Surface Enthalpy Research Articles

Simulation of the Downshear Reformation of a Tropical Cyclone

Abstract The downshear reformation of Tropical Storm Gabrielle (2001) was simulated at 1-km horizontal resolution using the Weather Research and Forecasting (WRF) Model. The environmental shear tilted the initial parent vortex downshear left and forced azimuthal wavenumber-1 kinematic, thermodynamic, and convective asymmetries. The combination of surface enthalpy fluxes and a lack of penetrative downdrafts right of shear allowed boundary layer moist entropy to increase to a maximum downshear right. This contributed to convective instability that fueled the downshear convection. Within this convection, an intense mesovortex rapidly developed, with maximum boundary layer relative vorticity reaching 2.2 × 10−2 s−1. Extreme vortex stretching played a key role in the boundary layer spinup of the mesovortex. Cyclonic vorticity remained maximized in the boundary layer and intensified upward with the growth of the convective plume. The circulation associated with the mesovortex and adjacent localized cyclonic vorticity anomalies comprised a developing “inner vortex” on the downshear-left (downtilt) periphery of the parent cyclonic circulation. The inner vortex was nearly upright within a parent vortex that was tilted significantly with height. This inner vortex became the dominant vortex of the system, advecting and absorbing the broad, tilted parent vortex. The reduction of tropical cyclone (TC) vortex tilt from 65 to 20 km in 3 h reflected the emerging dominance of this upright inner vortex. The authors hypothesize that downshear reformation, resulting from diabatic heating associated with asymmetric convection, can aid the TC’s resistance to shear by reducing vortex tilt and by enabling more diabatic heating to occur near the center, a region known to favor TC intensification.

Determination Of The Operating Point And The Enthalpy Per Unit Surface Of A Cold Battery With Icy Water And A Double Heat Exchanger

The cold battery is a heat exchanger between two fluids, air (secondary fluid) and iced water (primary fluid).The cold battery is composed of two heat exchangers in series, one of which is made up of flat-plate in galvanized steel serving as a reservoir for the iced water and the other one a copper shell- and-tube exchanger with aluminum cooling blades. The two heat exchangers are connected to a pipe of the same diameter. These pipes will permit the transit of the icy water coming from the flat-plate heat exchanger by gravitation towards the tubes of the second exchanger (1). The good operation of this cold battery depends on the knowledge of its operating point. We are proposing a technique of determination of the operating point by using one of the two fluids (water or air) and the efficiencies (2, 3).The Knowledge of that operating point will enable us, through experimental means, determine the mean surface temperatureand then determine the mean surface enthalpy from the specific heat capacity at saturation obtained from the linearization of the entrance and exit air temperatures on the saturation curves.

Contributions of Surface Sensible Heat Fluxes to Tropical Cyclone. Part II: The Sea Spray Processes

Abstract In Part II of this study, the roles of surface sensible heat fluxes (SHX) in tropical cyclones (TCs) are further investigated in the context of sea spray processes. Results show that the sea spray evaporation is favorable for the TC intensification through enhancing the surface latent heat fluxes (LHX). Unlike the results in Part I, the removal of SHX has led to a somewhat weaker TC by inclusion of sea spray. This is because the spray-mediated latent heat fluxes are simultaneously diminished after cutting down the SHX. Without the warming of SHX from the ocean, the surface air becomes cooler and thereby closer to saturation, which substantially hinders the evaporation of sea spray droplets. Therefore, the SHX are instrumental for sustaining the release of latent heat fluxes by sea spray evaporation. In the experiments of Part I and this study, the reduced total surface enthalpy fluxes as a result of the removal of SHX do not necessarily result in weakened TCs, while the larger LHX basically correspond to stronger TCs. This suggests that the TC intensity is largely dependent on the LHX rather than the total surface enthalpy fluxes, although the latter is generally dominated by the former. Relative roles of thermal and moisture effects in radially elevating the surface equivalent potential temperature θe are also compared. The contributions of thermal effects account for 30%–35% of the total changes in θe for mature TCs, no matter whether SHX from the ocean are included. This further implies that the SHX contribute insignificantly to the spinup of a TC.

Size dependence of the thermal decomposition kinetics of nano- CaC2O4: A theoretical and experimental study

In the processes of preparation and application of nanomaterials, the thermal decomposition of nanoparticles is often involved. An improved general theory of thermal decomposition kinetics of nanoparticles, developed over the past 10 years, was presented in this paper where the relations between reaction kinetic parameters and particle size were derived. Experimentally, the thermal decomposition kinetics of nano-sized calcium oxalate (nano- CaC2O4 with different sizes was studied by means of Thermogravimetry Analysis (TGA) at different heating rates. The values of the apparent activation energy and the logarithm of pre-exponential factor were calculated using the equation of Iterative Kissinger-Akahira-Sunose (IKAS) and its deformations. The influence regularities of particle size on the apparent activation energy and the pre-exponential factor were summarized, which are consistent with the thermal decomposition kinetics theory of nanoparticles. Based on the theory, the method of obtaining the surface thermodynamic properties by the determination of kinetic parameters was presented. Theoretical and experimental results show that the particle size, through the effect on the surface thermodynamic properties, has notable effect on the thermal decomposition kinetics. With the particle size decreasing, the partial molar surface enthalpy and the partial molar surface entropy increases, leading to the decrease of the apparent activation energy and the pre-exponential factor, respectively. Furthermore, the apparent activation energy, the pre-exponential factor, the partial molar surface enthalpy and the partial molar surface entropy are linearly related to the reciprocal of particle diameter, respectively.

Reaction Kinetic Parameters and Surface Thermodynamic Properties of Cu2O Nanocubes

Cuprous oxide (Cu2O) nanocubes were synthesized by reducing Cu(OH)2 in the presence of sodium citrate at room temperature. The samples were characterized in detail by field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction, and N2 absorption (BET specific surface area). The equations for acquiring reaction kinetic parameters and surface thermodynamic properties of Cu2O nanocubes were deduced by establishment of the relations between thermodynamic functions of Cu2O nanocubes and these of the bulk Cu2O. Combined with thermochemical cycle, transition state theory, basic theory of chemical thermodynamics, and in situ microcalorimetry, reaction kinetic parameters, specific surface enthalpy, specific surface Gibbs free energy, and specific surface entropy of Cu2O nanocubes were successfully determined. We also introduced a universal route for gaining reaction kinetic parameters and surface thermodynamic properties of nanomaterials.

Synthesis, characterization, physical and thermodynamic properties of diazobicyclo undecene based dicyanamide ionic liquids

Synthesis of new ionic liquids (ILs) based on diazobicyclo undacane (DBU) cation containing various alkyl groups such as ethyl, butyl, hexyl, octyl, decyl and tetradecyl group with dicyanamide anion were performed. The characterization of the ILs was carried out using NMR (1H and 13C) spectroscopy and elemental analysis. The water content, halide content and the thermal decomposition temperature of the synthesized ILs were determined. The density and viscosity of the ILs were measured in a large temperature range. The effect of temperature and alkyl spacer length on the physical properties such as density, viscosity and surface tension of the DBU based ILs were presented. The thermodynamic properties such as surface enthalpy and entropy, critical temperature and the total surface energy of the ILs were derived from their experimental surface tension and density data.

Synthesis and Surface Thermodynamic Functions of CaMoO4 Nanocakes

CaMoO4 nanocakes with uniform size and morphology were prepared on a large scale via a room temperature reverse-microemulsion method. The products were characterized in detail by X-ray powder diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. By establishing the relations between the thermodynamic functions of nano-CaMoO4 and bulk-CaMoO4 reaction systems, the equations for calculating the surface thermodynamic functions of nano-CaMoO4 were derived. Then, combined with in-situ microcalorimetry, the molar surface enthalpy, molar surface Gibbs free energy, and molar surface entropy of the prepared CaMoO4 nanocakes at 298.15 K were successfully obtained as (19.674 ± 0.017) kJ·mol−1, (619.704 ± 0.016) J·mol−1, and (63.908 ± 0.057) J·mol−1·K−1, respectively.

Evaluation of Thermophysical Properties of Imidazolium-Based Phenolate Ionic Liquids

Thermophysical properties of imidazolium-based phenolate ionic liquids (ILs) were investigated over a wide temperature range. Different alkyl groups such as ethyl, butyl, hexyl, octyl, and decyl were tethered to the 1-methylimidazolium cation to study the effect of alkyl chain length on thermophysical properties such as density, viscosity, refractive index, heat capacity, and surface tension. The thermal stability of the phenolate ILs was investigated using thermogravimetric analysis. From the experimental values of density and surface tension, the molecular volume, standard molar entropy, lattice energy, surface entropy, and surface enthalpy of the ILs were calculated at 303.15 K.

Synthesis and Thermophysical Properties of Hydrogensulfate Based Acidic Ionic Liquids

Three ionic liquids (ILs): 1-butyl-3-methyl-imidazolium hydrogensulfate [C4C1Im][HSO4], 1-butyl-imidazolium hydrogensulfate [C4C0Im][HSO4], and 1-methyl-imidazolium hydrogensulfate [C1C0Im][HSO4], were synthesized and characterized. The effect of alky group incorporation into the imidazolium cation was evaluated in terms of changes in density, surface tension, viscosity, and thermal degradation of the ILs. The viscosity and density were measured within the temperature range of 293.15–373.15 K, and experimental values of density were used to calculate molar volume, standard molar entropy, lattice energy, and thermal expansion coefficients. Glasser’s approach was used to calculate the lattice energies of the ILs. Surface tensions in the temperature range of 293.15–353.15 K were also measured and surface tension values were used to estimate the surface entropy and enthalpy of the ILs. Refractive indices were measured with an ATAGO refractometer (RX-5000α) within the temperature range of 293.15–323.15 K. Thermal gravimetric analysis was performed in the temperature range of 323.15–773.15 K.

Thermophysical properties of two ammonium-based protic ionic liquids.

Experimental data for density, viscosity, refractive index and surface tension are reported, for the first time, in the temperature range between 288.15 K and 353.15 K and at atmospheric pressure for two protic ionic liquids, namely 2-(dimethylamino)-N,N-dimethylethan-1-ammonium acetate, [N11{2(N11)}H][CH3CO2], and N-ethyl-N,N-dimethylammonium phenylacetate, [N112H][C7H7CO2]. The effect of the anion aromaticity and the cation's aliphatic tails on the studied properties is discussed. From the measured properties temperature dependency the derived properties, such as the isobaric thermal expansion coefficient, the surface entropy and enthalpy, and the critical temperature, were estimated.

Formation, stability, and solubility of metal oxide nanoparticles: Surface entropy, enthalpy, and free energy of ferrihydrite

Ferrihydrite (Fh) is an excellent model for understanding nanoparticle behavior in general. Moreover, Fh is one of the most important Fe (hydr) oxides in nature. Fh particles can be extremely small leading to a very high reactive surface area that changes its chemical potential, strongly affecting the solubility, nucleation, and stability. These characteristics can be coupled to the interfacial Gibbs free energy, being γ=0.186±0.01Jm−2 for Fh. The surface free energy has a relatively large contribution of surface entropy (−TSsurf=+0.079±0.01Jm−2). The surface entropy is primarily related to the formation of surface groups by chemisorption of water (−17.1Jmol−1K−1), for Fh equivalent with +0.064±0.002Jm−2 at a surface loading NH2O=12.6μmolm−2. The entropy contribution of physisorbed water has been estimated by analyzing, as model, the surface enthalpy, entropy, and Gibbs free energy of the principal interfaces of H2O, i.e. ice–water–gas. It is about 20% of the contribution of chemisorbed water.The surface enthalpy of Fh is exceptionally low (Hsurf=+0.107±0.01Jm−2), which can be explained by surface depletion (SD) of relatively unstable Fe polyhedra, or similarly, by additional surface loading of the non-depleted mineral core with specific Fe polyhedra for stabilization. The experimental enthalpy of Fh formation varies linearly with the surface area and correctly predicts the enthalpy value for the mineral core (−405.2±1.2kJmol FeO3/2), being similar to the literature value for Fh as virtual bulk material (−406.7±1.5kJmol FeO3/2) obtained with MO/DFT computations. The thermochemical quantities of the mineral core and surface are essentially the same for the entire range of Fh samples, in line with the SD model.The solubility of Fh suspensions as a whole may differ from the behavior of individual particles due to polydispersity. For 2-line Fh, the overall solubility is logKso∼−38.5±0.1 and for prolongedly aged 6-line Fh, logKso∼−39.5±0.1. The smallest Fh particles in a suspension react according to the Ostwald–Freundlich equation (RTΔlnKso=2/3 γA), but the suspension as a whole apparently reacts according to the Ostwald equation (RTΔlnKso=γA). This difference can be explained by the observed linear relation between the minimum (dmin) and mean (dmean) particle size (dmin=2/3 dmean) in Fh suspensions.With best estimates for the surface entropy of goethite, hematite, and lepidocrocite, predictions show that Fh becomes thermodynamically unstable above a diameter of ∼8.0nm at 298K, allowing formation of nano-goethite and nano-hematite, as experienced experimentally at Ostwald ripening. More generally, one observes that metal (hydr) oxides with the highest chemical stability also have the highest mean surface Gibbs free energy, which can be considered as the scientific explanation of the empirical rule of Ostwald–Lussac. In addition, it is shown that the surface Gibbs free energies of metal (hydr) oxides increase with the mean metal coordination number of oxygen in the lattices following the order: oxides>oxyhydroxides>hydroxides.

Morphology Effect on the Kinetic Parameters and Surface Thermodynamic Properties of Ag3PO4 Micro‐/Nanocrystals

Considerable effort has been exerted using theoretical calculations to determine solid surface energies. Nanomaterials with high surface energy depending on morphology and size exhibit enhanced reactivity. Thus, investigating the effects of morphology, size, and nanostructure on the surface energies and kinetics of nanomaterials is important. This study determined the surface energies of silver phosphate (Ag3PO4) micro‐/nanocrystals and their kinetic parameters when reacting with HNO3 by using microcalorimetry. This study also discussed rationally combined thermochemical cycle, transition state theory, basic theory of chemical thermodynamics with thermokinetic principle, morphology dependence of reaction kinetics, and surface thermodynamic properties. Results show that the molar surface enthalpy, molar surface entropy, molar surface Gibbs free energy, and molar surface energy of cubic Ag3PO4 micro‐/nanocrystals are larger than those of rhombic dodecahedral Ag3PO4 micro‐/nanocrystals. Compared with rhombic dodecahedral Ag3PO4, cubic Ag3PO4 with high surface energy exhibits higher reaction rate and lower activation energy, activation Gibbs free energy, activation enthalpy, and activation entropy. These results indicate that cubic Ag3PO4 micro‐/nanocrystals can overcome small energy barrier faster than rhombic dodecahedral Ag3PO4 micro‐/nanocrystals and thus require lower activation energy.

Surface Tension of Refrigerant Fluids from a Molecular-Based Model

Abstract This work addresses a revised method of Fowler’s approximation for predicting the surface tension of refrigerant liquids using a Lennard–Jones (LJ) (12–6) model potential. The required LJ parameters were determined from the second virial coefficients. The major finding in this work was that the effective soft-sphere diameters of the studied LJ-like fluids were found to be a function of temperature and the acentric factor (ω). The reliability of the proposed method was determined by comparison with the literature over a temperature range of 85–384 K. From the 296 data points examined for the above-mentioned liquids, the overall average absolute deviation (AAD) was found to be 2.50%. The uncertainty in the surface tension prediction was ±6.85%. Additionally, surface thermodynamic functions, such as the surface entropy (SS) and surface enthalpy (HS), were also computed via our method. The uncertainties were found to be ±8.93% and ±11.64%, respectively. Furthermore, the AADs of the estimated SS and HS values were found to be 7.50% and 4.79%, respectively. Finally, our method was also employed to estimate the critical temperature of some alkanes with an uncertainty equal to ±5.56%.

Density, Viscosity and Surface Tension of Binary Mixtures of 1-Butyl-1-Methylpyrrolidinium Tricyanomethanide with Benzothiophene.

The effects of temperature and composition on the density and viscosity of pure benzothiophene and ionic liquid (IL), and those of the binary mixtures containing the IL 1-butyl-1-methylpyrrolidynium tricyanomethanide ([BMPYR][TCM] + benzothiophene), are reported at six temperatures (308.15, 318.15, 328.15, 338.15, 348.15 and 358.15) K and ambient pressure. The temperature dependences of the density and viscosity were represented by an empirical second-order polynomial and by the Vogel–Fucher–Tammann equation, respectively. The density and viscosity variations with compositions were described by polynomials. Excess molar volumes and viscosity deviations were calculated and correlated by Redlich–Kister polynomial expansions. The surface tensions of benzothiophene, pure IL and binary mixtures of ([BMPYR][TCM] + benzothiophene) were measured at atmospheric pressure at four temperatures (308.15, 318.15, 328.15 and 338.15) K. The surface tension deviations were calculated and correlated by a Redlich–Kister polynomial expansion. The temperature dependence of the interfacial tension was used to evaluate the surface entropy, the surface enthalpy, the critical temperature, the surface energy and the parachor for pure IL. These measurements have been provided to complete information of the influence of temperature and composition on physicochemical properties for the selected IL, which was chosen as a possible new entrainer in the separation of sulfur compounds from fuels. A qualitative analysis on these quantities in terms of molecular interactions is reported. The obtained results indicate that IL interactions with benzothiophene are strongly dependent on packing effects and hydrogen bonding of this IL with the polar solvent.Electronic supplementary materialThe online version of this article (doi:10.1007/s10953-014-0257-1) contains supplementary material, which is available to authorized users.

Short-term effects of plant litter addition on mineral surface characteristics of young sandy soils

Initial stages of soil development are characterized by structural changes of mineral surfaces over time. The specific surface area (SSA) is closely related to pedogenic properties and soil organic matter (SOM). Interactions between SOM and mineral surfaces induce quantitative and qualitative changes in SSA and corresponding soil properties. However, the knowledge about ranges, effects and mechanisms of organic coverage in the very initial phase of pedogenesis is very limited. Therefore, our objective was to study these processes in young sandy soils and the effects of plant litter addition. Soil samples taken from the constructed catchment “Chicken Creek” were used in a microcosm experiment over 80weeks. The silt and clay fractions of samples (<63μm) were analyzed before the experiment and after 40 and 80weeks. The effects of litter addition and weathering on SSA were assessed using the BET-N2 sorption approach. We found increases of SSA between 16.4% and 41.6% within the 80week experimental period, but a relative reduction in SSA due to organic coverage of these new surfaces after plant litter addition. The removal of the soil organic matter (SOM) by muffling increased SSA (6.8–12.9%). The results for SSA corresponded to changes in surface specific parameters like cation exchange capacity (CEC), surface enthalpy and the fractional coverage of mineral surfaces by SOM. In conclusion, the results showed that the soils were clearly in a very initial state of soil development. However, the potential of these young sandy soils to adsorb nutrients and soil organic matter as one of the main important soil functions clearly increased within the relatively short experimental period and changes in SSA indicate relatively large increases in mineral surfaces within short time periods during the initial phase of soil development compared to long-term pedogenesis.

Re-evaluating the surface tension analysis of polyelectrolyte-surfactant mixtures using phase-sensitive sum frequency generation spectroscopy.

Surface tension (ST) has been the most important measure of a molecule's surface activity. However, in many cases the complex behaviors of ST are challenging to interpret. For example, aqueous solutions of sodium docecyl sulfate (SDS) and poly(diallyldimethylammonium chloride) (PDADMAC) show dramatic changes in ST when the concentration of SDS varies. Although surfactants are generally described as "substances that reduce surface tension", new evidence shows that ST may have little changes when a significant amount of SDS is present at the water surface. The decrease of surface entropy resulting from a better ordering of interfacial molecules, such as water, counteracts the decrease of surface enthalpy and is able to keep the ST nearly unchanged. The dramatic ST decrease and recovery of the SDS-PDADMAC mixtures was discovered to be a result of a surface charge reversal. Similar surface charge reversal was also observed in cationic surfactant and anionic polyelectrolyte mixtures.

Surface thermodynamic properties of different-sized nano octahedral cadmium molybdate

A series of nano octahedral CdMoO 4 with different sizes were prepared by reverse-microemulsion method at room temperature, and the constitute, structure and morphology were characterized. Based on the essential difference between thermodynamic properties of nano CdMoO 4 and bulk CdMoO 4 , the equations for acquiring surface thermodynamic properties of nano CdMoO 4 were derived via combining the basic theory of chemical thermodynamics with thermokinetics theory. According to the derived equations, surface thermodynamic functions such as specific surface Gibbs free energy, specific surface enthalpy and specific surface entropy of the prepared nano octahedral CdMoO 4 at 298.15 K were successfully gained by in situ microcalorimetry. Briefly, this work presented an effective and general method to obtain thermodynamic functions of nano materials.

Size effects on reaction kinetics and surface thermodynamic properties of nano-octahedral cadmium molybdate

Nano-octahedral cadmium molybdate (CdMoO4) samples of various particle sizes were prepared using an inverse-phase microemulsion method at room temperature. The thermodynamics of the reactions of the samples with hydrochloric acid were studied using in situ microcalorimetry. A combination of thermodynamic theory, transition-state theory, and thermochemical cycles was used to obtain the kinetic parameters and surface thermodynamic functions of the nano-octahedral CdMoO4 particles. The dependences of the reaction kinetics and surface thermodynamic properties on particle size and temperature were discussed, and the reasons for the dependences were explored. The results showed that the rate constant, specific Gibbs free energy, specific surface enthalpy, and specific surface entropy increased with decreasing particle size, whereas the activation energy decreased with decreasing particle size. The rate constant, activation Gibbs free energy, specific surface enthalpy, and specific surface entropy increased with increasing temperature; however, the opposite trend was observed for the specific Gibbs free energy. The surface thermal capacity decreased with increasing temperature in the critical size ranged from 30 to 200 nm; this is clearly different from the thermal capacity behavior of traditional heat-storage materials.

Response of Atmospheric Convection to Vertical Wind Shear: Cloud-System-Resolving Simulations with Parameterized Large-Scale Circulation. Part I: Specified Radiative Cooling

Abstract It is well known that vertical wind shear can organize deep convective systems and greatly extend their lifetimes. Much less is known about the influence of shear on the bulk properties of tropical convection in statistical equilibrium. To address the latter question, the authors present a series of cloud-resolving simulations on a doubly periodic domain with parameterized large-scale dynamics based on the weak temperature gradient (WTG) approximation. The horizontal-mean horizontal wind is relaxed strongly in these simulations toward a simple unidirectional linear vertical shear profile in the troposphere. The strength and depth of the shear layer are varied as control parameters. Surface enthalpy fluxes are prescribed. The results fall in two distinct regimes. For weak wind shear, time-averaged rainfall decreases with shear and convection remains disorganized. For larger wind shear, rainfall increases with shear, as convection becomes organized into linear mesoscale systems. This nonmonotonic dependence of rainfall on shear is observed when the imposed surface fluxes are moderate. For larger surface fluxes, convection in the unsheared basic state is already strongly organized, but increasing wind shear still leads to increasing rainfall. In addition to surface rainfall, the impacts of shear on the parameterized large-scale vertical velocity, convective mass fluxes, cloud fraction, and momentum transport are also discussed.

Viscoelastic, Surface, and Volumetric Properties of Ionic Liquids [BMIM][OcSO4], [BMIM][PF6], and [EMIM][MeSO3

Thermophysical properties viz. surface tension, viscosity, density, and ultrasonic velocity of three ionic liquids 1-butyl-3-methyl imadazolium octyl sulfate [BMIM][OcSO4], 1-butyl-3-methyl imadazolium hexafluorophosphate [BMIM][PF6], and 1-ethyl-3-methyl imadazolium methanesulfonate [EMIM][MeSO3] have been measured in a wide temperature range. Experimental data so obtained have been used to calculate isentropic compressibility, isothermal expansion coefficient, surface entropy, surface enthalpy, and critical temperature (temperature where the distinction between liquid and gas phase vanishes and the surface tension tends to zero). Structure–property correlation for different ILs is also discussed.