Liquid-vapor Phase Transition Research Articles

Simulating diffusion in the conditions of vapor-liquid phase transition by the molecular dynamics method

The molecular dynamics calculations of diffusion coefficients in binary Lennard-Jones systems have been carried out. The parameters of Lennard-Jones potentials correspond to argon and krypton atoms. The universal dependence of the reduced diffusion coefficient of krypton atoms on density for the homogeneous systems of low and middle densities is found. The deviations of the diffusion coefficients from the universal function are observed for the systems in the vapor – liquid phase transition region. The simulations have shown that almost all krypton atoms have situated inside the liquid phase of argon. Special numerical experiments have shown that the nanodroplets of argon are formed as a result of homogeneous nucleation and then the krypton atoms are captured by these droplets. This phenomenon decreases the diffusion coefficient of krypton atoms greatly.

Combined gravitation-flotation technology for technogenic gold placer concentration

Gold recovery from placer washing waste was carried out using a flotation method where circulating rough concentrate is used to increase the recovered metal content in the rougher flotation operation. Moreover, flotation is carried out with a mixture of air with hot steam. Pressure in bubbles drops and their sizes decrease as a result of vapor condensation at the first moment of time under conditions of vapor-air flotation. Heat exchange between the phases worsens when the bubble is compressed, and mass transfer stops at the minimum bubble size, while temperature and vapor pressure in the bubble reach their maximum. As the bubble grows in size, superheated steam becomes saturated and pressure in the bubble decreases resulting in resumed condensation. The bubble surface undergoes damped oscillations. When the bubble surface vibrates, the motion of a slowly developing concentration-capillary Marangoni flow to the center of the interphase film cannot compensate for its thinning by the counter thermocapillary flow with a high hydrodynamic stability potential from the film center to its periphery. The vapor-air flotation results obtained can be interpreted in the context of this mechanism of wetting film stability changes during the vapor-liquid phase transition. Pilot tests of gravity and gravity-flotation technologies for gold extraction from a technogenic placer of gold have been carried out. It has been proved that the main effect of using the developed configuration of the scheme and the mode of flotation with a vapor-air mixture is a decrease in the concentrate yield by ~ 25% rel. while maintaining the achieved level of recovery and concentrate quality. When using the combined technology, the added value of marketable products provides an increase in the value of net discounted income and the return on investment index, and a decrease in their payback period.

Lattice-Boltzmann model for van der Waals fluids with liquid-vapor phase transition

A lattice Boltzmann model (LBM) for two-phase flows with liquid-vapor phase transition based on a dynamic van der Waals theory [Phys. Rev. Lett. 94, 054501 (2005)] is proposed. The proposed model consists of two lattice Boltzmann equations (LBE): one for the Navier-Stokes-Korteweg (NSK) equations and the other for the temperature equation. In the thermal LBE, the equilibrium distribution function is redesigned by introducing a reference temperature, which is used to reduce the numerical errors of velocity divergence in the thermal LBE. A free-energy-based LBE is developed for the hydrodynamic equations and a novel force term is used to correctly recover the NSK equations. Several numerical simulations, including the liquid-vapor coexistence curve, phase separation, stationary droplet, droplet on partially wetting surface, droplet evaporation and bubble nucleate and departure, are conducted to validate the capability and performance of the present model. The numerical results of the proposed model are found to be in excellent agreement with the results of theoretical and/or the hybrid method. It is also shown that numerical stability and accuracy of the present models can be greatly improved by adjusting the reference temperature. The present models provide an effective predictive tool for two-phase flows involving phase change.

Passive building cooling achieved with a new class of thermal retrofit: The liquid vapour phase change material

For a period covering more than half of the last century and until now, the term “phase change material” (PCM) in context of passive building coolingunanimously referred to a class of materials undergoing solid–liquid phase transition in cyclic manner. In contrast to solid–liquid PCMs (SLPCMs), the liquid-vapour phase transition has not been capitalized in a similar way to cool buildings by passive means despite the clear notion that the latent heat of evaporation exceeds the latent heat of fusion by a significant margin. The present work is an endeavour towards offering a new passive cooling system for buildings in hot climate with the help of liquid–vapour phase transition. Unlike existing active evaporative cooling systems, the liquid–vapour PCM (LVPCM) system does not require any external power supply to induce cooling effect. In the hot climate of Delhi, India, a peak temperature dip of 2.22℃ was achieved with the LVPCM system. An average indoor heat gain reduction of 13.56% was realized which reached a maximum value of 20.51% during the experiment. This novel system could overcome the night time heating issue of SLPCM. Furthermore, several additional benefits (such as the use of environment friendly and low-cost materials, ease of installation etc) could make LVPCM a competitive alternative to the prevailing SLPCM technology.

Mesoscopic Lattice Boltzmann Modeling of the Liquid-Vapor Phase Transition.

We develop a mesoscopic lattice Boltzmann model for liquid-vapor phase transition by handling the microscopic molecular interaction. The short-range molecular interaction is incorporated by recovering an equation of state for dense gases, and the long-range molecular interaction is mimicked by introducing a pairwise interaction force. Double distribution functions are employed, with the density distribution function for the mass and momentum conservation laws and an innovative total kinetic energy distribution function for the energy conservation law. The recovered mesomacroscopic governing equations are fully consistent with kinetic theory, and thermodynamic consistency is naturally satisfied.

Thermodynamic Derivation of Scaling at the Liquid-Vapor Critical Point.

With the use of thermodynamics and general equilibrium conditions only, we study the entropy of a fluid in the vicinity of the critical point of the liquid–vapor phase transition. By assuming a general form for the coexistence curve in the vicinity of the critical point, we show that the functional dependence of the entropy as a function of energy and particle densities necessarily obeys the scaling form hypothesized by Widom. Our analysis allows for a discussion of the properties of the corresponding scaling function, with the interesting prediction that the critical isotherm has the same functional dependence, between the energy and the number of particles densities, as the coexistence curve. In addition to the derivation of the expected equalities of the critical exponents, the conditions that lead to scaling also imply that, while the specific heat at constant volume can diverge at the critical point, the isothermal compressibility must do so.

The EOS/resolution conspiracy: convergence in proto-planetary collision simulations

ABSTRACT We investigate how the choice of equation of state (EOS) and resolution conspire to affect the outcomes of giant impact (GI) simulations. We focus on the simple case of equal-mass collisions of two Earth-like 0.5-M⊕ proto-planets showing that the choice of EOS has a profound impact on the outcome of such collisions as well as on the numerical convergence with resolution. In simulations where the Tillotson EOS is used, impacts generate an excess amount of vapour due to the lack of a thermodynamically consistent treatment of phase transitions and mixtures. In oblique collisions this enhances the artificial angular momentum (AM) transport from the planet to the circum-planetary disc reducing the planet’s rotation period over time. Even at a resolution of 1.3 × 106 particles, the result is not converged. In head-on collisions, the lack of a proper treatment of the solid/liquid-vapour phase transition allows the bound material to expand to very low densities, which, in turn, results in very slow numerical convergence of the critical specific impact energy for catastrophic disruption $Q_{\rm {RD}}^{*}$ with increasing resolution as reported in prior work. The simulations where ANalytic Equation Of State (ANEOS) is used for oblique impacts are already converged at a modest resolution of 105 particles, while head-on collisions converge when they evidence the post-shock formation of a dense iron-rich ring, which promotes gravitational re-accumulation of material. Once sufficient resolution is reached to resolve the liquid-vapour phase transition of iron in the ANEOS case, and this ring is resolved, the value of $Q_{\rm {RD}}^{*}$ has then converged.

Effect of compositional variability due to thermal instability on critical phenomena in n-hexane + IL mixture

Isochoric heat capacity of binary n-hexane + IL (1-octyl-3-methylimidazolium chloride, abbreviated as [C8C1im]Cl) along the fixed isochore of 255.13 kg∙m−3 as a function of temperature near the critical point of pure solvent (n-hexane) have been measured. The measurements were performed for the selected concentration of 0.0089 mol fraction of IL in the three-, two-, and one-phase regions over a temperature range from (308 to 527) K at pressures to 4 MPa. The measurements were performed using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. The combined expanded uncertainty of the density (ρ), temperature (T), concentration (x), and isochoric heat capacity (CV) measurements at the 0.95 confidence level with a coverage factor of k = 2 is estimated to be 0.0015, 15 mK, 0.0001, and 0.03, respectively. The possibility of the chemical reactions occurring during isochoric heat capacity measurements at high temperatures has been discussed. The onset of the effects of thermal decomposition on the isochoric heat capacity of binary n-hexane + [C8C1im]Cl mixture was found at temperatures above approximately 420 K. The addition of n-hexane into the IL made little change in thermal stability of IL. The liquid–vapor phase transition parameters (TS=509.88 ± 0.05 K, ρS=255.13 kg∙m−3, and PS = 3.1175 MPa) have been measured using the technique based on isochoric heat capacity abrupt behavior. Addition of the IL (0.0089 mol fraction) increases the phase transition temperature of pure n-hexane by 2.17 K, while the phase transition pressure increases by 0.0734 MPa.

Spinodal and thermodynamic limit of superheat of gold

A four-parameter generalized Berthelot equation of state has been employed to determine the spinodal and the thermodynamic limit of superheat of liquid gold. It is established that gold obeys the two-parameter law of corresponding states. It is also established that the new parameters introduced in the attractive term of the equation of state are thermodynamic similarity parameters. It is shown that liquid gold can be superheated to a temperature 6719K. That is, liquid gold, under rapid heating, can be superheated to temperature 3476K above the boiling temperature without undergoing liquid-vapour phase transition. Above this temperature, liquid gold will undergo explosive boiling owing to homogeneous nucleation.

ПРИМЕНЕНИЕ СТРУЙНОЙ СХЕМЫ И РЕЖИМА ФЛОТАЦИИ ПАРОВОЗДУШНОЙ СМЕСЬЮ ПРИ ОБОГАЩЕНИИ ЗОЛОТОСОДЕРЖАЩИХ РУД

Increasing the economic efficiency of enrichment of refractory gold-bearing ores is possible by reducing the cost of opening sulphide gold-bearing concentrates by reducing the yield of flotation concentrate sent to pyro- or hydrometallurgical processing. It is important to maintain the achieved level of gold recovery into concentrate with a lower concentrate yield. In order to achieve this goal, the gold content in the main flotation operation is increased by mixing the rough concentrate separated from ½ part of the ore feed with another ½ part of it. Mixing in the flotation operation of products with a high level of wash ability (ability to separate) – initial feed and rough concentrate – is identical to an increase in the content of the extractable component in the original ore. In accordance with the new regime of flotation, the process is carried out in cold slurry with bubbles filled with hot steam. The physical basis of the new flotation regime is the dependence of the surface properties of air bubbles and surface forces that determine the stability of the liquid film separating the bubble and the particle on the temperature, which increases due to the heat of the vapor-liquid phase transition. Radial oscillations of the bubble surface as a result of pressure pulsations during condensation and vapor evaporation and surface thermal flows of liquid in the wetting film are factors that provide an increase in the completeness of gold recovery and the selectivity of flotation adhesion obtained in ore flotation experiments. In laboratory conditions, a comparison was made of the indicators obtained during the dressing of gold-bearing ores according to the factory and new schemes. It was revealed that the use of the developed technology allows, with a lower concentrate yield, to obtain an increase of 7.06% abs. extraction of gold into a concentrate of the best quality. A decrease in gold losses with flotation tailings is a consequence of an increase in the number of particles reaching the bubble surface due to radial oscillations of its surface and a weakening of the stability of the wetting film by the thermo-capillary mechanism. An increase in adhesion selectivity can be interpreted using the concept of surface forces of structural origin – an increase in the forces of hydrophobic attraction and hydrophilic repulsion with increasing temperature. The interaction of vapor bubbles with nanobubbles on the surface of the solid phase (wetting by the Cassie-Baxter mechanism) ensures efficient particle recovery by the coalescence mechanism of flotation.

Fluid-fluid and fluid-solid phase equilibria in carbon dioxide + waxy systems 1. CO2 + n-C17

The objective of the present work is to investigate the full phase diagram of a binary system composed of carbon dioxide and a heavy paraffin. An alkane with an odd carbon number was chosen since mixtures of paraffins crystallize in the orthorhombic structure like pure odd paraffins do. The normal-heptadecane was taken into consideration for this study as it has a melting temperature close to the ambient condition (295 K). The work consists in measuring both fluid phase equilibria and fluid-solid phase transition conditions. The measurement of liquid-vapor and liquid-liquid phase transition in the temperature range 273 - 363 K has been made as well as the measurements of solid crystallization up to 70 MPa. The influence of carbon dioxide content has been studied from 0 to 99%.

Scaling of Phase Diagram and Critical Point Parameters in Liquid-Vapour Phase Transition of Metallic Fluids

The first objective of this paper is to investigate the scaling behavior of liquid-vapor phase transition in FCC and BCCmetals starting from the zero-temperature four-parameter formula for cohesive energy. The effective potentials between the atoms in the solid are determined while using lattice inversion techniques as a function of scaling variables in the four-parameter formula. These potentials are split into repulsive and attractive parts, as per the Weeks–Chandler–Anderson prescription, and used in the coupling-parameter expansion for solving the Ornstein–Zernike equation that was supplemented with an accurate closure. Thermodynamic quantities obtained via the correlation functions are used in order to obtain critical point parameters and liquid-vapor phase diagrams. Their dependence on the scaling variables in the cohesive energy formula are also determined. An equally important second objective of the paper is to revisit coupling parameter expansion for solving the Ornstein–Zernike equation. The Newton–Armijo non-linear solver and Krylov-space based linear solvers are employed in this regard. These methods generate a robust algorithm that can be used to span the entire fluid region, except very low temperatures. The accuracy of the method is established by comparing the phase diagrams with those that were obtained via computer simulation. The avoidance of the ’no-solution-region’ of the Ornstein-Zernike equation in coupling-parameter expansion is also discussed. Details of the method and complete algorithm provided here would make this technique more accessible to researchers investigating the thermodynamic properties of one component fluids.

High-temperature and high-pressure density and liquid–vapor phase transition properties of methyl octanoate as main biofuel component

Thermodynamic properties of compressed fuels as density at liquids phase (PρT data) and two liquids-gas phases as saturated pressure, density, and temperature (PS,ρS,TS) are extremely important for engine performance as well as the transportation and storage of fuels. In this work single – and two–phase PρT data and liquid + gas phase equilibrium properties (PS,TS,ρS) of methyl octanoate (caprylate) as one of the key components of biofuels have been studied. The measurements were performed along 15 liquid and vapor isochores between (44.7 and 832.0) kg·m−3 over a temperature range from (298 to 438) K at pressures up to 17.33 MPa using a constant-volume piezometer technique. The study was concentrated in the two-phase region to accurately determine vapor-pressures and in the immediate vicinity of the phase-transition temperatures to precisely determine the phase boundary properties (PS,ρS,TS) on the liquid + gas equilibrium curve. In the low temperature range (far from the critical point) where the values of vapor-pressure are negligible small (<1 kPa, approximately at temperatures below 350 K), the saturated vapor phase of methyl octanoate was considered as ideal gas with volume of VG=RT/PS and ΔVLG≈VG=RT/PS, where the saturated liquid volume can be neglected, VG>>VL. This approach was used to simplify the calculation of the thermodynamic properties of methyl octanoate at saturation.

Monitoring of seismic attenuation change associated with vapor-liquid phase transition using time-lapse reflection seismic data in Kakkonda geothermal field, Japan

Seismic wave attenuation can potentially be used for the investigation of the fluid phase and flow properties in a fractured reservoir. However, seismic attenuation estimation is easily affected by various factors, such as tuning effects, source and receiver coupling, and effects from near-surface weathering layers. Time-lapse seismic attenuation estimation can avoid these problems because the above factors are canceled between surveys. We conducted time-lapse attenuation estimation using three reflection seismic surveys with different timings acquired in the Kakkonda geothermal field during a 12-day period spanning a well shut-in period. To investigate geothermal fluid changes associated with increased pore pressure, we propose an approach for estimating attenuation changes between time-lapse seismic surveys. Firstly, three seismic reflection sections were obtained from the corresponding time-lapse seismic data using the modified prestack time migration method, which can handle the uncertainties of migration velocity estimation in a highly fractured and structurally very complex medium, for which accurate velocity estimation is difficult to achieve using conventional methods. Then, time-lapse attenuation was evaluated for two of the three seismic reflection sections using the spectral ratio and the centroid frequency shift methods. Numerical modeling was conducted to verify our proposed procedure. Careful preprocessing was carried out to enhance the repeatability of time-lapse seismic data, especially on the frequency content, which is indirectly related to seismic attenuation. Finally, we demonstrated an increase of attenuation associated with an increase of pore pressure in and around the known super-shallow vapor-dominated reservoir during a short period (7 days) spanning from one day before the shut-in of producing well to a week after that. A possible cause of this short-period attenuation increase could be the vapor-liquid phase transition in the reservoir.

Investigation on the equilibrium distribution of methanol in transformer oil-immersed cellulosic insulation

Methanol in oil was used to indirectly evaluate the aging status of cellulosic paper insulation for oil-immersed transformers. However, the distribution of methanol in oil is affected by many factors, not only related to the oil–paper adsorption equilibrium, but also may be affected by the vapor–liquid phase transition. In this study, the adsorption experiments of mineral oil and standard cellulosic Kraft paper for methanol were designed to explore the adsorption equilibrium process at different oil–paper mass ratios under room temperature. The vapor–liquid equilibrium experiments of methanol between oil and gas were carried out to explore the effects of temperature and phase volume ratios. It turned out that: firstly, compared with mineral oil, the Kraft paper has a stronger adsorption capacity for methanol, which makes most of methanol adsorbed in paper when equilibrium at room temperature. Secondly, the increase of oil–paper mass ratios reduces the adsorption of Kraft paper for methanol and makes the equilibrium time longer. Particularly, at a higher oil–paper mass ratio, due to the less paper mass, methanol would “reverse diffusion” from paper to oil standard solution in the early stage of equilibrium. Finally, the presence of methanol in gas phase cannot be ignored. The increase of temperature makes more liquid methanol in oil transferred to the gas phase by the phase transition process, while increasing the oil–gas phase volume ratios in constant volume system can inhibit this process.

Robotic soft swim bladder using liquid–vapor phase transition

The swim bladder is crucial to underwater robots to enhance their overall performance and to expand their range of motion. However, previous attempts to incorporate this function have failed or have adopted mechanical swim bladders with high-disturbances. This study presents an entirely soft swim bladder capable of controlling buoyancy selectively and noiselessly, making it applicable to sensitive underwater environments. The soft swim bladder, which consists of an elastic cover layer, flexible heating elements, and three expandable pouches filled with low boiling point fluid, can express four modes of motion by varying buoyancy: sinking, suspending, rising, and fast-rising. The varying buoyancy is achieved through liquid-vapor phase transition of the fluid in the selected pouches when Joule heated above its boiling temperature. Moreover, the swim bladder is integrated with a shape memory alloy-based fishtail to form a soft fish robot. The synergy between the bladder and the tail allows the robot to explore a total of ten disparate modes of maneuvers, and their dynamic performance has been evaluated. The results of this study present the potential for the soft swim bladder to be utilized in any underwater robotic applications to enhance their swimming performance.

Vapor-Liquid Phase Transition in Fluctuating Hydrodynamics: The Most Probable Transition Path and its Computation

Vapor-Liquid Phase Transition in Fluctuating Hydrodynamics: The Most Probable Transition Path and its Computation

Estimation of the Critical Point Parameters of the Liquid–Vapor Phase Transition of Metals Using Experiments on the Isentropic Expansion of Shock-Compressed Porous Samples

The isentropic expansion of shock-compressed porous metals (Cu, W, Nb) are experimentally studied, and the experimental results are used to determine their thermodynamic parameters and electrical conductivity. These results allow us to conclude that some porous metals after shock compression and expansion have a two-phase structure. The presence of an additional phase at the isentropic expansion of these metals significantly changes the character of evaporation and the critical point parameters of the liquid–vapor phase transition that are estimated using experiments on the isentropic expansion of shock-compressed porous metals. In addition, the formation of the two-phase structure explains the large difference between the critical point parameters estimated by different methods for a large group of metals (U, W, V, Co, Mo, Ta, etc.).

Constant-volume vapor-liquid equilibrium for thermal energy storage: investigation of a new storage condition for solar thermal systems

The sector of thermal energy storage shows a number of alternatives that could have a relevant impact on the future of energy saving as well as renewable energy technologies. Among these, latent heat thermal energy storage technologies show promising results. Technologies that exploit solid-liquid phase change have already been widely proposed, but those technologies show common drawbacks limiting their application, such as high cost, low energy storage density and particularly low heat transfer properties. This work proposes to exploit the liquid-vapor phase transition in closed and constant volumes because it shows higher heat transfer properties. Consequently, the objective is to assess its energy storage performances in target temperature ranges. With respect to previous activity by the authors, this work proposes an exergy analysis of these systems, gives a methodology their deployment, and proposes a comparison between a new storage condition for solar thermal domestic hot water systems exploiting vapor-liquid equilibrium and conventional technologies. The exergy analysis is performed in reduced terms in order to have a generalized approach. Three hypothetical fluids with increasing degree of molecular complexity are considered in order to have a complete overview of the thermodynamic behavior of potential heat storage fluids. The analysis shows that the increased pressure of liquid systems has a major impact on exergy, resulting in vapor-liquid systems having less than 50% of the exergy variation of pressurized liquid systems. This is proven to have no impact on thermal energy storage. For the case study, the proposed methodology indicates that water itself is a strong candidate as a heat storage fluid in the new condition. Comparison shows that the new condition has a higher energy storage capacity at same volume. The useful temperature range is increased by 108% by setting a 10.5% volume vapor fraction at ambient temperature. The resulting improvement gives a 94% higher energy storage, with a maximum operating pressure of the system of less than 5 bar.

Self-propelled sessile droplets on a superheated and heterogeneous wetting surface

In this study, we investigated self-propelled sessile droplet evaporation on superheated surfaces with mixed wetting patterns. The primary reason for droplet motion was an increase in surface temperature and the difference in surface energy, which affected the moving contact line and moved droplets close to the wetting regions and then out to the heating surface. In this study, we observed that increases in temperature significantly influenced the changes in surface adhesion force. The force balance equation was used to demonstrate the existence of a moment of droplet movement. In addition, temperature data demonstrated energy conservation behaviour. The heterogeneous wetting surface exhibited greater differences in energy because of the energy expended during liquid–vapour phase transition and droplet movement.