Enthalpy Coefficients Research Articles

Experimental and computational study of binary mixture ethanolamine and 2-amino-2-methyl-1-propanol

The present work involves experimental and computational investigations into the density of pure and mixed states of ethanolamine (ET) and 2-amino-2-methyl-1-propanol (AMP) under a pressure of 1 atm and temperatures ranging from 293.15 K to 333.15 K The density data were used to derive the excess molar volume, thermal expansion coefficient, and isothermal coefficient of pressure excess molar enthalpy. The Redlich–Kister equation was employed to calculate the excess molar and its accompanying coefficients. In the gas phase, density functional theory (DFT) was utilized to explore the most stable structures of ET … ET, AMP … AMP, and the ET … AMP mixture. Molecular dynamics simulation (MD) was used to calculate the structural properties of these mixtures in the liquid phase. Radial distribution function (RDFs) combined distribution function (CDF) and spatial distribution function (SDF) in different mole fractions calculated in the liquid phase. The intramolecular and intermolecular interactions of ethanolamine and AMP were obtained using the radial distribution function in different molar fractions. It was found that the ethanolamine molecule has a greater tendency to form intramolecular hydrogen bonds, while the AMP molecule has a greater tendency to form intermolecular hydrogen bonds.

Structure effect of wall cooling channel on liquid metal heat transfer in aero-engines

In this study, a model of the cooling channel and an experimental system for heat transfer involving liquid metal are studied, to investigate the influence of the wall cooling channel structure of combustor on the heat transfer process. The error between the experimental and simulated outcomes fall is within 3 %, suggesting that the accuracy of the simulation is satisfactory. The simulation results found that the temperature non-uniformity coefficient can be reduced by 13 % and 7 % through adjusting the aspect ratio under the heat flux of 3 MW/m2 and 1.5 MW/m2 respectively, and the wall temperature of gas side can be reduced by 89 K and 47 K respectively. A smaller aspect ratio is favorable for homogenizing the liquid metal temperature distribution. Longer widths, however, can lead to horizontal thermal stratification, which can be unfavorable for heat transfer. With an aspect ratio and rib thickness of about 0.5 and 0.4 mm, respectively, the cooling channel outlet has the lowest non-uniformity coefficient of temperature and enthalpy, which is conducive to the improvement of the wall energy recovery rate. The optimal cooling channel effectively improves the thermal stratification in channel, and provides theoretical guidance for the suitable application of liquid metal to the combustor wall cooling channel.

Comparing the influence of cation order and composition in simulated Zn(Sn, Ge)N2 on structure, elastic moduli, and polarization for solid state lighting

Alloying and site ordering play complementary roles in dictating a material’s properties. However, deconvolving the impacts of these separate phenomena can be challenging. In this work, we simulate structures of Zn(Sn,Ge)N2 with varied Sn content and site ordering to determine the impacts of order and composition on structural and electronic properties. We assess the formation enthalpy, lattice parameters, elastic constants, spontaneous polarization, and piezoelectric coefficients. In mostly disordered structures (order parameters ranging from 0.2 to 0.4), the formation enthalpy exhibits local extrema as a function of the order parameter, deviating from the more linear trends seen in both fully disordered and fully ordered systems. This anomalous deviation from the otherwise linear trend in formation enthalpy with order manifests in each of the other properties calculated. This range of order parameters of interest may be caused by a transition in the ordering of the quaternary material similar to phase changes seen in ternary compounds but stretched over a region inclduing 20% of the order parameter range. Most parameters calculated are more sensitive to order than to composition in the limited composition range tested; however, the lattice parameter c, piezoelectric coefficient e33, and elastic moduli C12, C13, and C23 are more sensitive to composition. Of the properties compared, the piezoelectric coefficients are influenced most significantly by changes in both the composition and order parameter. Lattice parameters undergo the smallest changes with order and composition, but these small differences appear to impart large trends in the other properties. Better understanding the effects of disorder and group IV alloying in Zn(Sn,Ge)N2 allows for more accurate modeling of characteristics of this material system for solid state lighting and other applications.

Application of ERAS-model and PFP theory on excess and deviation properties for binary systems of ionic liquid + amine derivatives

Thermodynamics of mixtures includes ionic liquid 2-hydroxyethylammonium propionate [2-HEAPr] + 1-propanol, 3-amino-1-propanol [AP], 1-amino-2-propanol [MIPA], and monoethanolamine [MEA] were studied. Density ρ, speed of sound u, and refractive index nD of pure and mixtures were measured at T = (298.15, 308.15, 318.15) K. Excess molar volume VmE, excess partial molar volume Vm,iE, excess thermal expansion coefficient αE, isothermal coefficient of excess molar enthalpy (∂Hm∂P)T,x, deviations in isentropic compressibility Δ ks, and refractive index Δ nD were calculated and data correlated with Redlich-Kister polynomial relation. The Prigogine-Flory-Patterson (PFP) and Extended Real Associated Solution (ERAS) models were applied to analyze intramolecular and intermolecular interactions between like and unlike molecules. The accuracy of theoretical models were found to be in agreement with empirical results. Finally, the study confirmed the structures of the ILs using FT-IR and HNMR analysis.

Air–Sea Enthalpy and Momentum Exchange Coefficients from GPS Dropsonde Measurements in Hurricane Conditions

The intensity of tropical cyclones is highly dependent on air–sea enthalpy and momentum exchange. At extreme wind speeds, the values of the enthalpy, CK, and momentum, CD, exchange coefficients are characterized by high uncertainty. The present study aims to expand the previously used algorithm for CD retrieval to obtain the values of CK from wind speed measurements and the enthalpy profiles obtained from NOAA GPS dropsondes in hurricane conditions. This algorithm uses concepts from technical hydrodynamics, describing turbulent boundary layers on flat plates and pipes. According to this approach, the velocity (and enthalpy) defect profiles are self-similar in the entire boundary layer, including the layer of constant fluxes and the “wake” part, where the airflow adapts to the undisturbed flow region. By using the self-similarity property, the parameters of the constant flow layer (the roughness parameter, friction velocity, and the enthalpy and exchange coefficients CD and CK) could be obtained from measurements in the “wake” part for wind speeds from 20 m/s to 72 m/s. The estimates of the CK/CD ratio revealed values of 0.7 and 0.96 (depending on the self-similar approximation limits), and the results suggest that there are slight variations with the wind speed.

Estimation of secondary organic aerosol formation parameters for the volatility basis set combining thermodenuder, isothermal dilution, and yield measurements

Abstract. Secondary organic aerosol (SOA) is a major fraction of the total organic aerosol (OA) in the atmosphere. SOA is formed by the partitioning onto pre-existent particles of low-vapor-pressure products of the oxidation of volatile, intermediate-volatility, and semivolatile organic compounds. Oxidation of the precursor molecules results in a myriad of organic products, making the detailed analysis of smog chamber experiments difficult and the incorporation of the corresponding results into chemical transport models (CTMs) challenging. The volatility basis set (VBS) is a framework that has been designed to help bridge the gap between laboratory measurements and CTMs. The parametrization of SOA formation for the VBS has been traditionally based on fitting yield measurements of smog chamber experiments. To reduce the uncertainty in this approach, we developed an algorithm to estimate the SOA product volatility distribution, effective vaporization enthalpy, and effective accommodation coefficient combining SOA yield measurements with thermograms (from thermodenuders) and areograms (from isothermal dilution chambers) from different experiments and laboratories. The algorithm is evaluated with “pseudo-data” produced from the simulation of the corresponding processes, assuming SOA with known properties and introducing experimental error. One of the novel features of our approach is that the proposed algorithm estimates the uncertainty in the predicted yields for different atmospheric conditions (temperature, SOA concentration levels, etc.). The uncertainty in these predicted yields is significantly smaller than that of the estimated volatility distributions for all conditions tested.

Mathematical Modelling of Muña Leaf Drying (Minthostachys mollis) for Determination of the Diffusion Coefficient, Enthalpy, and Gibbs Free Energy

In Peru, there are more than four thousand plants with medicinal properties, including muña, which helps digestion and improves health. The way to preserve these plants is drying up. The objective of this research was to investigate the coefficient of diffusion, enthalpy, and Gibbs free energy in the drying kinetics of muña leaves. Different pretreatments were carried out on the samples (without pretreatment, as well as treated by immersion in 1% ascorbic acid and bleaching at 60 °C for 30 s), and they were dehydrated at three temperatures (40, 50, and 60 °C). The drying kinetics were modeled using eight mathematical models to represent the drying curve. The water content was reduced by the drying process. The logarithmic model was selected, as it showed the best fit to represent the drying kinetics of the muña. Activation energy values were similar between treatments (p > 0.05). The increase in temperature decreases the enthalpy and entropy and increases the Gibbs free energy with the effective diffusion coefficient. The drying kinetics allows one to determine the drying time for the storage of the product and the thermodynamic properties for the design of the equipment.

Research advances on internal processes affecting tropical cyclone intensity change from 2018–2022

This contribution summarizes the significant progress in a variety of topic areas related to internal tropical cyclone (TC) intensity change processes over 2018–2022 from the WMO Tenth International Workshop on Tropical Cyclones (IWTC-10). These topic areas include surface and boundary layer processes; TC internal structure and microphysical processes; and, radiation interactions with TCs. Recent studies better frame the uncertainty in the surface drag and enthalpy coefficients at high wind speeds. These parameters greatly impact TC intensity and it is therefore important that more direct measurements of these boundary layer parameters are made. Particularly significant scientific strides have been made in TC boundary layers. These advancements have been achieved through improved coupled models, large-eddy simulations, theoretical advancements, and detailed observations. It is now clear that the research field needs to better represent the eddy viscosity throughout the depth of the boundary layer. Furthermore, detailed study of coherent structures in TC boundary layers will likely be a propitious direction for the research community. Meanwhile, in-depth observational field campaigns and assiduous data analysis have made significant headway into verifying theory and modeling studies of intensification processes related to TC vortex alignment, efficient latent heating distributions, and overall 3D structure. Substantial efforts have also been made to better understand the intricate roles radiative processes play in TC evolution and intensity change. Finally, some promising progress has been made in the development of time-dependent theories of TC intensification and the predictability of internal TC intensity change. Overall, there have been well-earned gains in the understanding of intensity change processes intrinsic to the TC system, but the journey is not complete. This paper highlights some of the most relevant and important research areas that are still shedding new light into internal factors governing TC intensity change.

Analysis of Heat Recovery System Performance Using a Serpentine-Type Heat Exchanger on Water Heater with Fins Number Variation

The water heater is a common facility found in hotels or homes. There are alternative ways to do this besides using water heaters on the market, namely by utilizing the heat generated by the compressor and which will be discharged through the condenser, by adding a heat recovery system to the air conditioning unit. These research tests were carried out on variations of the serpentine-type heat exchanger with variations in the number of fin plates on the performance of the heat recovery system and on the split air conditioner. This research is an experimental study on a serpentine-type heat exchanger. Tests were carried out on a variety of heat exchangers with variations in the number of fin plates combined with a heat recovery system on a split AC. The independent variables in this study were three variations of the placement of the fin plate on the serpentine-type coil and the setting of the output air of the AC evaporator. Enthalpy values, refrigeration effects, compressor work, condenser, and coefficient of performance (COP) are calculated and presented in tables and graphs. The results of the performance of the heat recovery system obtained variations in the setting of the air burst coming out of the evaporator 24ºC has the highest COP value. The use of a heat recovery system can increase COP. With variations in the number of fin plates in a heat recovery system with a serpentine heat exchanger, the use of 5 fin plates has the hottest water temperature compared to the use of 3 fin plates and 1 fin plate.

Experimental evidence and computational results in the investigation of thermodynamic properties and molecular structure of hydrogen-bonded cyclohexylamine and ethyl methyl ketone system

Combining experimental and computational study is a fundamental and attractive method for analyzing intermolecular hydrogen bonds and specific interactions in binary mixtures of different liquids. An experimental and computational investigation of the structural interactions between the molecules of cyclohexylamine and ethyl methyl ketone (EMK) is presented. In the experimental part of the work, the density of mixtures of cyclohexylamine and EMK in the specific mole fractions is reported at 298.15, 303.15, 308.15, and 313.15 K and at an absolute pressure of 86.7 kPa. Densities data have been used to evaluate the excess molar volumes, the thermal expansion coefficients, and the isothermal coefficient of pressure excess molar enthalpy. The Jouyban–Acree model has been used for mathematical correlation of the densities. Using the Redlich-Kister equation, the results of excess molar volumes were fitted. Through computational technics such as density functional theory (DFT), quantum theory of atoms in molecules (QTAIM), and also molecular dynamics (MD) simulations, the analysis of intermolecular hydrogen-bonded associations has been accomplished. MD simulations computed density and radial distribution functions (RDFs) in the liquid phase at 298.15 K and at 1 atm.

Analytical modeling of mass transfer dynamics, velocity, heat transfer and enthalpy in a gas-liquid combustible mixture

The article studied the distribution of the droplet and temperature over the volume of the combustion chamber when liquid fuel was injected into it. The study showed that the portable mass in the combustion chambers and temperatures are directly proportional. Compiled systems of dynamic equations describing mass transfer, motion, heat transfer and enthalpy at the beginning inside the chamber phase and during combustion inside the chamber. Mathematically modeled a gasoline-hydrogen-air mixture with the mass transfer method. With this simulation, pressures are determined at the beginning inside the chamber phase and during combustion inside the chamber, taking into account the newly introduced enthalpy coefficient of gas kHg and steam kHp phase media.

New parameterization of air-sea exchange coefficients and its impact on intensity prediction under major tropical cyclones

Understanding and quantifying air-sea exchanges of enthalpy and momentum fluxes are crucial for the advanced prediction of tropical cyclone (TC) intensity. Here, we present a new parameterization of air-sea fluxes at extreme wind speeds from 40 m s−1 to 75 m s−1, which covers the range of major TCs. Our approach assumes that the TC can reach its maximum potential intensity (MPI) if there are no influences of external forces such as vertical wind shear or other environmental constraints.This method can estimate the ratio of the enthalpy and momentum exchange coefficient (Ck/Cd) under the most intense TCs without direct flux measurements. The estimation showed that Ck/Cd increases with wind speed at extreme winds above 40 m s−1. Two types of surface layer schemes of the Hurricane Weather and Research Forecast (HWRF) were designed based on the wind speed dependency of the Ck/Cd found at high winds: (i) an increase of Ck/Cd based on decreasing Cd (Cd_DC) and (ii) an increase of Ck/Cd based on increasing Ck (Ck_IC). The modified surface layer schemes were compared to the original HWRF scheme (using nearly fixed Cd and Ck at extreme winds; CTRL) through idealized experiments and real-case predictions. The idealized experiments showed that Cd_DC reduced frictional dissipation in the air-sea interface as well as significantly reduced sea surface cooling, making the TC stronger than other schemes. As a result, Cd_DC reduced the mean absolute error and negative bias by 15.0% (21.0%) and 19.1% (32.0%), respectively, for all lead times of Hurricane Irma in 2017 (Typhoon Mangkhut in 2018) compared to CTRL. This result suggests that new parameterization of Ck/Cd with decreasing Cd at high winds can help improve TC intensity prediction, which currently suffers from underestimating the intensity of the strongest TCs.

Comparison of pure component thermodynamic properties from CHEMCAD with direct calculation using the Soave–Redlich–Kwong equation of state

Gas-phase thermodynamic properties are routinely calculated with equations of state in process design software such as CHEMCAD [1], and users should be able to verify the calculations. In a previous study, we reproduced the enthalpy, entropy, compressibility factors, and fugacity coefficients obtained from CHEMCAD using the Lee–Kesler method [2, 3], and later extended this study to include the Peng–Robinson equation of state [4, 5]. An interesting feature of the earlier work is that compressibility and fugacity coefficients in CHEMCAD did not match up precisely with our independent calculations. We therefore extended the study to include the Soave–Redlich–Kwong (SRK) equation of state [6, 7]. Our results show consistency for most of the 48 molecules studied, with percent error in enthalpy decreasing significantly for the SRK method to generally less than 0.002% compared to about 0.3-1% for the Lee–Kesler and Peng–Robinson methods. Unlike the previous two studies, we now see nearly perfect agreement in the compressibility and fugacity coefficient. Furthermore, we show that compressibility and fugacity coefficient remain constant in CHEMCAD even when the equation of state is changed. For enthalpy, while the results are much closer than in the previous studies, we see deviations for methane, air, carbon monoxide, carbon dioxide, nitrogen, and oxygen. Discrepancies in entropy were also observed for bromine, carbon dioxide, chlorine, hydrogen sulfide, and nitrous oxide.

Binding and stability properties of PEG2000 to globular proteins: The case of lysozyme

• Lysozyme-PEG interaction was studied using calorimetry and spectroscopic techniques. • A PEG/lysozyme interaction in the low polymer concentration regime occurs. • The interaction process is weak, and it is entropically driven. • At low concentration, PEG induces an increase of the denaturation temperature. Poly(ethylene glycol) is a linear polymer widely used in many biotechnological and industrial applications. It is thought that PEG is an inert polymer and its effect on protein stability and dynamics is essentially due to the excluded volume effect which depends on its concentration. However, increasing evidence suggests that direct interactions can be established between PEG and proteins. With the aim to shed more light on PEG-protein interactions, this work evaluated the enthalpy pair interaction coefficient and the enthalpy cross-interaction coefficient for the system PEG2000-lysozyme. In addition, using calorimetry and spectroscopy, the binding, the stability and the conformational behaviour of lysozyme were evaluated in the low polymer concentration regime. We found that a weak interaction between lysozyme and PEG occurs with a binding constant of 1600 ± 230 M −1 . The interaction process is mainly entropically driven: the release of water molecules associated to protein surface and polymer chains may account for this phenomenon. In addition, we found that the general lysozyme structure was only marginally affected by PEG interaction. A small but significant increase in the denaturation temperature was observed most likely due to weak interactions with the polymer and to the dehydration of protein surface.

Atomistic modeling of the properties of gold in the region of phase transitions of the first order

The article presents the results of atomistic modeling of the equilibrium thermophysical properties of gold in a wide temperature range (T~ 0.3–3.50 kK), covering the regions of first-order phase transitions of melting and evaporation. The temperature dependences of the density, linear size of the sample, coefficient of linear expansion, enthalpy, and heat capacity are determined. The obtained dependences of the properties of gold are approximated by polynomials of low degrees. There is an acceptable agreement between the obtained characteristics of gold and the experimental data. Numerical and graphic information on the obtained properties and results of comparison with experimental data is presented.

Experimental, theoretical and computational study of binary systems of alkanolamines and alkylamines with cyclohexanol at different temperatures

Density, ρ, speed of sound, u, and the difference in the temperature before and after the mixing process , ΔT, were measured for binary mixtures containing of cyclohexanol (CYC) + diethanolamine (DEA) or triethanolamine (TEA) or butylamine (BUT) or hexylamine (HEX) at (303.15–318.15) K except ΔT at 303.15 K. The excess molar volume, VmE, excess partial molar volume, Vm,iE, excess thermal expansion coefficient, αE, isothermal coefficient of excess molar enthalpy,(∂HmE∂P)T,x, deviation in isentropic compressibility,Δκs, excess molar enthalpy,HmE, and excess partial molar enthalpy, Hm,iE, were also calculated. The calculated data were satisfactorily correlated by Redlich – Kister equation. Some empirical models such as (Prigogine–Flory–Paterson) PFP, Wilson, (Non-Random Two Liquid) NRTL and (universal quasi chemical) UNIQUAC. Computational methods were performed using density function theory (DFT) and molecular dynamics (MD) simulation and were used to discuss and compare intramolecular and intermolecular interactions. An acceptable agreement was found between empirical and theoretical data.

Influence of potential attraction term on Joule-Thomson coefficient, enthalpy and entropy of real gases

In the present work, two different intermolecular potentials are considered for the three real gases such as Ar, Kr and Xe. The effect of attraction term of the potential models on internal energy, enthalpy, entropy and Joule-Thomson (JT) coefficient of aforementioned gases has been investigated. To This end, the second virial coefficient of each potential was analytically derived. The suggested potential models have different attraction terms and the same repulsive terms. Our theoretical results in this work have been compared with experimental data. Our results reveal that the attraction term of the interaction potential has an important and main role to the thermodynamic properties of the selected gases. According to the results, it is found that the calculated thermodynamic function of the aforementioned gases obtained using both potential models are in acceptable agreement with available data. The degree of agreement depends strongly on the type of the used potential model and the range of pressures and temperatures. For instance, the JT coefficient of the Kr gas calculated by potential model (1) at high pressures and temperatures are in good agreement with experimental results. This property for the Ar gas has better agreement when we employ the potential model (2). This work allows us to select the suitable potential model and desired rages of pressure and temperature to give better results in comparison with experimental data.

Potential for New Constraints on Tropical Cyclone Surface-Exchange Coefficients through Simultaneous Ensemble-Based State and Parameter Estimation

AbstractThe tropical cyclone (TC) surface-exchange coefficients of enthalpy (Ck) and momentum (Cd) at high wind speeds have been notoriously challenging to estimate. This difficulty arises from many factors, including the difficulties in collecting observations within the turbulent TC boundary layer, and the complex coupled physical interactions between the TC boundary layer and ocean surface, which are challenging to accurately model. Motivated by recent studies highlighting the limited practical predictability of TC intensity as a result of uncertainty in the physical representation of the air–sea fluxes of momentum and enthalpy at high wind speeds, we investigate the potential to estimate the surface enthalpy and momentum exchange coefficients through ensemble data assimilation. Significant ensemble correlations between tangential wind, radial wind, and simulated infrared brightness temperatures with parameters controlling the enthalpy and momentum exchange coefficients suggest potential to use all-sky satellite and/or airborne radial velocity observations to estimate these unknown parameters. Using a series of observing system simulation experiments (OSSEs), simulated infrared brightness temperature observations, and a known truth, we demonstrate some potential for simultaneous state and parameter estimation with an ensemble-based data assimilation system to converge toward the correct known parameter values. In all OSSEs with either one or multiple unknown parameters, the initial parameter errors are reduced through simultaneous model state and parameter estimation. However, challenges still exist in converging to the precise true parameter values, as state errors during rapid intensification can project onto the parameter estimates.

Numerical investigation of steady state characteristics and stability of supercritical water natural circulation loop of a heater and cooler arrangements

The present paper studies the thermal-hydraulic behaviour of the rectangular supercritical natural circulation loop (SCNCL) using numerical model of one dimensional. Then the results of this model is confirmed with experimental and benchmark results. Variations with several geometric parameters like loop diameter, riser length, and heater length and operating conditions like heater inlet enthalpy, pressure, friction factor, and inlet and exit loss coefficient on steady-state performance are investigated for various orientations like HHHC, HHVC, VHVC and VHHC of the heater and cooler. The chances of existing static instability (Ledinegg excursion) has been investigated, which reveals that it can arise only in a low inlet enthalpy condition, far from the suggested various orientations of heater and cooler.

Assessment of extremely severe cyclonic storms over Bay of Bengal and performance evaluation of ARW model in the prediction of track and intensity

A detailed assessment was carried out for extremely severe cyclonic storms (ESCSs) that developed over the Bay of Bengal during 1990–2020 using the India Meteorological Department (IMD) best-fit track data. During the past 30 years, the maximum intensity of land-falling ESCS has increased 26%, which is an average of about 8% increase per decade. Analysis signifies an increasing trend in the life cycle, duration of ESCS stage, and maximum wind speed of land-falling ESCSs. It is observed that the stage of land-falling ESCSs was very severe, and therefore, reliable forecast of land-falling ESCSs is very important having wide socioeconomic implications. Furthermore, a case study investigated the performance of Advanced Research of Weather Research and Forecasting (ARW) model for a 6-day forecast of ESCS Hudhud that developed over the Bay of Bengal during 2014. Performance evaluation was based on the impact of model domain size, vertical resolution, data assimilation, sea surface temperature (SST), gravity wave option (GWO), and air-sea flux parameterization schemes. Initial condition was improved through WRF 3D variational data assimilation (WRF-3DVAR) system. Thereafter, the simulated track, intensity, and intensification of the storm were validated against available IMD best-fit track datasets. Results from the ARW model indicate that the track and intensity of ESCS Hudhud were influenced by domain size, vertical resolution, data assimilation, SST, GWO, and air-sea flux schemes. Study deciphers that bigger domain, higher vertical resolution, data assimilation, and air-sea flux scheme with enthalpy coefficients provided a better forecast for ESCS Hudhud. The track errors on day 1 to day 4 was 61 km, 73 km, 85 km, and 96 km, respectively, and absolute error in terms of MSW was about 8 ms−1, 7 ms−1, 2 ms−1, and 8 ms−1 respectively at 9-km horizontal resolution.