The present work presents a modification to the free volume theory (FVT) in order to obtain improved representations of the dynamic viscosity of various representative last-generation ionic fluids: ...pure ionic liquids (ILs) and deep eutectic solvents (DESs). Within the formalism of the current FVT approach, the barrier energy that a molecule must overcome to diffuse is proportional to the density of the fluid. We found that this barrier energy was better expressed in terms of (rather than the density) a cohesive energy between molecules of the ionic fluid, namely, the residual internal energy, which accounts for all the intermolecular forces that oppose to the breaking of bonds, including both ionic and hydrogen bonds, which are typically present in ILs and DESs. In addition, one of the characteristic parameters of the FVT approach is the length parameter, which is usually treated as a constant. However, for the present purposes, it was made density dependent. The thermodynamic potentials (residual internal energy and density) present in the resulting modified FVT model were estimated from two simple cubic equations of state of the van der Waals type: Soave−Redlich−Kwong or Peng–Robinson. The two aforementioned modifications introduced to the FVT approach were successfully verified during the representation of experimental dynamic viscosities of 3 families of imidazolium-based ILs (CXmimBF4, CXmimPF6 and CXmimTf2N), one pyridinium-based IL (b3mpyBF4), one pyrrolidinium-based IL (bmpyrTf2N), and one ammonium-based IL (N1114Tf2N) over a temperature range varying from 273.15 to 353.15 K and at pressures from 1 to 3000 bar. We also considered three archetypal choline chloride-based DESs for model validation: reline, ethaline, and glyceline within a temperature range varying from 293.15 to 373.15 K and at pressures from 1 to 1000 bar.
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In the present work, the well-known friction theory (FT) based on friction concepts of classical mechanics and the van der Waals theory of fluids has been modified to accurately represent the dynamic ...viscosity of pure ionic liquids in a rather simplified manner. Unlike previous FT applications to pure ionic liquids, the dilute gas limit for viscosity was excluded from the present model since it is negligible for ionic liquids which exhibit extremely low vapor pressures; the friction term thus prevailed for viscosity calculations. The latter was expressed in terms of new temperature-dependent friction coefficients whereas the repulsive and attractive pressure terms were in turn estimated from two simple cubic equations of state (Soave or Peng–Robinson) rather than using sophisticated multiparameter equations of state such as SAFT- or CPA-based expressions previously used by other authors. The resulting model was successfully validated during the representation of experimental dynamic viscosities of three families of imidazolium-based ionic liquids (CXmimBF4, CXmimPF6, and CXmimTf2N) within a temperature range varying from 0 to 80 °C and at pressures from 1 up to 3000 bar.
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Entropy scaling has emerged as a promising modeling technique for correlating and predicting the dynamic viscosity of diverse molecular liquids, encompassing non-polar, polar, and associating ...substances. Entropy scaling has not yet been assessed for viscosities of ionic liquids and we focus here on the application of this scaling procedure in combination with a cubic equation of state (Soave-Redlich-Kwong or Peng-Robinson) to model the dynamic viscosity of pure ionic liquids over wide temperature and density ranges. The use of a cubic equation of state presently served to estimate residual entropy data of reasonable accuracy needed by the scaling approach considered here. The resulting modeling approach was validated during the representation of experimental dynamic viscosities of 3 families of imidazolium-based ILs (CXmimBF4, CXmimPF6 and CXmimTf2N), one pyridinium-based IL (b3mpyBF4), one pyrrolidinium-based IL (P14Tf2N) and one ammonium-based IL (N1114Tf2N) over a temperature range varying from 0 to 80 °C and at pressures from 1 to 3,000 bar.
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The present modeling work formally introduces, for the very first time, the application of the residual-entropy scaling approach to adequately represent the dynamic viscosity of deep eutectic ...solvents (DESs) as a function of temperature and density. In doing so, diverse unreduced and reduced viscosity forms (total viscosity, Rosenfeld and dilute gas) were verified and compared. The use of a cubic equation of state (CEoS: Soave-Redlich-Kwong or Peng-Robinson) served here to provide sufficiently accurate residual entropy data required by the present scaling procedure. Experimental DES density data were also modeled by applying a modified Mathias volume translation to the density data originally obtained from the two CEoS during the present scalings. The resulting modeling approach was sucessfully validated during the representation of experimental dynamic viscosities and mass densities of three of the most representative choline chloride-based DESs: ChCl:Urea(1:2), ChCl:Ethylene Glycol(1:2) and ChCl:Glycerol(1:2) within a temperature range varying from 10 to 100 °C and at pressures from 1 to 1,000 bar.
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A simple yet accurate thermodynamic model was developed here to represent the nonideal behavior of single electrolytes in water at very high molalities and within a wide temperature range. The ...present model was obtained from an analytical expression of the excess Gibbs free energy (G-excess) which comprises three major contributions; in this context, a chemical term in the model handles the most predominant short-range ion–solvent interactions by means of a chemical equilibrium approach based on a stepwise ion solvation, whereas another term in the model of physical nature also contributes in describing the aforementioned interactions by incorporating a simple Margules equation, and last, a continuum-solvent term given by the explicit mean-spherical-approximation (MSA) expression serves to account for long-range ion–ion forces. The resulting G-excess model was applied to the representation of experimental mean ionic activity coefficients and osmotic coefficients of various representative aqueous electrolyte solutions: AgNO3, CaCl2, HCl, HClO4, HF, HNO3, KF, KOH, LiBr, LiCl, LiNO3, NaCNS, NaOH, NH4NO3, ZnBr2, and ZnCl2 salts in water at 25 °C (and from 0 up to 300 °C only in the case of KOH) and at high concentrations (up to 83.263 M). The results indicated a very good agreement between the experimental data and those calculated using the present G-excess model for the majority of the electrolyte solutions considered here.
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In this work, a three-parameter viscosity model based on the friction theory (FT) and coupled with a cubic equation of state was developed to correlate and predict the dynamic viscosity of deep ...eutectic solvents (DESs). The present viscosity model was derived from an existing six-parameter FT-based viscosity model, which was previously applied to pure ionic liquids. By focusing on the most dominant dragging forces affecting the viscosity of DESs, we were able to safely reduce the number of model parameters without a significant loss of model accuracy. The use of a volume-shifted cubic EoS (Soave–Redlich–Kwong or Peng–Robinson) served also to obtain improved density estimations of the DESs under study. The resulting modeling approach was successfully validated during the correlation of experimental dynamic viscosities and mass densities of three archetypal DESs (choline chloride-based DESs): reline, ethaline, and glyceline within a temperature range varying from 283.15 to 373.15 K and at pressures from 1 to 1000 bar. The average absolute relative deviations yielded by the present thermodynamic model varied from 0.27 to 0.93% for the density modeling and from 2.25 to 4.29% for the viscosity modeling of the three DESs.
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A thermodynamic model based on the combined use of the Eyring's activated state theory and a cubic equation of state was developed here to accurately represent the dynamic viscosity of pure ionic ...liquids (ILs). Within the Eyring's theory, the net viscous flow of a pure IL is assumed to be governed by four main variables: (1) the energy necessary for a molecule to jump from an initial equilibrium position to a new one, (2) the energy necessary to break the molecular bonds to create a hole (vacant sites) of molecular size in the liquid, (3) the availability of the vacant sites, and (4) the frequency or the mean residence time of the jumping molecules. The various activation-state variables were then related to well-known thermodynamic potentials that in turn were estimated from two simple cubic equations of state of the van der Waals type (Soave or Peng-Robinson). The resulting model was successfully validated during the representation of experimental dynamic viscosities of three families of imidazolium-based ILs (CXmimBF4, CXmimPF6 and CXmimTf2N), four pyridinium-based ILs (bmpyBF4, empyEtSO4, Et2NicEtSO4 and hemmpyTf2N) and two ammonium-based ILs (cpmamMeSO4 and 4bamdoc) within a temperature range varying from 0 to 80 °C and at pressures from 1 up to 3000 bar thus covering a wide viscosity range of 10–19,610 mPa-s.
•An Eyring's theory model was developed to estimate the viscosity of ionic liquids ILs.•Main model activated-state variables were calculated from two simple cubic EoS.•The resulting model was successfully validated for 16 ILs of various types.
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In this study, a previously developed model Macías-Salinas, R. ; Viscosity Modelling of Reservoir Fluids over Wide Temperature and Pressure Ranges. Chem. Eng. Trans. 2013, 32, 1573. based on the ...significant structure theory (SST) in conjunction with the Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) cubic equations of state (CEoS) was modified for the accurate correlation of the viscosity of 25 pure alcohols from methanol to n-dodecanol, branched alcohols, diols, and triols at temperatures from 0 to 272 °C and pressures from 0.98 to 4860 bar, obtaining two final model versions (SST-SRK and SST-PR) valid for both gas and liquid phases in the case of methanol, ethanol, 2-propanol, and 2-methyl-1-propanol and only in liquid phase for the rest of alcohols considered here. In regard to n-decanol, n-undecanol, n-dodecanol, 1,3-propanediol, and 1,4-butanediol, they were studied at different temperatures but only at a pressure of 1 bar. The resulting model versions were correlated with 2418 dynamic viscosity experimental data, obtaining overall values of average absolute deviation (AAD), statistical bias, and absolute maximum deviation (AMD) of 1.4808, 0.0503, and 7.9217%, respectively, with the SST-SRK approach and 1.4799, 0.0476, and 7.4515%, respectively, with the SST-PR approach. The two modeling approaches were compared with the friction theory Zéberg-Mikkelsen, C. K. ; Viscosity Modeling of Associating Fluids Based on the Friction Theory: Pure Alcohols. Fluid Phase Equilib. 2002, 194–197, 1191. (FT) and free volume theory Allal, A. ; A New Free Volume Model for Dynamic Viscosity and Density of Dense Fluids Versus Pressure and Temperature. Phys. Chem. Liq. 2001, 39, 1. (FVT), using the same experimental viscosity database of this work under the same conditions of temperature and pressure, obtaining more accurate results with the SST approach for most of the modeled alcohols.
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Background:
Brief episodes of atrial fibrillation (AF) may evolve into longer AF episodes increasing the chances of thrombus formation, stroke, and death. Classical methods for AF detection ...investigate rhythm irregularity or P-wave absence in the ECG, while deep learning approaches profit from the availability of annotated ECG databases to learn discriminatory features linked to different diagnosis. However, some deep learning approaches do not provide analysis of the features used for classification. This paper introduces a convolutional neural network (CNN) approach for automatic detection of brief AF episodes based on electrocardiomatrix-images (ECM-images) aiming to link deep learning to features with clinical meaning.
Materials and Methods:
The CNN is trained using two databases: the Long-Term Atrial Fibrillation and the MIT-BIH Normal Sinus Rhythm, and tested on three databases: the MIT-BIH Atrial Fibrillation, the MIT-BIH Arrhythmia, and the Monzino-AF. Detection of AF is done using a sliding window of 10 beats plus 3 s. Performance is quantified using both standard classification metrics and the EC57 standard for arrhythmia detection. Layer-wise relevance propagation analysis was applied to link the decisions made by the CNN to clinical characteristics in the ECG.
Results:
For all three testing databases, episode sensitivity was greater than 80.22, 89.66, and 97.45% for AF episodes shorter than 15, 30 s, and for all episodes, respectively.
Conclusions:
Rhythm and morphological characteristics of the electrocardiogram can be learned by a CNN from ECM-images for the detection of brief episodes of AF.
A density-independent thermodynamic model was presently developed to adequately represent the dynamic viscosity of pure ionic liquids (ILs). The present model adopts the simple form of the van der ...Waals equation of state under the basis of a previously established phenomenological similarity between the P-V-T and T-η-P surfaces for non-ionic fluids; however, we found that, in the particular case of pure ionic liquids, the surface P−f−T (where f is the fluidity, the reciprocal of viscosity) rather than the T-η-P surface conforms much better to the P-V-T surface. The resulting model was successfully validated during the representation of experimental dynamic viscosities of three families of imidazolium-based ILs (CXmimBF4, CXmimPF6 and CXmimTf2N), four pyridinium-based ILs (bmpyBF4, empyEtSO4, Et2NicEtSO4 and hemmpyTf2N) and two ammonium-based ILs (cpmamMeSO4 and 4bamdoc) within a temperature range varying from 0 to 80 °C and at pressures from 1 up to 3,000 bar thus covering a wide viscosity range of 10–19,610 mPa-s.
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