Convective instability mechanism for a binary mixture heated from above

It is shown that the intensification of a stabilizing buoyancy flux directed from the surface to the bulk of a binary mixture (e.g., salt water) may give rise to convective instability.     

Convective instability mechanism for a binary mixture at a vertical surface

It is shown that the mechanical equilibrium state of a two-component medium (e.g., salt sea water) in a gravity field can be unstable even in the case of indefinitely strong hydrostatic stability of this medium due to different boundary conditions for two substances (temperature and admixture concentration) at vertical boundaries. Instability criteria for long-wave perturbations at a vertical surface and in a vertical layer are obtained in analytic form.     

Mechanism of convective instability of a binary mixture

Even a very slow background vertical motion can strongly affect convection in a stratified fluid. A previously unknown mechanism of convective instability is demonstrated for a binary mixture in the flow field of such motion.     

Soret效应对具有自由表面的圆柱形浅池内双组分溶液热对流影响的实验研究

为了探究Soret效应对具有自由表面的圆柱形浅液池内双组分溶液热对流过程的影响, 通过实验观察了质量分数为50%的正癸烷/正己烷混合溶液在不同深宽比的液池内流动失稳后的自由表面耗散结构及液池内的温度波动. 结果表明, 双组分溶液流动失稳的临界热毛细Reynolds数小于纯工质的值, 且其随液层深宽比的变化规律与纯工质相同. 当深宽比小于0.0848时, 流动失稳后在自由表面观察到热流体波, 监测点处温度波动主频随热毛细Reynolds数增大而增加; 当深宽比大于0.0848时, 随热毛细Reynolds数的增大, 流动失稳后自由表面依次呈现轮辐状、花苞状、分离-合并-分离交替变化的条纹状结构.     

Surface instability on thin fluid layers of a binary mixture

A long-wave model for thin layers consisting of two miscible fluids is presented. The model is a development of a simplified 2D model variant which considers the temperature and the concentration fields as linear functions on the vertical coordinate and neglect the convective terms from the corresponding equations. Now, the 2D thin film equation is coupled to complete 3D energy and mass conservations equation. We discuss the extended system in the linear approximation and in the initial nonlinear stage.     

双组分混合流体中Eckhaus不稳定调谐的行波对流

在双组分混合流体的Rayleigh-Bénard对流系统中，数值模拟获得了周期性时空位错缺陷调谐的扩展行进波对流状态.研究了该状态的时空演化特性.结果表明，Eckhaus不稳定触发的对流涡卷对的产生是调谐的起源，对流涡卷在边界处生成与湮没频率的不同，又使系统返回不稳定区域，系统在稳定与不稳定的波数之间振荡.还探讨了一个周期内传热与混合特性的改变及其控制参数的变化规律. 关键词： 双组分混合流体 行波对流 时空位错缺陷 Eckhaus不稳定调谐     

Nonlinear effects in the convective instability of a binary mixture in a porous medium near threshold

An amplitude equation is derived near threshold for both the stationary and the oscillatory instabilities and an oscillatory behavior in time for the Nusselt and the Froude number is predicted for the oscillatory instability.     

Optical study of a convective instability in a binary liquid mixture heated from above

We report the results of optical measurements performed on a thin horizontal layer of a binary liquid mixture characterized by a negative thermal diffusion ratio. We present evidence of the onset of a new type of convective instability occuring when heating is done from above.     

The effect of compressibility of the medium on the instability of gravity waves in the presence of a shear flow

The instability of a shear flow is analyzed in the framework of a two-dimensional model. Special consideration is given to a linear flow profile. As a continuation of the previous studies [3, 4], it is shown in a more rigorous way that the presence of an inflection point is not necessary if one takes into account the coupling of potential and eddy field components, i.e., the nonlinear effect. The presence of compressibility is necessary for the instability mechanism to be realized. Some effects accompanying the instability are also discussed. In particular, it is shown that the presence of a turning point $\frac{{\partial \omega }}{{\partial k}} = \infty $ , which is typical of the instability in a shear flow, does not indicate that the group velocity of a wave packet tends to infinity.     

准二维二元混合颗粒动态循环反转分层的体积效应

对垂直振动作用下准二维二元混合颗粒系统的动态循环反转分层现象进行了系统研究,得到了频率与加速度的关系相图,并观测到分层的动态循环反转区域. 发现动态循环的反转周期与颗粒总体积的变化有单调递增关系. 利用Hong的竞争机制理论对动态循环反转的现象及其体积效应的机理给出了解释. 关键词： 颗粒 分层 周期     

Convective instabilities in films of binary mixtures

We present a model for the evolution of films of isothermal binary liquid mixtures with a free evolving surface. The model is based on model-H supplemented by appropriate boundary conditions at the free surface and the solid substrate. The equations account for the coupled transport of the concentration of a component (convective Cahn-Hilliard equation) and the momentum (Korteweg-Navier-Stokes equation). The inclusion of convective motion makes surface deflections possible, i.e., the model allows to study couplings between the decomposition of the mixture and the evolving surface corrugations. We present selected steady layered film states for representative polymer mixtures, and show that convective motion favors their destabilization and qualitatively changes the linear instability modes in experimentally accessible ranges of parameters.     

Convective burning of an aluminum-water mixture

The burning of a stoichiometric mixture of aluminum (PAP-2 powder) with water in a constant-volume bomb is studied. It is shown that, depending on the charge diameter and igniter-generated pressure, three situations can arise: the mixture does not burn, burns slowly (in the layer-by-layer mode), or burns rapidly in the convective mode. The characteristics of the rapid burning, such as the effect of the igniter-generated burning, charge length, and initial charge density, are in general similar to those of the convective burning of mixtures of aluminum powder with an oxidizing agent (AP or PA), described in the literature. The difference lies in the fact that, due to a relatively low water activity as an oxidant, the convective burning of aluminum-water mixtures is harder to initiate, and it proceeds at a much lower velocity.     

Investigation of the Soret effect in binary liquid mixtures by thermal-diffusion-forced Rayleigh scattering (contribution to the benchmark test)

Within the framework of an international benchmark test we have performed measurements of the transport coefficients S T (Soret coefficient), D (mutual diffusion coefficient) and D T (thermal diffusion coefficient) on the three binary organic liquid mixtures 1,2,3,4-tetrahydronaphthalene- n -dodecane, 1,2,3,4-tetra- hydronaphthalene-isobutylbenzene and isobutylbenzene- n -dodecane with the weight fraction c = 0.5 at T = 298.15 K by means of thermal-diffusion-forced Rayleigh scattering (TDFRS) for benchmarking purposes. Our results for the coefficients are in good agreement with those obtained by annular and parallelepipedic thermogravitational columns and by other benchmark tests which also apply TDFRS measurements.