Showing papers in "International Journal of Thermophysics in 2022"

A Review of Electrolyte Equations of State with Emphasis on Those Based on Cubic and Cubic-Plus-Association (CPA) Models

Abstract: Electrolyte thermodynamics is a complex and broad subject of immense importance in very diverse applications. The models proposed for electrolyte solutions have some similarities to those for non-electrolytes but also significant differences. Not just due to additional contributions but also because of the way the models are developed for electrolytes vs. non-electrolytes. Moreover, there are still fundamental issues unresolved in electrolyte thermodynamics. It is still today the activity coefficient models, often extensions of local-composition models that are used in engineering practice for electrolytes e.g., the Pitzer, electrolyte NRTL and extended UNIQUAC. In this review, however, we investigate the area of equations of state (EoS) for electrolytes, a very rich field which essentially started with the Fürst and Renon model in 1993. Since then numerous electrolyte EoS (e-EoS) have been proposed; the literature is both rich and confusing. We have decided in this work to review mostly electrolyte versions of cubic and CPA (Cubic-Plus-Association) EoS, although some of the observations made may be applicable to e-EoS of the SAFT type as well, and some of them are also briefly discussed. Reviewing e-EoS is not an easy task due to especially the diversity of modeling and parameter estimation approaches which are followed as well as the way the models have been validated. Almost none of the e-EoS proposed in literature can be compared “on equal terms” with another e-EoS. Thus, a critical comparative analysis is proposed here, including some recent developments of the e-CPA approach. When possible, different modeling—parameter estimation—validation approaches are compared. It is hoped that this review can provide an insight on the current state-of-the-art of some e-EoS proposed in literature and point out areas where further research is needed.

A Review of Electrolyte Equations of State with Emphasis on Those Based on Cubic and Cubic-Plus-Association (CPA) Models

Abstract: Electrolyte thermodynamics is a complex and broad subject of immense importance in very diverse applications. The models proposed for electrolyte solutions have some similarities to those for non-electrolytes but also significant differences. Not just due to additional contributions but also because of the way the models are developed for electrolytes vs. non-electrolytes. Moreover, there are still fundamental issues unresolved in electrolyte thermodynamics. It is still today the activity coefficient models, often extensions of local-composition models that are used in engineering practice for electrolytes e.g., the Pitzer, electrolyte NRTL and extended UNIQUAC. In this review, however, we investigate the area of equations of state (EoS) for electrolytes, a very rich field which essentially started with the Fürst and Renon model in 1993. Since then numerous electrolyte EoS (e-EoS) have been proposed; the literature is both rich and confusing. We have decided in this work to review mostly electrolyte versions of cubic and CPA (Cubic-Plus-Association) EoS, although some of the observations made may be applicable to e-EoS of the SAFT type as well, and some of them are also briefly discussed. Reviewing e-EoS is not an easy task due to especially the diversity of modeling and parameter estimation approaches which are followed as well as the way the models have been validated. Almost none of the e-EoS proposed in literature can be compared “on equal terms” with another e-EoS. Thus, a critical comparative analysis is proposed here, including some recent developments of the e-CPA approach. When possible, different modeling—parameter estimation—validation approaches are compared. It is hoped that this review can provide an insight on the current state-of-the-art of some e-EoS proposed in literature and point out areas where further research is needed.

Experimental Analysis and Neural Network Model of MWCNTs Enhanced Phase Change Materials

Abstract: In this article, the thermophysical properties of binary eutectic PCM salt (LiNO3 + NaCl) are investigated experimentally using the dispersion of multi-walled carbon nanotubes (MWCNTs) with varying weight fractions (i.e., 0.25 %, 0.5 %, and 1 %). According to the XRD and FTIR results, MWCNTs physically amalgamated with base eutectic salt without affecting their chemical structure. The Kissinger model is used to assess the phase change kinetics of the prepared nano-PCM composites. With the addition of MWCNTs, the activation energy of the chosen PCM is significantly increased. The thermophysical properties of the nano-PCM samples, such as phase transition temperature and latent heat value, are measured using differential scanning calorimetry (DSC) and thermal conductivity using a laser flash apparatus. The results show that dispersing 1 % MWCNTs in PCM salt improved the thermal conductivity enhancement ratio by 38.59 %, while decreasing the latent heat storage capacity by 14.98 %. Furthermore, by training the experimental DSC values of nano-PCM samples at various heating rates, an artificial neural network is developed to predict the thermophysical properties of nanocomposites. With an R2 value of 0.998, the developed neural network accurately predicted the experimental DSC values.

Experimental and Numerical Investigations on Exergy and Second Law Efficiency of Shell and Helical Coil Heat Exchanger Using Carboxymethyl Cellulose Based Non-Newtonian Nanofluids

Abstract: The main goal of this paper is to study the second law characteristics of carboxymethyl cellulose (CMC)-based non-Newtonian nanofluids with different nanoparticles of aluminum oxide (Al2O3), copper oxide (CuO), and titanium oxide (TiO2) through a helical coil heat exchanger. The present investigation has been carried out for the volume flow rate of non-Newtonian nanofluids ranges from 1 (L⋅min) to 10 (L⋅min). In this study, the effect of nanoparticles, nanoparticle volume fraction, and inlet temperature of hot fluid exergy loss, second law efficiency, and heat transfer effectiveness are investigated. It is observed that on increasing the volume flow rate of nanofluids the exergy losses increase for all the nanofluids. Moreover, with the increase in particle volume fraction from 0.01% to 0.04%, the exergy loss reduced by 33%, 30%, and 14% for CuO, Al2O3, and TiO2 nanofluids, respectively, as compared to base fluid, while the exergy loss increases as the inlet temperature of hot fluid increases. Also, the maximum value for second law efficiency is found to be 67% for base fluid, whereas the second law efficiency has been achieved to 71%, 74%, and 77% for TiO2, Al2O3, and CuO non-Newtonian nanofluids, respectively. Therefore, it is concluded from the present study that the use of non-Newtonian nanofluids in helical coil heat exchanger reduces the exergy loss and improves the second law efficiency.

Viscosity and Interfacial Tension of Binary Mixtures Consisting of Linear, Branched, Cyclic, or Oxygenated Hydrocarbons with Dissolved Gases Using Surface Light Scattering and Equilibrium Molecular Dynamics Simulations

Abstract: Abstract In the present study, the influence of the molecular characteristics of the solvent and solute on the dynamic viscosity and interfacial tension of binary mixtures consisting of a liquid with a dissolved gas is investigated using surface light scattering (SLS) and equilibrium molecular dynamics (EMD) simulations. In detail, binary mixtures consisting of linear, branched, cyclic, or oxygenated hydrocarbons and the solutes hydrogen, helium, methane, water, carbon monoxide, or carbon dioxide are studied in the temperature range between (298 and 573) K and for solute mole fractions up to 0.2. With SLS, the liquid dynamic viscosity and interfacial tension of the binary mixtures could be accessed in macroscopic thermodynamic equilibrium with average expanded uncertainties (coverage factor k = 2) of (2.4 and 2.3)%, respectively. While EMD simulations were able to predict the influence of the dissolved gases on the interfacial tension of the binary mixtures, the simulations fail to represent the influence of the dissolved gas on the viscosity. Due to the systematic variation of the solvent and solute molecules, the influence of the molecular characteristics, e.g., in the form of size, shape, or polarity, on the thermophysical properties of the mixtures is discussed. Dissolving carbon dioxide, e.g., leads to a reduction of both properties by up to 60% compared to the properties of the pure solvent. Dissolved helium, on the other hand, has only a small influence on the properties of the pure solvent. The influence of dissolved water was found to be negligible in mixtures with an alkane but strongly increases both properties when dissolved in an alcohol, which may be explained by the formation of hydrogen bonds.

Speed of Sound Measurements of Binary Mixtures of Difluoromethane (R-32) with 2,3,3,3-Tetrafluoropropene (R-1234yf) or trans-1,3,3,3-Tetrafluoropropene (R-1234ze(E)) Refrigerants

Abstract: Sound speed data measured using a dual-path pulse-echo instrument are reported for binary mixtures of difluoromethane (R-32) with 2,3,3,3-tetrafluoropropene (R-1234yf) or trans-1,3,3,3-tetrafluoropropene (R-1234ze(E)). The sound speed is reported at two compositions for each binary mixture of approximately (0.33/67) and (0.67/0.33) mole fraction at temperatures between 230 K and 345 K. Data are reported from pressures slightly above the bubble point to 12 MPa for R-32/1234yf mixtures to avoid potential polymerization reactions and to 53 MPa for the R-32/1234ze(E) mixtures. The mean uncertainty of the sound speed data are less than 0.1% of the measured value where uncertainties at individual state points range from 0.04% to 0.5% of the measured value as the conditions approach the mixture critical region. The reported data are compared to available Helmholtz-energy-explicit EOS included in REFPROP and all systems studied have average absolute deviations greater than 2%. The comparisons show that further adjustments to the mixture models are needed to provide a reasonable representation of the data within its experimental uncertainty.

High-Temperature Collision Integrals for m-6-8 and Hulburt–Hirschfelder Potentials

Abstract: Abstract This study is aimed to determine collision integrals for atoms interacting according to the m-6-8 and Hulburt–Hirschfelder potentials and analyze the differences between potentials. The precision of four significant digits was reached at all tested temperatures, and for high-temperature applications, six digits were calculated. The proposed method was tested on the Lennard-Jones potential and found to excellently agree with the recent high-quality data. In addition, the Hulburt–Hirschfelder potential was used for determining the collision integrals of the interaction of nitrogen atoms in the ground electronic state and compared with other known values. The calculations were performed using Mathematica computation system which can deal with singularities (so-called orbiting).

Speed of Sound, Density, and Related Thermophysical Properties of the Methyl Caprate + Methyl Oleate Binary System from 0.1 MPa to 70 MPa at 303.15 K

Abstract: In this work, we reported values of speed of sound and density of the methyl caprate + methyl oleate binary system over the whole composition range from 0 % to 100 % for pressures ranging from 0.1 MPa to 70 MPa and at 303.15 K. A pulse-echo technique working by reflection was used to measure the speed of sound w at 3 MHz. A vibrating U-tube densimeter was used to obtain density data. From the combination of both these measurements, the isothermal and isentropic compressibilities were determined. Finally, the speed of sound molecular weight product and the molecular compressibility $${\kappa }_{m}$$ , also known as Wada’s constant, were calculated and represented as function of molar fraction in order to determine the best combining rule for predicting the speed of sound of the mixture from pure Fatty Acid Methyl Ester properties.

Speed of Sound, Density, and Related Thermophysical Properties of the Methyl Caprate + Methyl Oleate Binary System from 0.1 MPa to 70 MPa at 303.15 K

Abstract: In this work, we reported values of speed of sound and density of the methyl caprate + methyl oleate binary system over the whole composition range from 0 % to 100 % for pressures ranging from 0.1 MPa to 70 MPa and at 303.15 K. A pulse-echo technique working by reflection was used to measure the speed of sound w at 3 MHz. A vibrating U-tube densimeter was used to obtain density data. From the combination of both these measurements, the isothermal and isentropic compressibilities were determined. Finally, the speed of sound molecular weight product and the molecular compressibility $${\kappa }_{m}$$ , also known as Wada’s constant, were calculated and represented as function of molar fraction in order to determine the best combining rule for predicting the speed of sound of the mixture from pure Fatty Acid Methyl Ester properties.

Speed of Sound Measurements of Binary Mixtures of Difluoromethane (R-32) with 2,3,3,3-Tetrafluoropropene (R-1234yf) or trans-1,3,3,3-Tetrafluoropropene (R-1234ze(E)) Refrigerants

Abstract: Sound speed data measured using a dual-path pulse-echo instrument are reported for binary mixtures of difluoromethane (R-32) with 2,3,3,3-tetrafluoropropene (R-1234yf) or trans-1,3,3,3-tetrafluoropropene (R-1234ze(E)). The sound speed is reported at two compositions for each binary mixture of approximately (0.33/67) and (0.67/0.33) mole fraction at temperatures between 230 K and 345 K. Data are reported from pressures slightly above the bubble point to 12 MPa for R-32/1234yf mixtures to avoid potential polymerization reactions and to 53 MPa for the R-32/1234ze(E) mixtures. The mean uncertainty of the sound speed data are less than 0.1% of the measured value where uncertainties at individual state points range from 0.04% to 0.5% of the measured value as the conditions approach the mixture critical region. The reported data are compared to available Helmholtz-energy-explicit EOS included in REFPROP and all systems studied have average absolute deviations greater than 2%. The comparisons show that further adjustments to the mixture models are needed to provide a reasonable representation of the data within its experimental uncertainty.

A Reference Correlation for the Viscosity of Krypton From Entropy Scaling

Abstract: We present a new wide-ranging correlation for the viscosity of krypton based on critically evaluated experimental data. For the first time, such a correlation has as its basis the entropy scaling approach. We base the residual contribution on the Lennard-Jones fluid, resulting in one adjustable parameter for the entire phase diagram away from the dilute-gas limit. The estimated uncertainty is less than 2.0 % (at the 95 % confidence level) over the entire phase diagram, except in the extended critical region. The correlation is valid from 70 K to 5000 K for the dilute gas, and from 115.775 K to 750 K in the fluid phase, with a pressure limit equal to that of the melting curve

Combined Surface Light Scattering and Pendant-Drop Experiments for the Determination of Viscosity and Surface Tension of High-Viscosity Fluids Demonstrated for Ionic Liquids

Abstract: Abstract The present study provides a strategy for the determination of the viscosity and surface tension of high-viscosity fluids in the form of ionic liquids (ILs) at equilibrium conditions by combining surface light scattering (SLS) and the pendant-drop (PD) method within one experimental setup. Through the study of the same sample under identical conditions by both methods inside a closed system, the surface tension determined via the PD method can be directly used to evaluate the dynamics of surface fluctuations of ILs with an overdamped behavior probed by SLS for accessing their viscosity. In connection with the SLS experiments, variations in the applied detection geometries in reflection and transmission direction and in the probed wave vectors down to relatively small values were also addressed. The reliability and self-consistency of SLS and the PD method applied within the same sample cell has been proven by investigating the reference fluids tris(2-ethylhexyl) trimellitate (TOTM) and n -dodecane featuring relatively high and low viscosities. For the two studied model ILs of opaque to non-transparent color, i.e. , the hydrophobic 1-methyl-3-octylimidazolium hexafluorophosphate ([OMIM][PF 6 ]) and the hydrophilic 1,3-bis(2-(2-methoxyethoxy)ethyl)imidazolium iodide ([(mPEG 2 ) 2 Im]I), the combination of PD measurements and SLS experiments in reflection direction performed at ambient pressure between (303 and 373) K allowed access to the viscosity and surface tension with typical relative expanded uncertainties of (4 and 2) %. These results agree well with own viscosity data from capillary viscometry and experimental data in the literature, demonstrating the performance of the novel approach for the contactless in-situ measurement of viscosity and surface tension of fluids with relatively high-viscosity such as ILs.

Experimental Investigation of Stability, Properties and Thermo-rheological Behaviour of Water-Based Hybrid CuO and Fe3O4 Nanofluids

Abstract: In this study, the effect of surfactant on the stability of hybrid nanofluids is explored. The thermal, rheological, and thermo-rheological performance of the three most stable nanofluid samples (one each of CuO, Fe3O4 and CuO + Fe3O4) is studied in detail. Stability analysis is carried out by monitoring the agglomerations in the nanofluids over a period of 20 days. The behaviour of stability indicators (i.e., zeta potential and hydrodynamic diameter) shows that the nanofluid stability is highly dependent on the type of surfactant utilized. It is seen that CuO-water nanofluid shows a maximum 5.47 % enhancement in thermal conductivity compared to its base fluid, while Fe3O4-water and hybrid CuO + Fe3O4-water nanofluids show a maximum enhancement of 3.11 % and 3.95 %, respectively. The results also show that the presence of CTAB surfactant increases the viscosity of the nanofluid. The contact angles for all the nanofluids are lower than that of the base fluid, confirming their superior wettability characteristics. The thermal performance of the nanofluids is also assessed by determining the property enhancement ratio and the figure of merit.