Kinetic and electrical phenomena in gas–liquid systems

Disperse systems consisting of a liquid and gas bubbles located in it are considered. Two possible versions of evolution of bubbles under the conditions studied are assessed. In simple liquids, contact between two bubbles causes them to merge, as the separating film breaks. In the case of complex organic liquids, amphiphilic film is formed on the surface of bubbles, and the lifetime of bubbles in contact increases with their size. Under an external electric field, chains of bubbles are formed, lined up along the electric field potential lines. The presence of bubbles in liquid greatly lowers the breakdown threshold, as the critical parameters of the breakdown field in liquids are two to three orders of magnitude higher than those in gases at atmospheric pressure. Various breakdown mechanisms in liquids are discussed from the viewpoint of formation of the gas phase during the passage of an electric current through a liquid medium. The character of propagating a streamer in separate bubbles is studied with their random distribution in liquid and in the case of formation of some structures of bubbles; the critical parameters of disperse systems, that can lead to their electrical breakdown, are presented. Along with the general concepts of electrical breakdown in dispersed systems, experimental studies of these processes are considered, and the nature of electrical breakdown in liquid dielectrics, including transformer oil, is discussed.     

Measurements of the thermal magnetoresistance of aluminum

The transverse thermal magnetoresistance of single-crystal plates of pure aluminum has been measured at liquid helium temperatures. It is shown that the high field Lorentz ratio is practically independent of field in agreement with theoretical predictions, and the value of the Lorentz ratio in high fields is discussed in terms of thermal and electrical relaxation times. It is also shown that the previously observed linear increase of the electrical resistivity in high fields is reflected in the thermal resistivity, and the origin of this effect is discussed. It is believed that the linear behavior is not caused by a magnetic breakdown effect in this case, but is due to other intrinsic or nonintrinsic effects.     

Electrical properties of CFC- and HCFC-substitutes

Electrical properties of refrigerants are of importance as soon as bushings are surrounded by a refrigerant. This is the case e. g. for hermetic sealed motor compressors as well as for some control devices such as liquid level control units or capacity controls for compressors. This paper presents a survey of existing data for HFC refrigerants and presents new measurements for those HFC blends that have been identified as long term replacements for CFCs and HCFCs. The data collection includes permittivity, electrical conductivity and breakdown voltage. Values are given for the HFC blends R404A, R407C, R410A and R507 as well as for R134a.     

Microgravity conditions and electrical resistivity of liquid alloys with critical mixing

The phenomena of two-liquid phase separations are significantly influenced by the gravity on the ground because of the difference in the densities of the constituent components, particularly, in the case of liquid alloys with critical mixing. In this paper, experimental techniques and results are reported for the measurements of the electrical resistivity for typical liquid alloys with critical mixing, such as Bi−Ga, under microgravity by the use of a rocket S520-19 belonging to ISAS (Institute of Space and Astronautical Science, Japan). It was found that the temperature coefficient of the electrical resistivity, on cooling of the homogeneous liquid phase, increases with the approach to the critical temperature. This trend under microgravity by the rocket experiment is more pronounced compared to the trend of the reference experiment on the ground. In addition, the supercooling of homogeneous liquids under microgravity is larger than that on the ground. These differences are explained by the difference in the degree of the growth of concentration fluctuations; the concentration fluctuations are far greater under microgravity than on the ground. Therefore, it is found to be very important to study the process and the critical phenomena of two-liquid phase separations under microgravity. Measurement of electrical resistivity is an effective method to obtain informations about the process, the critical phenomena, and the supercooling of two-liquid phase separations in liquid alloys with critical mixing. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

QCM Operation in Liquids: An Explanation of Measured Variations in Frequency and Q Factor with Liquid Conductivity

Recently, several reports have shown that when one side of a quartz crystal microbalance (QCM) is exposed to a liquid, the parallel (but not the series) resonant frequency is influenced by the conductivity and dielectric constant of the liquid. The effect is still controversial and constitutes a serious complication in many applications of the QCM in liquid environments. One suggestion has been that acoustically induced surface charges couple to charged species in the conducting liquid. To explore this effect, we have measured the parallel and the series mode resonance frequencies, and the corresponding Q factors, for a QCM with one side facing a liquid. These four quantities have all been measured versus liquid conductivity, using a recently developed experimental setup. It allows the simultaneous measurement of the resonant frequency and the Q factor of an oscillating quartz crystal, intermittently disconnected from the driving circuit. Based on these results, a simple model together with an equivalent circuit for a quartz crystal exposed to a liquid is presented. The analysis shows that it is not necessary to infer the existence of surface charges (or other microscopic phenomena such as electrical double layers) to account for the influence of the liquid's electrical properties on the resonant frequency. Our results show that the contacting conductive liquid, in effect, enlarges the electrode area on the liquid side and thereby changes the parallel resonant frequency. By proper design of the QCM measurement, perturbing effects due to the liquid's electrical properties can be circumvented.     

Heat transfer from Ni–W tapes in liquid nitrogen at different orientations in the field of gravity

Ni–W tapes of the micrometric thickness are considered as the basis for the cost-effective manufacturing of coated conductors – the 2nd generation of high-temperature superconductor (HTS). Many HTS applications involve widely-available and inexpensive liquid nitrogen. The transition from superconducting to normal state may however occurs due to unexpected temperature fluctuations. In this case Ni–W tape is significantly heated by electrical current propagating through it. The amount of heat transferred from the tape to coolant is defined by heat transfer from the surface of tape to liquid nitrogen. The heat transfer, in turn, is strongly dependent on the tape orientation in the field of gravity. The present paper reports the experimental results on the heat transfer from Ni–W tape to a pool of liquid nitrogen. The heat transfer coefficients are quantified for three subsequent heat transfer regimes: natural convection of liquid nitrogen, nucleate boiling regime and film boiling. The dependence of heat transfer coefficient on inclination angle of the tape from vertical are experimentally clarified for each regime. The expression for the heat transfer coefficient at different inclination angles is derived for the case of nucleate boiling.     

新型电解质材料[BMIM]ClO3离子液体的合成及其物化性能

以N-甲基咪唑为原料合成了室温离子液体1-丁基-3-甲基咪唑氯酸盐([BMIM]ClO3),用IR、NMR、DSC-TGA等手段对产物进行了表征,测定了相关物化性能,如密度、表面张力、黏度、电导率和电化学窗口等,并考察了该离子液体的溶剂性能。结果表明,该离子液体作为新型的电解质材料,具有低黏度、高电导率,密度、表面张力、黏度均随温度升高而减小,电导率随温度升高而增大,与温度符合Arrhenius方程。该离子液体与多数常规溶剂互溶,并对某些金属氧化物具有较高的溶解度,为离子液体在选矿、电解金属氧化物等方面的应用奠定了基础。     

液压流体吸振器用圆形压电发电装置的建模与性能分析

提出一种用于液压流体吸振器的压电发电装置。为提高所用圆形压电振子的发电能力,获得最优的结构及材料性能参数,利用板壳理论建立了固支边界条件下的位移曲线及发电量的理论分析模型,研究了半径比(陶瓷/基板)、厚度比(陶瓷/总厚度)及弹性模量比(基板/陶瓷)等对其发电能力的影响规律。研究表明,在压电振子材料确定时,存在最佳的半径比和厚度比使其发电能力最大;在压电振子结构尺寸确定时,存在最佳的弹性模量比使发电量最大,且厚度比确定时的最佳弹性模量比与半径比无关、半径比确定时的最佳弹性模量比随厚度比的减小而降低;减小弹性模量比有助于提高压电振子的发电能力。铝基板及铍青铜基板压电振子的最佳半径比/厚度比分别为0.45/0.45和0.585/0.60,最大发电量分别为1.146 43×10-4J和1.018 93×10-4 J。     

The electrical resistivity of liquid carbon under rapid heating of dense isotropic graphite in different media

Experiments are considered which involve pulsed heating of graphite (in several microseconds) and registering of electrical resistance of liquid carbon. Samples of MF-307 dense (2 g/cm³) isotropic graphite with a cross section of ∼0.3 × 0.3 mm and 10–15 mm long are heated in water or in thick-walled (outside diameter D ∼ 10 mm, inside diameter d ∼ 0.5 mm) sapphire capillary tubes. It is confirmed that the heating in water at atmospheric pressure does not enable one to obtain and investigate liquid carbon: at best, only the beginning of the liquid state region is attained. The heating in sapphire tubes causes the emergence of pulsed pressure (up to ten kilobars) after expanding graphite comes against the tube wall. This growing pressure (within several microseconds) enables one to investigate the liquid state of carbon in a confined volume. The isochoric heating provided the possibility of measuring the electrical resistivity of liquid carbon at high specific energies (up to ∼32 kJ/g) and high pressures; such measurements are quite expensive in the case of stationary investigations.     

Thermal Entry Length and Heat Transfer Phenomena in Laminar Wavy Falling Films

There are many techniques for the cooling of the parts of industrial apparatuses and electrical components. The use of liquid film flow is a possible technique, offering solutions for the problems associated with the microgravity applications and for the case of normal earth conditions. In this work the thermal entry length of laminar wavy falling films was determined experimentally under full gravity conditions by means of infrared thermography. The dependence of the entry length on the Reynolds, Prandtl and Kapitza number as well as the ratio Pr₀/Pr_W between the Prandtl numbers at inflow and wall temperatures, presented 2 year ago in the same journal, was modified for the case of a larger area of Reynolds numbers as well as for the case of a nonlinear dependence of viscosity from the temperature.     

Controlling electrical percolation in multicomponent carbon nanotube dispersions

Carbon nanotube reinforced polymeric composites can have favourable electrical properties, which make them useful for applications such as flat-panel displays and photovoltaic devices. However, using aqueous dispersions to fabricate composites with specific physical properties requires that the processing of the nanotube dispersion be understood and controlled while in the liquid phase. Here, using a combination of experiment and theory, we study the electrical percolation of carbon nanotubes introduced into a polymer matrix, and show that the percolation threshold can be substantially lowered by adding small quantities of a conductive polymer latex. Mixing colloidal particles of different sizes and shapes (in this case, spherical latex particles and rod-like nanotubes) introduces competing length scales that can strongly influence the formation of the system-spanning networks that are needed to produce electrically conductive composites. Interplay between the different species in the dispersions leads to synergetic or antagonistic percolation, depending on the ease of charge transport between the various conductive components.     

Heat transfer and resistance to movement in a rotationally advancing flow of conducting liquid in the presence of a magnetic field

Conclusions The functional relationships thus obtained for the resistance and heat-transfer coefficients in a rotationally-advancing flow of a conducting liquid in a pipe with a constant internal axial magnetic field and small Reynolds magnetic numbers (Re_m1) contains only a single longitudinal magnetic field strength component equal in the above case to the external magnetic field strength. It follows from the above that the formulas thus obtained hold both in the case when the flowing liquid does not perform any useful work, i.e., when electrical energy is not tapped off (or injected) in the form of a current, and for the case when it is tapped off (or injected).The difference consists only in the fact that in the second instance the velocity of the liquid drops along the pipe according to the amount of the work thus obtained (and, obviously, to the work in overcoming the resistance forces). In the first instance the reduction in the velocity is due only to the overcoming of the resistance forces.It is appropriate to note that formulas (17), (18), (20), and (21) for H_o=0 are converted into corresponding formulas for a rotationally-advancing liquid flow in a pipe without a magnetic field. The latter formulas are adequately confirmed by practical experience (see [2]). This provides grounds for assuming that the formulas will also be fully confirmed in practice.Translated from Izmeritel'naya Tekhnika, No. 5, pp. 41–45, May, 1968.     

Optical router for optical fiber sensor networks based on a liquid crystal cell

Optical fiber sensor networks are evolving rapidly. They are used because of the inert nature of optical fibers allowing no electromagnetic interference and safe applications in inflammable atmospheres; other relevant characteristics are their low weights and wide bandwidths as a transmission medium. In any case, it is very interesting to have specific components such as optical routers for selecting a certain path in a network with no optical to electrical and electrical to optical conversions. In this paper, we propose an all-optical router based on liquid crystals, polarizers, and a spatial split polarization beam splitter. The implemented device is designed to operate with visible light and it has been tested with plastic optical fibers. It has a crosstalk of 14 dB between selected ON channels and nonoperative OFF channels and 11-dB insertion losses. An average switch time of 100 ms is measured. The device checks the optical power level in each channel and, in case of failure, automatically switches to an operative channel while an alarm is activated.     

液态金属电子输运性质的理论研究

液体的许多重要物理性质及结构稳定性都直接或间接与价电子状态有关,电子输运性质的研究因较直接揭示液体中价电子的变化而倍受重视。主要介绍液态金属电阻率和电势的理论研究现状,分析了获得其中关键参数熔体结构因子及原子间作用势的途径。     

Decomposition of phenol by hybrid gas/liquid electrical discharge reactors with zeolite catalysts

Application of hybrid gas/liquid electrical discharge reactors and a liquid phase direct electrical discharge reactor for degradation of phenol in the presence and absence of zeolites have been investigated. Hybrid gas/liquid electrical discharges involve simultaneous high voltage electrical discharges in water and in the gas phase above the water surface leading to the additional OH radicals in the liquid phase and ozone formation in the gas phase with subsequent dissolution into the liquid. The role of applied zeolites, namely NH4ZSM5, FeZSM5 and HY, were also studied. Phenol degradation and production of primary phenol by-products, catechol and hydroquinone, during the treatment were monitored by HPLC measurements. The highest phenol removal results, 89.4-93.6%, were achieved by electrical discharge in combination with FeZSM5 in all three configurations of corona reactors. These results indicate that the Fenton reaction has significant influence on overall phenol removal efficiency in the electrical discharge/FeZSM5 system due to the additional OH radical formation from hydrogen peroxide generated by the water phase discharge.     

Mechanical and electrical failures leading to major fires

Major fires cause very large financial losses every year and determination of their cause is important from the point of view of insurance and also to attempt to avoid future occurrences from the same cause. While arson, natural effects such as lightening strikes, hurricanes and earthquakes, and human carelessness contribute significantly to fire losses, many fires are caused as a result of electrical and mechanical failures and malfunctions. The authors describe a number of cases in which mechanical and electrical failures have been the initiating causes. The cases include one where fracture of a structure occurred as a result of poor design and construction, leading to discharge of flammable liquid that was ignited from a build-up of static electric charge; a refinery fire caused by the presence of hidden defects that propagated under transient loading conditions, and cases where vehicle fires occurred as a result of poor design or construction of electrical circuits, or from electrical discharges.     

Modeling the Responses of Thickness-Shear Mode Resonators under Various Loading Conditions

We develop a general model that describes the electrical responses of thickness-shear mode resonators subject to a variety of surface conditions. The model incorporates a physically diverse set of single-component loadings, including rigid solids, viscoelastic media, and fluids (Newtonian or Maxwellian). The model allows any number of these components to be combined in any configuration. Such multiple loadings are representative of a variety of physical situations encountered in electrochemical and other liquid-phase applications, as well as gas-phase applications. In the general case, the response of the composite load is not a linear combination of the individual component responses. We discuss application of the model in a qualitative diagnostic fashion to gain insight into the nature of the interfacial structure, and in a quantitative fashion to extract appropriate physical parameters such as liquid viscosity and density and polymer shear moduli.     

Investigation of the liquid crystal alignment layer: effect on electrical properties

We investigate the electrical behavior of a symmetric liquid crystal (LC) cell: elecrode-silane-LC-silane-electrode. The silane (chlorodimethyloctadecyl-silane) layer induces a homeotropic orientation of the nematic liquid crystal (NLC) molecules. The wettability technique is used to detect the change of the surface energy of the electrode upon cleaning and silane layer deposition. We report on the dynamic impedance measurements of the nematic liquid crystal cell. It is found that the silane alignment layer has a blocking effect on the liquid crystal (LC) cell. We also study the relaxation behavior of the cell which is later assimilated as an electrical equivalent circuit.     

Axisymmetric waves in electrohydrodynamic flows

The formation of nonlinear axisymmetric waves on inviscid irrotational liquid jets in the presence of radial electric fields is considered. Gravity is neglected but surface tension is considered. Electrohydrodynamic waves of arbitrary amplitude and wavelength are computed using finite-difference methods. Particular attention is paid to nonlinear traveling waves. In the first class of problems, an electric field generated by placing the liquid jet inside a hollow cylindrical electrode held at constant voltage, its axis coinciding with that of the jet, is studied. The jet is assumed to be a perfect conductor whose free surface is stressed by the electric field acting in the hydrodynamically passive annulus. In the second class of problems, the annular gas is a perfect conductor that transmits a constant voltage onto the liquid/gas surface. The liquid axisymmetrically wets a constant-radius cylindrical rod electrode placed coaxially with respect to the hollow outer electrode, and held at a different constant voltage. The fluid dynamics and electrostatics need to be addressed simultaneously in the inner region. Axisymmetric interfacial waves influenced by surface tension and electrical stresses are computed in both cases. The computations are capable of following highly nonlinear solutions and predict, for certain parameter values, the onset of interface pinching accompanied with the formation of toroidal bubbles. For given wave amplitudes, the results suggest that, for the former case, the electric field delays bubble formation and reduces wave steepness, while for the latter case the electric field promotes bubble formation, all other parameters being equal.     

Investigation of the liquid crystal alignment layer: effect on electrical properties

Abstract

We investigate the electrical behavior of a symmetric liquid crystal (LC) cell: elecrode-silane-LC-silane-electrode. The silane (chlorodimethyloctadecyl-silane) layer induces a homeotropic orientation of the nematic liquid crystal (NLC) molecules. The wettability technique is used to detect the change of the surface energy of the electrode upon cleaning and silane layer deposition. We report on the dynamic impedance measurements of the nematic liquid crystal cell. It is found that the silane alignment layer has a blocking effect on the liquid crystal (LC) cell. We also study the relaxation behavior of the cell which is later assimilated as an electrical equivalent circuit.