Vapor Surface Tension Research Articles

Reproducibility of Gaseous Phase Area on Journal Bearing Utilizing Multi-Phase Flow CFD Analysis under Flooded and Starved Lubrication Conditions

It is important to predict the gaseous phase area of journal bearing. However, a detailed calculation method for such gaseous phase areas has not yet been proposed. In this study, the gaseous-phase areas in small bore journal bearings under flooded and starved lubrication conditions are analyzed in terms of the computational fluid dynamics (CFD) of two-phase flow while using a volume of fluid (VOF) method. Furthermore, the influence of surface tension and vapor pressure conditions were investigated, and the analytical and experimental results were compared. The analytical results of VOF for vapor pressure and surface tension were observed to be consistent with the experimental observations under both flooded and starved lubrication conditions. Furthermore, under starved lubrication condition, the analytical results agree well with the observed results for the interface of the oil film and cavitation upon the rupture of the oil film. While using these results, CFD analysis of the two-phase flow of the VOF can be conducted in terms of vapor pressure and surface tension to estimate the gaseous-phase areas of journal bearings under flooded and starved lubrication conditions.

High vapour pressure nanofuel droplet combustion and heat transfer: Insights into droplet burning time scale, secondary atomisation and coupling of droplet deformations and heat release

Combustion characteristics of ethanol-water (EW) droplets laden with ceria nanoparticles are investigated. The present experimental study focuses on three facets of droplet combustion (i) burning time scale of droplets with and without NPs, (ii) pathways of secondary atomisation due to interface deformations and (iii) coupling of droplet shape deformations and flame heat release. A theoretical vaporisation timescale is advocated which considers natural convection-based evaporation, mass loss due to daughter droplet ejections, and flow through porous media. Droplets seeded with ceria nanoparticles, exhibit arrested surface undulations although internal ebullition is discernibly enhanced as compared to EW droplets without NPs. Deformations and formation of surface craters in EW droplets are traced to the imbalance between local vapour recoil (due to rapid ethanol vaporisation) and surface tension. Such craters collapse and form high-speed ligaments which eventually break at the tip through Rayleigh–Plateau mechanism. This pathway of secondary atomisation of EW droplets has been elucidated using a modified local weber number. On the contrary, for nanofuels, bubble rupture is the mechanism behind the surface crater formation. Proper orthogonal decomposition (POD) technique is utilised for investigating the droplet shape and flame heat release coupling. EW droplet shape and HR are found to be a synced system with a phase lag arising from the flame response timescale. However, a weak coupling is detected for nanofuel droplets.

Densities, Vapor Pressures, and Surface Tensions of Selected Terpenes

The knowledge of physico-chemical properties of terpenes and terpenoids are necessary for understanding of formation of cloud condensation nuclei. In this work properties of $$\upalpha$$ -pinene and $$\upbeta$$ -pinene, namely liquid densities, saturated vapor pressure, surface tension and interfacial tension in mixtures with water were measured in the temperature range between 300 and 370 K. Saturated vapor pressures were also modelled by COSMO-RS and compared both with our mesurements and literature values measured at lower temperatures. A modern nonstatistical technique based on mathematical gnostics was used for data analysis.

New estimations of vapor density and surface tension of water at low temperatures using scaled model

In this work, we were able to estimate the values of critical temperature, surface tension, excess surface entropy/k per particle and vapor density of all of TIP3P, SPCE, TIP4P, and TIP4P 2005 water models, using a scaled model. This model is based on scaling the free energy difference of n-molecules and (n − 1)-molecules plus a probe to the critical temperature. The unitless free energy difference, using the Bennett acceptance ratio versus the number of molecules to the power minus one-third, shows a behavior of straight line for n > 7. The slope of the straight line is proportional to both surface tension and the excess surface entropy/k per particle, while the intercept is proportional to the logarithmic ratio of liquid density to that of vapor density. By calculating the free energy difference for at least three different temperatures and scaling the results to Tc/T − 1, we were able to estimate the critical temperature as well as the surface tension and the vapor density at a temperature range of 200-300 K.

The relationship between the surface tension and the saturated vapor pressure of model nanofluids

Information on surface tension is necessary for modeling boiling processes in nanofluids. It was shown that the problem of predicting the surface tension of complex thermodynamic systems, such as nanofluids, remains outstanding. It should be noted that the surface tension of liquids and the saturated vapor pressure are due to a specific intermolecular interaction in the region of spatial heterogeneity of the substance (surface layer). Moreover, the compositions of the surface layer of nanofluid and its liquid phase are not equal. The presence of nanoparticles in the base fluid affects the composition of the surface layer of liquids. However, there are no methods for determining the composition of the surface layer of nanofluids and this fact complicates establishing the dependence of the surface tension on the state parameters of nanofluids. It should be mentioned that the number of possible methodological errors in measurements of the saturated vapor pressure of nanofluids is significantly lower than for the surface tension measurements. Therefore, in the development of models for predicting the surface tension, scientific and practical interest has establishing the relationship between the surface tension and the saturated vapor pressure of nanofluids. In the presented work, we consider the nanofluids of isopropanol/Al2O3 nanoparticles and o-xylene/fullerenes C60. Saturated vapor pressure and surface tension of nanofluids of isopropanol/Al2O3 nanoparticles have been studied in the temperature range 293 – 363 K and concentrations of Al2O3 nanoparticles 0-8.71 g/kg. Measurement of saturated vapor pressure and surface tension of nanofluids of o-xylene/fullerenes C60 have been performed in the temperature range 283 – 348 K and the concentration of C60 0-7.5 g/kg. It is shown that additives of Al2O3 nanoparticles and fullerenes C60 lead to a decrease in the surface tension and increase in the saturated vapor pressure. It is shown that there is a universal dependence between the reduced surface tension and saturated vapor pressure for the researched nanofluids.

Single Parameter for Predicting the Morphology of Atmospheric Black Carbon

Black carbon (BC) from fuel combustion is an effective light absorber that contributes significantly to direct climate forcing. The forcing is altered when BC combines with other substances, which modify its mixing state and morphology, making the evaluation of its atmospheric lifetime and climate impact a challenge. To elucidate the associated mechanisms, we exposed BC aerosol to supersaturated vapors of different chemicals to form thin coatings and measured the coating mass required to induce the restructuring of BC aggregates. We found that studied chemicals fall into two distinct groups based on a single dimensionless parameter, χ, which depends on the diameter of BC monomer spheres and the coating material properties, including vapor supersaturation, molar volume, and surface tension. We show that when χ is small (low-volatility chemicals), the highly supersaturated vapor condenses uniformly over aggregates, including convex monomers and concave junctions in between monomers, but when χ is large (intermediate-volatility chemicals), junctions become preferred. The aggregates undergo prompt restructuring when condensation in the junctions dominates over condensation on monomer spheres. For a given monomer diameter, the coating distribution is mostly controlled by vapor supersaturation. The χ factor can be incorporated straightforwardly into atmospheric models to improve simulations of BC aging.

Selection and characterization of liquids for a low pressure interferometric liquid column manometer

At PTB, the development of a new primary interferometric liquid column manometer for measurement of absolute and gauge pressures in the range up to 2 kPa is an ongoing project. For measurements in this pressure range, liquids with a low density are advantageous because of a better pressure resolution determined through differential column height measurements. In addition, low vapor pressure is a precondition for an accurate measurement of absolute pressure. The choice of liquid is crucial for the accuracy of the new instrument. This paper discusses the effect of liquid properties such as vapor pressure, density, viscosity, surface tension and gas absorption capacity on the performance of the micromanometer. Seven liquids – all oils used in vacuum applications (vacuum oils) – representing different classes of chemical compounds were analyzed in respect to their viscosity, density, thermal expansion and compressibility. Detailed investigations were performed on three liquids out of seven to determine their density versus gas saturation, ab- and desorption kinetics and surface tension, as well as the wettability of the micromanometer’s materials. Results of the measurements and recommendations for the use of the liquids are presented.

Enhanced Solar Thermal Evaporation of Ethanol-Water Mixtures, through the Use of Porous Media.

A significant enhancement of solar irradiation induced evaporation of water, and ethanol-water mixtures, through the use of carbon foam based porous media, is demonstrated. A relationship between the consequent rate of mass loss, with respect to the equilibrium vapor pressure, dynamic viscosity, surface tension, and density, was developed to explain experimental observations. The evaporative heat loss was parametrized through two convective heat transfer coefficients-one related to the surface and another related to the vapor external to the surface. The work promotes a better understanding of thermal processes in binary liquid mixtures with applications ranging from phase separation to distillation and desalination.

A generalized Young’s equation to bridge a gap between the experimentally measured and the theoretically calculated line tensions

A generalized Young’s equation, which takes into account two corrections to the line tension by the curvature dependence of the liquid–vapor surface tension and by the contact angle dependence of the intrinsic line tension, is derived from the thermodynamic free-energy minimization. The correction from the curvature dependence can be qualitatively estimated using Tolman’s formula. The correction from the contact angle dependence can be estimated for nanometer-scale droplets for which the analytical formula for the intrinsic line tension determined from the van der Waals interaction is available. The two corrections to the apparent line tension of this van der Waals nano-droplets are as small as nN, and lead to either a positive or a negative apparent line tension. The gravitational line tension for millimeter-scale droplets by the gravitational acceleration is also considered. The gravitational line tension is of the order of N so that the correction from the curvature dependence can be neglected. Yet, the contact angle dependence is so large that the apparent line tension becomes always negative though the intrinsic line tension without the correction is always positive. These two examples demonstrate clear distinction between the theoretically calculated intrinsic line tension and the experimentally determined apparent line tension which includes these two corrections. Naive comparison of the experimentally determined and the theoretically calculated line tension is not always possible.

A model of transient internal flow and atomization of propellant/ethanol mixtures in pressurized metered dose inhalers (pMDI)

This article reports the extension to binary propellant/excipient mixtures of the multiphase model of transient internal flow and atomization in pressurized metered dose inhalers (pMDIs) of Gavtash and colleagues for propellant-only flows. The work considers different accounts of the effect of less volatile ethanol on the saturated vapor pressure (SVP), viscosity and surface tension of HFA-based pMDI formulations. Representation of the SVP of HFA/ethanol mixtures by Raoult's law is compared with the empirical model developed by Gavtash and colleagues as well as different theoretical mixing rules for surface tension and viscosity. For initial ethanol contents ranging from 0 to 20% by mass, the temperature, pressure and spray velocity were predicted to be almost independent of ethanol concentration when using the empirical SVP model of Gavtash and colleagues. The predicted aerosol droplet size increases with increasing concentration of ethanol. These model predictions compare favorably with phase Do...

Effect of Al $$_2$$ 2 O $$_3$$ 3 Nanoparticles Additives on the Density, Saturated Vapor Pressure, Surface Tension and Viscosity of Isopropyl Alcohol

This paper presents results of an experimental study of the density, saturated vapor pressure, surface tension and viscosity of Al $$_2$$ O $$_3$$ nanoparticle colloidal solutions in isopropyl alcohol. Studies of the thermophysical properties of nanofluids were performed at various temperatures and concentrations of Al $$_2$$ O $$_3$$ nanoparticles. The paper gives considerable attention to a turbidimetric analysis of the stability of nanofluid samples. Samples of nanofluids remained stable over the range of parameters of the experiments, ensuring the reliability of the thermophysical property data for the Al $$_2$$ O $$_3$$ nanoparticle colloidal solutions in isopropyl alcohol. The studies show that the addition of Al $$_2$$ O $$_3$$ nanoparticles leads to an increase of the density, saturated vapor pressure and viscosity, as well as a decrease for the surface tension of isopropyl alcohol. The information reported in this paper on the various thermophysical properties for the isopropyl alcohol/Al $$_2$$ O $$_3$$ nanoparticle model system is useful for the development of thermodynamically consistent models for predicting properties of nanofluids and correct modeling of the heat exchange processes.

Experiment investigation of two-phase flow pattern transition and frictional pressure drop of R600a in a horizontal tube

With the growing concern of environment problems, there are urgent demands for environment-friendly refrigerants in the refrigeration industry. As a natural refrigerant, R600a not only has zero ozone depletion potential and quite low global warming potential, but also has better cooling performance than other refrigerants. Due to its good cooling performance and environment-friendly characteristics, R600a has been used as an alternative refrigerant in heat transfer applications such as refrigerators, freezers, and heat pumps. It is known that accurate prediction of two phase flow pattern transition and frictional pressure drop of R600a in a horizontal tube play an important role in design and optimization of refrigerators, freezers, and heat pumps. According to this issue, a detailed experimental study was carried out to investigate the two-phase flow pattern transition and frictional pressure drop characteristics of R600a in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation temperature from 282.4 to 304 K, mass fluxes from 67 to 194 kg/(m2 s). Based on a high speed camera, four main flow regimes can be observed: plug flow, stratified-wavy flow, slug flow and annular flow. The flow map of R600a has been drawn and comparisons between the experimental data of flow patterns and transition lines in the literature have been made. The results showed that with the increase of mass flux, the inception of the annular flow regime occurs earlier. The intermittent flow regime takes place over a narrow range of vapor quality and annular flow regime occupies a wide range of vapor quality. In addition, the trend of Barbieri and Ong and Thome I / A transitions lines are consistent with the experimental data. However, both of them overestimate the inception of the annular flow regime. After taking the influence of vapor inertia, liquid viscous and surface tension forces into account, a modified Weber number We * has been introduced to the new flow pattern transition model. Based on the relationship of X tt and We *, a new correlation has been proposed and it can well fit with the experimental data of flow pattern. Furthermore, a detailed discuss of frictional pressure drop of annular flow and non-annular flow has been made. The results indicated that frictional pressure drop increases with the increases of vapor quality. The tendency of frictional pressure drop presents different the changing laws in different flow regime. The frictional pressure drop increases slowly in the non-annular flow regime while it increases rapidly when the flow pattern turns into the annular flow regime. The reason is that the vapor-phase pressure drop often dominates the total two-phase frictional pressure drop. The annular flow regime owns higher void fraction than the non-annular flow regime. Nine classic prediction correlations of pressure drop were evaluated and the results showed that the correlation of Gronnerud and Muller-Steinhagen and Heck give the best fit to the experimental frictional pressure drop of annular flow and non-annular flow with a mean absolute relative deviation of 38.5% and 19.7% respectively.

A highly sensitive and durable electrical sensor for liquid ethanol using thermally-oxidized mesoporous silicon

A capacitive detection of liquid ethanol using reactive, thermally oxidized films constructed from electrochemically synthesized porous silicon (PSi) is demonstrated. The sensor elements are fabricated as meso-PSi (pore sizes <50 nm, pore thickness ∼7 μm), with Ag metallic contacts made exclusively at the backside of bulk silicon, and ethanol sensing is achieved by measurement of the real-time capacitance and conductance. The thermally oxidized sensor displays excellent infiltration-evaporation behavior with a tremendous reversible capacitance change towards ethanol. The capacitance increased by forty-fold more than its margin which is the greatest capacitance response ever recorded compared to previously investigated devices. The control device of non-porous Si showed no response, while the sensor response using the original hydrophobic PSi surface exhibited almost a half sensitivity of the thermal oxide sensor. The response to water is achieved only at the oxidized surface and found to be ∼one quarter of the ethanol sensitivity, dependent on parameters such as vapor pressure and surface tension. The capacitance response retains ∼92% of its initial value after continuous nine cyclic runs and the sensors presumably keep long-term stability after three weeks storage, demonstrating excellent durability and storage stability. The observed behavior in current system is likely explained by the interface interaction due to dipole moment effect. The results suggest that the current sensor structure and design can be easily made to produce notably higher sensitivities for reversible detection of various analytes.

Fibre laser welding of high-alloyed Al–Zn–Mg–Cu alloys

The theoretical fundamentals of laser weldability of metals are surveyed and relevant thermophysical parameters are identified – such as vapour pressure, keyhole pressure, beam irradiance, surface tension and viscosity. The derived approach for improving the laser weldability implies the use of a Yb fibre laser with an initial large beam diameter, a top-hat beam profile and a high laser power, which enables the formation of a large and stable keyhole during deep penetration welding. For validating the effectiveness of the developed approach, it is applied to various high-alloyed and hard-to-weld Al–Zn–Mg–Cu alloys. Defect-free welds are obtained even for AA7034 – the alloy with the highest (Zn+Mg+Cu) content commercially available. As reference, the same alloys are welded by using a conventional Nd:YAG laser with a small beam diameter, a Gaussian beam profile and medium laser power. The laser weldability deteriorates with increasing (Zn+Mg+Cu) content in terms of porosity and excess of penetration. The obtained results highlight the importance of the laser system used on the laser weldability of Al–Zn–Mg–Cu alloys.

Condensation of refrigerants in a multiport tube with rectangular minichannels

This study investigated the condensation heat transfer and pressure drop characteristics of refrigerants R134a, R32, R1234ze(E), and R410A in a horizontal multiport tube with rectangular minichannels, in the mass velocity range of 100–400 kg m−2 s−1 and saturation temperature set at 40 and 60 °C. The effect of mass velocity, vapor quality, saturation temperature, refrigerant properties, and hydraulic diameter of rectangular channels on condensation characteristics is clarified. A new correlation is proposed for predicting the frictional pressure drop for condensation flow in minichannels. A heat transfer model for condensation heat transfer in rectangular minichannels is developed considering the flow patterns and effects of vapor shear stress and surface tension. Then, based on this model, a new heat transfer correlation is proposed. The proposed correlations successfully predict the experimental frictional pressure drop and heat transfer coefficients of the test refrigerants in horizontal rectangular minichannels.

Sonochemical heating profile for solvents and ionic liquid doped solvents, and their application in the N-alkylation of pyrazoles

The heating profile for 25 solvents was determined in ultrasonic probe equipment at amplitudes of 20%, 25%, and 30%. Each solvent was heated in accordance with its boiling point. The effect of vapor pressure, surface tension, and viscosity of the solvents in dissipated ultrasonic power (Up) was evaluated. Multiple regression analysis of these solvent properties and dissipated Up reveals that solvent viscosity is the property that most strongly affected dissipated Up. Experimentation involving acetonitrile doped with [BMIM][BF4] indicated faster heating than MeCN. Aprotic polar solvents such as DMSO, DMF, and MeCN were tested in the N-alkylation of pyrazoles under ultrasonic conditions. After 5min at 90°C, the reactants had been totally converted into product in these solvents. Solvents, with low dissipated Up (e.g., toluene) were tested. Conversions were lower compared to those of aprotic polar solvents. When the reactions were done in hexane, no conversion to product was observed. To check the effect of doping in solvents with low Up, [BMIM][BF4], DMSO, and DMF were selected. The conversions for toluene doped with [BMIM][BF4], DMSO, and DMF were 100%, 59%, and 25%, respectively. These conversions were greater than when done in just toluene (46%). Thus, [BMIM][BF4] was the best polar doping solvent, followed by DMSO. DMF was not considered to be a satisfactory doping solvent. No conversion was observed for reactions in the absence of base performed in DMSO, DMF, and MeCN doped with [BMIM][BF4].

ЕКСПЕРИМЕНТАЛЬНЕ І РОЗРАХУНКОВЕ ДОСЛІДЖЕННЯ ВПЛИВУ НАНОЧАСТОК Al2O3 НА ТЕПЛОФІЗИЧНІ ВЛАСТИВОСТІ РОЗЧИНІВ ХОЛОДОАГЕНТУ R600а З КОМПРЕСОРНИМ МАСТИЛОМ

The results of experimental and theoretical studies of the effect of Al 2 O 3 nanoparticle additives on the viscosity, saturation vapor pressure, surface tension of R600a/mineral oil solutions are presented in the article. The model SP-QSPR - Skaling Principles - Quantitative Structure-Property Relationship to describe the experimental data and predict nanofluid thermophysical properties at wide range of parameters of state has been applied for the first time. It has been shown, that viscosity increase, saturation vapor pressure and surface tension decrease for refrigerant / oil solutions with additives of nanoparticles. These effects should be considered at assessment of nanotechnology prospects in the refrigeration equipment.

Effects of Free Surface Evaporation on Water Nanodroplet Wetting Kinetics: A Molecular Dynamics Study

The wetting kinetics of a water nanodroplet undergoing evaporation on a heated gold substrate were examined using molecular dynamics (MD) simulations. Various substrate and initial droplet temperatures were used to obtain different evaporation rates. The water molecule absorption–desorption behavior was analyzed in the vicinity of the contact line region to show the microscopic details of the spreading–evaporating droplet. Increasing substrate temperatures greatly affected the dynamic wetting process, while the initial water droplet temperature had very little effect. The effects of droplet size and substrate wettability on the droplet spreading–evaporating process were also examined. The radius versus time curves agree well with molecular kinetics theory (MKT) for spreading without evaporation but differ from MKT when the spreading induced evaporation. The enhancement of the wetting kinetics by the evaporation can be attributed to the reduction of the liquid–vapor surface tension and the increased water molecule motion in the contact line region and in the bulk droplet.

Numerical analysis on molten droplet hydrodynamic deformation and surface waves under high pressure pulse

A multi-phase hydrodynamic code using volume of fluid method (VOF) is used to simulate the molten droplet deformation, and the surface waves at the stages of pressure propagation and expansion in steam explosion (SE). Both melt-liquid system and melt-gas system are simulated using the code. A benchmark case of Joseph et al.’s experimental data (1999) is performed to validate the code. In this paper, effects of vapor film and surface tension on the droplet behavior under high pressure pulse are investigated. In addition, effects of material density and pressure pulse magnitude on the droplet deformation, and the growth of surface waves are also analyzed. Results of simulation analysis suggested that vapor film can be neglected and the effect of surface tension is not significant for hydrodynamic process under high pressure pulse. Results of simulation also demonstrate that material density and pressure pulse play a significant role in the process of droplet deformation and surface wave growth. The research shows that the effect of hydrodynamic deformation is significant for droplet fragmentation, and droplet penetration can more likely be achieved by surface wave instability at the stages of propagation and expansion in steam explosion.

Evaporation of sessile droplets affected by graphite nanoparticles and binary base fluids.

The effects of ethanol component and nanoparticle concentration on evaporation dynamics of graphite-water nanofluid droplets have been studied experimentally. The results show that the formed deposition patterns vary greatly with an increase in ethanol concentration from 0 to 50 vol %. Nanoparticles have been observed to be carried to the droplet surface and form a large piece of aggregate. The volume evaporation rate on average increases as the ethanol concentration increases from 0 to 50 vol % in the binary mixture nanofluid droplets. The evaporation rate at the initial stage is more rapid than that at the late stage to dry, revealing a deviation from a linear fitting line, standing for a constant evaporation rate. The deviation is more intense with a higher ethanol concentration. The ethanol-induced smaller liquid-vapor surface tension leads to higher wettability of the nanofluid droplets. The graphite nanoparticles in ethanol-water droplets reinforce the pinning effect in the drying process, and the droplets with more ethanol demonstrate the depinning behavior only at the late stage. The addition of graphite nanoparticles in water enhances a droplet baseline spreading at the beginning of evaporation, a pinning effect during evaporation, and the evaporation rate. However, with a relatively high nanoparticle concentration, the enhancement is attenuated.