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Due to discrepancies observed between many experimental results and predictions from the Bell–Cameron–Lucas–Washburn (BCLW) imbibition equation, the BCLW equation was often modified by considering the effects of pore/throat characteristics. As previous works mainly focused on liquid–gas systems, the effects of the viscosity ratios are neglected. In this study, the nonwetting-/wetting-phase-viscosity ratio ( $$ \Psi $$ ) is varied by four orders of magnitude (0.018 to 8), which covers the common fluid viscosity in waterflooded tight reservoirs. Capillaries with irregular cross sections (namely, complex capillaries), which are recognized to more representative for porous media, are used to theoretically study imbibition kinetics in both the liquid–gas and liquid–liquid system. To considering the effects of viscosity ratio, we propose a modified imbibition equation based on the Poiseuille law and a piecewise method to calculate the equivalent radius for complex capillaries. The predictivity of the new imbibition equation is mathematically validated in varying viscosity ratios and geometries characteristics (such as the radius levels and the numbers/length ratios of radius levels). The study proves that an equivalent straight capillary can globally predict imbibition behaviors in complex capillaries. Except for a few scenarios, the equivalent radius of the straight capillary is affected by capillary geometries and viscosity ratios. Only in the early stage of imbibition ( $$ l_{x} /l \le 0.12\Psi /\left( {\Psi - 1} \right) $$ ), the modified imbibition equation can be expressed as a power-law relation (i.e., $$ l_{x} /l \propto \frac{1}{\Psi }t^{\alpha } $$ ) as $$ {\Psi } $$ is higher than 1. In general, it is more suitable to express the imbibition equations in a quadratic form, especially for liquid–liquid imbibition systems.

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International audience; Two-point statistical equations of the liquid phase indicator function are used to appraise the physics of liquid-gas shear flows. The contribution of the different processes in the combined scale/physical space is quantified by means of direct numerical simulations of a temporally liquid-gas shear layer. Light is first shed onto the relationship between twopoint statistics of the phase indicator and the geometrical properties of the liquid/gas interface, namely its surface density, mean and Gaussian curvatures. Then, the theory is shown to be adequate for highlighting the preferential direction of liquid transport in either scale or flow positions space. A direct cascade process, i.e. from large to small scales, is observed for the total phase indicator field, while the opposite applies for the randomly fluctuating part suggesting a transfer of 'energy' from the mean to the fluctuating component. In the space of positions within the flow, the flux tend to redistribute energy from the centreline to the edge of the shear layer. The influence of the mean shear rate and statistical inhomogeneities on the different scales of the liquid field are revealed.

Properties of the liquid-gas (LG) phase transition of thermal nuclear matter are investigated within the relativistic Hartree-Fock (RHF) theory, focusing on the role played by the in-medium balance between nuclear attraction and repulsion. Applying the RHF Lagrangian PKA1, rather different critical properties and LG phase diagrams are obtained in contrast to the other popular relativistic Lagrangians. Aiming at such notable model deviations, a series of testing parametrizations $x{\ensuremath{\kappa}}_{\ensuremath{\rho}}$ (${\ensuremath{\kappa}}_{\ensuremath{\rho}}$ being the $\ensuremath{\rho}$-tensor coupling strength) are proposed to bridge PKA1 and other popular Lagrangians. Along the systematics from PKA1 to the $x{\ensuremath{\kappa}}_{\ensuremath{\rho}}$ series and further to other popular Lagrangians, it is illustrated that the in-medium balance of nuclear attraction and repulsion, manifested as various modeling of the nuclear in-medium effects, is essential for the van der Waals-like behaviors of thermal nuclear matter, in which the residual nuclear in-medium effects deduced from the dominant attractive and repulsive channels play a significant role. Our study paves a way to model the in-medium nuclear interactions from the thermal statistic aspects of nuclear systems, e.g., referring to the critical temperature from future delicate experiments.

A simplified Anisimov–Wang variant of the complete scaling approach makes it possible to determine the amplitudes of singularities for the diameter of the phase coexistence curve (CXC) on the basis of the coefficients in the power series expansion of the mean-field free energy in the reduced temperature and pressure near the critical point. This method is applied to obtain the amplitudes for the leading critical singularities of the CXC diameter in the case of a fluid described in the framework of the mesoscopic mean-field model. The results obtained demonstrate that the amplitudes of leading singularities of the CXC diameter are determined by the mesoscopic asymmetry parameters of the heterophase fluid., Метод спрощеного “повного” скейлiнгу Анiсiмова–Ванга дозволяє знайти амплiтуди сингулярностей дiаметра кривої спiвiснування (КС) фаз за коефiцiєнтами розкладання середньопольової вiльної енергiї за ступенями приведених температури i густини в околi критичної точки. Цей метод застосовано при визначеннi амплiтуд головних критичних сингулярностей дiаметра КС для плину, що описується мезоскопiчною теорiєю. Згiдно з одержаними результатами, амплiтуди головних сингулярностей дiаметра КС визначаються мезоскопiчними параметрами асиметрiї гетерофазного плину.

Additive manufacturing is a key enabling technology in the manufacture of highly complex shapes, having very few geometric limitations compared to traditional manufacturing processes. The present paper aims at investigating mechanical properties at cryogenic temperatures for a 316L austenitic stainless steel, due to the wide possible cryogenic applications such as liquid gas confinement or superconductors. The starting powders have been processed by laser powder bed fusion (LPBF) and tested in the as-built conditions and after stress relieving treatments. Mechanical properties at 298, 77 and 4.2 K from tensile testing are presented together with fracture surfaces investigated by field emission scanning electron microscopy. The results show that high tensile strength at cryogenic temperature is characteristic for all samples, with ultimate tensile strength as high as 1246 MPa at 4.2 K and 55% maximum total elongation at 77 K. This study can constitute a solid basis for investigating 316L components by LPBF for specific applications in cryogenic conditions.

To describe the thermodynamic properties of xenon, a new fundamental low-parametric equation of state (in the form of reduced Helmholtz energy) is obtained with the help of the methods and approaches developed by the authors. It allows us to describe the thermal properties of gas, liquid, and fluid with a sufficiently high accuracy close to the accuracy of experiment in a range from the density in the ideal gas state to the density at the triple point, excluding the critical region. The caloric properties and speed of xenon sound are calculated without involving any caloric data, with the exception of ideal gas enthalpy. The values of isobaric heat capacity, sound speed, and other thermodynamic properties obtained by calculations are in good agreement with the experimental data.

This study investigates the multiphase flow of a liquid-gas-particle mixture in dam break. The open source codes, OpenFOAM and CFDEMproject, were used to reproduce the multiphase flow. The results of the present study are compared with those of previous results obtained by numerical and experimental methods, which guarantees validity of present numerical method to handle the multiphase flow. The particle density ranging from 1100 to 2500 kg/m3 is considered to investigate the effect of the particle density on the behavior of the free-surface and the particles. The particle density has no effect on the liquid front, but it makes the particle front move with different velocity. The time when the liquid front reach at the opposite wall is independent of particle density. However, such time for particle front decrease as particle density increases, which turned out to be proportional to particle density. Based on these results, we classified characteristics of the movement by the front positions of the liquid and the particles. Eventually, the response of the free-surface and particles to particle density is identified by three motion regimes of the advancing, overlapping and delaying motions.

In this paper, a qualitative explanation of the causes of surface tension forces at a liquid - gas interface acting parallel to an interface is presented. None of the common explanations of surface tension given in preliminary physics courses consider the reasons behind the attractive forces between nearest neighbor molecules acting parallel to a surface. The earlier proposed explanations are based on the assumption that there is a concentration gradient at the liquid - gas interface. The analysis is based on considering the anisotropic pressure tensor in the interface layer. Unfortunately, these explanations are difficult to understand in preliminary physics courses. Additionally, they do not pay enough attention to the physical reasons for the formation of a special surface layer with the distance between the nearest neighbors in the direction parallel to the surface greater than in the direction normal to it. In this paper, a simple qualitative explanation of surface tension forces at a liquid - gas interface is provided. The consideration includes the reasons for the formation of a special liquid - gas interface and the reasons for the appearance of tangent surface tension forces. The instability of the liquid - gas interface and the associated fluctuations are also discussed.

In the vicinity of critical point neither the nominal liquid nor the nominal gas is a single, homogeneous phase. This is a consequence of the presence of heterophase fluctuations. Theoretical models accounting for such fluctuations are necessary to estimate their role and importance at the gas-liquid criticality. Two mesoscopic models of the heterophase fluid are formulated here to solve this problem. The first one is a mean-field mesoscopic lattice model of fluid in which the lattice cells are occupied by “bubbles” and “droplets” called liquid-like and gas-like fluctuons respectively. In this model an order parameter is introduced to characterize the two-state mesoscopic structure. Its relation to the Van der Waals order parameter is found, an equation of state is deduced, and the phase coexistence curve is determined. The Yang-Yang anomaly amplitude and the amplitudes of the leading singular terms of the diameter of the density-temperature coexistence curve (density diameter) are determined in terms of the mesoscopic parameters of asymmetry. In the second model, which generalizes the first one, the fluctuons have no fixed shape and volume. Criticality of the irregular array of fluctuons is then studied.

Results from classical molecular dynamics simulations of infinite nuclear systems with varying density, temperature and isospin content are used to calculate the symmetry energy at low densities. The results show an excellent agreement with the experimental data and corroborate the claim that the formation of clusters has a strong influence on the symmetry energy in the liquid–gas coexistence region.

This paper describes a proposition of use of Hilbert Transform to time delay estimation in radioisotope measurements of two-phase flow. It presents results of simulation study of the modified crosscorrelation method, in which the Hilbert Transform of one measured signal is used. The simulations have been carried out for models of stochastic signals, corresponding to signals received in investigations of liquid-gas flow through horizontal pipeline, carried out with use of gamma-ray absorption technique. It has been stated that the described method provides better metrological properties than classical cross-correlation.

Based on the isospin-dependent quantum molecular dynamics model, finite-size scaling effects on nuclear liquid--gas phase transition probes are investigated by studying the de-excitation processes of six thermal sources of different sizes with the same initial density and similar $N/Z$. Using several probes including the total multiplicity derivative ($dM_{tot}/dT$), second moment parameter ($M_2$), intermediate mass fragment (IMF) multiplicity ($N_{IMF}$), Fisher's power-law exponent ($\tau$), and Ma's nuclear Zipf's law exponent ($\xi$), the relationship between the phase transition temperature and the source size has been established. It is observed that the phase transition temperatures obtained from the IMF multiplicity, Fisher's exponent, and Ma's nuclear Zipf's law exponent have a strong correlation with the source size. Moreover, by employing the finite-size scaling law, the critical temperature $T_c$ and the critical exponent $\nu$ have been obtained for infinite nuclear matter., Comment: 5 pages, 7 figures

In this paper, we demonstrate experimentally that by generating two orthogonal standing waves at the liquid surface, one can control the motion of floating microparticles. The mechanism of the vortex generation is somewhat similar to a classical Stokes drift in linear progression waves. By adjusting the relative phase between the waves, it is possible to generate a vortex lattice, seen as a stationary horizontal flow consisting of counter-rotating vortices. Two orthogonal waves which are phase-shifted by &pi, / 2 create locally rotating waves. Such waves induce nested circular drift orbits of the surface fluid particles. Such a configuration allows for the trapping of particles within a cell of the size about half the wavelength of the standing waves. By changing the relative phase, it is possible to either create or to destroy the vortex crystal. This method creates an opportunity to confine surface particles within cells, or to greatly increase mixing of the surface matter over the wave field surface.

High-temperature and pressure boundaries of the liquid and gas states have not been defined thermodynamically. Standard liquid-state physics texts use either critical isotherms or isobars as ad hoc boundaries in phase diagrams. Here we report that percolation transition loci can define liquid and gas states, extending from super-critical temperatures or pressures to “ideal gas” states. Using computational methodology described previously we present results for the thermodynamic states at which clusters of excluded volume (VE) and pockets of available volume (VA), for a spherical molecule diameter σ, percolate the whole volume (V = VE + VA) of the ideal gas. The molecular-reduced temperature (T)/pressure(p) ratios ( ) for the percolation transitions are = 1.495 ± 0.015 and = 1.100 ± 0.015. Further MD computations of percolation loci, for the Widom-Rowlinson (W-R) model of a partially miscible binary liquid (A-B), show the connection between the ideal gas percolation transitions and the 1st-order phase-separation transition. A phase diagram for the penetrable cohesive sphere (PCS) model of a one-component liquid-gas is then obtained by analytic transcription of the W-R model thermodynamic properties. The PCS percolation loci extend from a critical coexistence of gas plus liquid to the low-density limit ideal gas. Extended percolation loci for argon, determined from literature equation-of-state measurements exhibit similar phenomena. When percolation loci define phase bounds, the liquid phase spans the whole density range, whereas the gas phase is confined by its percolation boundary within an area of low T and p on the density surface. This is contrary to a general perception and opens a debate on the definitions of gaseous and liquid states. info:eu-repo/semantics/publishedVersion

We present a novel methodology for accurate treatment of viscous terms in evaporation problems. The proposed scheme is an extension of the sharp viscous treatment of Kang et al. (2000) [7] to 3D phase change problems. To ensure accuracy and grid converging solutions, a new implicit approach to computing viscous fluxes across the phase interfaces is proposed, which was previously unavailable in fixed grid numerical schemes. Analytical relations were derived for the jump in velocity gradients across the 2D and 3D phase interfaces, an important constituent of the proposed scheme. The relations show a non-vanishing jump in the tangential gradients across the phase interface that are associated with evaporative flux and interfacial curvature. The proposed methodology demonstrated first order accuracy in canonical test cases. It is general and applicable to arbitrarily oriented interfaces, and can be readily implemented in existing evaporation flow solvers.

The behavior of fluids in the vicinity of the liquid–gas critical point is studied within the cell fluid model framework. The analytic method for deriving the equation of state of a cell fluid model in the low-temperature region (T Tc are discussed.

Flexible risers transporting hydrocarbon liquid–gas flows may be subject to internal dynamic fluctuations of multiphase densities, velocities and pressure changes. Previous studies have mostly focused on single-phase flows in oscillating pipes or multiphase flows in static pipes whereas understanding of multiphase flow effects on oscillating pipes with variable curvatures is still lacking. The present study aims to numerically investigate fundamental planar dynamics of a long flexible catenary riser carrying slug liquid–gas flows and to analyse the mechanical effects of slug flow characteristics including the slug unit length, translational velocity and fluctuation frequencies leading to resonances. A two-dimensional continuum model, describing the coupled horizontal and vertical motions of an inclined flexible/extensible curved riser subject to the space–time varying fluid weights, flow centrifugal momenta and Coriolis effects, is presented. Steady slug flows are considered and modelled by accounting for the mass–momentum balances of liquid–gas phases within an idealized slug unit cell comprising the slug liquid (containing small gas bubbles) and elongated gas bubble (interfacing with the liquid film) parts. A nonlinear hydrodynamic film profile is described, depending on the pipe diameter, inclination, liquid–gas phase properties, superficial velocities and empirical correlations. These enable the approximation of phase fractions, local velocities and pressure variations which are employed as the time-varying, distributed parameters leading to the slug flow-induced vibration (SIV) of catenary riser. Several key SIV features are numerically investigated, highlighting the slug flow-induced transient drifts due to the travelling masses, amplified mean displacements due to the combined slug weights and flow momenta, extensibility or tension changes due to a reconfiguration of pipe equilibrium, oscillation amplitudes and resonant frequencies. Single- and multi-modal patterns of riser dynamic profiles are determined, enabling the evaluation of associated bending/axial stresses. Parametric studies reveal the individual effect of the slug unit length and the translational velocity on SIV response regardless of the slug characteristic frequency being a function of these two parameters. This key observation is practically useful for the identification of critical maximum response.

We are concerned with the vortex sheet solutions for the inviscid two-phase flow in two dimensions. In particular, the nonlinear stability and existence of compressible vortex sheet solutions under small perturbations are established by using a modification of the Nash-Moser iteration technique, where a priori estimates for the linearized equations have a loss of derivatives. Due to the jump of the normal derivatives of densities of liquid and gas, we obtain the normal estimates in the anisotropic Sobolev space, instead of the usual Sobolev space. New ideas and techniques are developed to close the energy estimates and derive the tame estimates for the two-phase flows.

Motivated by ultrasound-induced pulmonary hemorrhage, we computationally study acoustic waves in water interacting with a perturbed water-air interface. We demonstrate that baroclinic vorticity due to the misaligned pressure (waves) and density (interface) gradients drives the perturbation growth.

The experimental measures of the multiplicity derivatives---the moment parameters, the bimodal parameter, the fluctuation of maximum fragment charge number (normalized variance of ${Z}_{\mathrm{max}}$, or NVZ), the Fisher exponent ($\ensuremath{\tau}$), and the Zipf law parameter ($\ensuremath{\xi}$)---are examined to search for the liquid-gas phase transition in nuclear multifragmention processes within the framework of the statistical multifragmentation model (SMM). The sensitivities of these measures are studied. All these measures predict a critical signature at or near to the critical point both for the primary and secondary fragments. Among these measures, the total multiplicity derivative and the NVZ provide accurate measures for the critical point from the final cold fragments as well as the primary fragments. The present study will provide a guide for future experiments and analyses in the study of the nuclear liquid-gas phase transition.

The paper presents application of the gamma-absorption method to a two-phase liquid-gas flow investigation in a horizontal pipeline. The water-air mixture was examined by a set of two Am-241 radioactive sources and two NaI(Tl) scintillation probes. For analysis of the electrical signals obtained from detectors the cross-spectral density function (CSDF) was applied. Results of the gas phase average velocity measurements for CSDF were compared with results obtained by application of the classical cross-correlation function (CCF). It was found that the combined uncertainties of the gas-phase velocity in the presented experiments did not exceed 1.6% for CSDF method and 5.5% for CCF.

The rapid development of tomography methods particularly electrical, X and gamma rays allows for a wide range of the information about flow structure. However, all of such methods are quite complicated. At the same time much simpler systems as the measuring system of gamma rays absorption, allows to obtain a all key flow information which describe the two-phase flow. In the article the results of analyzes of radiometric signal that not only allow to recognize the type of flow, but also the assessment of forming structures are presented. Calculation and interpretation of the data were based on the crosscorrelation and cross-spectral density function. In order to verify the calculations the photographic documentation made during the measurements was used.

We present first-principle predictions for the liquid-gas phase transition in symmetric nuclear matter employing both two- and three-nucleon chiral interactions. Our discussion focuses on the sources of systematic errors in microscopic quantum many body predictions. On the one hand, we test uncertainties of our results arising from changes in the construction of chiral Hamiltonians. We use five different chiral forces with consistently derived three-nucleon interactions. On the other hand, we compare the ladder resummation in the self-consistent Green's functions approach to finite temperature Brueckner--Hartree--Fock calculations. We find that systematics due to Hamiltonians dominate over many-body uncertainties. Based on this wide pool of calculations, we estimate that the critical temperature is $T_c=16 \pm 2$ MeV, in reasonable agreement with experimental results. We also find that there is a strong correlation between the critical temperature and the saturation energy in microscopic many-body simulations., Comment: 14 pages, 7 figures

This study focuses on students’ understandings of a liquid–gas system with liquid–vapor equilibrium in a closed system using a pressure–temperature (P–T) diagram. By administrating three assessment questions concerning the P–T diagrams of liquid–gas systems to students at the beginning of undergraduate general chemistry course, lack of understanding of the fundamental concepts concerning liquid–vapor equilibria, the ideal gas law, and boiling points was identified. A learning program for liquid–gas systems was then designed for students at the undergraduate general chemistry level to address this issue. It consists of a laboratory experiment and postlaboratory exercise and is intended to provide integrated student understanding. During the learning program, students actively used the related concepts to explain the physical chemistry of a liquid–gas system and integrated the concepts to explain practical systems in their daily lives using a P–T diagram. An outline of the learning program is reported on th...

Two-phase flows are commonly found in the extraction and production of petroleum and the separation process involving the liquid gaseous phases has great importance. The separators used for this purpose have usually high separation efficiency, however their large dimensions make difficult the construction, installation and maintenance of these equipment in offshore applications. An alternative to reduce the dimensions of these systems is to use a distribution method that can divide the flow, making it possible to use more than one separator. This distributor ideally will produce flow rates equitably distributed across all outlets. The distribution system proposed in this work has a cyclonic chamber, where a vertical ascendant liquid film flow occurs under the action of centrifugal and gravitational fields. This study aims to analyze the development and behavior of the liquid film flow and the efficiency of the distribution system as a function of the liquid and gas flow rates, using an experimental setup and CFD simulations performed with the software ANSYS-CFX 15.0. For the experimental setup a Wire-mesh sensor with 12×12 wires and two others with 8×8 wires were used in order to analyze the variation of the thickness of the liquid film formed in the cyclonic chamber and evaluate the flow pattern at the inlet of the system. In the numerical study, a three-dimensional hybrid mesh was constructed, using the Eulerian-Eulerian two fluid model coupled with the compressive discretization scheme to capture the liquid-gas interface, the Shear Stress Transport (SST) turbulence model and the finite volume based on finite elements. It was possible to carry out a numerical model validation through a comparison with the experimental data. The development of this numerical model might help the advance of new technologies applied in the petroleum industry and this study is focused on area that lacks more studies related to vertical ascendant liquid film flows under centrifugal and gravitational field effects.

In this work, exploratory numerical simulations of liquid–gas flows in horizontal pipes are conducted for three different sets of conditions in the annular and stratified-annular flow regimes. Careful dimensional analysis is used to choose governing parameters in a way that yields flows that are relevant to realistic engineering applications, while remaining computationally tractable. Statistics of the velocity field and height of the liquid film are computed as a function of circumferential location in the pipe, demonstrating the existence of a viscous sublayer within the liquid film, as well as a viscous layer near the interface and a log law region within the gas core. The probability of dry-out conditions at the wall in upper regions of the pipe is shown to increase as gravitational effects increase. Circumferential motion of the liquid and gas phases within the pipe cross section are analyzed, informing possible mechanisms for sustainment of the liquid film. A simple model is developed that helps to characterize the dynamics of the liquid annulus and aids in understanding the effect of secondary gas flow on the circumferential motion of the film. Void fraction, film height, and film asymmetry are compared with experimental correlations available in the literature.

Electrical resistance tomography (ERT) reconstructs internal resistance images of the field from electrical measurements on the surface. The objective of this paper is to obtain the tomogram of the liquid-gas regime of ERT system by using multiple excitation sources. A linear back projection algorithm was implemented as a basic algorithm. Then, it was modified to suit the implementation of multiple excitation sources. A liquid-gas regime in the steel pipe was used as a tested medium. The analysis and performance of the image reconstructed which applies multiple excitation sources were compared with the single excitation technique. As a common strategy applied a single excitation source and produce problem especially at the center of the pipe, this paper mainly focuses on image reconstruction of multiple excitation sources. As a conclusion, 50% of the excitation source cannot produce the image as expected. Tomograms that produced by using the single excitation source were much better than the images obtained by using 50% of the excitation source.

Our early experimental investigation has demonstrated the anomalous surface tension temperature dependence σ(T) at the interface between coexisting liquid-gas phases in magnetic fluids that undergo field-induced first-order phase transition. The σ(T) dependence is anomalous because the drops of a liquid phase condensed under the action of the applied magnetic field H at high temperature T2 exhibit larger surface tension σ(T2) > σ(T1) than the drops condensed at low temperature T1 σ(T1) than the drops condensed at low temperature T1 < T2. This study verifies and confirms the results of the previous experimental investigation of σ(T) in magnetic fluids by performing the experiment, which is based on the analysis of the Plateau-Rayleigh instability of a gas-liquid interface in a zero magnetic field. A novel explanation of this phenomenon is given in the framework of the Stockmayer model. The anomalous increase in σ(T) is explained by the increase in particle concentration difference in gas and liquid phases, which can be attributed to the high field intensity ...

Within a relaxation time approach using free nucleon-nucleon cross sections modified by the in-medium nucleon masses that are determined from an isospin- and momentum-dependent effective nucleon-nucleon interaction, we investigate the specific shear viscosity ($\eta/s$) of neutron-rich nucleonic matter near its liquid-gas phase transition. It is found that as the nucleonic matter is heated at fixed pressure or compressed at fixed temperature, its specific shear viscosity shows a valley shape in the temperature or density dependence, with the minimum located at the boundary of the phase transition. Moreover, the value of $\eta/s$ drops suddenly at the first-order liquid-gas phase transition temperature, reaching as low as $4\sim5$ times the KSS bound of $\hbar/4\pi$. However, it varies smoothly for the second-order liquid-gas phase transition. Effects of the isospin degree of freedom and the nuclear symmetry energy on the value of $\eta/s$ are also discussed., Comment: 6 pages, 5 figures

Recent advances in the knowledge of heat transport near the liquid-gas critical point under the influence of the piston effect are reviewed with an emphasis on the different physical mechanisms and timescales in regard to thermal and density relaxations. Near the critical point, thermophysical properties exhibit singular behaviors, such as the diverging compressibility and vanishing thermal diffusivity. The resulting fast thermalization leads to the unexpected discovery of the piston effect. We describe the previous theoretical, numerical, and experimental investigations of this unique critical phenomenon and related topics, including its thermoacoustic nature with various nonlinear features on the acoustic timescale. Hydrodynamic and thermovibrational instabilities on the diffusion timescale in near-critical fluids are addressed as well. The review ends with a brief discussion of the merits and limitations of selected research methods in common use.

A new method of describing the liquid-gas phase transition is presented. It is assumed that the phase transition is characterized by a significant change of the particle density distribution as a result of energy supply at the boiling point that leads to structural changes but not to heating. Structural changes are described by an additional state characteristics of the system—the distribution density of the particles which is presented by an independent balance equation. The mathematical treatment is based on a special form of the internal energy and a source term in the particle balance equation. The presented method allows to model continua which have different specific heat capacities in liquid and in gas state.

Problems of acoustic wave propagation near the interface between media are discussed. The processes that occur at a liquid-gas interface are considered, and their characteristic features related to the effect of inhomogeneous waves are pointed out. The transmission factors of spherical and cylindrical waves incident on the aforementioned interface are calculated with allowance for the contribution of the inhomogeneous component. Experimental dependences of the transmission factor on frequency and source depth measured with respect to the interface are presented. It is shown that the lower the frequency generated by the source and the closer the source to the water-air interface, the higher the acoustic transparency of the interface.

On the basis of horizon thermodynamics, we study the thermodynamic stability and $P-V$ criticality of topological black holes constructed in Ho\v{r}ava-Lifshitz (HL) gravity without the detailed-balance condition (with general $\epsilon$). In the framework of horizon thermodynamics, we do not need the concrete black hole solution (the metric function) and the concrete matter fields. It is shown that the HL black hole for $k=0$ is always thermodynamically stable. For $k=1$, the thermodynamic behaviors and $P-V$ criticality of the HL black hole are similar to those of RN-AdS black hole for some $\epsilon$. For $k=-1$, the temperature is classified into six types by their different features. Among them, we mainly focus on the type with triply degenerate thermodynamic state. It is also shown that there is a "thermodynamic singularity" for the $k=-1$ HL black hole, where the temperature and Gibbs free energy both diverge apart from a special pressure $P_s$., Comment: 10 pages, 11 figures

The study of liquid gas phase transition in fragmentation of nuclei in heavy ion collisions has been extended to the strangeness sector using the statistical model for multifragmentation. Helmholtz's free energy, specific heat and few other thermodynamic observables have been analyzed in order to examine the occurence of phase transition in the strange matter. The bimodal behaviour of the largest cluster formed in fragmentation also strongly indicates coexistence of both the phases. The presence of hyperons strengthens the signals and also shifts the transition temperature to lower values., 5 Pages, 7 Figures

Three-phase liquid-gas-solid flows under microgravity condition are studied. An Eulerian-Lagrangian computational model was developed and used in the simulations. In this approach, the liquid flow was modeled by a volume-averaged system of governing equations, whereas motions of particles and bubbles were evaluated using the Lagrangian trajectory analysis procedure. It was assumed that the bubbles remained spherical, and their shape variations were neglected. The bubble-liquid, particle-liquid and bubbl-particle two-way interactions were accounted for in the analysis. The discrete phase equations used included drag, lift, buoyancy, and virtual mass forces. Particle-particle interactions and bubble-bubble interactions were accounted for by the hard sphere model. Bubble coalescence was also included in the model. The transient flow characteristics of the three-phase flow were studied; and the effects of gravity, inlet bubble size and g-jitter acceleration on variation of flow characteristics were discussed. The low gravity simulations showed that most bubbles are aggregated in the inlet region. Also, under microgravity condition, bubble transient time is much longer than that in normal gravity. As a result, the Sauter mean bubble diameter, which is proportional to the transient time of the bubble, becomes rather large, reaching to more than 9 mm. The bubble plume in microgravity exhibits a plug type flow behavior. After the bubble plume reaches the free surface, particle volume fraction increases along the height of the column. The particles are mainly located outside the bubble plume, with very few particles being retained in the plume. In contrast to the normal gravity condition, the three phases in the column are poorly mixed under microgravity conditions. The velocities of the three phases were also found to be of the same order. Bubble size significantly affects the characteristics of the three-phase flows under microgravity conditions. For the same inlet bubble number density, the flow with larger bubbles evolves faster. The simulation results showed that the effect of g-jitter acceleration on the gas-liquid-particle three phase flows is small.

Despite numerous investigations in the literature on slip flows in textured microchannels, experimental results were seldom in agreement with the theory. It is conjectured that contamination of the liquid-gas interface by impurities might be one of the sources of this discrepancy. However, the effect of impurities on slippage at the liquid-gas interface is neither understood nor previously reported. To this end, this work presents numerical investigation on the flow past a liquid-gas interface embedded with solid particles in textured microchannels. Initially, we present numerical simulations past transverse ribs with cylindrical particles on the liquid-gas interface. A reduction in effective slip length (or slip loss) with respect to the particle-free interface as a function of gas fraction, constriction ratio, and particle position was quantified. A significant slip loss (∼20-80%) was induced, owing to acceleration-deceleration cycles experienced by the liquid advecting across the particle-laden liquid-...

Condensation and evaporation are ubiquitous phenomena in nature. When we have a liquid partially filling a closed container, evaporation starts to happen, causing vapour formation in the remaining space. As the gaseous molecules bounce around, some of them hit the liquid surface and condense back into their original phase. This process evolves until there are as many molecules condensing as there are evaporating, that is, when the system reaches equilibrium. In this paper we introduce a very simple model addressed to undergraduate students and teachers that provides the temporal behaviour of this process. Using the results we propose an experimental technique to measure condensation coefficients.

By numerical simulation of basic flow, this paper extends Floquet stability analysis of interfacial flow with periodic fluctuation into large density ratio range. Stability of a liquid aluminum jet in a coaxial nitrogen stream with velocity fluctuation is investigated by Chebyshev collocation method and the Floquet theory. Parametric resonance of the jet and the influences of different physical parameters on the instability are discussed. The results show qualitative agreement with the available experimental data.

The effects of air-flow pulsation and water and air flowrates on the hydrodynamics of liquid—gas and three-phase fluidized beds containing 3-mm glass beads have been studied in a 90-mm i.d. column. Under steady-flow conditions, both types of bed contained a relatively large number of small bubbles. With a pulsing air flow, however, a smaller number of much larger bubbles or slugs were formed. This was attributed to different mechanisms of bubble formation at the distributor. Variations in phase holdup were explained in terms of the effects of the operating parameters on the bubble characteristics. On a etudie dans une colonne de 90 mm de diametre interieur les effets de la pulsation air-ecoulement et des debits d'eau et d'air sur l' hydrodynamique de lits fluidises gaz—liquide et triphasiques contenant des billes de verre de 3 mm. Dans des conditions d'ecoulement en regime permanent, les deux types de lit contenaient un nombre relativement important de petites bulles. Toutefois, avec un ecoulement a air pulse, il s 'est forme un moins grand nombre de bulles de tres grande dimension ou de bouchons. Ceci est imputable aux differents mecanismes de formation des bulles au niveau du distributeur. Les variations dans la retention des phases sont expliquees par les effets des parametres operatoires sur les caracteristiques des bulles.

The nuclear equation of state (EOS) is probed from statistical parameters, determined in an excitation function experiment on p + Xe-nat reactions at 200-1400 MeV. Total charge (Z) distributions follow a cascade-[multi]fragmentation-evaporation (CFEM) model well. The caloric curve in regions supposedly dominated by fast processes is compatible with a pure statistical multifragmentation (SMM) process, where the temperature (T)-excitation energy (epsilon*) relation starts in the Fermi liquid phase and progresses into a liquid/gas coexistence region, where it remains up to 1400 MeV. A local peak in T at epsilon* = 2.1 MeV agrees with the idea of sudden fragmentation. (c) 2006 Elsevier B.V. All rights reserved.

In this paper, we investigate the liquid gas phase transition for the spin polarized nuclear matter. Applying the lowest order constrained variational (LOCV) method, and using two microscopic potentials, $AV_{18}$ and $UV_{14}$+TNI, we calculate the free energy, equation of state, order parameter, entropy, heat capacity and compressibility to derive the critical properties of spin polarized nuclear matter. Our results indicate that for the spin polarized nuclear matter, the second order phase transition takes place at lower temperatures with respect to the unpolarized one. It is also shown that the critical temperature of our spin polarized nuclear matter with a specific value of spin polarization parameter is in good agreement with the experimental result., 26 pages, 13 figures, 4 tables

We compare two approaches to describe the inner crust of neutron stars: on the one hand, the simple coexistence of a liquid (clusters) and a gas phase, and on the other hand, the energy minimization with respect to the density profile, including Coulomb and surface effects. We find that the phase-coexistence model gives a reasonable description of the densities in the clusters and in the gas, but the precision is not high enough to obtain the correct proton fraction at low baryon densities. We also discuss the surface tension and neutron skin obtained within the energy minimization., 7 pages, 8 figures, to be published in Phys. Rev. C

The fragmentation of excited hypernuclear system formed in heavy ion collisions has been described by the canonical thermodynamical model extended to three component systems. The multiplicity distribution of the fragments has been analyzed in detail and it has been observed that the hyperons have the tendency to get attached to the heavier fragments. Another important observation is the phase coexistence of the hyperons, a phenomenon which is linked to liquid gas phase transition in strange matter., 5 pages, 6 figures

When a container is set in motion, the free surface of the liquid starts to oscillate or slosh. Such effects can be observed when a glass of water is handled carelessly and the fluid sloshes or even spills over the rims of the container. However, beer does not slosh as readily as water, which suggests that foam could be used to damp sloshing. In this work, we study experimentally the effect on sloshing of a liquid foam placed on top of a liquid bath. We generate a monodisperse two-dimensional liquid foam in a rectangular container and track the motion of the foam. The influence of the foam on the sloshing dynamics is experimentally characterized: only a few layers of bubbles are sufficient to significantly damp the oscillations. We rationalize our experimental findings with a model that describes the foam contribution to the damping coefficient through viscous dissipation on the walls of the container. Then we extend our study to confined three-dimensional liquid foam and observe that the behavior of 2D and confined 3D systems are very similar. Thus we conclude that only the bubbles close to the walls have a significant impact on the dissipation of energy. The possibility to damp liquid sloshing using foam is promising in numerous industrial applications such as the transport of liquefied gas in tankers or for propellants in rocket engines., Comment: 17 pages, accepted in Physics of Fluids

The paper presents idea and an exemplary application of gamma-absorption in the measurement of gas bubbles transportation in a gas-liquid mixture flow through a horizontal pipeline. In the tests on laboratory installation two 241 Am radioactive sources and probes with NaI(Tl) scintillation crystals have been used. For analysis of electrical signals obtained from detectors the modified conditional averaging of the absolute value of delayed signal (CAAV) is proposed. The proposed method is based on the quotient of classical cross- correlation (CCF) and CAAV. Results of the time delay estimation and gas-phase velocity measurements are compared with one obtained using CCF. The combined uncertainties of the mean velocity of air bubbles evaluation in the presented experiment did not exceed 2.1% (CCF) and 1.7% (CCF/CAAV), which is a satisfactory result in industrial applications.

Thermal multifragmentation of hot nuclei is interpreted as the nuclear liquid-fog phase transition inside the spinodal region. The exclusive data for p(8.1 GeV) + Au collisions are analyzed within the framework of the statistical model SMM. It is found that the partition of hot nuclei is specified after expansion to a volume equal to V t = (2.6 ± 0.3)V 0. The freeze-out volume is found to be twice as large: V f = (5 ± 1)V 0. The similarity between multifragmentation and ordinary fission is discussed.