Interfacial transport of evaporating water confined in nanopores

A semianalytical, continuum analysis of evaporation of water confined in a cylindrical nanopore is presented, wherein the combined effect of electrostatic interaction and van der Waals forces is taken into account. The equations governing fluid flow and heat transfer between liquid and vapor phases are partially integrated analytically, to yield a set of ordinary differential equations, which are solved numerically to determine the flow characteristics and effect on the resulting shape and rate of evaporation from the liquid-vapor interface. The analysis identifies three important parameters that significantly affect the overall performance of the system, namely, the capillary radius, pore-wall temperature, and the degree of saturation of vapor phase. The extension of meniscus is found to be prominent for smaller nanoscale capillaries, in turn yielding a greater net rate of evaporation per unit pore area. The effects of temperature and ambient vapor pressure on net rate of evaporation are shown to be analogous. An increase in pore-wall temperature, which enhances saturation pressure, or a decrease in the ambient vapor pressure result in enhancing the net potential for evaporation and increasing the curvature of the interface.     

A model of the two-stage condensation mechanism of water adsorption on nonporous carbon adsorbents

The mechanism of adsorption of water molecules on nonporous carbon adsorbents has been suggested in terms of two different states of adsorbed water; stretched liquid water and water that occupies an intermediate state between the liquid and vapor. Two stages of adsorption were distinguished: condensation and pre-condensation that assumes the formation of molecular associates. The BET model was used to describe the pre-condensation stage. The equations of the adsorption isotherm for water vapor in the region of condensation process and the expression for the determination of the specific hydrophilic surface of adsorbents were found. Examination of the experimental data on adsorption of water vapor on nongraphitized samples of carbon adsorbents shows that in the region of polymolecular adsorption, all isotherms fall into a common curve determined by the equation of the stretched liquid film and can be calculated regardless of the properties of individual liquid water. The equation for adsorption of water vapor on the hydrophobic surface was obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1933–1939, October, 1998.     

Equation of state of water under negative pressure

We report on the simultaneous measurements of the speed of sound and the density in liquid water under negative pressure. Application of a focused acoustic wave to the bulk liquid is able to generate negative pressures before nucleation of the vapor phase occurs. A method for time-resolved Brillouin scattering is developed to measure the speed of sound during the passage of a 1 MHz ultrasonic wave. This is coupled with a fiber optic probe hydrophone which allows the determination of the density. Together, these methods give an ambient temperature equation of state of metastable liquid water down to the acoustic cavitation threshold. Empirical equations of state of water are based on experimental data at positive pressure; the validity of their extrapolation to negative pressures had been tested only indirectly or with very weakly metastable liquid. We provide thermodynamic data that prove the fidelity of recent equations of state down to -26 MPa. However, this raises questions regarding the nature of the cavitation threshold observed in acoustic experiments, which is far less negative than expected.     

Isotopic self-exchange reactions of water: evaluation of the rule of the geometric mean in liquid-vapor isotope partitioning

Deviations from the random distribution of hydrogen isotopes among isotopic species of liquid and vapor water (the rule of the geometric mean) were critically assessed theoretically and experimentally from the triple to critical point of water. A third-order polynomial equation of the classical near-critical expansion was used to accurately describe the liquid-vapor isotope fractionation of H2O and D2O on the basis of their equations of state. It was found that experimental data for the enthalpy of mixing of H2O-D2O can be used to calculate accurately the deviation from the rule of the geometric mean in liquid and vapor water, ln(KD(v)/KD(l)). A new equation obtained in this study shows that the value of ln(KD(v)/KD(l)) smoothly decreases from +0.009 to 0 with increasing temperature from the triple to critical temperature of water. In contrast, the equation available in the literature and that derived from mass spectrometric measurements of liquid-vapor partitioning of H2O and HDO show complex behavior, including maximum, minimum, and crossover.     

A molecular beam study of the evaporation of water from a liquid jet

A method to maintain a clean surface of a liquid in a high vacuum is described. Using a very thin and fast liquid jet it is not only possible to prevent freezing of the liquid but also to reduce the number of collisions between evaporating molecules to negligibly small values. Thus many of the standard, vacuum dependent, particle probing techniques for solid surfaces can be used for studies of rapidly vaporizing, high vapor pressure liquids. In a first molecular beam investigation we have used time-of-flight analysis to measure the velocity distribution of H₂O molecules vaporizing from thin jets of pure liquid water. The experiments were carried out for liquid jet diameters between 50 and 5 µm. In this range the expanding vapor is observed to undergo the transition to the collision-free molecular flow regime. From the measured velocity distributions the local surface temperature is determined to be less than 210 K. This appears to be the lowest temperature ever reported for supercooled liquid water.     

Relative Permittivities for Glucose+Glycine+Water Solution at 278.15 to 313.15 K

The relative permittivities(ε) for the glucose+glycine+water mixtures were measured at temperatures of 278.15 to 313.15 K. The experimental values for a complete data set were critically analyzed. The experimental va- lues were fitted to some empirical equations as the functions of temperature and/or compositions of the solution. At given temperatures and compositions of glycine, the dependences of the relative permittivities on the molar fraction of glucose(Glc) and glycine(Gly) can be described by a linear or quadratic equation, respectively. A comparison of the εGlc values of glucose solution with the εGla values of galactose solution indicates that the relative permittivities of the ternary solutions containing glucose are smaller than those containing galactose under the same conditions. This difference arises from the slight difference in the stereo-structures of the saccharide molecules.     

Accurate thermodynamic and dielectric equations of state for high-temperature simulated water

The thermodynamic and dielectric properties of the simple point charge extended (SPC/E) water model are examined over wide temperature and density range by means of molecular dynamic simulations. Accurate analytical thermodynamic and dielectric equations of state for the SPC/E pair-potential are presented. Parameterizations cover a broad range of high temperature states including the critical region. The critical point parameters of SPC/E water were determined to be ρ_c = 0.276 g/cm³, T_c = 640.25 K and p_c = 164.37 bar. The value of the static dielectric constant of SPC/E water at its critical point was calculated to be 5.35, which compares remarkably well with the corresponding experimental value of 5.36. Analytical thermodynamic and dielectric equations for the saturated liquid and vapor densities are also given.     

Investigation on spontaneous ignition of two kinds of organic material with water

A systematic investigation was performed to elucidate the cause of spontaneous ignition of Refuse Derived Fuel (RDF) and Meat Bone Meal (MBM). Heat generation in both RDF and MBM with addition of water liquid and vapor at room temperature was determined by isothermal calorimetry. Compared with water liquid, the heat of wetting by sorption of water vapor at 80% relative humidity and 25 °C was larger, which can raise the temperature of RDF and MBM more than 30 and 56 °C, respectively. Heat generation due to fermentation occurred and the temperature of RDF and MBM reached or exceeded 80 °C after 5 days for RDF and 4 days for MBM at 100% RH. The spontaneous ignition for RDF and MBM results from heat of wetting and fermentation at room temperature and a further exothermic reaction at higher temperature.     

Surface tension of water droplets upon homogeneous droplet nucleation in water vapor

A method has been proposed for determining interfacial free energy from the data of molecular dynamics simulation. The method is based on the thermodynamic integration procedure and is distinguished by applicability to both planar interfaces and those characterized by a high curvature. The workability of the method has been demonstrated by the example of determining the surface tension for critical nuclei of water droplets upon condensation of water vapor. The calculation has been performed at temperatures of 273–373 K and a pressure of 1 atm, thus making it possible to determine the temperature dependence of the surface tension for water droplets and compare the results obtained with experimental data and the simulation results for a “planar” vapor–liquid interface.     

Characterization of the TIP4P-Ew water model: vapor pressure and boiling point

The liquid-vapor-phase equilibrium properties of the previously developed TIP4P-Ew water model have been studied using thermodynamic integration free-energy simulation techniques in the temperature range of 274-400 K. We stress that free-energy results from simulations need to be corrected in order to be compared to the experiment. This is due to the fact that the thermodynamic end states accessible through simulations correspond to fictitious substances (classical rigid liquids and classical rigid ideal gases) while experiments operate on real substances (liquids and real gases, with quantum effects). After applying analytical corrections the vapor pressure curve obtained from simulated free-energy changes is in excellent agreement with the experimental vapor pressure curve. The boiling point of TIP4P-Ew water under ambient pressure is found to be at 370.3+/-1.9 K, about 7 K higher than the boiling point of TIP4P water (363.7+/-5.1 K; from simulations that employ finite range treatment of electrostatic and Lennard-Jones interactions). This is in contrast to the approximately +15 K by which the temperature of the density maximum and the melting temperature of TIP4P-Ew are shifted relative to TIP4P, indicating that the temperature range over which the liquid phase of TIP4P-Ew is stable is narrower than that of TIP4P and resembles more that of real water. The quality of the vapor pressure results highlights the success of TIP4P-Ew in describing the energetic and entropic aspects of intermolecular interactions in liquid water.     

Thermodynamic properties of new heat pump working pairs: 1,3-Dimethylimidazolium dimethylphosphate and water,ethanol and methanol

Ionic liquid 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) + water/ethanol/methanol mixtures exhibit properties which render them suitable as candidates for working pairs in industrial applications of absorption heat pumps or chillers. In this paper, the thermodynamic properties including vapor pressure, density, viscosity, heat capacity as well as excess enthalpy of these binary systems were measured at various temperatures with different ionic liquid concentrations. The thermodynamic properties were correlated by different equations, respectively. The correlated values were significantly consistent with the experimental ones. In conclusion, the vapor–liquid equilibrium (VLE) data indicated that the vapor pressures of the three solvents in [MMIM][DMP] displayed a considerable negative deviation from Raoult's law, and the excess enthalpies of the three binary systems are negative. These characteristics are necessary and important for an absorption working pair.     

Isotope fractionation of water during evaporation without condensation

The microscopic events engendering liquid water evaporation have received much attention over the last century, but remain incompletely understood. We present measurements of isotope fractionation occurring during free molecular evaporation from liquid microjets and show that the isotope ratios of evaporating molecules exhibit dramatic differences from equilibrium vapor values, strong variations with the solution deuterium mole fraction, and a clear temperature dependence. These results indicate the existence of an energetic barrier to evaporation and that the evaporation coefficient of water is less than unity. These new insights into water evaporation promise to advance our understanding of the processes that control the formation and lifetime of clouds in the atmosphere.     

Acetonitrile - 2-Methyl-Propan-1-ol and Acetonitrile - 2-Methyl-Propan-2-ol Binary Mixtures and their Physicochemical Properties

The 1 H-NMR spectra of liquid binary mixtures of acetonitrile with 2-methyl-propan-1-ol (i-BtOH) and 2-methyl-propan-2-ol (t-BtOH), were recorded at 298 K over almost the whole range of mixed solvent compositions. From these data the values of spectral parameters, j i (ACN-i-BtOH) and j i (ACN-t-BtOH) were found. The relative permittivities ( k 12 ) and the densities ( d 12 ) of the mixed solvents were measured at 288.15 K, 293.15 K, 298.15 K, 303.15 K and 308.15 K. The experimental data were used to test some empirical equations of the type: y 12 = y 12 ( t ) and y 12 = y 12 ( X 1 ) [where: y 12 = d 12 or k 12 ]. From all these data, the deviations from ideality molar volumes , temperature coefficients of relative permittivities ( f 12 ) and the excess extrathermodynamic parameters were calculated. The values of these structural parameters are discussed in terms of interactions of acetonitrile with both alcohols.     

Stochastic diffusion interactions and coarsening in a system of droplets growing from a supersaturated gas mixture

In this work we study diffusion interactions among liquid droplets growing in stochastic population by condensation from supersaturated binary gas mixture. During the postnucleation transient regime collective growth of liquid droplets competing for the available water vapor decreases local supersaturation leading to the increase of critical radius and the onset of coarsening process. In coarsening regime the growth of larger droplets is prevailing noticeably broadening the droplet size-distribution function when the condensation process becomes more intensive than the supersaturation yield. Modifications in the kinetic equation are discussed and formulated for a stochastic population of liquid droplets when diffusional interactions among droplets become noteworthy. The kinetic equation for the droplet size-distribution function is solved together with field equations for the mass fraction of disperse liquid phase, mass fraction of water vapor component of moist air, and temperature during diffusion-dominated regime of droplet coarsening. The droplet size and mass distributions are found as functions of the liquid volume fraction, showing considerable broadening of droplet spectra. It is demonstrated that the effect of latent heat of condensation considerably changes coarsening process. The coarsening rate constant, the droplet density (number of droplets per unit volume), the screening length, the mean droplet size, and mass are determined as functions of the temperature, pressure, and liquid volume fraction.     

Robust three-body water simulation model

The most common potentials used in classical simulations of liquid water assume a pairwise additive form. Although these models have been very successful in reproducing many properties of liquid water at ambient conditions, none is able to describe accurately water throughout its complicated phase diagram. The primary reason for this is the neglect of many-body interactions. To this end, a simulation model with explicit three-body interactions was introduced recently [R. Kumar and J. L. Skinner, J. Phys. Chem. B 112, 8311 (2008)]. This model was parameterized to fit the experimental O-O radial distribution function and diffusion constant. Herein we reparameterize the model, fitting to a wider range of experimental properties (diffusion constant, rotational correlation time, density for the liquid, liquid/vapor surface tension, melting point, and the ice Ih density). The robustness of the model is then verified by comparing simulation to experiment for a number of other quantities (enthalpy of vaporization, dielectric constant, Debye relaxation time, temperature of maximum density, and the temperature-dependent second and third virial coefficients), with good agreement.     

Phase behavior of binary mixtures of water,carbon dioxide and decane predicted with a lattice-gas model

The Kleintjens—Koningsveld lattice-gas model is used to predict the phase behavior of pure CO₂, water and decane, and of binary mixtures of CO₂ with water and decane. The model, with parameters fitted to experimental data, predicts very accurate vapor pressures and liquid—vapor coexistence densities for the pure fluids. For the binary mixtures, the model correctly predicts the qualitative patterns of phase behavior using two temperature-dependent mixture parameters fitted to simple polynomials over a small range of temperature. For quantitative predictions over wide temperature ranges, however, the temperature dependence of the mixture parameters must be fitted carefully over the same ranges of temperatures. The performance of the Kleintjens—Koningsveld model is compared to that of the Peng—Robinson model.     

Proton magnetic shielding tensor in liquid water

The nuclear magnetic shielding tensor is a sensitive probe of the local electronic environment, providing information about molecular structure and intermolecular interactions. The magnetic shielding tensor of the water proton has been determined in hexagonal ice, but in liquid water, where the tensor is isotropically averaged by rapid molecular tumbling, only the trace of the tensor has been measured. We report here the first determination of the proton shielding anisotropy in liquid water, which, when combined with chemical shift data, yields the principal shielding components parallel (sigma(parallel)) and perpendicular (sigma(perpendicular)) to the O-H bond. We obtained the shielding anisotropy sigma(parallel)-sigma(perpendicular) by measuring the proton spin relaxation rate as a function of magnetic induction field in a water sample where dipole-dipole couplings are suppressed by H/D isotope dilution. The temperature dependence of the shielding components, determined from 0 to 80 degrees C, reflects vibrational averaging over a distribution of instantaneous hydrogen-bond geometries in the liquid and thus contains unique information about the temperature-dependent structure of liquid water. The temperature dependence of the shielding anisotropy is found to be 4 times stronger than that of the isotropic shielding. We analyze the liquid water shielding components in the light of previous NMR and theoretical results for vapor and ice. We show that a simple two-state model of water structure fails to give a consistent interpretation of the shielding data and we argue that a more detailed analysis is needed that quantitatively relates the shielding components to hydrogen bond geometry.     

Multiphase equilibria for binary and ternary mixtures containing propionic acid,n-butanol,butyl propionate,and water

Isothermal vapor–liquid equilibrium (VLE) data were measured for propionic acid + butyl propionate at 373.15 and 393.15 K, and isothermal vapor–liquid–liquid equilibrium (VLLE) data were also measured for n-butanol + water, butyl propionate + water, and water + n-butanol + butyl propionate at temperatures ranging from 323.15 to 393.15 K. No azeotrope was found in propionic acid + butyl propionate. The mutual solubility data of the binary aqueous systems were correlated well with the NRTL model accompanying with temperature-dependent parameters. Improvement on the calculation of saturated vapor compositions has been made by using two-term virial equation with one adjustable binary interaction parameter to represent the non-ideality of the vapor phase. The model parameters determined from the binary VLLE data of n-butanol + water and butyl propionate + water and the binary VLE data of n-butanol + butyl propionate are capable of predicting satisfactorily the VLLE properties for the ternary system of water + n-butanol + butyl propionate.     

Phase equilibrium in the system water–acetonitrile–cyclohexene–cyclohexanone

Phase equilibrium in the water–acetonitrile–cyclohexene–cyclohexanone quaternary system and in its binary and ternary constituents was studied using experimental and calculation methods. The parameters were determined for the NRTL equation that adequately describes liquid–vapor, liquid–liquid–vapor, and liquid–liquid–liquid equilibria. The evolution of the three-phase splitting region inside the concentration tetrahedron was studied on the basis of the obtained model, and its transformation into the two-phase region through the critical node was shown. Thermodynamic analysis involving topological representation for the diagram of the phase equilibrium in a quaternary system was performed, and schemes for the complete separation of the reaction mixture were proposed.     

Liquid-vapor and liquid-liquid phase equilibria of the Brodholt-Sampoli-Vallauri polarizable water model

Liquid-vapor and liquid-liquid phase equilibria of the polarizable Brodholt-Sampoli-Vallauri water model have been investigated by Gibbs ensemble Monte Carlo computer simulations. The coexisting liquid and vapor densities and energy of vaporization of the model is found to be in a reasonable agreement with experimental data in the entire temperature range of liquid-vapor coexistence. The critical temperature and density of the model are found to be 615 K and 0.278 gcm(3), respectively, close to the experimental values of 647.1 K and 0.322 gcm(3). In the supercooled state two distinct liquid-liquid coexistence regions are observed. The existence of liquid-liquid phase separation of a polarizable water model is demonstrated for the first time.