Surfactants for Exploring the Liquid–Solid Surface Free Energy

Helium-3 and helium-4 can be used as surfactants to modify the observed wetting transitions of hydrogen and deuterium on rubidium. The effect of these surfactants on the wetting temperature is calculated. Prewetting induced by ⁴ He in H ₂ on Rb is studied, and found to be re-entrant. Experiments can use the effect to measure the difference in temperature and concentration dependence of a free solid surface and a liquid/solid interface. This may help to resolve some unresolved questions pertaining to the wetting behavior of helium isotopic mixtures on cesium.     

3D Ordering at the Liquid–Solid Polar Interface of Nanowires

The nature of the liquid–solid interface determines the characteristics of a variety of physical phenomena, including catalysis, electrochemistry, lubrication, and crystal growth. Most of the established models for crystal growth are based on macroscopic thermodynamics, neglecting the atomistic nature of the liquid–solid interface. Here, experimental observations and molecular dynamics simulations are employed to identify the 3D nature of an atomic-scale ordering of liquid Ga in contact with solid GaAs in a nanowire growth configuration. An interplay between the liquid ordering and the formation of a new bilayer is revealed, which, contrary to the established theories, suggests that the preference for a certain polarity and polytypism is influenced by the atomic structure of the interface. The conclusions of this work open new avenues for the understanding of crystal growth, as well as other processes and systems involving a liquid–solid interface.     

Vibrational Coupling and Kapitza Resistance at a Solid–Liquid Interface

The rapid development and application of nanotechnologies have promoted an increasing interest in research on heat transfer across the solid/liquid interface. In this study, molecular dynamics simulations are carried out to elucidate the effect of vibrational coupling between the solid and the liquid phases on the Kapitza thermal resistance. This is accomplished by altering the atomic mass and interatomic interaction strength in the solid phase (thus, the vibrational properties), while keeping the solid–liquid interfacial interaction unchanged. In this way, the Kapitza resistance can be altered with a constant work of adhesion between the solid and the liquid phases. The simulation results show that the overlap degree between the vibrational density of states profiles of the interfacial liquid layer and the outermost solid layer, which measures the degree of interfacial vibrational coupling, increases with larger atomic mass and weaker inter-atomic interaction in the solid phase. An inverse relation exists between the Kapitza resistance and the overlap degree of the vibrational density of states profiles. It means that the Kapitza resistance decreases with better interfacial vibrational coupling. The simulations show that the Kapitza resistance is not only affected by the interfacial bonding strength but also the vibrational coupling between the solid and the liquid atoms. The interfaces with better thermal transport efficiency should be the ones with stronger interfacial interaction and preferable vibrational coupling between solid and liquid phases.     

Probing Contact-Electrification-Induced Electron and Ion Transfers at a Liquid–Solid Interface

As a well-known phenomenon, contact electrification (CE) has been studied for decades. Although recent studies have proven that CE between two solids is primarily due to electron transfer, the mechanism for CE between liquid and solid remains controversial. The CE process between different liquids and polytetrafluoroethylene (PTFE) film is systematically studied to clarify the electrification mechanism of the solid–liquid interface. The CE between deionized water and PTFE can produce a surface charges density in the scale of 1 nC cm⁻², which is ten times higher than the calculation based on the pure ion-transfer model. Hence, electron transfer is likely the dominating effect for this liquid–solid electrification process. Meanwhile, as ion concentration increases, the ion adsorption on the PTFE hinders electron transfer and results in the suppression of the transferred charge amount. Furthermore, there is an obvious charge transfer between oil and PTFE, which further confirms the presence of electron transfer between liquid and solid, simply because there are no ions in oil droplets. It is demonstrated that electron transfer plays the dominant role during CE between liquids and solids, which directly impacts the traditional understanding of the formation of an electric double layer (EDL) at a liquid–solid interface in physical chemistry.     

Methane Gas Hydrates Viewed through Unified Solid–Liquid–Vapor Equations of State

The phase behavior of methane gas hydrates (clathrates) has been investigated with unified equations of state for solid–liquid–vapor phases. This is a new way to look at the clathrate-containing system, being radically different from the traditional statistical thermodynamic model for clathrates. The present paper includes modifications and refinements of the previously published method with the unified equations of state. The univariant three-phase equilibrium lines containing clathrates have been successfully predicted with the present equation-of-state model for a wide temperature and pressure range. Particularly, the phase behavior in very high-pressure regions has been modeled for the first time by the present work. Although the present results at high pressures are still tentative, they will shed some light on the unsettled problem of high pressure phases as reported in the literature.     

Evolution of the Inner Liquid–Solid Interface During Metal Freezing

The influence of the inner interface initiation method on the interface shape (formation of the planar interface or the interface with the dendrites growing into the liquid metal) was studied both theoretically and experimentally. The results of numerical simulation of the process of heat removal from the metal, corresponding to different initiation methods, revealed the existence of different species of the inner interface. The interface modification during freezing arises from the inequality of temperature gradients on opposite sides of the interface, i.e., from imbalance of heat fluxes on the interphase boundary (Stefan problem). For indium point, the results of numerical simulation were confirmed experimentally.     

Local Forecast of the Heat‐Moisture State of the Soil Surface as a Problem of Energy and Mass Transfer in the System of Soil–atmosphere

Consideration is given to the dynamic problem of forecasting a frost on the soil surface, namely, of establishing the fact and the moment of the water–ice and water vapor–ice phase transitions at the soil–atmosphere interface, in calculating the evolution of the heatmoisture state of the viscousbuffer layer of air and the nearsurface layer of soil that are adjacent to this interface. The results obtained can be used for prediction of ice formation on runways of airfields and on roads.     

Fractal Description of the Solid/Liquid Interface of a Directionally Solidified Superalloy with Different Phosphorus Content

The solid/liquid interface of a directionally solidified Ni-base superalloy with different phosphoruscontents was quantitatively described by means of fractat method.When the solidification rate wasfixed,the relationship between the fractal dimensionality of the solid/liquid interface and the phos-phorus content of the test alloy was given.Combined the thermodynamics and fractal theory,the ef-fect mechanism of phosphorus content on fractal dimensionality of the solid/liquid interface wasdiscussed.     

The Precise Measurement of Vapor–Liquid Equilibrium Properties of the CO$$_{}$$/Isopentane Binary Mixture,and Fitted Parameters for a Helmholtz Energy Mixture Model

Natural working fluid mixtures, including combinations of CO\(_{2}\), hydrocarbons, water, and ammonia, are expected to have applications in energy conversion processes such as heat pumps and organic Rankine cycles. However, the available literature data, much of which were published between 1975 and 1992, do not incorporate the recommendations of the Guide to the Expression of Uncertainty in Measurement. Therefore, new and more reliable thermodynamic property measurements obtained with state-of-the-art technology are required. The goal of the present study was to obtain accurate vapor–liquid equilibrium (VLE) properties for complex mixtures based on two different gases with significant variations in their boiling points. Precise VLE data were measured with a recirculation-type apparatus with a 380 cm\(^{3}\) equilibration cell and two windows allowing observation of the phase behavior. This cell was equipped with recirculating and expansion loops that were immersed in temperature-controlled liquid and air baths, respectively. Following equilibration, the composition of the sample in each loop was ascertained by gas chromatography. VLE data were acquired for CO\(_{2}\)/ethanol and CO\(_{2}\)/isopentane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were used to fit interaction parameters in a Helmholtz energy mixture model. Comparisons were made with the available literature data and values calculated by thermodynamic property models.     

Metastable States in Liquid–Gas Phase Transition. Simulation by the Method of Molecular Dynamics

The method of molecular dynamics is used to investigate the p, , T-properties and the structural characteristics of the Lennard–Jones fluid in the stable and metastable states in the liquid–gas phase transition. The calculation results demonstrate the presence of phase separation in molecular models at close-to-spinodal supersaturation. The effect of the cut-off radius of the interparticle potential on the process of phase transformation is analyzed, and the position of spinodal of superheated liquid and supersaturated vapor is estimated.     

On Failures of van der Waals’ Equation at the Gas–Liquid Critical Point

This comment is in response to a recent “new comment” by Umirzakov on the article “Gibbs density surface of fluid argon: revised critical parameters.” It was incorrectly asserted that van der Waals equation “proves” the existence of a scaling singularity with a divergent isochoric heat capacity (C_v). Van der Waals’ equation, however, is inconsistent with the universal scaling singularity concept; it erroneously predicts, for instance, that C_v is a constant for all fluid states. Van der Waals hypothetical singular critical point is based upon a common misconception that van der Waals equation represents physical reality of fluids. A comparison with experimental properties of argon shows that state functions of van der Waals’ equation fail to describe the thermodynamic properties of low-temperature gases, liquids and of gas–liquid coexistence. The conclusion that there is no “critical point” singularity on Gibbs density surface remains scientifically sound.     

Dynamics of Stoneley Waves at the “Water–Water-Saturated or Gas Hydrate-Saturated Sand” Interface

Journal of Engineering Physics and Thermophysics - The process of propagation of the Stoneley wave at the “water–water saturated or gas hydrate-saturated sand” interface is...     

Application of the Multifrequency Doppler Backscattering Method for Studying Alfvén Modes at a Tokamak

Technical Physics Letters - The results of a study of toroidal Alfvén modes using the multifrequency method of Doppler backscattering at the Globus-M tokamak have been presented. The method...     

Thermophysical Properties of a Chromium–Nickel–Molybdenum Steel in the Solid and Liquid Phases

Numerical simulation of vacuum arc re-melting, pressurized or protective electro-slag re-melting, and ingot casting have become quite important in the metal industry. However, a major drawback of these simulation techniques is the lack of accurate thermophysical properties for temperatures above 1,500 K. Heat capacity, heat of fusion, density, and thermal conductivity are important input parameters for the heat transfer equation. Since, direct measurements of thermal conductivity of alloys in the liquid state are almost impossible, its estimation from electrical conductivity using the Wiedemann–Franz law is very useful. The afore-mentioned thermophysical properties of several steels are investigated within the context of an ongoing project. Here, we present a full set of thermophysical data for the chromium–nickel–molybdenum steel meeting the standard DIN 1.4435 (X2CrNiMo18-14-3); these values will be used by our partner to simulate various re-melting and solidification processes. Wire-shaped samples of the steel are resistively volume-heated, as part of a fast capacitor discharge circuit. Time-resolved measurements with sub-μs resolution of current through the specimen are performed with a Pearson probe. The voltage drop across the specimen is measured with knife-edge contacts and ohmic voltage dividers, the temperature of the sample with a pyrometer, and the volumetric expansion of the wire with a fast acting CCD camera. These measurements enable the heat of fusion, the heat capacity, and the electrical resistivity to be determined as a function of temperature in the solid and liquid phases. The thermal conductivity and thermal diffusivity are estimated via the Wiedemann–Franz law.     

Determination of Critical Parameters Based on the Intensity of Transmitted Light Around Gas–Liquid Interface: Critical Parameters of CO_{2}

A precise determination of the critical temperature and density for technically important fluids would be possible on the basis of the digital image for the visual observation of the phase boundary in the vicinity of the critical point since the sensitivity and resolution are higher than those of naked eyes. In addition, the digital image can avoid the personal uncertainty of an observer. A strong density gradient occurs in a sample cell at the critical point due to gravity. It was carefully assessed to determine the critical density, where the density profile in the sample cell can be observed from the luminance profile of a digital image. The density-gradient profile becomes symmetric at the critical point. One of the best fluids, whose thermodynamic properties have been measured with the highest reliability among technically important fluids, would be carbon dioxide. In order to confirm the reliability of the proposed method, the critical temperature and density of carbon dioxide were determined using the digital image. The critical temperature and density values of carbon dioxide are ( \(304.143\,\pm \,0.005)\hbox { K}\) and ( \(467.7\,\pm \,0.6)\) kg \(\cdot \) m \(^{-3}\) , respectively. The critical temperature and density values agree with the existing best values within estimated uncertainties. The reliability of the method was confirmed. The critical pressure, 7.3795 MPa, corresponding to the determined critical temperature of 304.143 K is also proposed. A new set of parameters for the vapor-pressure equation is also provided.     

On the Structure of the Superfluid State and Quasiparticle Spectrum in a Bose Liquid with a Suppressed Bose–Einstein Condensate

A self-consistent model of the superfluid (SF) state of a Bose liquid with strong interaction between bosons and a weak single-particle Bose–Einstein condensate (BEC) is considered. The ratio of the BEC density n ₀ to the total particle density n of the Bose liquid is used as a small parameter of the model, n ₀/n?1, unlike in the Bogolyubov theory of a quasi-ideal Bose gas, in which the small parameter is the ratio of the number of supracondensate excitations to the number of particles in an intensive BEC, (n?n ₀)/n ₀?1. A closed system of nonlinear integral equations for the normal ~Σ₁₁(p, ω) and anomalous ~Σ₁₂(p, ω) self-energy parts is obtained with account for terms of first order in the BEC density. A renormalized perturbation theory is used, which is built on combined hydrodynamic (at p→0) and field (at p≠0) variables with analytic functions ~Σ _ij (p, ε) at pε0 and ε→0 and a nonzero SF order parameter ~Σ₁₂(0, 0)≠0, proportional to the density ρ _s of the SF component. Various pair interaction potentials U(r) with inflection points in the radial dependence and with an oscillating sign-changing momentum dependence of the Fourier component V(p) are considered. Collective many-body effects of renormalization (“screening”) of the initial interaction, which are described by the bosonic polarization operator Π(p, ω), lead to a suppression of the repulsion [V(p)<0] and an enhancement of the effective attraction [V(p)<0] in the respective domains of nonzero momentum transfer, due to the negative sign of the real part of Π(p, ω) on the “mass shell” ω=E(p). In the framework of the “soft spheres” model with the single fitting parameter—the value of the repulsion potential at r=0—the quasiparticle spectrum E(p) is calculated, which is in good accordance with the experimental spectrum E _exp(p) of elementary excitations in superfluid ⁴He. It is shown that the roton minimum in the quasiparticle spectrum is directly associated with the first negative minimum of the Fourier component of the renormalized (“screened”) potential of pair interaction between bosons.     

Estimation of the Heat Transfer Coefficient in a Liquid–Solid Fluidized Bed Using an Artificial Neural Network

A non-iterative procedure has been developed using an artificial neural network (ANN) for estimating the fluid–particle heat transfer coefficient, h_fp, in a liquid–solid fluidized system. It is assumed that in a liquid–solid system, the liquid temperature is time dependent, and the input parameters and output parameters for the ANN are considered on a linear scale. The output configuration yields an optimal ANN model with 10 neurons in each of the three hidden layers. This configuration is capable of predicting the value of Bi in the range of 0.1–10 with an error of less than 3%. The heat transfer coefficient estimated using the ANN has been compared with the data reported in the literature and found to match satisfactorily.© Koninklijke Brill NV, Leiden and Society of Powder Technology, Japan, 2008