative frictional pressure drops were observed for some cases of two-phase slug and churn flows in pipes, challenging the general sense of thermodynamic irreversibility. In order to solve this puzzling problem, theoretical investigations were performed for the entropy generation in slug and churn flows. It is found that the frictional pressure drop along with a buoyancy-like term contributes to the entropy generation due to mechanical energy loss for steady, incompressible slug and churn flows in vertical and inclined pipes. Experiments were conducted in a vertical pipe with diameter as 0.04 m for slug and churn flows. Most of the experimental data obtained for frictional pressure drop are negative at high gas–liquid ratios from 100 to 10,000. Entropy generation rates were calculated from experimental data. The results show that the buoyancy-like term is positive and responsible for a major part of entropy generation rate while the frictional pressure drop is responsible for a little part of entropy generation rate, because of which the overall entropy generation due to mechanical energy loss is still positive even if the frictional pressure drop is negative in vertical slug and churn flows. It is clear that the negative frictional pressure drops observed in slug and churn flows are not against the thermodynamics irreversibility. 相似文献
4.
液滴碰撞聚合是气体/液滴两相流动中的重要现象.为研究碰撞聚合引起的液滴数目变化,考虑液相仅包含大小两类尺寸液滴的情形,计算不同尺寸的两个液滴间的碰撞概率,对固定观察区域内液滴的碰撞聚合、迁入及迁出因素作随机分析,建立描述液滴数目变化的生灭过程模型.由无条件概率模型方程,得出模型方程的相应平稳分布.以雨滴下落过程的质量增长为例,说明所得分布在气体液滴两相流动中的应用. 相似文献
5.
Motivated by its importance for microfluidic applications, we study the stability of jets formed by pressure-driven concentric biphasic flows in cylindrical capillaries. The specificity of this variant of the classical Rayleigh-Plateau instability is the role of the geometry which imposes confinement and Poiseuille flow profiles. We experimentally evidence a transition between situations where the flow takes the form of a jet and regimes where drops are produced. We describe this as the transition from convective to absolute instability, within a simple linear analysis using lubrication theory for flows at low Reynolds number, and reach remarkable agreement with the data. 相似文献
6.
N. N. Simakov 《Technical Physics》2004,49(2):188-193
When processing experimental data for the hydrodynamics of a two-phase flow in a spray produced by a mechanical nozzle, we revealed an anomaly in the behavior of the hydrodynamic drag of drops: the drag coefficient turns out to be four to seven times lower than the previously known values. Several hypotheses are put forward to explain the anomaly. It is found that, when the gas flows around drops under highly turbulent conditions, an “early” (i.e., observed even at transition Reynolds numbers, Re>50) crisis of drag resistance of drops takes place. This new physical phenomenon allows us to account for a number of features of the two-phase flow that are observed in the experiment. Among these features is, in particular, the fact that the momentum transferred to the gas is roughly half the initial momentum of the liquid jet. 相似文献
7.
Per Haugen Edward I. Hayes Hans-Henrik von Benzon 《Particle & Particle Systems Characterization》1994,11(1):63-72
Particles comparable in size to or larger than the measurement volume need extra consideration when measured by a phase-Doppler system. The phase of the Doppler burst received when such particles traverse the measurement volume depends not only on the size of the particle but also on its trajectory, since the particle is not uniformly illuminated. This paper presents a strategy for securing correct measurements even under such conditions, taking advantage of the three-detector receiving optics of the Dantec Particle Dynamics Analyzer. The effectiveness of the approach is demonstrated for sizing drops in liquid-gas and liquid-liquid two-phase flows: water drops in air, water drops in FC72 and FC72 drops in water. The combination of water and FC72 is also of interest because the relative refractive index is close to unity. Measurements of drops size were made on a monodisperse stream of drops about 2 mm in diameter, i.e. substantially larger than the measurement volume, and polydisperse distributions of drops ranging in diameter from below 0.2 mm to about 1 mm. 相似文献
8.
A. I. Grigor’ev 《Technical Physics》2005,50(12):1583-1591
Second-order calculations show that, when a gas flows about a charged drop, the fundamental mode of the multimode initial
deformation of its equilibrium shape builds up through nonlinear secondary Raman resonant interaction with higher modes if
this mode is present in the mode spectrum specifying the initial deformation. This circumstance accounts for large-amplitude
spheroidal oscillations of drops in natural liquid-drop systems and provides an insight into corona initiation in the vicinity
of drops in thunderstorm clouds and into lightning initiation. 相似文献
9.
10.
The conventional boundary conditions at the interface between two flowing liquids include continuity of the tangential velocity. We have tested this assumption with molecular dynamics simulations of Couette and Poiseuille flows of two-layered liquid systems, with various molecular structures and interactions. When the total liquid density near the interface drops significantly compared to the bulk values, the tangential velocity varies very rapidly there, and would appear discontinuous at continuum resolution. The value of this apparent slip is given by a Navier boundary condition. 相似文献
11.
《Comptes Rendus Physique》2004,5(5):547-555
Various aspects of microfluidic flows with different immiscible constituents are addressed. The fundamental physical characteristics are proposed, as well as the flow regimes which are determined by the wetting and surface tension properties. These fundamental aspects are followed by engineering applications that emerge in microfluidics, namely the creation of microbubbles or drops. Further applications are also discussed, such as the transfer of heat in bubbly flows, or the transport of colloids and emulsions. To cite this article: C.N. Baroud, H. Willaime, C. R. Physique 5 (2004). 相似文献
12.
G. Yu. Yalamov 《Technical Physics》2004,49(2):183-187
A new theory of diffusiophoresis of large volatile spherical aerosol drops that is an extension of investigations [1–8] is developed. The influence of the radius of the drop, the surface tension coefficient varying over the surface of the drop, the evaporation coefficient α of the liquid, and the flows inside the drop on the diffusiophoresis rate are taken into account. Expressions obtained allow for direct determination of the velocity of large individual aerosol drops in a binary gas mixture nonuniform in component concentration. It is shown that both the magnitude and the direction of the diffusiophoresis velocity depend on α and the size of the drop. It is assumed that the size of the drop varies but remains considerably greater than the mean free path of gas molecules. 相似文献
13.
《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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15.
Bipolar liquid crystal drops moving inside microchannels exhibit periodic director field transformations due to induced circulating flows inside them. These modifications are characterized by changes in the type of point surface disclinations; they periodically change from splay to bend disclinations, implying the drop changes between bipolar and escaped concentric configurations. Upon stopping the flow, this structure does not relax to the lower energy bipolar configuration; we argue this is due to drop flattening inside the channels. 相似文献
16.
We show that wetting properties crucially control the patterns in two-phase flows of immiscible fluids in microchannels. Ordered patterns, continuously entrained by the flow, are obtained when one phase completely wets the walls, while disordered patterns, intermittently adhering to the channel walls, are unavoidably produced when wetting is partial. A lower limit for the channel sizes capable of generating well structured objects (drops, pears, pearl necklaces, ...) is presented. 相似文献
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18.
S. O. Shiryaeva 《Technical Physics》2011,56(6):782-787
The influence of the finiteness of the charge transfer rate on the electrostatic instability of the lateral surface of a viscous
liquid jet is studied. The study is based on the analysis of a dispersion relation for flexural-deformation capillary waves
on the surface of the jet with allowance for charge relaxation. The jet is subjected to a superposition of two electrostatic
fields one of which is collinear with the jet’s axis and the other is directed radially to the former. It is found that the
finiteness of the potential equalization rate influences jets of a poorly conducting liquid most strongly. The charge relaxation
shows up in the appearance of both periodic and aperiodic “purely relaxation” flows. Relaxation flows give rise to electrostatic
instability in low-permittivity liquids. When the conductivity of the liquid drops, the instability growth rate of relaxation
waves grows and their spectrum expands toward shorter waves. An increase in the charge surface diffusion coefficient introduces
destabilization into the relaxation flows of the liquid, which may eventually become unstable. 相似文献
19.
An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focuses on the influence of heat transfer area upon the condensation heat transfer coefficients. The test sections were made of double tubes using the counter-flow type; the refrigerants condensation inside the test tube enabled heat to exchange with cooling water that flows from the annular side. The saturation temperature and pressure of the refrigerants were measured at the inlet and outlet of the test sections to defined state of refrigerants, and the surface temperatures of the tube were measured. A differential pressure transducer directly measured the pressure drops in the test section. The heat transfer coefficients and pressure drops were calculated using the experimental data. The condensation heat transfer coefficient was measured at the saturation temperature of 48°C with mass fluxes of 50–380 kg/(m2s) and heat fluxes of 3–12 kW/m2. The values of experimental heat transfer coefficient results are compared with the predicted values from the existing correlations in the literature, and a new condensation heat transfer coefficient correlation is proposed. 相似文献
20.
Xiufeng Yang Manjil Ray Song-Charng Kong Chol-Bum M. Kweon 《Proceedings of the Combustion Institute》2019,37(3):3279-3286
The interaction of liquid drops and heated surfaces is of great importance in many applications. This paper describes a numerical method, based on smoothed particle hydrodynamics (SPH), for simulating n-heptane drop impact on a heated surface. The SPH method uses numerical Lagrangian particles, which obey the laws of fluid dynamics, to describe the fluid flows. By incorporating the Peng–Robinson equation of state, the present SPH method can directly simulate both the liquid and vapor phases and the phase change process between them. The numerical method was validated by two experiments on drop impact on heated surfaces at low impact velocities. The numerical method was then used to predict drop-wall interactions at various temperatures and velocities. The model was able to predict the different outcomes, such as rebound, spread, splash, breakup, and the Leidenfrost phenomenon, consistent with the physical understanding. 相似文献