Chemical Thermodynamics and Thermal Analysis最新文献

A precise description of energy and mass transport across the liquid-vapor interface of water is central in disciplines spanning from climatology to seawater desalination. We present a critical assessment of six recent experimental data sets that report temperature jumps, vapor pressures, and evaporation rates during steady-state evaporation of water. The experimental data were used to test available theories. Three state-of-the-art theories that take the resistance of the liquid-vapor interface into account were compared; statistical rate theory, non-equilibrium thermodynamics, and kinetic theory of gases. Statistical rate theory appears to under-predict the difference between the saturation pressure and the actual pressure of the vapor phase. Interface transfer coefficients for water compatible with non-equilibrium thermodynamics theory were determined. These coefficients predict the right order of magnitude of the evaporation fluxes from the different data sets. However, inconsistencies between the different data sets and indications of systematic measurement errors were identified during the determination and evaluation of these coefficients. The condensation coefficient in kinetic theory of gases computed from the experimental data span two orders of magnitude. All three theories were found to depend much on a precise determination of the conditions at the interface, in particular on the difference between the vapor phase pressure and the saturation pressure. Already a shift of 1–5 Pa changes the predicted evaporation rates significantly. For certain experiments, a change of 2 Pa modifies the evaporation rate predicted by statistical rate theory by one order of magnitude. Overall, we show that determination of vapor pressures to a higher accuracy ($<$0.3 Pa) is needed to enhance the understanding of evaporation mechanisms and which theory to use.

For over two decades, deep eutectic solvents have offered pre-eminence characteristics with the purpose of improving the issues of both ionic liquids and traditional solvents. The affordability, ease of preparation, in-flammability, non-or low toxicity, biodegradability, and other environmental advantages of DESs make them more appealing as green solvents. In the present study, 1-ethyl-1-methylpyrrolidinium bromide, a hydrogen bond accepter (HBA), was paired with 1,6-hexanediol (1,6-HDO), a hydrogen bond donor (HBD), to produce a DES with a mole ratio of 1:2. With the use of gas liquid chromatography (GLC), the infinite dilution activity coefficients (IDACs) of 32 different solutes were measured at different temperatures (313.15–343.15) K and atmospheric pressures. The partial molar properties, i.e., enthalpy, entropy, and Gibbs free energy, were calculated from the IDAC values at a reference temperature of T = 313.15 K to give more details for molecular interaction interpretation. Lastly, the selectivity and capacity values of separation problems such as benzene/acetone, benzene/cyclohexane, and cyclohexane/acetone were calculated from the IDAC values. The investigated DES was discovered to have good performance and could be used in industrial processes such as petroleum distillation, separation, extraction, and so on.

Boiling refers to the heat transfer mechanism that occurs due to the phase transition from liquid to vapor. In comparison with single phase heat transfer, this mechanism has several advantages such as much higher rate at lower temperature differences. Regarding the complexities of two phase heat transfer simulation, due to the involvement of various parameters in this phenomenon, applying intelligent methods such as artificial neural networks could be useful for modeling this type of heat transfer mechanism. In the present article, studies on the modeling of pool boiling heat transfer utilizing machine learning methods have been reviewed, and their findings are reflected. According to the outcomes of the reviewed works, it can be concluded that using intelligent methods can provide accurate predictions of pool boiling heat transfer with a R² of around 0.99 in some cases. In addition, by applying these methods it would be possible to predict the heat transfer in cases of utilizing nanofluids or porous media. The exactness and applicability range of these models is influenced by several elements such as the considered inputs, applied methods and employed functions. Using an appropriate method with optimal parameter values for the relevant intelligent method would lead to higher precision in modeling.

Differential scanning calorimetry (DSC) was used to measure the enthalpies of reaction for the dehydration of the potassium Tutton salts, K₂M(SO₄)₂ ^. 6 H₂O with M = Mg, Co, Ni, Cu and Zn. The values determined ranged from 335 kJ mol⁻¹ for K₂Mg(SO₄)₂ 6 H₂O to 355 kJ mol⁻¹ for K₂Ni(SO₄)₂^. 6 H₂O with a measured standard deviation of ± 5 kJ mol⁻¹. Although the information needed to obtain precise values for the enthalpies of formation is not available in the literature for all of these salts, values calculated by modeling the amorphous dehydrated compound as an ideal solid solution produced values within 10 kJ mol⁻¹ of the values determined for K₂M(SO₄)₂^. 6 H₂O (M= Mg, Cu, and Zn) where the information needed for this calculate was available. DSC was also used to determine the entropies of reaction for the dehydration of these salts. Since there is little information about the entropies of these compounds in the literature, the entropies of reaction were used with the ideal solution model for the amorphous compound to estimate the standard molar entropies for these salts. The values determined ranged from 490 J K⁻¹ mol⁻¹ for K₂Cu(SO₄)₂ ^. 6 H₂O to 540 J K⁻¹ mol⁻¹ for K₂Co(SO₄)₂ ^. 6 H₂O. Since these values are based upon estimated values, they have an estimated error of ± 5 percent.

The effect of single (Cu or Ag) and hybrid (Cu+Ag) metallic nanoparticles on the thermophysical properties, namely viscosity and thermal conductivity of water-based nanofluids, has been studied using Equilibrium Molecular dynamics (EMD) simulation. The TIP3P (three-site transferrable intermolecular potential) water model has been chosen. The interaction of water molecules has been modelled by the Lennard-Jones (L J) potential in combination with Coulomb potential. The embedded-atom (EAM) potential method has been used for hybrid (Cu and Ag) atom interaction. Simulation has been performed at 303 K and atmospheric pressure using the Berendsen algorithm under NVT (constant number, constant volume, and constant temperature) ensemble with production steps of 2 ns and integral step of 1fs. Interestingly, nanofluids containing one metallic nanoparticle (Cu or Ag) have lower thermal conductivity and viscosity than nanofluids having hybrid metallic nanoparticles with the same volume fraction.

The phase equilibria in the ternary system ZrO₂–HfO₂–Sm₂O₃ were studied by X-ray diffraction and microstructural analyses. The formation of new phases in the ZrО₂–HfO₂–Sm₂O₃ system at 1500 °С was not observed. It is established that in the studied system at 1500°C the fields of solid solutions based on tetragonal (T) modification of ZrО₂, monoclinic (M) modifications of HfO₂, and monoclinic (B) modifications of Sm₂O₃, and ordered phase with the structure of pyrochlore-type (Py) Ln₂Zr₂O₇ (Ln₂Hf₂O₇) are present. The boundaries of the phase fields and the parameters of the unit cells of the formed phases are determined. The studied isothermal cross section of the ZrО₂–HfO₂–Sm₂O₃ system is characterized by the formation of continuous series of cubic solid solutions based on a phase with a structure of the pyrochlore-type Sm₂Zr₂O₇ (Sm₂Hf₂O₇) and a structure of the fluorite type F-ZrO₂ (HfO₂). It is established that two regions of homogeneity of cubic solid solutions are formed in the determined system. The existence of these regions of homogeneity is due to the rupture of the solubility of the F-ZrO₂ (HfO₂) phase in the region of the existence of an ordered phase with a pyrochlore-type structure Sm₂Zr₂O₇ (Sm₂Hf₂O₇). It is established that the solid solution based on a cubic modification with fluorite-type structure exists in equilibrium with all phases observed in the system. Isothermal section of the phase diagram of the system ZrO₂–HfO₂–Sm₂O₃ at 1500°C has been characterized by the presence of one three-phase (F + T + M), as well as five two-phase (B + F, two - F + Py, M + F, T + F) regions.

The UMR-PRU group contribution equation of state (EoS), which couples the Peng-Robinson EoS with UNIFAC via the Universal Mixing Rules, is extended to pure imidazolium-based ionic liquids (ILs), as well as to their mixtures with CO₂ and H₂S. The studied ILs consist of alkyl-methylimidazolium cations and tetrafluoroborate, hexafluorophosphate and bis(trifluoromethylsulfonyl)imide anions. The EoS parameters of pure ionic liquids, are determined by fitting experimental vapor pressure and liquid density data. For the extension of UMR-PRU to binary CO₂/IL and H₂S/IL mixtures, the model parameters are determined by fitting experimental binary vapor-liquid equilibrium data of acid gases with ionic liquids. For comparison, the Peng-Robinson coupled with the conventional van der Waals one-fluid mixing rules (vdW1f) is also applied to the same systems, using adjustable attractive and co-volume cross interaction parameter. It is shown that Peng-Robinson accurately describes pure ionic liquid vapor pressures and liquid densities, while UMR-PRU yields very satisfactory vapor-liquid equilibrium results for binary and ternary mixtures containing ILs and acid gases. Overall, UMR-PRU yields much better results than Peng-Robinson coupled with the vdW1f mixing rules, which indicates the superiority of the UMR mixing rules over the vdW1f ones.