Structure Of Molecular Liquids Research Articles

Investigations on streamers phenomena in mineral, synthetic and natural ester oils under lightning impulse voltage

This paper presents the experimental results of a comparative study of mineral, synthetic and natural ester oils issued from different origins through the analyze of the initiation threshold voltage of streamers, their pattern and their stopping length (final length) L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> as well as the associated current and electrical charge, in a point - plane electrodes arrangement submitted to a standard lightning impulse voltage (1.2/50 μs). It's shown that the streamers are filamentary in the different tested oils whatever the polarity of voltage. The stopping lengths L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> are longer and the conductivity higher when the point is positive than when it's negative. L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> is generally longer in ester oils (natural and synthetic) than in some mineral oils. When the point is negative, L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> can be ten times higher in ester oils than in mineral ones. Different modes of propagation of streamers are also observed; the transition between these modes of propagation depends on the experimental conditions and the molecular structure of liquid. This transition is well pronounced with some mineral oils when the point is negative.

The effect of clustering of particles on Rayleigh scattering of radiation in a turbulent flow

The effect of clustering of particles under conditions of homogeneous isotropic turbulence on Rayleigh scattering of radiation is analyzed. It is demonstrated that, similarly to the diagnostics of molecular structure of liquid using X-ray scattering, the radial distribution function of macroscopic particles, which characterizes the clustering phenomenon, may be determined by way of measuring the intensity of scattering of infrared or microwave radiation. An approximate relation for clustering coefficient is obtained, which may be employed for estimating the increase in reflected radiation of microwave radar from cumulus clouds owing to turbulent clustering of water drops in the cloud.

Structure of molecular liquids: Closure relations for hard spheroids

We present the results of Monte Carlo simulations of hard spheroids of revolution of different elongations. Both prolate and oblate shapes are examined. A systematic study of the bridge function b(1,2), and direct comparison with the indirect correlation function gamma(1,2)=h(1,2)-c(1,2) at densities spanning the isotropic fluid range, allow us to evaluate the accuracy of various proposed closure relations for integral equations.

Structure of molecular liquids: Cavity and bridge functions of the hard spheroid fluid

We present methodologies for calculating the direct correlation function c(1,2), the cavity function y(1,2), and the bridge function b(1,2), for molecular liquids, from Monte Carlo simulations. As an example we present results for the isotropic hard spheroid fluid with elongation e = 3. The simulation data are compared with the results from integral equation theory. In particular, we solve the Percus-Yevick and hypernetted chain equations. In addition, we calculate the first two terms in the virial expansion of the bridge function and incorporate this into the closure. At low densities, the bridge functions calculated by theory and from simulation are in good agreement, lending support to the correctness of our numerical procedures. At higher densities, the hypernetted chain results are brought into closer agreement with simulation by incorporating the approximate bridge function, but significant discrepancies remain.

Nonequilibrium structural transitions as a mechanism of turbulence

A possible mechanism for turbulence is proposed and substantiated for the first time, whereby turbulence is considered as a nonequilibrium transition in ensembles of defects of the microscopic shear type, which are treated as real defects in the molecular structure of liquids. A statistical foundation is given for the evolution equations for the tensor order parameter, which characterizes an ensemble of such defects and has the meaning of nonequilibrium fluctuations of the strain rate. The types of macroscopic fluctuation modes of the strain rate are determined as self-similar solutions of the evolution equations for this tensor order parameter under conditions of nonequilibrium transitions, and qualitative correspondences are established between these solutions and real scenarios for the transition to turbulence. The Kolmogorov scaling laws (the natures of the “viscous” and “ inertial” intervals) are explained for fully developed turbulence.

Liquid-Grain theory. The molecular structure of liquids

Liquid-Grain theory. The molecular structure of liquids

Dependence of polarity effect of dielectric breakdown on molecular structure of liquids

In liquid hydrocarbon, at short electrode distance, the negative needle indicates lower strength than that of positive needle and it reverses at longer electrode distance. The critical distance of this polarity reversal is very short for liquids with large electron mobility like neopentane. In perfluorocarbon liquids, the difference of breakdown voltage for both polarities is much less than that of hydrocarbon liquids. In liq.N 2, the polarity effect of breakdown is similar to that of hydrocarbons and strongly dependent on pulse width, applied pressure. The polarity effect in liq.He is completely different from other liquids and due to the unique behaviour of electrons in liq.He. The polarity effect in liq.Ne is similar to liq.He. These polarity effects in various liquids seem to have some correlation with the mobility in these liquids and are discussed in terms of bubble process and electronic processes like streamer.

Perturbation theory for diatomic molecules using a non-spherical reference system

A perturbation theory for predicting the thermodynamic properties and structure of a molecular liquid is described. The theory is applied to a two-centre Lennard-Jones fluid and the properties of this fluid are calculated from the properties of a hard dumbell fluid. The liquid structure of the dumbell reference system is calculated using the RISM equations. The free energy of the reference system is calculated by scaled particle theory and by Monte Carlo simulation. The non-spherical hard-core system is softened before the anisotropic perturbation is added. The theory makes qualitative predictions about the structure of molecular liquids and quantitative predictions of the internal energy, pressure and mean squared force. The perturbation expansion is rapidly convergent and the principal source of error is the reference system distribution function. The extension to more complex models and the addition of multipole interactions is discussed.

Dependence of Dielectric Breakdown of Liquids on Imolecular Sturcture

High field carrier transport, electron multiplication and breakdown in liquids of various molecular structure are discussed. Breakdown characteristics depend on the molecular structure of liquids. Breakdown strength and its polarity effect are determined by the combination of the energy input from electric field and energy loss which depend on electron mobility and internal vibrational mode respectively, therefore on molecular structure. In rare gas liquids with high electron mobility like liquid Ar, Kr and Xe the electron avalanche is the mechanism of the breakdown. However, in liquid He, electron injection from cathode is the determining process for breakdown and the polarity effect of breakdown in liquid He is completely different from other liquids. In hydrocarbon liquids of ultra-high purity, which have high electron mobility in the case of spherical molecules, and also even in the case of linear molecules at high fields, the electron avalanche (or positive streamer) is also important in the short time range (nsec). However, thermal effects are significant in the long time range. Change of breakdown mechanism from bubble process to positive streamer process with decreasing pulse width and increasing pressure is indicated clearly in liquid N2 as an example. Effect of impurities on breakdown is also dependent on the molecular structure of liquids and solutes. Laser induced breakdown is strongly dependent on the molecular structuire and also can be explained in terms of electron avalanche by the high-frequency breakdown theory.

Optical Study of Conduction and Breakdown in Dielectric Liquids

On the optical studies of electrical conduction and breakdown in dielectric liquids, recent works which have been studied in Japan are briefly reviewed first. Next, the results of study in our laboratory on the measurement of ion mobility and on the breakdown process in liquids are presented. When an electrode system such as razorblade emitter-grid-collector is used for the measurement of ion mobility by the time of flight method, the field uniformity between grid-collector is calculated, and the space charge effect related to the current density is investigated. Through these researches suitable condition for ion mobility measurement are revealed. On the breakdown process, the schlieren method and high-speed photography are used under a pulse voltage applied to a needle-plane gap. Various aspects of the breakdown process from streamer initiation to main stroke, the polarity effect of streamer propagation, the relation between the mean velocity of positive streamer Vm and molecular structure of liquid, the relation between vm and pre-breakdown current, Vm of mixed liquid etc. are described.

Structure of molecular liquids

Structure of molecular liquids

Recent Developments in Liquid State Physics

AbstractIntroduction — Equilibrium Properties of Atomic Liquids — Transport Processes — Structure of Molecular Liquids — Transport in Molecular Liquids — Conclusion.

The structure of molecular liquids by neutron scattering

Abstract A review is given of the use of slow neutron scattering methods for the study of the structure of molecular liquids. The experimental and theoretical considerations which are involved in relating the experimental data to the desired structure factors, pair-correlation functions, etc. are considered in some detail. Many formulae and relations, previously rather scattered in the literature, as well as some new ones, are brought together, and particular attention is given to their utility, validity and physical content. A generalization of the Placzek corrections is proposed. The effects of correlation of relative molecular orientation are considered in some detail. The generalizations required for the analysis of data on molecular as compared with atomic liquids are considered in detail. It is concluded that the structure of molecular liquids is at present poorly understood both experimentally and theoretically but that the field is ripe for development.

The electric strength and molecular structure of liquids

Further measurements of the electric strength of liquids are used to support the theory of a breakdown criterion, suggested in an earlier paper, in which conduction electrons in the liquid excite molecular vibrations associated with individual groups within the molecules. It has been demonstrated that collision cross-sections could be assigned to these groups and the breakdown strength derived. This criterion is used to relate the breakdown strengths of a series of alkyl benzenes recently measured by Sharbaugh, Crowe and Cox and a cross-section for the benzene ring is determined. The additive effect of the various group cross-sections is found as before, but it is necessary to consider dipole effects as well as liquid structure in order to explain the increased cross-section values for the alkyl groups.