Wall-adjacent Layers Research Articles

Operational characteristics of new biological lubricants

The lubricating characteristics of ultrathin interlayers of bio-oil RMO made from coastal algae P.Moriformis are investigated in this work. One of the most important qualities of the oil is its lubricity of the friction surfaces. It determines the possibility of formation of a stable separating film between contact surfaces, with orientational ordering in wall adjacent layers, with the strength value required in the boundary friction regime. The structural characteristics of such epitropic-liquid crystal (ELC) layers are essential when choosing a lubricant. Static friction pair was studied by the optical method of admixtured absorption dichroism. It was found that the value of the order parameter of ELC layer and its equilibrium thickness are much higher in compare with the layers of aliphatic hydrocarbons, which are the basis of modern mineral lubricants. The rheological characteristics of ultrathin interlayers were studied in a dynamic triad of friction. Processing of the effective viscosity coefficient dependence on the shear rate, interlayer thickness and temperature allowed us to estimate the value of equilibrium thickness of the ELC layer, which coincides with the results of optical measurements. The marked structural peculiarities of the ELC in the biooil interlayers are conditioned with the formation of molecular associates of oleic acid, which is the main component of studied oil.

Thickness Dependence of Refractivity in Wall-Adjacent Epitropic Liquid Crystal

Peculiarities of the behavior of some optical characteristics of orientationally ordered wall-adjacent layers of nonmesogenic liquids – epitropic liquid crystals (ELC) – are analyzed. A suggested model develops the well-known Maier–Saupe–Neugebauer theory and takes a two-component structure of ELC (dynamic equilibrium between monomers and dimers) into account. The experimentally measured thickness and temperature dependences of the refractive index and the value of birefringence are in good agreement with theoretical calculations.

Determination of heat of transition ELC – isotropic bulk liquid

The temperature dependence of transition heat value ELC – isotropic bulk liquid was calculated in the framework of two-component theory of wall-adjacent layers of nonmesogenic liquids. This dependence is described by quadratic law because of dipole-dipole interaction between monomers. The experimental data for nitrobenzene layers near lyophilic substrate are in satisfactory agreement with the calculation results.

Properties of Wall-Adjacent Epitropic Liquid Crystalline Layers

A two-component theoretical model of orientational ordering in wall-adjacent layers of a nonmesogenic liquid (consisting of monomers and dimers) with anisotropic intermolecular interaction has been developed. In the framework of the model, a number of experimental results such as the isotherms of disjoing pressure and some peculiarities in the behavior of heat capacity and dielectric permittivity of the liquid interlayers have been explained.

Structural rheological model of two-phase interlayer shear flow

This paper presents a study of an epitropic liquid crystal layer formation at a metal substrate. Such layer structurization leads to non-Newtonian flow of thin interlayer with wall-adjacent orientation-ordered layers. Rheological characteristics of micron interlayers of n-hexadecane and Vaseline oil with surfactant addition are investigated. The features of structural “variable viscosity” layer are defined within the framework of a proposed rheological model. An increase in the rate of shear deformation leads to a reduction in near-surface layer viscosity due to molecular reorientation. Estimation of model parameters, performed on basis of the experimental rheological data, is carried out.

Near-wall effects in micro scale Couette flow and heat transfer in the Maxwell-slip regimes

The effects of modified transport characteristics within an extremely thin layer adjacent to the fluid–solid interfaces are investigated for fully developed laminar micro-scale Couette flows with slip boundary conditions. The wall-adjacent layer effects are incorporated into the continuum-based mathematical model by imposing variable viscosity and thermal conductivity values close to the channel walls, for solving the momentum and energy conservation equations. Analytical expressions for the velocity profiles are derived and are subsequently utilized to obtain the temperature variations within the parallel plate channel, as a function of the significant system parameters. It is revealed that the variations in effective viscosity and thermal conductivity values within the wall-adjacent layer have profound influences on the fluid flow and the heat transfer characteristics within the channel, with an interesting interplay with the wall slip boundary conditions. These effects cannot otherwise be accurately captured by employing classical continuum based models for microscale Couette flows that do not take into account the alterations in effective transport properties within the wall adjacent layers.

Dielectric investigations of associate formation process in thin nitrobenzene interlayers formed between metal substrates

Studies of thickness and temperature dependencies of the dielectric susceptibility of nitrobenzene interlayers formed on conductive substrates were carried out. The obtained data were processed under the assumption of the existence of dimers (with opposite directions of molecular dipole moments) in orientationally ordered wall-adjacent layers. The results were treated on the basis of Lifshits theory.

Two component model of orientationally ordered wall adjacent liquid layers

Electronic-vibrational absorption spectra of anisole in isotropic bulk liquid phase and in orientationally ordered wall adjacent layers formed on quartz surface were measured. The spectra were registered at room (∼20 °C) temperature. The series of spectra measured for different thickness of the liquid interlayer and normalized by area manifests the existence of isobestic points. It determines the presence of different types of absorption centers there. Statistical analysis of obtained spectra shows that the number of these centers is equal to two; one of them is conditioned by a monomer and another one by the dimer. The thickness dependence of the relative concentration of monomers was investigated.

Dielectric susceptibility of wall adjacent nitrobenzene layers

Measurements of thickness dependence of dielectric susceptibility of nitrobenzene interlayers formed on conductive substrates were carried out. The obtained data were processed under the assumption of existence of dimers (with opposite directions of molecular dipole moments) in orientationally ordered wall-adjacent layers. The value of the orientationally ordered layer thickness coincides with the one determined by other methods.

Ising model of the epitropic liquid crystalline phase

Some thermodynamic properties of wall-adjacent layers of non-mesogenic liquids near lyophilic substrates have been investigated. The theoretical calculation of the equilibrium parameters of the layers have been performed.

Magnetohydrodynamic Heat Transfer Research Related to the Design of Fusion Blankets

Lithium or any lithium alloy like the lithium lead alloy Pb-17Li is an attractive breeder material used in blankets of fusion power reactors because it allows the breeding of tritium and, in the case of self-cooled blankets, the transfer of the heat generated within the liquid metal and the walls of the cooling ducts to an external heat exchanger. Nevertheless, this type of liquid-metal-cooled blanket, called a self-cooled blanket, requires specific design of the coolant ducts, because the interaction of the circulating fluid and the plasma-confining magnetic fields causes magnetohydrodynamic (MHD) effects, yielding completely different flow patterns compared to ordinary hydrodynamics (OHD) and pressure drops significantly higher than there. In contrast to OHD, MHD flows depend strongly on the electrical properties of the wall. Also, MHD flows reveal anisotropic turbulence behavior and are quite sensitive to obstacles exposed to the fluid flow.A comprehensive study of the heat transfer characteristics of free and forced convective MHD flows at fusion-relevant conditions is conducted. The general ideas of the analytical and numerical models to describe MHD heat transfer phenomena in this parameter regime are discussed. The MHD laboratory being installed, the experimental program established, and the experiments on heat transfer of free and forced convective flow being conducted are described. The theoretical results are compared to the results of a series of experiments in forced and free convective MHD flows with different wall properties, such as electrically insulating as well as electric conducting ducts. Based on this knowledge, methods to improve the heat transfer by means of electromagnetic/mechanic turbulence promoters (TPs) or sophisticated, arranged electrically conducting walls are discussed, experimental results are shown, and a cost-benefit analysis related to these methods is performed. Nevertheless, a few experimental results obtained should be highlighted:1. The heat flux removable in rectangular electrically conducting ducts at walls parallel to the magnetic field is by a factor of 2 higher than in the slug flow model previously used in design calculations. Conditions for which this heat transfer enhancement is attainable are presented. The measured dimensionless pressure gradient coincides with the theoretical one and is constant throughout the whole Reynolds number regime investigated (Re = 103 → 105), although the flow turns from laminar to turbulent. The use of electromagnetic TPs close to the heated wall leads to nonmeasurable increase of the heat transfer in the same Re regime as long as they do not lead to an interaction with the wall adjacent boundary layers.2. Mechanical TPs used in an electrically insulated rectangular duct improved the heat transfer up to seven times compared to slug flow, but the pressure drop can increase also up to 300%. In a cost-benefit analysis, the advantageous parameter regime for applying this method is determined.3. Experiments performed in a flat box both in a vertical and a horizontal arrangement within a horizontal magnetic field show the expected increase of damping of the fluid motion with increasing Hartmann number M. At high M, buoyant convection will be completely suppressed in the horizontal case. In the vertical setup, the fluid motion is reduced to one large vortex leading to a decreasing heat transfer between heated and cooled plate to pure heat conduction.From an analysis of the experimental and theoretical results, general design criteria are derived for the orientation and shape of the first wall coolant ducts of self-cooled liquid metal blankets. Methods to generate additional turbulence within the flow, which can improve the heat transfer further are elaborated.

Electronic-vibrational spectra of nitrobenzene in solutions, liquid phase and orientationally arranged wall-adjacent layers

The electronic-vibrational spectra of nitrobenzene in the frequency region v ≊50000−30000 cm−1 were investigated. The shape and main parameters of five fundamental absorption bands were determined. The absorption spectrum of ultrathin wall-adjacent orientationally ordered layers (with thicknessd≤100 nm) formed near a lyophilic quartz surface (so called epitropic liquid crystals — ELC) differs essentially from that of a bulk specimen and alters with decreasing thickness. In particular the half width of the intramolecular charge transition band decreased, and a bathochromic shift was observed. Parameters of other bands also change. It is probably connected with existence of ELC phase internal inhomogeneity.

Liquid-crystalline state of the wall-adjacent layers of some polar liquids

Donnees theoriques et etudes en particulier de l'interface entre du verre et du quartz lyophilises et du nitrobenzene ou d'autres derives du benzene

Liquid crystalline state of the wall-adjacent layers of some polar liquids

Liquid crystalline state of the wall-adjacent layers of some polar liquids

Liquid-crystalline state of the wall-adjacent layers of some polar liquids

Donnees theoriques et etudes en particulier de l'interface entre du verre et du quartz lyophilises et du nitrobenzene ou d'autres derives du benzene