Physicochemical properties of ionic liquid mixtures containing choline chloride,chromium (III) chloride and water: effects of temperature and water content

The effects of water addition and temperature on some physicochemical properties of room temperature ionic liquids containing chromium chloride, choline chloride and water in the molar ratio of 1:2.5:x (where x = 6, 9, 12, 15 or 18) have been studied. The density, viscosity, surface tension and conductivity of the liquid mixtures were measured for the temperature range of 25 to 80 °C. Increasing both water content and temperature resulted in decreasing density, surface tension and viscosity and increasing electrical conductivity. The average void radii (hole sizes) for the liquid systems under study were calculated; they were in the range of 1.21 to 1.82 Å. The average hole size was stated to grow with increasing both temperature and water content in the mixture. The variation of the average void radii correlates with the change in viscosity and conductivity. The activation energies of viscous flow and conductivity diminishes with increasing water content in the liquid mixture. There is a strong linear correlation between conductivity and fluidity which indicates that the conductivity of the ionic liquid mixtures is generally controlled by the ionic mobility. A moderate viscosity and higher conductivity of the Cr(III)-containing ionic liquids with extra-water addition (at x > 9) make them suitable for the development of chromium electrodeposition processes.     

Folding of viscous threads in diverging microchannels

We study the folding instability of a viscous thread surrounded by a less viscous miscible liquid flowing from a square to a diverging microchannel. Because of the change in the flow introduced by the diverging channel, the viscous thread minimizes viscous dissipation by oscillating to form bends rather than by simply dilating. The folding frequency and the thread diameter can be related to the volume flow rates and thus to the characteristic shear rate. Diffusive mixing at the boundary of the thread can significantly modify the folding flow morphologies. This microfluidic system enables us to control the bending of the thread and to enhance mixing between liquids having significantly different viscosities.     

On derivation of the analytical expression for damping ratios in a low-viscosity approximation

The damping ratios of waves and oscillations in nonlinear dispersion equations are found for planar, cylindrical, and spherical geometries as applied to finite-volume liquids. For a cylindrical jet and a plane interface between viscous liquids, the damping ratios are determined for the first time. When the radius of curvature of the liquid jet surface decreases, so does the damping ratio of capillary waves. In a system of immiscible liquids, the damping ratio may be both larger and smaller than that for the pure liquid depending on the viscosity of the liquids and the ratio of their densities. This is because the damping ratio depends on the kinematic viscosities of pure liquids. The damping ratio is also estimated for waves arising at the liquidgas interface due to a tangential discontinuity of the velocity field.     

Instability of a charged interface of two immiscible viscous liquids with charge relaxation taken into account

On the basis of an analysis of a derived dispersion relation, it is demonstrated that there can be two different types of instability relative to the free charge of a charged, planar interface between two viscous immiscible liquids with finite electrical conductivity in a gravitational field. For large values of the surface charge density, depending on the viscosities and ratio of conductivities of the media, one can observe either an aperiodic (of the Tonks-Frenkel type) or oscillatory instability of the interface. Increasing the viscosity of the lower liquid leads to a substantial drop in the increments of the mentioned instability types and alters the critical conditions for manifestation of the oscillatory instability, whereas varying the viscosity of the upper surface has only a very weak effect on these characteristics. Zh. Tekh. Fiz. 68, 13–19 (September 1998)     

Shear viscosity of glass-forming melts in the liquid-glass transition region

A new approach to interpreting the hole-activation model of a viscous flow of glass-forming liquids is proposed. This model underlies the development of the concept on the exponential temperature dependence of the free energy of activation of a flow within the range of the liquid-glass transition in complete agreement with available experimental data. The “formation of a fluctuation hole” in high-heat glass-forming melts is considered as a small-scale low-activation local deformation of a structural network, i.e., the quasi-lattice necessary for the switching of the valence bond, which is the main elementary event of viscous flow of glasses and their melts. In this sense, the hole formation is a conditioned process. A drastic increase in the activation free energy of viscous flow in the liquid-glass transition region is explained by a structural transformation that is reduced to a limiting local elastic deformation of the structural network, which, in turn, originates from the excitation (critical displacement) of a bridging atom like the oxygen atom in the Si-O-Si bridge. At elevated temperatures, as a rule, a necessary amount of excited bridging atoms (locally deformed regions of the structural network) always exists, and the activation free energy of viscous flow is almost independent of temperature. The hole-activation model is closely connected with a number of well-known models describing the viscous flow of glass-forming liquids (the Avramov-Milchev, Nemilov, Ojovan, and other models).     

Production of Fine Particles from Melts of Metals or Highly Viscous Fluids by ultrasonic standing wave atomization

Ultrasonic standing wave atomization (USWA) is a new process capable of atomizing both high surface energy liquids and highly viscous liquids. Atomization is achieved through acoustic forces acting upon a liquid jet which is guided into the central pressure node of a standing wave field. Spherical metal powders with minimum mass median diameters of less than 15 μm have been produced from metal melts with surface tensions of about 0.5 N/m. Organic liquids with viscosities between 1 and 10 Pas have been atomized, yielding mass median diameters from 20 to 330 μm. The influence of different operating parameters on the mass median diameter of metal melts and highly viscous liquids was evaluated. Parameters which were varied were ambient gas pressure, vibration amplitude of the transducers, mass flow rate, density of liquid, viscosity of the liquid, surface tension and the outlet diameter. The powders and sprays were analyzed with laser diffraction particle sizers. The physical background of the atomization process is discussed and an equation for the prediction of the mass median diameter is derived.     

The partial distribution functions and effective pair potentials of some H-bonded liquids from diffraction data

The partial structures and distribution functions are directly linked to structural model of molecular liquids. The comparative study of partial distribution function of different hydrogen-bonded liquids gives the information that hydrogen-bonding is stronger in alcohols than in water and ammonia. The effective pair potential is directly related to the pair correlation function. The comparative study of such potentials for different hydrogen-bonded liquids gives some characteristic features.     

粘性流体对涡轮流量计仪表系数影响的实验研究

流体的粘性对涡轮流量计的仪表系数有很大影响．本文使用活塞式液体标准体积管在不同粘度下对涡轮流量计进行了实验研究，得出了仪表系数与流量、流体的粘度之间关系曲线．     

Thermodynamic properties of the mixtures of some ionic liquids with alcohols using a simple equation of state

In the present work, we have used a simple equation of state called the GMA EoS to calculate the density of three ionic liquid mixtures including 1-butyl-3-methylimidazolum hexafluorophosphate, [BMIM] [PF₆] + methanol, 1-butyl-3-methylimidazolum tetrafluoroborate, [BMIM] [BF₄] + methanol, and [BMIM] [BF₄] + ethanol at different temperatures, pressures, and compositions. The isothermal compressibility, excess molar volumes, and excess Gibbs molar energy of these mixtures have been computed using this equation of state. The values of statistical parameters show that the GMA EoS can predict these thermodynamic properties very well within the experimental errors. The results show that isothermal compressibility of ionic liquids is lower than alcohols and the effect of temperature and pressure on the isothermal compressibility of ionic liquids is lower than alcohols. The excess molar volumes and excess molar Gibbs energy for these ionic liquid mixtures with alcohols are all negative at various temperatures and pressures over the whole composition range. The results have been interpreted in terms of intermolecular interactions and structural factors of the ionic liquids and alcohols.     

Stability of a charged drop of a viscous electrically conducting liquid in a viscous electrically conducting medium

A dispersion relation is derived for capillary oscillations of a charged electrically conducting viscous drop in an electrically conducting viscous medium. It is shown that aperiodic instability of the charged interface between the two media can arise in this system, with a growth rate that depends qualitatively differently on the ratio of their conductivities in different ranges of values of this ratio. In a certain range of conductivity ratios the drop undergoes oscillatory instability. Zh. Tekh. Fiz. 69, 34–42 (October 1999)     

高速通道压裂裂缝的高导流能力分析及其影响因素研究

高速通道压裂是近年在非常规致密油气资源开采中出现的新工艺, 已在世界范围内推广实施, 并取得了良好的增产效果. 该技术可使支撑剂在人工压裂缝中形成簇团式分布, 从而形成油气高速流动通道, 提高裂缝的导流能力. 但目前对于高速通道压裂裂缝高导流能力的形成机理及其影响因素尚不清楚. 对此, 本文从流体力学理论出发, 首先将高速通道压裂裂缝内形成的支撑剂簇团视为渗流区域, 簇团间的大通道视为自由流动区域; 然后基于Darcy-Brinkman方程建立了裂缝内的流动数学模型, 采用均匀化理论对该流动数学模型进行了尺度升级, 推导得到了高速通道压裂裂缝的渗透率, 揭示了其高导流能力的形成机理; 并以此为基础, 分析了不同支撑剂簇团形状、大小以及分布方式等因素对其导流能力的影响, 可为高速通道压裂工艺参数设计与优化提供基础.     

Sonolysis of organic liquid: effect of vapour pressure and evaporation rate

Various kinds of organic liquids, such as hydrocarbons, ethers, ketones and alcohols, were subjected to ultrasonic irradiation and the effects of vapour pressure and evaporation rate of the liquids on decomposition rates and the distribution of decomposition products were investigated. The main decomposition products from hydrocarbons were hydrogen, methane, ethylene and acetylene, and hydrogen, methane, ethylene, carbon monoxide and aldehydes from alcohols. The decomposition rates of organic liquids were generally faster than that of water, and the reaction would proceed via gas-phase chain reactions in the high temperature site by comparison of the product with pyrolysis data in the literature and by considering the results of DPPH experiments. In the relationship between decomposition rate and vapour pressure, different features were observed in alcohols and other liquids. The hydrocarbons most efficiently decomposed under conditions in which their vapour pressures ranged from 0.1 to 0.5 Torr. On the other hand, the most efficient vapour pressure for alcohol sonolysis was about 15 Torr. The deviations became smaller when the evaporation rate was employed instead of vapour pressure, and as the reactive index of sonolysis of organic liquids, evaporation rate may be a better probe than vapour pressure, which is often chosen as the index.     

A theory of electric polarisation in liquids: II. Polar liquids

In the frame of a theory previously developed by the author for non-polar liquids, the static dielectric constant of polar liquids is described through a new formula without adjustable parameters, valid for spherical molecules carrying a mathematical dipole. The application of the formula to 20 polar liquids shows that the dipole moments resulting from the theory are satisfactorily compared with those deduced from vapour phase data. The agreement obtained in this way between theory and experiment is better than that obtained through the analogous Onsager's formula.     

Thermodynamic aspects of the glass transition of silicates

The marked increase in second-order thermodynamic properties observed at the glass-transition signals the onset of configurational changes in viscous liquids. Experimental determinations in the glass-transition range will illustrate this point for thermal expansivity and demonstrate that the kinetics of volume, enthalpy and structural relaxation are identical for silicate liquids. Within the framework of the Adam–Gibbs theory, heat capacity and viscosity data may be combined to calculate configurational entropies and gain insights into the potential energy barrier to viscous flow. Finally, the considerable effect of water on the glass transition temperature of geologically relevant silicates is presented.     

水平空腔多孔介质自然对流各向异性和非达西效应研究

本文应用Ｄａｒｃｙ模型的改进型式－Ｂｒｉｎｋｍａｎ模型数值研究了填充各向异性多孔介质的水平空腔内部自然对流的非达西效应。结果表明：（１）较大的渗透率比导致空腔内的流动强度下降，传热速率降低；（２）较大的导热率比导致空腔内的等温线扭曲加剧，近壁流动速度加大，传热速率增加；（３）非达西效应在低渗透率比时尤为显著，忽略非达西效应的理论分析将会导致较大的误差。     

Self-propelled Leidenfrost droplets

We report that liquids perform self-propelled motion when they are placed in contact with hot surfaces with asymmetric (ratchetlike) topology. The pumping effect is observed when the liquid is in the Leidenfrost regime (the film-boiling regime), for many liquids and over a wide temperature range. We propose that liquid motion is driven by a viscous force exerted by vapor flow between the solid and the liquid.     

离心油泵输送粘性流体空蚀性能实验研究

本文通过实验研究了离心油泵输送粘性流体时的空蚀性能和油泵的空蚀性能与输送介质粘度的关系,研究了油泵的性能参数(流量、扬程、功率和效率)随进口真空度的变化规律,并与输送清水时的空蚀性能进行了对比,研究了进口真空度对油泵水力性能的影响。离心油泵的空蚀性能随输送介质的不同存在很大差异。实验结果表明:在相同的流量工况下,输送粘性流体比输送清水具有较高的临界空蚀余量。     

Effect of multipolar interaction on the effective thermal conductivity of nanofluids

Nanofluids or liquids with suspended nanoparticles are likely to be the future heat transfer media, as they exhibit higher thermal conductivity than those of liquids. It has been proposed that nanoparticles are apt to congregate and form clusters, and hence the interaction between nanoparticles becomes important. In this paper, by taking into account the interaction between nearest-neighbour inclusions, we adopt the multiple image method to investigate the effective thermal conductivity of nanofluids. Numerical results show that then the thermal conductivity ratio between the nanoparticles and fluids is large, and the two nanoparticles are close up and even touch, and the point-dipole theory such as Maxwell--Garnett theory becomes rough as many-body interactions are neglected. Our theoretical results on the effective thermal conductivity of CuO/water and Al$_{2}$O$_{3}$/water nanofluids are in good agreement with experimental data.     

缠结高分子液体在管中挤出胀大动力学理论：一组新的增长和最终挤出胀大比方程

基于O-W-F本构方程和自由回复机制，从Poioeuille流出发建立了一种新的缠结高分子液体挤出胀大动力学理论，该理论能有效地预测高分子流体的动静态挤出胀大行为同高分子粘弹性参数和成型条件间的相关性. 基于稳态剪切量可分解为自由“回复线团”和“不可回复热耗”两部分事实，定义了一个稳态剪切下自由“回复线团”和“不可回复热耗”的配分函数和它们两者间分配指数上可回复和不可回复构象分数，从而在理论上得到了瞬时、推迟和最终三者可回复形变量和可回复线团量同配分函数、分配指数上可回复构象分数、分子粘弹性参数和成型条件     

Influence of charge relaxation on the capillary disintegration of a jet of a viscous dielectric liquid placed in an electrostatic field collinear with the axis of the jet

A dispersion relation is derived for capillary waves with an arbitrary symmetry on the surface of a charged jet of a finite-conductivity viscous liquid placed in an electric field collinear with the axis of the jet. Analytical calculations are carried out in an approximation that is linear in dimensionless wave amplitude. In the case of axisymmetric waves, the instability of which causes disintegration of the jet into drops, the finiteness of the potential equalization rate has a noticeable effect only for jets of poorly conducting liquids. The charge relaxation shows up in that “purely relaxation” periodic and aperiodic liquid flows arise. When the conductivity of the liquid declines, the instability growth rates for unstable waves increase and their spectrum extends toward short waves. A charge present on the surface of the jet enhances its instability. An increase in the charge surface diffusion coefficient variously influences the capillary and relaxation branches of the solution: the damping ratio increases in the former case and decreases in the latter. As the diffusion coefficient rises, relaxation flows may become unstable.