Journal of Chemical Thermodynamics最新文献

The solid–liquid equilibrium solubility of DHA in thirteen pure solvents (methanol, ethanol, n-propanol, isopropanol, n-pentanol, ethyl formate, ethyl acetate, N, N-dimethyl acetamide (DMA), N, N-dimethyl formamide (DMF), acetonitrile, acetone, 2-butanone, dimethyl sulfoxide (DMSO)) was determined at temperatures ranging from 288.15–323.15 K under local atmosphere by gravimetric method. The experimental results showed that the solubility of DHA was positively correlated with the rising of temperatures. Five thermodynamic models, including Ideal model, Apelblat model, λh model, NRTL model and Wilson model, were employed to fit the experimental data and Wilson model provided a better correlation. The KAT-LSER model and molecular dynamic simulations were also carried out to investigate the effects of solvent–solute interactions on solubility. Furthermore, the thermodynamic properties of the dissolution process were calculated and the results argued a spontaneous, exothermic and entropy-driven process.

Speed-of-sound measurements for normal hydrogen (n-hydrogen) in a temperature range between 273 K and 323 K were carried out using a cylindrical resonator at pressures from 1 MPa to 10 MPa and a dual-path pulse-echo system at pressures from 20 MPa to 100 MPa. The relative expanded uncertainties (k = 2) of the measurements range from 0.04 % to 0.08 %. Based on these measurements and data from the literature, a fundamental equation of state (EOS) was developed for the calculation of thermodynamic properties of n-hydrogen. It is expressed in terms of the Helmholtz energy with the independent variables temperature and density. Due to the fundamental nature of the Helmholtz energy, the equation can be used to calculate all thermodynamic properties from one mathematical expression. In contrast to typical EOS of this kind, the boundary conditions are somewhat more restricted. The relevant temperature and pressure ranges are limited to typical pipeline and storage conditions of gaseous hydrogen, including temperatures relevant for measurements with critical nozzles (140 K to 370 K with pressures up to 100 MPa). The computational speed for the implementation of the correlation in measurement sensors plays a superior role. Therefore, the equation is kept as short as possible, and exponents are of integer-kind. Most of the experimental data are still reproduced within their measurement uncertainties.

The purpose of this work is to investigate the influence of concentration, temperature and molecular size on intermolecular interactions in the mixtures of 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF₆] with some alkyl acetates. The densities, ρ and speeds of sound, u for the 1-butyl-3-methylimidazolium hexafluorophosphate + ethyl acetate/propyl acetate/n-butyl acetate binary mixtures were measured over the entire range of composition at the temperatures, T = (293.15 – 323.15) K at 5 K intervals and at pressure, p = 101 kPa. The experimental data was used to calculate various excess properties, viz., excess molar volume, excess isentropic compressibility, excess intermolecular free length, excess speed of sound, excess molar isentropic compressibility and excess acoustic impedance. The partial molar volumes and compressibilities; and excess partial molar volumes and compressibilities of the components over the entire composition range and at infinite dilution have also been calculated. The results clearly indicated the presence of intermolecular interactions in these mixtures and the magnitude of [BMIM][PF₆]-alkyl acetate interactions followed the order: ethyl acetate > propyl acetate > n-butyl acetate, i.e., the interactions were found dependent on the size of alkyl group of acetates. The speeds of sound were estimated theoretically using scaled particle theory and compared with experimental findings. FT-IR spectra of pure [BMIM][PF₆], ethyl acetate, propyl acetate. n-butyl acetate and their equimolar mixtures were also recorded and analysed for better understanding of prevailing intermolecular interaction.

There is a continuous demand for accurate data on the thermodynamic properties of environmentally friendly working fluids, specifically hydrofluoroalkenes (HFO) and hydrocarbons (HC). For two emerging binary mixture fluids in organic Rankine cycle and heat pump, [R1234ze(Z) (or named cis-1,3,3,3-tetrafluoropropene) + R1233zd(E) (or named trans-1-chloro-3,3,3-trifluoro-1-propene)] and [R1234ze(Z) + isobutane], the speed of sound was experimentally obtained at pressure between 40 and 960 kPa and temperature interval of 300 to 370  K. The experimental instruments of the fixed-path acoustic resonance method have been re-calibrated and repaired to confirm the experimental precision, and the relative combined expanded uncertainty (k = 2) of the speed of sound is less than 0.038 %. Due to the signal peak overlapping in gas chromatography, the molar fractions are instead calculated by the experimental data using the thermodynamic rules, with the absolute combined expanded uncertainty (k = 2) of 0.0027 and 0.0008 for R1234ze(Z) + R1233zd(E) and R1234ze(Z) + isobutane, respectively. Acoustic virial coefficients were derived according to the truncated acoustic virial equation using the experimental data of this and previous work. The obtained data were compared with themselves to confirm the basic reliability. The experimental data were also compared with the reference values calculated by the state of art of thermodynamic models and a maximum deviation was found up to 20 times the experimental uncertainty, proposing needs and references for new dedicated mixing models.

Fatty acids are commonly used as phase change materials (PCMs) for thermal energy storage due to their high latent heat, non-toxicity, and biocompatibility. However, the thermodynamic properties of fatty acids have not been systematically studied, especially for their heat capacity data over a wide temperature range. This limitation greatly restricts their practical applications in designing and constructing fatty acids based PCMs and corresponding thermal management techniques. Herein, the heat capacities of a series of fatty acids (octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid) have been measured using a combined relaxation, adiabatic, and differential scanning calorimetry techniques over a temperature range from 1.9 K to 380 K. The corresponding thermodynamic functions and phase transition thermodynamic parameters have been calculated based on heat capacity data fitting. Additionally, the thermal stability and thermal conductivity of these fatty acids have also been determined using a thermogravimetric analysis instrument and a thermal constant analyzer, respectively. These obtained thermodynamic properties can provide crucial fundamental information for the study and application of fatty acid PCMs and related thermal energy storage techniques.

The thermophysical characteristics of pure liquids and their mixes are substantial in applied as well as theoretical research. This paper presents the measured data on: density ($\rho$), viscosity $\left(\eta \right)$, refractive index ($n_D$) and consequent calculated parameters: {excess molar volume ($V_m^E$), partial molar volume (${\overline{V}}_m$), excess partial molar volume (${\overline{V}}_m^E$), deviation in viscosity $\left(\Delta \eta \right)$, excess Gibbs energy of activation of viscous flow ($\Delta G^{\ast E}$), deviation in refractive index (${\Delta }_{\varphi }{n}_D$) and deviation in molar refraction (${\Delta }_x{R}_M$)} of binaries containing 1-butyl-3-methylimidazolium bromide ([BMIM]Br) with glycol oligomers (mono/di/tri/tetra-ethylene glycol) at T/K = 298.15–313.15 and pressure p/MPa = 0.1. The Redlich-Kister equation efficiently estimates the standard deviation between the experimental and calculated excess properties. The interactions between constituents were considered while interpreting the obtained results. The values of $V_m^E$, ${\overline{V}}_m^E$, $\Delta \eta$, ${\Delta }_{\varphi }{n}_D$ and ${\Delta }_x{R}_M$ exhibited negative trends throughout the range, whereas $\Delta G^{\ast E}$ values displayed a sigmoidal shift (negative to positive) with increasing [BMIM]Br concentration. The $V_m^E$ data has been explored in terms of Prigogine-Flory-Patterson (PFP) and Graph theories to elucidate the deviations in thermophysical properties of the mixtures caused by variations in strength and magnitude of interactions. Additionally, the $\eta$