Surface Enthalpy Research Articles

A temperature-dependent model for tensile strength characteristic curve of unsaturated soils

Tensile strength is a key parameter controlling the formation of desiccation cracks in soils. Desiccation cracks are triggered in unsaturated soils due to drying imposed by natural processes or engineering applications mainly involving elevated temperatures. However, there is no closed-form model in the literature to capture the effect of temperature on tensile strength. This study presents a temperature-dependent model for the tensile strength characteristic curve (TSCC) of unsaturated soils. The model employs the suction stress characteristic curve (SSCC) to represent the uniaxial tensile strength of unsaturated soils at different water contents and temperatures. The model incorporates the effects of temperature into adsorptive and capillary suction stress components. The temperature-dependent adsorptive suction stress is obtained by accounting for thermal induced changes in suction stress at dry state through the Hamaker constant and the density of water. The temperature-dependent form of capillary suction stress is derived by employing temperature-dependent forms of surface tension, contact angle and enthalpy of immersion. Upon comparison, results from the proposed TSCC exhibited a very good agreement against laboratory-measured tensile strength data for two clayey soils tested at different temperatures ranging from 20 to 60 °C. The presented model can improve the analysis of desiccation cracking in unsaturated soils.

Volume-based thermodynamics of organic liquids: Surface tension and the Eötvös equation

Many thermodynamic properties, such as entropy, lattice energy, and so forth, correlate with some function of formula volume. We here report on a recently rediscovered modified Eötvös equation which relates surface tension values to molar Gibbs surface energies, surface entropies and surface enthalpies. The resulting thermodynamic values are valuable in understanding molecular configurations of surfaces. The molar surface entropy, Δs, in what may be considered to be a Trouton surface entropy, is roughly constant at 20 J K−1 mol−1 compared with the Trouton entropy of (80–100) J K−1 mol−1 for evaporation at the boiling point of liquids.Weakly-bonded molecular liquids like alkanes have a relatively large molar surface entropy, Δs ≅ 25 J K−1 mol−1, suggesting a loss in order on surface formation, while the rather smaller molar surface entropy, Δs ≅ 13 J K−1 mol−1, for the hydrogen-bonded alcohols indicates that the surface molecules are quite strongly bound to that surface.

A Numerical Study of Typhoon Megi (2010). Part II: Eyewall Evolution Crossing the Luzon Island

AbstractTyphoon Megi (2010) experienced drastic eyewall structure changes when it crossed the Luzon Island and entered the South China Sea (SCS), including the contraction and breakdown of the eyewall after landfall over the Luzon Island, the formation of a new large outer eyewall accompanied by reintensification of the storm after it entered the SCS, and the appearance of a short-lived small inner eyewall. These features were reproduced reasonably well in a control simulation using the Advanced Weather Research and Forecasting (ARW-WRF) Model. In this study, the eyewall processes of the simulated Megi during and after landfall have been analyzed. Results show that the presence of the landmass of the Luzon Island increased surface friction and reduced surface enthalpy flux, causing the original eyewall to contract and break down and the storm to weaken. The formation of the new large eyewall results mainly from the axisymmetrization of outer spiral rainbands after the storm core moved across the Luzon Island and entered the SCS. The appearance of the small inner eyewall over the SCS was due to the increased surface enthalpy flux and the revival of convection in the central region of the storm core. In a sensitivity experiment with the mesoscale mountain replaced by flat surface over the Luzon Island, a new large outer eyewall formed over the western Luzon Island with its size about one-third smaller after the storm entered the SCS than that in the control experiment with the terrain over the Luzon Island unchanged.

Surface Thermodynamics, Viscosity, Activation Energy of N-Methyldiethanolamine Aqueous Solutions Promoted by Tetramethylammonium Arginate

The surface tension and viscosity values of N-methyldiethanolamine (MDEA) aqueous solutions promoted by tetramethylammonium arginate ([N1111][Arg]) were measured and modeled. The experimental temperatures were 303.2 to 323.2 K. The mass fractions of MDEA (wMDEA) and [N1111][Arg] (w[N1111][Arg]) were 0.300 to 0.500 and 0.025 to 0.075, respectively. The measured surface tension and viscosity values were satisfactorily fitted to thermodynamic models. With the aid of experimentally viscosity data, the activation energy (Ea) and H2S diffusion coefficient (DH2S) of MDEA-[N1111][Arg] aqueous solution were deduced. The surface entropy and surface enthalpy of the solutions were calculated using the fitted model of the surface tension. The quantitative relationship between the calculated values (surface tension, surface entropy, surface enthalpy, viscosity, activation energy, and H2S diffusion coefficient) and the operation conditions (mass fraction and temperature) was demonstrated.

Comparison of momentum roughness lengths of the WRF-SWAN online coupling and WRF model in simulation of tropical cyclone Gonu

The surface enthalpy fluxes (latent and sensible heat fluxes) provide the necessary energy to intensify tropical cyclones (TCs). The surface momentum fluxes modify the intensity of TCs. Various parameters affect the surface fluxes. Drag and enthalpy exchange coefficients are known as parameters that lead to ambiguity in the surface fluxes. Thus, for simulating a TC, various drag and enthalpy exchange coefficients are tested in numerical simulations. Exchange coefficients directly relate to roughness lengths. The main goal of this study was comparing derived roughness lengths of the COAWST (WRF-SWAN online coupling) and WRF models with one another. The TC Gonu formed over the Arabian Sea in 2007 was selected for this study. Employing self-reliant WRF, it is found that track and intensity of the TC Gonu can be best simulated when Donelan parameterization is applied for momentum roughness length and Large-Pond parameterization for enthalpy roughness length. In the second section, simulations were conducted in the coupled mode using the COAWST model with the Large-Pond parameterization (for the enthalpy roughness length). Results cleared that the use of Oost parameterization leads to a high overestimation of simulated momentum roughness length compared with other parameterizations while both the Drennan and Taylor parameterizations were somewhat close to reality. Differences of simulated maximum 10-m wind speed between the Oost parameterization and other parameterizations were more than differences of their simulated minimum central pressure. These results proved that the momentum roughness length affects the maximum 10-m wind speed more significantly than the minimum central pressure. In the last section, a simulation was performed using the COAWST model with the Donelan–Large-Pond parameterization. In this simulation, only 10-m wind speed from the WRF model transferred to the SWAN model. The results showed that simulated wave heights in the open ocean were in good agreement with the results of other researchers. In general, the SWAN model performance is evaluated satisfactorily while the parameterizations using the wave information need to be more investigated.

The Impact of Storm-Induced SST Cooling on Storm Size and Destructiveness: Results from Atmosphere-Ocean Coupled Simulations

In this study, both an atmospheric model [Weather Research and Forecasting (WRF) model] and an atmosphere (WRF)-ocean (Princeton Ocean Model; POM) coupled model are used to simulate the tropical cyclone (TC) Kaemi (2006). By comparing the simulation results of the models, effects of oceanic elements, especially the TC-induced sea surface temperature (SST) cooling, on the simulated TC size and destructiveness are identified and analyzed. The results show that there are no notable differences in the simulated TC track and its intensity between the uncoupled and coupled experiments; however, there are large differences in the TC size (i.e., the radius of gale-force wind) between the two experiments, and it is the TC-induced SST cooling that decreases the TC size. The SST cooling contributes to the decrease of air-sea moisture difference (ASMD) outside the TC eyewall, which subsequently leads to the decreases in surface enthalpy flux (SEF), radial sea-level pressure gradient, absolute vorticity advection, and wind speed outside the TC eyewall. As a result, the TC size and size-dependent TC destructive potential all decrease remarkably.

Consistent Impacts of Surface Enthalpy and Drag Coefficient Uncertainty between an Analytical Model and Simulated Tropical Cyclone Maximum Intensity and Storm Structure

Abstract Several previous studies have demonstrated the significant sensitivity of simulated tropical cyclone structure and intensity to variations in surface-exchange coefficients for enthalpy (Ck) and momentum (Cd), respectively. In this study we investigate the consistency of the estimated peak intensity, intensification rate, and steady-state structure between an analytical model and idealized axisymmetric numerical simulations for both constant Ck and Cd values and various wind speed–dependent representations of Ck and Cd. The present analysis with constant Ck and Cd values demonstrates that the maximum wind speed is similar for identical Ck/Cd values less than 1, regardless of whether changes were made to Ck or Cd. However, for a given Ck/Cd greater than 1, the simulated and theoretical maximum wind speed are both greater if Cd is decreased compared to Ck increased. This behavior results because of a smaller enthalpy disequilibrium at the radius of maximum winds for larger Ck. Additionally, the intensification rate is shown to increase with Ck and Cd and the steady-state normalized wind speed beyond the radius of maximum winds is shown to increase with increasing Cd. Experiments with wind speed–dependent Ck and Cd were found to be generally consistent, in terms of the intensification rate and the simulated and analytical-model-estimated maximum wind speed, with the experiments with constant Ck and Cd.

Pronounced Impact of Salinity on Rapidly Intensifying Tropical Cyclones

AbstractTropical cyclone (TC) rapid intensification (RI) is difficult to predict and poses a formidable threat to coastal populations. A warm upper ocean is well known to favor RI, but the role of ocean salinity is less clear. This study shows a strong inverse relationship between salinity and TC RI in the eastern Caribbean and western tropical Atlantic due to near-surface freshening from the Amazon–Orinoco River system. In this region, rapidly intensifying TCs induce a much stronger surface enthalpy flux compared to more weakly intensifying storms, in part due to a reduction in SST cooling caused by salinity stratification. This reduction has a noticeable positive impact on TCs undergoing RI, but the impact of salinity on more weakly intensifying storms is insignificant. These statistical results are confirmed through experiments with an ocean mixed layer model, which show that the salinity-induced reduction in SST cold wakes increases significantly as the storm’s intensification rate increases. Currently, operational statistical–dynamical RI models do not use salinity as a predictor. Through experiments with a statistical RI prediction scheme, it is found that the inclusion of surface salinity significantly improves the RI detection skill, offering promise for improved operational RI prediction. Satellite surface salinity may be valuable for this purpose, given its global coverage and availability in near–real time.

Modulation of Clouds and Rainfall by Tropical Cyclone's Cold Wakes

AbstractTropical cyclones can pump heat into the ocean by producing a long‐lasting subsurface warm anomaly while leaving a relatively short‐term surface cold anomaly via mixing the upper ocean. Although the heat pumping has been found to be crucial in driving oceanic heat transport and thereby regulating climate changes, the contribution of surface cold anomaly to the atmosphere remains unclear. Here we show that local clouds and rainfall are effectively modulated by cold wakes left behind by tropical cyclones using a combination of satellite observations. On average, the negative surface enthalpy flux anomaly associated with the cold wake results in a reduction of rainfall by ~16.6 ± 0.6% (standard error) and a decline of cloud fraction by ~6.7 ± 0.4% over the wake region. Clouds and rainfall tend to be more suppressed for slower moving or stronger TCs. With more intense or slower moving TCs in a warming climate, such a modulation could be amplified accordingly.

Numerical investigation on the drag characteristics of supercritical water flow past a sphere

Numerical simulation has become a useful approach to explore the complex physical and chemical process inside the supercritical water (SCW) fluidized bed reactor. Due to the drastic and non-linear variation of water properties near pseudocritical point, the flow field and drag coefficient of SCW flow past a cold particle are considerably different from that of conventional flow. Therefore, in this work, particle-resolved numerical investigation is conducted to study the flow field and drag characteristics under the influence of the special water properties variation. Through varying the enthalpy corresponding to the particle surface temperature, which will be called the particle surface enthalpy for short, in a wide range, it realizes the study under different properties variation tendencies. The simulated results demonstrate that the variations of drag coefficient versus Reynolds number (Re) and particle surface enthalpy are in good regularity when taking the freestream temperature as reference temperature. The drag coefficient is enhanced greatly at high enthalpy difference between particle surface and inflow, and the enhancement is mainly contributed by that of the frictional drag coefficient. Moreover, the drag coefficient variations under different pressures are in good agreement when cases are set with the same inflow and particle surface enthalpies, respectively. By fitting the simulated results, a new drag coefficient correlation is developed for Re range of 10–200 with consideration of the influence of the special properties variation. The fitting quality is good that the maximum deviation between the new correlation and simulated data is 13.92%, and the mean deviation is 3.67%.

Surface thermodynamics and viscosity of 1-dimethylamino-2-propanol + 1-(2-aminoethyl)piperazine and 1-dimethylamino-2-propanol + 1,5-diamino-2-methylpentane aqueous solutions

The surface tensions (γ) and viscosities (η) of 1-dimethylamino-2-propanol (DMA2P) − 1-(2-aminoethyl)piperazine (AEP) and DMA2P − 1,5-diamino-2-methylpentane (DAMP) were measured and correlated. According to the CO2 capture temperature from the thermal power plant flue gas (around 313 K), the experimental temperatures were selected to be 303.2 K, 313.2 K and 323.2 K. The mass fractions of DMA2P ranged from 0.300 to 0.500, and those for activators (AEP and DAMP) ranged from 0.050 to 0.150. Temperature and composition dependences of γ and η were demonstrated on the basis of experiments and calculations. The activation energy (Ea) was estimated from the temperature dependence of viscosity. Analytical formulations of surface entropy (SS) and surface enthalpy (HS) were deduced from the analytical equation of γ. SS and HS were calculated and their variations with respect to mass fraction were analyzed.

Different effects of latent heat in planetary boundary layer and cloud microphysical processes on Typhoon Sarika (2016)

Three simulation experiments were conducted on Typhoon (TC) “Sarika” (2016) using the WRF model, different effects of the latent heat in planetary boundary layer and cloud microphysical process on the TC were investigated. The control experiment well simulated the changes in TC track and intensity. The latent heat in planetary boundary layer or cloud microphysics process can affect the TC track and moving speed. Latent heat affects the TC strength by affecting the TC structure. Compared with the CTL experiment, both the NBL experiment and the NMP experiment show weakening in dynamics and thermodynamics characteristics of TC. Without the effect of latent heat, the TC cannot develop upwards and thus weakens in its intensity and reduces in precipitation; this weakening effect appears to be more obvious in the case of closing the latent heat in planetary boundary layer. The latent heat in planetary boundary layer mainly influences the generation and development of TC during the beginning stage, whereas the latent heat in cloud microphysical process is conducive to the strengthen and maintenance of TC in the mature stage. The latent heat energy of the cloud microphysical process in the TC core region is an order of magnitude larger than the surface enthalpy. But the latent heat release of cloud microphysical processes is not the most critical factor for TC enhancement, while the energy transfer of boundary layer processes is more important.

Downhole measurement of enthalpy in geothermal wells – An analytical, experimental and numerical study

The enthalpy of two-phase geothermal fluids is typically monitored at the surface to understand the performance of a geothermal field. Surface enthalpy, however, cannot reflect real reservoir conditions downhole because of the heat loss along the wellbore. In addition, with only the surface enthalpy, the energy contributions from separate feed zones cannot be evaluated individually. A technique for determining downhole enthalpy in two-phase geothermal wells using surface inputs and chloride concentrations was developed in this study, including analytical models, experimental work and numerical studies, so that the downhole flowing enthalpy, the energy contribution from each feed zone and the heat loss along the wellbore can be evaluated. Chloride always stays in the liquid phase and becomes more concentrated as the geothermal fluid ascends to the surface and boils, and the change in chloride concentration along the wellbore can be utilized to calculate the change in the flowing steam fraction and the enthalpy. Analytical models to implement this idea were established for geothermal wells with a single feed zone or multiple feed zones, and the calculation procedures are elaborated with detailed flow diagrams and examples. The analytical models involve mass balance, energy balance and an assumption that the chloride concentration in the liquid from the feed zone is determinable. Inputs to the analytical model include two-phase mass flow rates and enthalpy at the surface and chloride concentrations at the surface and in the downhole. Temperature or pressure measurements are utilized to apply the energy balance in the model for multiple feed zones. Experiments were conducted to test the feasibility of an accurate determination of chloride concentration in two-phase fluids and validate the assumption in the analytical model. Chloride concentration distribution in the mixing area at the inlet of the feed zone was determined and visualized in the experiments. At the same time, similar mixing processes were visualized by a numerical simulation using ANSYS Fluent, and results from the numerical simulation are consistent with those from the experiments. Therefore, both the experiments and the simulation support the assumption in the analytical model that chloride concentration in the liquid from the feed zone can be determined accurately. It is demonstrated that the proposed method provides a fast and cost-effective way to determine the downhole two-phase flowing enthalpy in geothermal wells with multiple feed zones and estimate flow rates and energy contribution from each individual feed zone.

Density and surface tension of binary mixture of 1-nonanol +n-octane, +n-nonane, and +n-decane from (293.15 to 323.15) K at P = 0.1 MPa

We present the density and surface tension of binary mixtures n-octane, n-nonane and n-decane with 1-nonanol in the entire composition range at atmospheric pressure. The surface tension is measured from 293.15 K to 313.15 K while the density is measured from 293.15 to 323.15 K. Densities are obtained from a vibrating tube densimeter and surface tensions are from a drop volume tensiometer. Excess molar volumes and surface tension deviations are calculated from the experimental measurements and they are represented using Redlich-Kister type equations. Surface entropy and enthalpy are calculated using the temperature dependence of the surface tension.

Determination of the vaporisation enthalpies for amino acid ionic liquids [Cnmim][Ala](n = 5, 6) and applications of the molar surface Gibbs energy

Amino acid ionic liquids (ILs) 1-alkyl-3-methylimidazolium alanine [Cnmim][Ala] (n = 5,6) were prepared and characterized. The enthalpy of vaporisation at the average temperature, Δ1gHmo(Tav), for the two ILs were determined by means of isothermogravimetrical analysis, and in terms of Δ1gCp,mo, the value of Δ1gHmo(Tav) can be adjusted to Δ1gHmo(2 9 8); then, the polarity, δμ, of the two ILs were estimated, in which the order of the δμ is in consistent with our experiences. In terms of molar surface Gibbs energy, gs, the traditional Eötvös equation was improved, the parameters of new Eötvös one have clear physical meanings: Its slope and intercept are the molar surface entropy, s, and the molar surface enthalpy, h, respectively. In addition, combining gs with Lorentz–Lorenz equation, an expression for predicting surface tension, γ, of the ILs was obtained, and the predicted values of γ are in good agreement with the experimental ones.

Investigation of the size- and morphology-dependence of surface thermodynamic properties of nano-silver

Surface thermodynamic properties related to nanoparticles size and morphology generate significant influences on their thermodynamic behaviors in different physicochemical processes. Herein, the electrode potentials of Ag nanoelectrodes formed with various particle sizes and morphologies of nano-Ag were determined at varying temperatures. Based on the method of electrochemistry, the surface thermodynamic properties of nano-Ag were gotten and a comparison was made with theoretical results. It is revealed that with decreasing nano-Ag size, these surface thermodynamic properties become larger and correlate linearly with inverse particle size. Furthermore, for nanoparticles with the same equivalent size, the change regularity of surface Gibbs energy, enthalpy and entropy with morphology follow the same sequence as: cube > sphere > wire. This study is valuable to provide insights to the influence mechanisms and regularities of nanoparticle size and morphology on these properties.

Quantification of the Land Surface and Brown Ocean Influence on Tropical Cyclone Intensification over Land

AbstractAn investigation of Tropical Cyclone (TC) Kelvin in February 2018 over northeast Australia was conducted to understand the mechanisms of the brown ocean effect (BOE) and to develop a comprehensive analysis framework for landfalling TCs in the process. NASA’s Land Information System (LIS) coupled to the NASA Unified WRF (NU-WRF) system was employed as the numerical model framework for 12 land/soil moisture perturbation experiments. Impacts of soil moisture and surface enthalpy flux conditions on TC Kelvin were investigated by closely evaluating simulated track and intensity, midlevel atmospheric thermodynamic properties, vertical wind shear, total precipitable water (TPW), and surface moisture flux. The results suggest that there were recognized differentiations among the sensitivity simulations as a result of land surface (e.g., soil moisture and texture) conditions. However, the intensification of TC Kelvin over land was more strongly related to atmospheric moisture advection and the diurnal cycle of solar radiation (i.e., radiative cooling) than to overall soil moisture conditions or surface fluxes. The analysis framework employed here for TC Kelvin can serve as a foundation to specifically quantify the factors governing the BOE. It also demonstrates that the BOE is not a binary influence (i.e., all or nothing), but instead operates in a continuum from largely to minimally influential such that it could be utilized to help improve prediction of inland effects for all landfalling TCs.

Determination of surface tension and surface thermodynamic properties of nano-ceria by low temperature heat capacity

The surface tension and surface thermodynamic properties play a decisive role in research and applications of nano materials, but they are difficult to be determined, as there is no precise method to measure these properties of nano materials. Herein, we derived the relations between the molar surface thermodynamic functions, surface heat capacity, and particle size. On this basis, a new low-temperature heat capacity method for determining the surface tension and the surface thermodynamic functions of nano materials was proposed. We measured the low temperature heat capacities of nano-CeO2 and bulk CeO2 in temperature range from 1.9 K to 300 K at constant pressure by the Physical Property Measurement System (PPMS). The surface tensions and corresponding temperature coefficients of nano-CeO2 were calculated at different temperatures, and then the surface thermodynamic functions were obtained. The results show that the molar heat capacities of nano-CeO2 are greater than that of the corresponding bulk CeO2 in temperature range from 1.9 K to 300 K. The molar surface enthalpy and molar surface entropy of nano-CeO2 increase with the increase of temperature, while surface tension, temperature coefficient, and molar surface Gibbs energy decrease with the increase of temperature. The proposed low temperature heat capacity method can not only accurately measure surface tension, temperature coefficient, and surface thermodynamic functions of nanoparticles at different temperatures, it also provides a reliable and an accurate experimental method for solving the thermodynamic problems of nanoparticles.

Slow Modes of the Equatorial Waveguide

AbstractA recently developed linear model of eastward-propagating disturbances has two separate unstable modes: convectively coupled Kelvin waves destabilized by the wind dependence of the surface enthalpy flux, and slow, MJO-like modes destabilized by cloud–radiation interaction and driven eastward by surface enthalpy fluxes. This latter mode survives the weak temperature gradient (WTG) approximation and has a time scale dictated by the time it takes for surface fluxes to moisten tropospheric columns. Here we extend that model to include higher-order modes and show that planetary-scale low-frequency waves with more complex structures can also be amplified by cloud–radiation interactions. While most of these waves survive the WTG approximation, their frequencies and growth rates are seriously compromised by that approximation. Applying instead the assumption of zonal geostrophy results in a better approximation to the full spectrum of modes. For small cloud–radiation and surface flux feedbacks, Kelvin waves and equatorial Rossby waves are destabilized, but when these feedbacks are strong enough, the frequencies do not lie close to classical equatorial dispersion curves except in the case of higher-frequency Kelvin and Yanai waves. An eastward-propagating n = 1 mode, in particular, has a structure resembling the observed structure of the MJO.

New Methods to Characterize the Surface and Interface Acid–Base Properties of Some Hydrocarbons by Inverse Gas Chromatography

The thermodynamic surface and interfacial properties of some hydrocarbons used as process oils in rubber industry were determined using the inverse gas chromatography technique at infinite dilution. In this paper, four different common process oils, such as distillated aromatic extract, treated distillate aromatic extract, mildly extracted solvate, and hydro-processed naphthenic oil, were studied. An important effect of the temperature on the dispersive component of the surface energy of different hydrocarbons was proved. These hydrocarbon materials exhibit a strong dependency of their surface acid–base properties on the temperature. The specific surface enthalpy and entropy, as well as the acid–base constants KA, KD and the amphoteric constant K of hydrocarbon surfaces, strongly depend on the temperature. It was proved that the hydro-processed naphthenic oil presents the highest acidity relative to other hydrocarbon materials.