Semi-empirical Thermodynamic Model Research Articles

At the Limit of Interfacial Sharpness in Nanowire Axial Heterostructures.

As semiconductor devices approach dimensions at the atomic scale, controlling the compositional grading across heterointerfaces becomes paramount. Particularly in nanowire axial heterostructures, which are promising for a broad spectrum of nanotechnology applications, the achievement of sharp heterointerfaces has been challenging owing to peculiarities of the commonly used vapor-liquid-solid growth mode. Here, the grading of Al across GaAs/AlxGa1-xAs/GaAs heterostructures in self-catalyzed nanowires is studied, aiming at finding the limits of the interfacial sharpness for this technologically versatile material system. A pulsed growth mode ensures precise control of the growth mechanisms even at low temperatures, while a semiempirical thermodynamic model is derived to fit the experimental Al-content profiles and quantitatively describe the dependences of the interfacial sharpness on the growth temperature, the nanowire radius, and the Al content. Finally, symmetrical Al profiles with interfacial widths of 2-3 atomic planes, at the limit of the measurement accuracy, are obtained, outperforming even equivalent thin-film heterostructures. The proposed method enables the development of advanced heterostructure schemes for a more effective utilization of the nanowire platform; moreover, it is considered expandable to other material systems and nanostructure types.

Detection of Rydberg Lines from the Atmosphere of Betelgeuse

Emission lines from Rydberg transitions are detected for the first time from a region close to the surface of Betelgeuse. The H30α line is observed at 231.905 GHz, with an FWHM ∼42 km s−1 and extended wings. A second line at 232.025 GHz (FWHM ∼21 km s−1 ), is modeled as a combination of Rydberg transitions of abundant low first ionization potential metals. Both H30α and the Rydberg combined line X30α are fitted by Voigt profiles, and collisional broadening with electrons may be partly responsible for the Lorentzian contribution, indicating electron densities of a few 108 cm−3. X30α is located in a relatively smooth ring at a projected radius of 0.9× the optical photospheric radius R ⋆, whereas H30α is more clumpy, reaching a peak at ∼1.4 R ⋆. We use a semiempirical thermodynamic atmospheric model of Betelgeuse to compute the 232 GHz (1.29 mm) continuum and line profiles making simple assumptions. Photoionized abundant metals dominate the electron density, and the predicted surface of continuum optical depth unity at 232 GHz occurs at ∼1.3 R ⋆, in good agreement with observations. Assuming a Saha–Boltzmann distribution for the level populations of Mg, Si, and Fe, the model predicts that the X30α emission arises in a region of radially increasing temperature and turbulence. Inclusion of ionized C and non-LTE effects could modify the integrated fluxes and location of emission. These simulations confirm the identity of the Rydberg transition lines observed toward Betelgeuse and reveal that such diagnostics can improve future atmospheric models.

Numerical modeling of flashing in TFC expanders for the efficient exploitation of low-grade heat

This paper presents a novel semi-empirical thermodynamic model for the simulation of two-phase expansion in twin-screw expanders. The model utilizes a limited number of unknown parameters, the values of which are calculated through a calibration-optimization process that exploits numerical experiments available in the literature. Two-phase expansion simulations are performed for a wide variety of operating conditions, revealing that the vapor quality at the suction port of the expander is the main factor affecting its efficiency. Increased vapor qualities at the onset of expansion lead to an increase in the expander’s efficiency because a better matching between the WF’s volume ratio and the expander’s built-in volume ratio can be achieved. The thermodynamic model is applied to assess the performance of a TFC engine operating under varying heat duties and temperatures of the heat source, indicating that a detailed analysis is necessary to conclude whether the TFC or the ORC is the optimal solution for a given application.

First principles prediction of NRTL binary interaction parameters for furfural derivatives

AbstractBiobased molecules constitute sustainable alternatives for fossil‐based chemicals. However, to allow further valorization, the complex product mixtures resulting from biomass processing typically require downstream separation. Although many (semi)empirical thermodynamic models, like NRTL, are available for separation process design, their application for biobased molecules is hampered due to the lack of the necessary data to determine the binary interaction parameters used in these models. Therefore, in this work a case study comprising a set of furfural derivates has been used to showcase a methodology to efficiently determine these parameters. Based on first principles, COSMO‐RS is used to generate a dataset of thermodynamic activities, which is subsequently used to regress the NRTL model against. Comparison of NRTL‐HOC simulated vapor–liquid equilibria (VLE's) with experimental VLE's showed excellent agreement, confirming that COSMO‐RS can be used to extend the use of (semi)‐empirical models toward applications involving biobased molecules of which limited experimental data is available.

Synthesis of Ni(Cr)–hBN Nanocomposite by Mechanical Alloying and Its Thermodynamical Evaluation

In the present study, the feasibility of fabricating an Ni(Cr)/hBN self-lubricating nanocomposite by mechanical alloying technique was studied. To achieve this goal, a Ni–20 wt % Cr powders mixture was first milled up to 40 h to produce the nanostructured Ni(Cr) solid solution. hBN particles were subsequently added to Ni(Cr) and further mixed for 3 h. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) were performed to study phase transformations and microstructural evolutions during the milling process. The results showed that the dissolution of Cr in Ni started after 5 h and completed after 30 h of mechanical alloying. TEM studies also showed that the 40 h milled Ni(Cr) solid solution had the average grain size of 50 nm. Miedema’s semi-empirical thermodynamic model was used to predict the most stable phases in the Ni–Cr binary system. The results showed that the Gibbs free energy change of solid solution formation (–8.44 kJ/mol) was much lower than that of the amorphous phase (–1.3 kJ/mol) in the chemical composition of Ni–20 wt % Cr, thereby confirming the experimental results. The formation of a fine lamellar structure during the milling process was found to be the main reason for the solid solution formation. The nanostructured Ni(Cr) solid solution showed suitable thermal stability at 800°C. It was also observed that hBN particles were homogenously distributed in the as-fabricated Ni(Cr) after 3 h of mixing. The results of the present study also revealed that the mechanical alloying process could be regarded as a high-potential technique for the fabrication of metal-based self-lubricating composites.

Modeling and experiments of equilibrium solubility of carbon dioxide in aqueous N-(2-hydroxyethyl) pyrrolidine solution

Abstract In this work, the equilibrium CO2 solubilities of the aqueous N-(2-hydroxyethyl) pyrrolidine (N-(2-HE) PRLD) at different concentrations (1.0 mol/L–5.0 mol/L) were measured at different temperatures (298 K–333 K) and pressures (8 kPa–101 kPa), using a vapor–liquid equilibrium apparatus. Four semi-empirical thermodynamic models (Cf model, Kent–Eisenberg model, Hu–Chakma model and Li–Shen model) were used to correlate and predict the CO2 solubility data of the N-(2-HE) PRLD-CO2–H2O system. The results showed that the Hu–Chakma model, which is one of the models that incorporates the effect of amine concentration and CO2 loading, and accounted for nonideality caused by higher temperature, species concentrations and CO2 loadings, was best able to predict results that are in agreement with the experimental vapor–liquid equilibrium measurements in this work.

Semi-empirical model of a multi-diaphragm pump in an Organic Rankine Cycle (ORC) experimental unit

Organic Rankine Cycle (ORC) power systems represent an effective option to exploit low grade heat fluxes. Several papers have been published on ORCs systems, most of them dealing with the maximization of overall system performance and selection of the working fluid. Recently, the attention has moved also to system components with specific focus on the expander. Less attention was paid to the pump which, however, may contribute significantly to the system consumption, especially in small size systems.This paper presents a semi-empirical thermodynamic model of a displacement pump integrated into an ORC experimental unit. The pump behavior at design and off-design conditions is modeled as a set of thermodynamic processes the main geometrical parameters of which are calibrated using experimental data. Calibration is performed by setting an optimization procedure which minimizes the error between operation parameters calculated by the model and measured in the test rig. Maximum errors were in the range 0.06%–7%. Differently from the few papers on similar models in the literature, this model takes into account the trapped mass flow rate, and is used to calculate the pump characteristic curves and identify incipient cavitation. A good agreement with experimental data was found in both cases.

Iron K-edge X-ray absorption near-edge structure spectroscopy of aerodynamically levitated silicate melts and glasses

The local structure about Fe(II) and Fe(III) in silicate melts was investigated in-situ using iron K-edge X-ray absorption near-edge structure (XANES) spectroscopy. An aerodynamic levitation and laser heating system was used to allow access to high temperatures without contamination, and was combined with a chamber and gas mixing system to allow the iron oxidation state, Fe3+/ΣFe, to be varied by systematic control of the atmospheric oxygen fugacity. Eleven alkali-free, mostly iron-rich and depolymerized base compositions were chosen for the experiments, including pure oxide FeO, olivines (Fe,Mg)2SiO4, pyroxenes (Fe,Mg)SiO3, calcic FeO-CaSiO3, and a calcium aluminosilicate composition, where total iron content is denoted by FeO for convenience. Melt temperatures varied between 1410 and 2160K and oxygen fugacities between FMQ – 2.3(3) to FMQ+9.1(3) log units (uncertainties in parentheses) relative to the fayalite-magnetite-β-quartz (FMQ) buffer. Remarkably, XANES pre-edge peak areas imply mean Fe-O coordination numbers (nFeO) close to 5 in all cases, with only a slight tendency toward higher values in the most iron rich melts, suggesting an intermediate role for both Fe(II) and Fe(III) in terms of network formation. End member coordination numbers for Fe(II)-O and Fe(III)-O are estimated to be similar, having means (and standard deviations) of 5.0(2) and 4.9(1), respectively. As such, the preference for ferric iron to occupy lower coordination sites than ferrous is weak, in contrast to published behavior in some alkali-rich systems, which may explain the larger published viscosity variations with Fe3+/ΣFe in alkali-, compared to alkaline earth-iron silicates. Temperature effects on nFeO are inferred to be small based on the melt data, as well as by comparison to glasses formed on quenching. Positive shifts of the pre-edge peak centroids observed in many cases on quenching are attributed to rapid oxidation enabled by the stirring of the melt droplets by the levitation gas jet. Fe3+/ΣFe values were estimated from XANES pre-edge peaks using published calibrations and compared to semi-empirical thermodynamic model calculations and Mössbauer measurements on quench products. Whilst showing positive correlation, the comparisons highlight the limitations involved in applying XANES calibrations and models for Fe3+/ΣFe derived from measurements on glasses, to high temperature basic melts. Fe3+/ΣFe varies from approximately zero up to about 65% in the high temperature melts and 75% in the glasses.

Solubility measurement, model evaluation and thermodynamic analysis of rivaroxaban polymorphs in organic solvents

This work measured the solubility of forms I and II of anticoagulant drug rivaroxaban in a series of organic solvents in which the solubility of form II was firstly reported as supplementary to the work of Zhang et al. [22]. A dynamic dissolution method was used to determine the solubility of both forms in acetonitrile, methyl acetate, acetone, 2-butanone, 3-pentanone and 2-hexanone from (273.15 to 318.15)K and in 1,4-dioxane from (288.15 to 333.15)K. The results showed that, the solubility of both forms generally increased with the temperature and decreased with an increase in the carbon number of ketones at the same temperature. The two forms were monotropically related and form II was the metastable form giving a higher solubility than form I. Meanwhile, such semiempirical thermodynamic models based on local composition concept as Wilson, nonrandom two-liquid (NRTL) and universal quasi chemical (UNIQUAC) equations with the correlation between model parameters and temperature were employed to model the studied solid-liquid equilibrium. It was found that UNIQUAC was the most appropriate model among the selected thermodynamic equations for the correlation of the solubility of rivaroxaban polymorphs in organic solvents. Finally, the apparent standard enthalpy change of dissolution was acquired from the experimental solubility data and the positive values of the apparent standard enthalpy change revealed that the dissolution of both forms of rivaroxaban in the selected solvents was an endothermic process.

Setting the process parameters for the coating process in order to assure tablet appearance based on multivariate analysis of prior data

Designing efficient, robust process parameters in drug product manufacturing is important to assure a drug⿿s critical quality attributes. In this research, an efficient, novel procedure for a coating process parameter setting was developed, which establishes a prediction model for setting suitable input process parameters by utilizing prior manufacturing knowledge for partial least squares regression (PLSR). In the proposed procedure, target values or ranges of the output parameters are first determined, including tablet moisture content, spray mist condition, and mechanical stress on tablets. Following the preparation of predictive models relating input process parameters to corresponding output parameters, optimal input process parameters are determined using these models so that the output parameters hold within the target ranges. In predicting the exhaust air temperature output parameter, which reflects the tablets⿿ moisture content, PLSR was employed based on prior measured data (such as batch records of other products rather than design of experiments), leading to minimal new experiments. The PLSR model was revealed to be more accurate at predicting the exhaust air temperature than a conventional semi-empirical thermodynamic model. A commercial scale verification demonstrated that the proposed process parameter setting procedure enabled assurance of the quality of tablet appearance without any trial-and-error experiments.

Measurement and correlation of the solubility of rivaroxaban (form I) in binary mixtures of ethyl acetate with tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide from T = (278.15 to 318.15) K

In this work, the solubility of rivaroxaban (form I) in binary solvent mixtures of ethyl acetate (EA) with N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) and tetrahydrofuran (THF) was firstly experimentally measured over the temperature range from (278.15 to 318.15)K. Then the measured solubility data were correlated with such semiempirical thermodynamic models as Jouyban–Acree (JA) equation and Buchowski (λh) equation. The crystal form of the residual solids in equilibrium with liquids was identified by powder X-ray diffraction (PXRD). The melting temperature and fusion enthalpy were determined using differential scanning calorimetry (DSC). The results show that, the solubility of rivaroxaban generally increases with the temperature and decreases with the increase in the content of EA in the binary solvent mixtures. Furthermore, when λh equation is used to correlate the solubility of rivaroxaban with the temperature in each solvent mixture, the average relative deviation (ARD) between the experimental and calculated values is about 0.0671, while it is about 0.0905 when JA equation is employed to correlate the solubility with the temperature and the composition of solvent mixtures simultaneously.

Discrete fragment model for apparent formation constants of actinide ions with humic substances

Abstract A semi-empirical thermodynamic model was applied to estimate the apparent formation constants of actinide ions, i.e., Th(IV), Pu(IV) and Np(V), with humic substances (HSs), including humic and fulvic acids, over a wide range of solution conditions, i.e., pH, ionic strength, and HS and metal concentrations. The hypothetical HSs consist of humic and fulvic acids with nine types of simple organic ligands, which include aromatic and aliphatic carboxyl groups and phenol groups, as binding sites. The abundance of each binding site in the hypothetical HSs was determined via a fitting analysis using an acid-dissociation dataset for several HSs. To determine the apparent formation constant of a given metal ion with HSs, 54 specific binding sites were considered, including nine monodentate sites (1:1 metal/ligand complexes) and 45 bidentate sites (1:2 metal/ligand complexes). The formation constant of each monodentate binding was determined from the experimental data, while those of the bidentate bindings were determined by considering two monodentate bindings and the chelating effect, for which one of the adjustable parameters was introduced in the model. Introduction of the other parameter, which is related to the fraction of monodentate to bidentate sites (i.e., the heterogeneity), afforded the parameter values with good correlation with the apparent formation constant data. The present model with adjusted parameter values well reproduced the experimental apparent complex formation constants for actinide ion interaction with HSs in a wide range of solution conditions except for those obtained at trace concentrations.

Energy consumption analysis for CO2 separation using imidazolium-based ionic liquids

CO2 solubility in ionic liquids has been measured extensively in order to develop ionic liquid-based technology for CO2 separation. However, the energy consumption analysis has not been investigated well for such technology. In order to carry out the energy consumption analysis for CO2 separation using ionic liquids based on available experimental data, in this work, the experimental data of the CO2 solubility in imidazolium-based ionic liquids at pressures below 10MPa was surveyed and evaluated by a semi-empirical thermodynamic model firstly. Based on the reliable experimental solubility data, the enthalpy of CO2 absorption was further calculated by the thermodynamic model. The results show that the CO2 absorption enthalpy in the studied ionic liquids is dominated by the enthalpy of CO2 dissolution and the contribution of excess enthalpy increases with increasing CO2 solubility in ionic liquids. The magnitude of the CO2 absorption enthalpy decreases with increasing chain length in cation and strongly depends on the anion of ionic liquids. Furthermore, the energy consumption for a CO2 separation process by pressure swing and/or temperature swing was investigated. For the pressure swing process, the Henry’s constant of CO2 in ionic liquids is an important factor for energy consumption analysis; If CO2 is absorbed at 298K and 1MPa and ionic liquid is regenerated by decreasing the pressure to 0.1MPa at the same temperature, among the studied ionic liquids, [emim][EtSO4] is the solvent with the lowest energy consumption of 9.840kJ/mol CO2. For the temperature swing process, the heat capacity of ionic liquids plays a more important role; If CO2 is absorbed at 298K and desorbed at 323K and 0.1MPa, [emim][PF6] is the solvent with the lowest energy demand of 888.9kJ/mol CO2. If the solvent is regenerated by releasing pressure and increasing temperature, both the Henry’s constant of CO2 in ionic liquids and the heat capacity of ionic liquids are important for analyzing the energy consumption; If CO2 is absorbed at 298K and 1MPa and ionic liquid is regenerated at 323K and 0.1MPa, [bmim][Tf2N] is the solvent with the lowest energy consumption of 57.71kJ/mol CO2.

Modeling and measurement of CO2 solubility in salty aqueous solutions and application in the Erdos Basin

Geological carbon storage (GCS) is recognized as an effective method for mitigating the greenhouse effect. Deep saline aquifers hold the highest potential capacity for CO2 storage. CO2 solubility in salty aqueous solutions under geological sequestration conditions plays a key role in GCS. However, most CO2 solubility studies focus mainly on single-salt solutions (NaCl and CaCl2), and extrapolation of these studies to aqueous solutions with mixed ions is unavailable. To fill the research gap, based on the collection of CO2 solubility data, a semi-empirical thermodynamic model is proposed in this paper to calculate CO2 solubility in aqueous solutions containing K+, Na+, Ca2+ and Mg2+ in the temperature and pressure ranges from 313K to 378K and from 50bar to 220bar. To describe the CO2–liquid phase equilibrium, the Peng–Robinson equation of state (PR EoS) and the Setschenov equation are applied. The former has been modified to improve its performance in the studied T–P range, and the latter shows excellent accuracy with only three optimized parameters. Before modeling was done, experimental studies were conducted. Brine sampling from five reservoirs potentially chosen for CO2 sequestration in the Erdos Basin was carried out using a monitoring well in the support of the Shenhua Group carbon capture and storage (CCS) site project. The chemical composition of the samples was determined, and experiments measuring CO2 solubility were carried out in synthetic brine with 64 valid data points reported. An analytical method with a simplified sampling technique was chosen. In the range studied, the average absolute deviation of CO2 solubility between the model and experimental results was 2.01%, and the maximum absolute deviation in this study was less than 4.79%. The proposed model and experimental data therefore possess broad adaptability to GCS with satisfactory accuracy.

Prediction and experimental determination of the binary and ternary phase diagrams of (±)medetomidine hydrochloride

The binary phase diagram of medetomidine hydrochloride was determined based on thermogravimetric differential thermal (TGA/DTA) measurements. The binary phase diagram presented a eutectic point in the 19:81 [(R)/(S)] composition and the ternary phase diagram in the presence of 2-propanol showed a eutectic point in the 75:25 [(S)/(R)] composition, both characterizing the product as a racemic compound forming system. The solubility of enantiomeric mixtures in 2-propanol was measured at 10, 20 and 30°C. The ideal solubility curves of the mixtures were calculated and the activity coefficients derived. A semi-empirical thermodynamic model UNIversal QUAsi-Chemical (UNIQUAC) was used to predict the solubility of various compositions of enantiomers at different temperatures. There was good agreement between the experimental solubility data of medetomidine hydrochloride and the results obtained from the UNIQUAC equation.

An activity model for phase equilibria in the H2O–CO2–NaCl system

We present a semi-empirical thermodynamic model with uncertainties that encompasses the full range of compositions in H2O–CO2–NaCl mixtures in the range of 10–380°C and 1–3500bars. For binary H2O–CO2 mixtures, the activity–composition model is built from solubility experiments. The parameters describing interactions between H2O and CO2 are independent of the absolute thermodynamic properties of the end-members and vary strongly non-linearly with pressure and temperature. The activity of water remains higher than 0.88 in CO2-saturated solutions across the entire pressure–temperature range. In the H2O–NaCl system, it is shown that the speciation of aqueous components can be accounted for by a thermodynamic formalism where activities are described by interaction parameters varying with intensive properties such as pressure and temperature but not with concentration or ionic strength, ensuring consistency with the Gibbs–Duhem relation. The thermodynamic model reproduces solubility experiments of halite up to 650°C and 10kbar, and accounts for ion pairing of aqueous sodium and chloride ions with the use of associated and dissociated aqueous sodium chloride end-members whose relative proportions vary with salinity. In the H2O–CO2–NaCl system, an activity–composition model reproduces the salting-out effect with interactions parameters between aqueous CO2 and the aqueous species created by halite dissolution. The proposed thermodynamic properties are compatible with the THERMOCALC database (Holland and Powell, 2011) and the equations used to retrieve the activity model in H2O–CO2 can be readily applied to other systems, including minerals.

Measurement of polarization curve and development of a unique semi empirical model for description of PEMFC and DMFC performances

In this study, a single polymer electrolyte membrane fuel cell (PEMFC) in H2/O2 form with an effective dimension of 5?5 cm as well as a single direct methanol fuel cell (DMFC) with a dimension of 10?10 cm were fabricated. In an existing test station, the voltage-current density performances of the fabricated PEMFC and DMFC were examined under various operating conditions. As was expected DMFC showed a lower electrical performance which can be attributed to the slower methanol oxidation rate in comparison to the hydrogen oxidation. The results obtained from the cell operation indicated that the temperature has a great effect on the cell performance. At 60?C, the best power output was obtained for PEMFC. There was a drop in the cell voltage beyond 60?C which can be attributed to the reduction of water content inside the membrane. For DMFC, maximum power output was resulted at 64oC. Increasing oxygen stoichiometry and total cell pressure had a marginal effect on the cell performance. The results also revealed that the cell performance improved by increasing pressure differences between anode and cathode. A unified semi-empirical thermodynamic based model was developed to describe the cell voltage as a function of current density for both kinds of fuel cells. The model equation parameters were obtained through a nonlinear fit to the experimental data. There was a good agreement between the experimental data and the model predicted cell performance for both types of fuel cells.

Partitioning behavior of an acid-cleavable, 1,3-dioxolane alkyl ethoxylate, surfactant in single and binary surfactant mixtures for 2- and 3-phase microemulsion systems according to ethoxylate head group size

Partition coefficients for a pH-degradable 1,3-dioxolane alkyl ethoxylate surfactant, 4-CH(3)O (CH(2)CH(2)O)(5.6)-CH(2), 2,2-(CH(2))(12)CH(3), 2-(CH(2)) CH(3), 1,3-dioxolane or "cyclic ketal" surfactant, CK-2,13-E(5.6,ave), between isooctane- and water-rich phases of 2- and 3-phase microemulsion systems (K(n)) were determined as functions of the ethoxylate size, n, and temperature for the neat surfactant and its binary surfactant mixtures, to understand the partitioning of alkyl ethoxylates possessing a broad distribution of ethoxylate size and to determine conditions required for formation of 3-phase microemulsion systems at an optimal temperature where phase separation occurs rapidly, important for protein purification via proteins' selective partitioning to the middle phase, driven by affinity to the second surfactant of the binary mixture. A semi-empirical thermodynamic mathematical model described the partitioning data well, provided optimal temperature values consistent with phase diagrams and theory, and demonstrated that the tail region of CK-2,13-E(5.6,ave) is more polar than the hydrophobes of fatty alcohol ethoxylates. The addition of Aerosol-OT (AOT) removed the temperature sensitivity of CK-2,13-E(5.6,ave)s partitioning, producing 3-phase microemulsion systems between 20 °C and 40 °C. Analysis of the bottom phases of the 2- and 3-phase microemulsion systems formed by CK-2,13-E(5.6,ave) via small-angle neutron scattering demonstrated the presence of spherical, monodisperse oil-in-water microemulsions.

First-Principles Prediction of Vapor−Liquid−Liquid Equilibrium from the PR+COSMOSAC Equation of State

We present the prediction of vapor−liquid−liquid equilibrium (VLLE) from a newly developed PR+COSMOSAC equation of state (EOS). Unlike semiempirical thermodynamic models whose parameters vary with the data used in regression and reparameterization are usually necessary for describing VLLE, this theoretically sound model with its parameters determined from first-principles calculations is not biased against descriptions of either VLE or LLE and can thus be used to predict the occurrence conditions of VLLE. In this model, the molecular interaction and size parameters in the Peng−Robinson EOS are determined directly from a solvation model based on first principle solvation calculations. This new EOS contains neither species dependent parameter nor binary interaction parameters and can be used to predict vapor pressure, liquid density, critical properties of pure substances, and VLE and LLE of mixtures. Without adjustment to the model parameters, this method can predict VLLE with accuracy similar to that of the method modified UNIFAC model. This model is particular useful for the design of new processes involving chemicals whose interaction parameters are not available due to the lack of experimental data.

Size dependency of melting point of crystalline nano particles and nano wires: A thermodynamic modeling

A semi-empirical thermodynamic model for size dependency of melting point of nano particles and wires has been proposed by introducing a size dependency of surface energy. The model predicts the size dependency of melting point of nano particles and wires for a wide range of elements: fcc (Au, Pt, Ni), hcp (Mg), and bcc (W), all in good agreement with experimental data and/or molecular dynamics simulations. Since the model is free from adjustable parameters, it is applicable to a wider range of materials.