Modeling of vapor–liquid–liquid equilibria in binary mixtures

Vapor compression and Joule–Thomson (JT) cycles provide cooling power at the boiling temperatures of the refrigerants. Maintaining a fixed pressure in the evaporator allows for a stable cooling temperature at the boiling point of a pure refrigerant. In these coolers enhanced cooling power can be achieved by using mixed refrigerants. However, gas mixtures usually do not change their phase at a constant temperature, therefore, the cooling temperature has to be actively controlled. An exception to this rule holds for binary mixtures that can form a vapor–liquid–liquid equilibrium (VLLE).Phase equilibria in binary mixtures are usually modeled based on experimental results only. In the present study only the vapor pressures of the pure mixture components are required. The calculated results of nitrogen–ethane, nitrogen–ethylene, and nitrogen–propane mixtures are compared with experimental data presented in literature showing deviations of less than 1%.     

Numerical analysis of liquid fraction in solid–liquid phase transformation of semisolid alloy

Abstract

The non-linear mathematical expression of liquid fraction in solid–liquid phase transformation of semisolid alloy was derived by thermodynamic equations, and the numerical solution of the non-linear mathematical expression was obtained by the Gauss Newton iteration algorithm. The solid–liquid phase transformation of hypereutectic Al–20Si–3Fe–1Mn–4Cu–1Mg alloy was studied by differential scanning calorimetry, and it was used for the expression reliability validation and compared with the Scheil linear regression expression. The results showed that the liquid fraction of the semisolid alloy was not increased linearly with the heating temperature increasing, but increased non-linearly, which was not consistent with the Scheil expression, and the growth rate of liquid fraction was not entirely the same in different temperature ranges. The non-linear mathematical expression data fit well with the experimental data, and the non-linear mathematical expression had a smaller discrete degree and higher credibility compared with the Scheil linear regression expression. The relationship of liquid fraction and heating temperature of the semisolid alloy can be reflected by means of the non-linear mathematical expression in the case of solid–liquid phase transformation.     

Shock waves in multi-component “liquid — gas bubbles — liquid drops” media

Shock waves are experimentally investigated in multi-component “liquid — gas bubbles — liquid drops” media. The data are obtained on the shock wave structure and properties in these multi-component media.     

Kinetic and electrical phenomena in gas–liquid systems

Disperse systems consisting of a liquid and gas bubbles located in it are considered. Two possible versions of evolution of bubbles under the conditions studied are assessed. In simple liquids, contact between two bubbles causes them to merge, as the separating film breaks. In the case of complex organic liquids, amphiphilic film is formed on the surface of bubbles, and the lifetime of bubbles in contact increases with their size. Under an external electric field, chains of bubbles are formed, lined up along the electric field potential lines. The presence of bubbles in liquid greatly lowers the breakdown threshold, as the critical parameters of the breakdown field in liquids are two to three orders of magnitude higher than those in gases at atmospheric pressure. Various breakdown mechanisms in liquids are discussed from the viewpoint of formation of the gas phase during the passage of an electric current through a liquid medium. The character of propagating a streamer in separate bubbles is studied with their random distribution in liquid and in the case of formation of some structures of bubbles; the critical parameters of disperse systems, that can lead to their electrical breakdown, are presented. Along with the general concepts of electrical breakdown in dispersed systems, experimental studies of these processes are considered, and the nature of electrical breakdown in liquid dielectrics, including transformer oil, is discussed.     

Spin relaxation in normal liquid3He:T 1 in the Fermi liquid (T≪T F) regime

The low-temperature (TT _F) spin relaxation timeT ₁ in normal liquid³He is calculated. First an expression forT ₁ is obtained using the Landau kinetic equation, which is in terms of the perturbations of the scattering amplitudes due to nuclear dipole-dipole interactions. These perturbations are obtained using the induced interaction model, which explicitly includes the effects of many-body correlations arising from the Pauli principle. The results are in good agreement with experiment, as well as with previous calculations.     

Acetylation of β-cyclodextrin in ionic liquid green solvent

The ionic liquid (IL), 1-butyl-3-methylimidzolium bromide ([C₄mim]Br), synthesized under supercritical CO₂, was developed as a green solvent for the dissolution, regeneration and acetylation of β-cyclodextrin (β-CD). The dissolution of β-CD in [C₄mim]Br of 25 wt% could be reached at 25 °C. The acetylation of β-CD was carried out under acetic anhydride in [C₄mim]Br in the absence of catalyst. β-CD acetates with different degrees of substitution of 0.07–1.14 were obtained directly under the homogeneous reaction conditions. The reaction medium of IL applied can be easily recycled and reused after the synthesis of β-CD acetate. The effects of reaction time, temperature, and acetic anhydride/AGU on the acetylation of β-CD were investigated. The acetylated β-CD samples were characterized by NMR, FT-IR, and X-ray diffraction (XRD) spectroscopy. It is the first time that we have demonstrated that ILs can be used as an environmentally friendly solvent for the acetylation of β-CD, which will open a new route to acetylation of β-CD under green solvent without catalyst.     

Application of dispersion–solidification liquid–liquid microextraction for the determination of triazole fungicides in environmental water samples by high-performance liquid chromatography

A simple, rapid and environmentally friendly method has been developed for the determination of four triazole fungicides (myclobutanil, tebuconazole, triadimenol, hexaconazole) in water samples by dispersion–solidification liquid–liquid microextraction coupled with high performance liquid chromatography-diode array detection. Several variables that affect the extraction efficiencies, including the type and volume of the extraction solvent and dispersive solvent, extraction time, effect of pH and salt addition, were investigated and optimized. Under the optimum conditions, the proposed method is sensitive and shows a good linearity within a range of 0.5–200 ng mL⁻¹, with the correlation coefficients (r) varying from 0.9992 to 0.9998. High enrichment factors were achieved ranging from 190 to 450. The recoveries of the target analytes from water samples at spiking levels of 1.0, 5.0 and 50.0 ng mL⁻¹ were between 84.8% and 110.2%. The limits of detection (LODs) for the analytes were ranged in 0.06–0.1 ng mL⁻¹, and the relative standard deviations (RSD) varied from 3.9% to 5.7%. The proposed method has been successfully applied for the determination of the triazole fungicides in real water samples.     

Is an oscillator-based measurement adequate in a liquid environment?

Oscillator-based measurements with quartz crystal resonators are analyzed. The investigations have shown that classical thickness monitors as well as many chemical vapor sensors based on a quartz crystal microbalance (QCM) work properly, even with simple oscillators. It was demonstrated that, for applications in a liquid environment, more sophisticated electronics are necessary. Also a comparison between the experimental results in liquids and the theoretical predictions is hardly possible without the knowledge of the oscillator behavior. As our solution, we present an automatic gain-controlled oscillator with two output signals, the oscillator frequency, and a signal that represents the damping of the quartz resonator. A calibration method is introduced, which allows one to calculate the series resonance frequency f/sub s/ and the series resistance R/sub s/ from these oscillator signals.     

Entrainment phenomenon in gas–liquid two-phase flow: A review

The gas–liquid separation equipments are aimed to be designed for maximum efficiency of phase separation. In order to maximize their capacity the flow rates are required to be optimized for the capital cost of equipment. This leads to the situation where the gas phase leaves the separation interface with high velocities and carry liquid phase along with it in the form of droplets reducing the equipment efficiency. This is known as entrainment or carryover. Depending on the nature of the separation interface i.e., turbulence intensity, bubble dynamics, the size and velocity distribution of liquid fragments, droplets at the separation interface varies. This is the main source of empiricism involved in the analysis of such equipments. The mechanics of motion of the dispersed liquid phase in bulk of gas is relatively well studied. In the present paper the various experimental, analytical and numerical investigations carried out to address the issues of entrainment/carryover are carefully analyzed. Further, a critical review has been presented for bringing out a coherent theme and a current status of the subject under reference.     

On the metastable miscibility gap in liquid Cu–Cr alloys

Electromagnetically levitated Cu–Cr alloy melts containing 5–70 at.% Cr were splat-quenched onto a chill substrate. The microstructure of the solidified alloys was investigated by scanning electron microscopy. The alloys containing 5–60 at.% Cr showed a droplet-shaped microstructure consisting of Cr-rich spheroids or and dendrites in a Cu-rich matrix, whereas those containing 65 and 70 at.% Cr showed a banded microstructure consisting of alternative Cu-rich and Cr-rich bands. Both types of microstructure presented evidence for metastable phase separation in Cu–Cr alloy compositions, thus verifying the existence of a broad miscibility gap in the undercooled liquid. However, the results suggested that the miscibility gap has a Cr-rich critical composition and a skewed geometry.     

The “slip” coefficient in two-phase liquid—gas flows

We present experimental data on the variation of the slip coefficient in two-phase liquid-gas flows.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 1, pp. 20–25, July, 1982.     

Numerical simulation of flow behavior of liquid and particles in liquid–solid risers with multi scale interfacial drag method

Formation of particle clusters in liquid–solid circulating fluidized beds significantly affects macroscopic hydrodynamic behavior of the system. A multi scale interfacial drag coefficient (MSD) is proposed to determine effects of particle clusters on the mesoscale structure, by taking momentum and energy balance of dense phase, dilute phase and interphase into account. Based on the transportation and suspension energy-minimization method, the multi scale interfacial drag coefficient model used in this work is combined with the Euler–Euler two fluid model to simulate the heterogeneous behaviors of liquid–solid circulating fluidized bed. It was found that the reduction in drag coefficient is at least an important factor for the simulation of clusters formation, and the core-annulus flow is observed in the riser. The liquid–solid flow regime was significantly affected by the down-flow of particles in the form of clusters near the walls of the riser. The calculated concentration of particles inside the riser compared reasonably well with the available experimental data obtained by Razzak et al.     

Application of pulsed electric current in immiscible liquid and droplet processing

Electromagnetic, chemical and thermo-mechanical processing can be applied to the fabrication of polymeric materials which react to external fields such as stress, temperature, moisture, pH, electric or magnetic fields to optimise properties. In this article, the application of the pulsed electromagnetic field in an immiscible liquid phase is reviewed. The droplet behaviour of polymer emulsion's liquid phases is enriched with significant complex phenomena. In emulsion, droplet break-up, size evolution, coalescence, coarsening, flocculation and interfacial interaction among droplets are assessed as a function of processing.

This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

Cavitation flow instability of subcooled liquid nitrogen in converging–diverging nozzles

The cavitation flow instability of subcooled liquid nitrogen in two types of converging–diverging (C–D) circular nozzles with throat diameters of 1.5 and 2.0 mm was experimentally investigated. Flow observations were also performed to clarify the instability phenomenon and the differences in cavitation behavior between the two nozzles. The cavitation mode changed from continuous mode to intermittent mode as the temperature of the subcooled liquid nitrogen decreased. This change occurred in both C–D nozzles when the temperature of the liquid reached approximately 76 K. Occurrence of the intermittent mode accompanying very large pressure-oscillations was considered to be caused by a drastic reduction of the speed of sound in the single-component, vapor–liquid flow because the speed of sound restricted the throat velocity in the C–D nozzle during cavitation. Oscillation pressure values in intermittent mode were much larger than those in continuous mode, peaking between 74 and 76 K. The magnitude of the oscillation pressure in intermittent mode could be evaluated from the difference between the throat static-pressure immediately prior to the occurrence of cavitation and that during cavitation.     

Modeling of the solid–liquid bubble interface in partial nucleate boiling

Several models of heat transfer in partial nucleate boiling are identified in order to determine the relationship between the dominant physical parameters. The correlations are different for different models, so the main goal of this analysis is to determine the validity of each model and to identify the most dominant physical phenomenon in the nucleate boiling heat transfer. This is done by comparing the results of different models with a vast range of reliable experimental data. The comparison shows that the Sakashita and Kumada model gives the best results in the nucleate boiling heat transfer. It is also shown that the most dominating phenomenon in isolated partial bubbles zones is the transient conduction taking place mainly under the bubbles. This is in contradiction with a majority of the models that consider convection as the most important mode in the nucleate boiling heat transfer. The selected model can also be extrapolated and used in the case of fully developed bubbles zones.     

Determination of diffusivity of sodium in liquid tin using Na-ß″ alumina

Diffusivity of sodium in molten tin was determined using an electrochemical cell of the type Na/Na-β″-Al₂O₃/(Na)Sn where Na-β″-Al₂O₃, which is a sodium-ion conductor, was the solid electrolyte. Using the above cell in which a small amount of sodium dissolved in tin was transported through β″-Al₂O₃ upon application of an external voltage, and using a known solution to Fick's second law for appropriate boundary conditions, the diffusivity was determined to be $$D{\text{ = 4}}{\text{.4 }}\left( {\begin{array}{*{20}c} {{\text{ + 1}}{\text{.0}}} \\ {{\text{ - 0}}{\text{.5}}} \\ \end{array} } \right){\text{ x 10}}^{{\text{ - 4}}} {\text{ exp }}\left( {{\text{ - }}\frac{Q}{{RT}}} \right){\text{ cm}}^{\text{2}} {\text{ sec}}^{{\text{ - 1}}} $$ withQ = 16320 J mol^?1 over a range of temperatures from 240 to 440° C. From the solution to Fick's second law, it was shown that first term approximations, which have often been used in the past, lead to an estimate of diffusivity which is about a factor of 2 too high indicating that more terms should be considered. The diffusivity was also determined using a transient technique in which the decay in voltage upon removal of externally applied voltage was recorded as a function of time. The diffusivity so determined, in which it was assumed that the only polarization was the concentration polarization, was higher than the previous method. The difference between the two diffusivities became smaller with increasing temperature. These experiments thus suggested that interfacial or activation polarization must also be present.     

Unstable crack propagation—a fractographic study using PMMA in liquid environments

Double-torsion tests have been performed in liquid environments on PMMA samples with and without a grease coating to restrict the access of liquid, and over a range of testing speeds. Stable or stick-slip crack propagation could be obtained at will by varying the test conditions. Characteristic fracture markings accompanying unstable crack propagation provide evidence concerning the mechanism of crack arrest.     

Solid ? liquid phase transformations in hypereutectic P/M Al-Si-Fe-X alloys

In this study, the metastable and stable solid liquid phase transformations of the hypereutectic alloys Al-20Si-5Fe-2Ni (wt%) and Al-17Si-5Fe-3.5Cu-1.1Mg-0.6Zr in as-atomised powder and in as-hot-forged material have been investigated. Differential Scanning Calorimetry (DSC) measurements at high temperatures have been performed. The resultant products have been thoroughly analysed using Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) microanalysis. During solidification large Si, (Al₄FeSi₂), FeNiAl₉, Al₇Cu₂Fe and Q(Cu₂Mg₈Si₆Al₅) are formed. A cooling rate of 5 °C/min and 1 °C/min is too high for the formation of the equilibrium phases (Al₅FeSi) and Al₇Cu₂Fe. The understanding of the sequence of transformations is useful in order to define appropriate processing parameters for these alloys produced by powder metallurgy. The temperature at which the first liquid phase appears during heating at 5 °C/min is 559 °C for the Al-Si-Fe-Ni powder and 506 °C for the Al-Si-Fe-Cu-Mg-Zr powder.