Dependence Of Surface Tension Research Articles

G0600-5-3 ブタノール水溶液のミニチャネル内流動沸騰特性(熱工学部門一般講演(5):伝熱(5))

Some alcohol solutions such as butanol show non-linear surface tension dependence. It is known that dryout of the heat surface is inhibited by Thermal Marangoni Effect of non-linear surface tension. These solutions are called Self-rewetting Liquids. Boiling heat transfer of butanol aqueous solution is studied in experimental systems of forced convection boiling. This test is also performed inside a mini channel. Mass flux is 1286kg/m^2s or 2374kg/m^2s, subcooling was changed from 0K to 50K. Bulk liquid concentration changed from 0.00wt% to 7.15wt%. Wall temperature was measured by using thermocouple and radiation thermometer. At high mass flux (G=2374kg/m^2s), CHF of butanol aqueous solution is from 20% to 50% higher than that of pure water in subcooled region. Burnout of butanol aqueous solution was Fast Burnout (Upper stream CHF).

C121 高性能薄型ヒートパイプの開発(OS-7:電子機器における熱流動現象(II))

The present authors have been conducting experimental study of high performance flat heat pipes to apply cooling of electronic devices, especially CPU in server. By using self-rewetting fluids, which show positive surface tension dependence on temperature, as working fluids, the thermal performances of flat heat pipes were improved. In addition, nanofluids with wire-shaped nano particles that nano particles directly synthesized in base fluids by the microwave polyol method are also used for heat transfer enhancement. Demonstration experiment of cooling system with these thin flat heat pipes for CPU was also carried out in real server, and cooling effect comparable to current air cooling system by fans was shown. In the meanwhile, thin plate-type heat pipes which have several kinds of wick structures have been developed and the encouraging thermal performance was obtained.

Oxygen partial pressure dependence of surface tension and its temperature coefficient for metallic melts: a discussion from the viewpoint of solubility and adsorption of oxygen

Surface tension of molten Si, Ag, and Fe–18Cr–8Ni alloy (Type-304 stainless steel) were measured as a function of the temperature and oxygen partial pressure of an ambient atmosphere by an oscillating drop method using electromagnetic levitation, which assures measurement over a wide range of temperatures below and above the melting point and of oxygen partial pressure. For molten silicon, the lower limit of measured temperature was determined by equilibrium oxygen partial pressure for SiO2 formation; as oxygen partial pressure increases, undercooled conditions necessary for taking measurements become smaller. This is attributed to the low solubility of oxygen in molten silicon. For Ag, however, surface tension can be measured in a wide range of temperature and oxygen partial pressures due to the high solubility of oxygen. A boomerang-shaped behavior of surface tension was observed for Ag in an atmosphere with high oxygen partial pressure; surface tension has a maximum value when plotted against temperature. This boomerang-shaped behavior is attributed to desorption of oxygen at high temperature; surface tension increases with increasing temperature. The boomerang-shaped behavior was also observed for Fe–18Cr–8Ni alloy.

Effect of metal purity and testing procedure on surface tension measurements of liquid tin

The surface tension of liquid tin of three different grades of purity (99.85, 99.96, and 99.999%) was measured by the classical sessile drop method over the temperature range 523–1023 K, in heating and cooling regimes. The results obtained show that the metal purity affects the values of surface tension and its temperature dependence. The highest values of surface tension and smooth linear temperature dependence were obtained in cooling regime for tin of the highest purity. With increasing content of impurities, both surface tension and its temperature coefficient decrease while the scatter of the data increases. The surface tension values measured on heating regime show higher scatter, compared to those obtained in cooling regime, and the temperature dependence of the surface tension is curvilinear rather than linear.

Nanoroughness, Intrinsic Density Profile, and Rigidity of the Air-Water Interface

From large-scale molecular dynamics simulations of the free water surface the capillary wave spectrum is obtained and analyzed in terms of a wave vector dependent surface tension. The bending rigidity is positive but suggested to change sign in the presence of long-range dispersive interactions. Nanoroughness and capillary waves give rise to a scale-dependent density profile that displays minimal broadening at a nanometer scale which defines the intrinsic density profile.

Surface tension measurements with validated accuracy for four 1-alkyl-3-methylimidazolium based ionic liquids

Air–liquid interfacial surface tension measurements are reported on four 1-alkyl-3-methylimidazolium ([C n -mim], n = 2, 4, 6) based ionic liquids at 15 temperatures from (283 to 353) K at atmospheric pressure. To validate the accuracy of the results, the Wilhelmy plate method and the du Noüy ring method were employed in parallel, using the Krűss K100MK2 tensiometer. At each temperature from 29 to 44 individual readings were taken. The surface tension average values at particular temperatures are presented with the estimated overall standard uncertainty ranging from (±0.025 to ±0.1) mN · m −1. An empirical surface tension–temperature equation has been developed describing the temperature dependence of each ionic liquid surface tension. Some details of the measurement procedure that have been found to be important in achieving the highest possible accuracy are discussed.

The liquid–gas interface of oxygen–nitrogen solutions 2: Description in the Framework of the van der Waals gradient theory

The van der Waals gradient theory (vdW GT) is used to calculate surface tension, density profiles, adsorption, the Tolman length and to determine the position of dividing surfaces in the liquid–gas interface of an oxygen–nitrogen solution. The Helmholtz energy density (HED) is determined via an equation of state (EOS), unified for a liquid and gas, which describes stable, metastable and two-phase states of solutions. The influence parameters are calculated from data on the surface tension of pure components with the use of the mixing rule. At temperatures T > 100 K the vdW GT describes experimental data on the surface tension of oxygen–nitrogen solutions [V.G. Baidakov, A.M. Kaverin, V.N. Andbaeva, The liquid–gas interface of oxygen–nitrogen solutions: 1. Surface tension, Fluid Phase Equilib. 270 (2008) 116–120] within the experimental error. It is shown that the Tolman length, which determines the dependence of surface tension on the curvature of the dividing surface, depends considerably on the solution concentration.

Convection in molten pool created by a concentrated energy flux on a solid metal target

During surface evaporation of metals by use of a concentrated energy flux such as electron beam or lasers, a liquid metal pool having a very high temperature gradient is formed around the hot zone created by the beam. Due to temperature dependence of surface tension, density, and depression of the evaporating surface caused by back pressure of the emitted vapor in this molten pool, a strong convective current sets in the molten pool. A proposition is made that this convection may pass through three different stages during increase in the electron beam power depending upon dominance of the various driving forces. To confirm this, convective heat transfer is quantified in terms of dimensionless Nusselt number and its evolution with power is studied in an experiment using aluminum, copper, and zirconium as targets. These experimentally determined values are also compared to the theoretical values predicted by earlier researchers to test the validity of their assumptions and to know about the type of flow in the melt pool. Thus, conclusion about the physical characteristics of flow in the molten pool of metals could be drawn by considering the roles of surface tension and curvature of the evaporating surface on the evolution of convective heat transfer.

VARIATIONAL FORMULATION FOR THE KPZ AND RELATED KINETIC EQUATIONS

We present a variational formulation for the Kardar–Parisi–Zhang (KPZ) equation that leads to a thermodynamic-like potential for the KPZ as well as for other related kinetic equations. For the KPZ case, with the knowledge of such a potential we prove some global shift invariance properties previously conjectured by other authors. We also show a few results about the form of the stationary probability distribution function for arbitrary dimensions. The procedure used for KPZ was extended in order to derive more general forms of such a functional leading to other nonlinear kinetic equations, as well as cases with density dependent surface tension.

Classical Nucleation Theory Applied to Homogeneous Bubble Nucleation in the Continuous Microcellular Foaming of the Polystyrene−CO2 System

In the continuous production of microcellular thermoplastic foam, a polymer−physical foaming agent (PFA) solution is subjected to a rapid pressure drop through an extrusion foaming die. Simulations were run for the flow of a polymer−PFA solution through an extrusion foaming die with an abrupt axisymmetric contraction. The pressure drops across the die obtained through the simulations showed good qualitative agreement with experimental pressure drop measurements on the foaming extrusion die obtained in our laboratory. Field values of pressure, temperature, and velocity were obtained at each point in the foaming die. Once the values of pressure and temperature were obtained along each point in the foaming die, classical nucleation theory for bubble nucleation was invoked to predict the local bubble nucleation rate downstream of the saturation surface. The hydrodynamic constraints to the nucleation rate were calculated by using a modified form of the classical nucleation theory that accounted for the diffusional and viscosity constraints to the rate of homogeneous nucleation. The capillarity approximation was found not to be valid for bubble nucleation of CO2 in polymers; a correction accounting for the curvature dependence of surface tension was applied to get nonzero nucleation rates for the system to reconcile theoretically predicted rates with experimental observations.

On the dependence of the surface tension at the crystal-melt interface on the impurity concentration

The stationary task of impurity diffusion in a melt has been solved within a two-dimensional crystallization model in a second-order approximation with respect to the amplitude of deviation from a smooth crystallization front. The dependence of the surface tension Γ at the interface on the impurity concentration C is taken into account in the form Γ = Γ0 + ζdC, where Γ0 and ζd are constants. The variational method is used to obtain the condition for the transition from a smooth crystallization front to a cellular one. It is shown that calculated cell sizes are in agreement with the experimental data in the literature only when the parameter ζd ≠ 0. For binary systems with distribution coefficients k 1, ζd should be positive and negative, respectively.

Surface tension of high density polyethylene (HDPE) in supercritical nitrogen: Effect of polymer crystallization

Surface tension of a polymer melt in a supercritical fluid is a principal factor in determining cell nucleation and growth in microcellular foaming. This work focuses on the surface tension of a crystalline polymer, high density polyethylene (HDPE), in supercritical nitrogen under various temperatures and pressures. The surface tension was determined by Axisymmetric Drop Shape Analysis-Profile (ADSA-P). The dependence of the surface tension on temperature and pressure, at temperatures above the HDPE melting point, ∼125 °C, was found to be similar to that of the amorphous polymer polystyrene (PS) in supercritical CO 2, previously reported, i.e., the surface tension decreased with increasing temperature and gas content. Below 125 °C and above 100 °C, HDPE underwent the process of crystallization, where the surface tension dependence on temperature was different from that above the melting point, and decreased with decreasing temperature. Differential scanning calorimetry (DSC) characterization of the polymer was carried out to reveal the process of HDPE crystallization and relate this to surface tension behavior. It was found that the amount of the decrease in surface tension was related to the rate of temperature change and hence the extent of polymer crystallization.

Kinetics of Adsorption Layer Formation in Solutions of Polyacid/Surfactant Complexes

The dynamic dilational elasticity of adsorption layers of the complexes between polyacids and dodecyltrimethyl ammonium bromide were measured by the oscillating ring method as a function of surface age and surfactant concentration. The concentration dependencies of surface tension and dilational surface elasticity are similar to the corresponding dependencies of other polyelectrolyte/surfactant solutions. At the same time, the kinetic dependencies of the dynamic surface elasticity differ significantly from the results for other systems and exhibit in respective concentration ranges one or two local maxima. The first maximum and the associated distortion of the harmonical surface tension oscillations are caused by an aggregate formation in the surface layer. The second maximum occurs simultaneously with a multilayer formation at the liquid surface, which probably results in a new relaxation mechanism of surface stresses. The hydrophobic interactions influence the height and position of the second elasticit...

Surface Tension Measurements for Four 1-Alkyl-3-methylimidazolium-Based Ionic Liquids with Hexafluorophosphate Anion

Air−liquid interfacial surface tension measurements were performed on four 1-alkyl-3-methylimidazolium-based ([Cnmim], n = 3, 4, 6, 8) ionic liquids at 15 temperatures from (287 to 353) K at atmospheric pressure. To validate the accuracy of the results, the Wilhelmy plate method and the du Noüy ring method were employed in parallel using the Krűss K100MK2 tensiometer. At each temperature, from 33 to 55 Wilhelmy plate and from 10 to 30 du Noüy ring individual readings were taken in most cases. The surface tension average values at particular temperatures are presented with estimated overall standard uncertainty of 0.05 mN·m−1. An empirical surface tension−temperature equation has been developed describing the temperature dependence of each ionic liquid surface tension. To the 69 up-to-now published surface tension values of the above-mentioned four ionic liquids, the present study adds an additional 102 data points representing means calculated from about 3000 individual surface tension readings that altogether have been taken.

Dependence of the liquid-vapor surface tension on the range of interaction: A test of the law of corresponding states

The validity of the principle of corresponding states is investigated for the case of a potential with more than one intrinsic length scale. The planar surface tension of coexisting liquid and vapor phases of a fluid of Lennard-Jones atoms is studied as a function of the range of the potential using both Monte Carlo simulations and density functional theory (DFT). The interaction range is varied from r(c)(*) = 2.5 to r(c)(*) = 6 and the surface tension is determined for temperatures ranging from T(*) = 0.7 up to the critical temperature in each case. The simulation results are consistent with previous studies and are shown to obey the law of corresponding states even though the potential has two intrinsic length scales. It is further shown that the corresponding states principle can also be used to enhance the accuracy of some, but not all, DFT calculations of the surface tension. The results show that most of the cutoff dependence of the surface tension can be explained as a result of changes in the cutoff-dependent phase diagram and that corresponding states can be a useful tool for explaining differences between theory and simulation.

Coupling the Level-Set Method with Molecular Mechanics for Variational Implicit Solvation of Nonpolar Molecules

We construct a variational explicit-solute implicit-solvent model for the solvation of molecules. Central in this model is an effective solvation free-energy functional that depends solely on the position of solute-solvent interface and solute atoms. The total free energy couples altogether the volume and interface energies of solutes, the solute-solvent van der Waals interactions, and the solute-solute mechanical interactions. A curvature dependent surface tension is incorporated through the so-called Tolman length which serves as the only fitting parameter in the model. Our approach extends the original variational implicit-solvent model of Dzubiella, Swanson, and McCammon [Phys. Rev. Lett. 2006, 96, 087802 and J. Chem. Phys. 2006, 124, 084905] to include the solute molecular mechanics. We also develop a novel computational method that combines the level-set technique with optimization algorithms to determine numerically the equilibrium conformation of nonpolar molecules. Numerical results demonstrate that our new model and methods can capture essential properties of nonpolar molecules and their interactions with the solvent. In particular, with a suitable choice of the Tolman length for the curvature correction to the surface tension, we obtain the solvation free energy for a benzene molecule in a good agreement with experimental results.

The influence of side substituents in α-amino acids on their sorption by a cation-exchange membrane

The isotherms of sorption of ornithine, lysine, arginine, and histidine by an MK-40 membrane were obtained by the method of variable concentrations. The influence of the geometric parameters of side groups in the basic amino acids and pH on the degree of their absorption by the membrane was studied. The formation of doubly charged amino acid cations in the membrane phase when membranes in the H+ form were used was substantiated IR spectroscopically. The distribution coefficient was found to depend linearly on the size of amino acid side groups. The dependence of interphase surface tension at the membrane-solution interface on the degree of membrane filling was indicative of the formation of sorbate associates in the membrane phase.

Measurement of Temperature Dependence of Surface Tension of Alcohol Aqueous Solutions by Maximum Bubble Pressure Method

The surface tension of some high-carbon alcohol aqueous solutions increases as the temperature rises above a certain temperature. There have been attempts to use such special solutions in thermal devices to promote heat transfer. In this study, the authors analyzed the temperature dependence of surface tension of these solutions to investigate this peculiar characteristic in detail. The test fluids were butanol and pentanol aqueous solutions as peculiar solutions, while pure water and ethanol aqueous solution were normal fluids. First, the authors adopted Wilhelmy's method to measure the surface tension during heating, but found that the influence of evaporation of the solution could not be completely eliminated. In this study, the maximum bubble pressure method was employed, which made it possible to isolate the measured solution from ambient air and eliminate the influence of evaporation of the solution. The authors succeeded in measuring the temperature dependence of surface tension, and obtained more reasonable data.

An explanation for the charge on water’s surface

Measurements with different techniques point to a strong affinity of hydroxide ions for interfaces between water and hydrophobes, but some spectroscopic experiments do not detect excess hydroxide at the interface, while others do. Hydroxide ions are unusual in that they reduce the relative permittivity of an electrolyte solution more than other monovalent, monatomic ions. This implies that they suppress the collective dipole-moment fluctuations of nearby waters. We show that the absence of these fluctuations leads to a Hamaker-like force on the hydroxide ion that attracts it to regions where dipole-moment fluctuations are smaller than in bulk water, in other words, to regions of low relative permittivity. We show also that there is no contradiction between the picture of the basic, negatively charged interface and spectroscopic measurements. This is, in part, because the hydroxides are mostly below the outermost molecular layers. By combining a simple model for this fluctuation force with a modified Poisson-Boltzmann equation, we reproduce the dependence of the zeta-potential on pH, including the low isoelectric point, the approximate magnitude of the experimental surface charge density, and the Jones-Ray data for the dependence of surface tension on electrolyte concentration. We discuss also the apparent contradiction between molecular-dynamics simulations that deny and experiments that support a basic, negatively charged interface.

Direct numerical simulation of single gas bubbles in pure and contaminated liquids

AbstractDisperse gas bubbles play an important role in many industrial applications. Knowing the rising velocity, the interfacial area, or the critical size for break–up or coalescence in different systems can be crucial for the process design. Hence, knowing the fundamental behaviour of a single bubble appears mandatory for the examination of bubble swarms and for the Euler–Lagrange or Euler–Euler modelling of disperse systems. In the present work a level–set–based volume–tracking method is implemented into the CFD–code OpenFOAM to follow the free interface of a single bubble. The volume–tracking method is coupled with a transport model for surfactants on the interface, including adsorption and desorption processes. The dependency of surface tension on the local surfactant concentration on the interface is modelled by a non–linear (Langmuir) equation of state. Marangoni forces, resulting from surface tension gradients, are included. The rise of a single air bubble (i) in pure water and (ii) in the presence of surfactants of different strengths is simulated. The results show good agreement with available correlations from literature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)