International Journal of Thermophysics最新文献

The in-plane thermal conductivity (k) of ultrathin films is of great scientific and engineering importance as the ultrafine thickness will cause remarkable energy carrier scattering. However, the in-plane k is extremely difficult to measure as the in-plane heat conduction is highly overshadowed by the substrate. To date, very rare experimental data and understanding have been reported. Here we report an advanced differential transient electro-thermal (TET) technique to characterize the in-plane k of supported nm-thin Iridium films down to < 2 nm thickness. The ultrathin (500 nm) organic substrate and its low k makes it possible to distinguish the in-plane k of the film with high confidence. The radiation effect is rigorously treated and subtracted from the measured k. Also measurements under different temperature rise levels allow us to determine the k at the zero temperature rise limit. All these physics treatments lead to high accuracy determination of the in-plane k, and understanding of the strong structural effects. The k of ultrathin Ir films supported on polyethylene terephthalate is determined to be 11.7 W·m⁻¹·K⁻¹, 20.1 W·m⁻¹·K⁻¹, 23.5 W·m⁻¹·K⁻¹, and 34.3 W·m⁻¹·K⁻¹ for thicknesses of 1.83 nm, 3.11 nm, 5.86 nm, and 9.16 nm, respectively. This is more than one order of magnitude reduction from the bulk’s k of 147 W·m⁻¹·K⁻¹. The film’s electrical conductivity is found to have more than two orders of magnitude reduction from that of bulk Ir (1.96 × 10⁷ Ω⁻¹·m⁻¹). The Lorenz number of the studied Ir films increases significantly with decreased film thickness, and is upto 14-fold higher (3.97 × 10^–7 W·Ω·K⁻²) than that of bulk Ir (2.54 × 10^–8 W·Ω·K⁻²). It underscores the significant and deviated influence of structure and film dimension on heat and electrical conductions and provides invaluable knowledge for future applications in nanoelectronics.

The present work reviews different approaches from the literature and suggests an empirical correlation scheme for calculating Fick diffusion coefficients in binary electrolyte mixtures. The mixtures consist of either an electrolyte component dissolved in a molecular solvent or of two electrolyte components sharing a common ion. For both types of mixtures, the diffusive mass transport is characterized by a single Fick diffusion coefficient D₁₁. Prediction models for electrolytes and non-electrolytes mixtures are evaluated, considering experimental D₁₁ data in the literature from dynamic light scattering experiments for binary mixtures, which have a solute amount fraction of 0.05 and include a systematic variation of the solute and solvent components. It could be shown that including information about the fluid structure obtained from molecular dynamics (MD) simulations, such as the formation of solvation shells, the predictive performance of the models can be greatly improved. In general, most models are able to predict D₁₁ in mixtures where the ions are well dissociated by the solvent molecules, but can fail for mixtures where the ionic species tend to aggregate. For binary electrolyte mixtures based on a molecular solvent, an empirical correlation is developed, which can predict D₁₁ for all mixtures with an average absolute relative deviation (AARD) of 21% from the experimental values. For binary mixtures consisting of two electrolyte components sharing a common ion, it could be shown that D₁₁ can be predicted by using only the self-diffusivities of the three ions with an AARD of 15% from experimental data.

The gradient theory of the interface is combined with the cubic plus association and perturbed chain statistical association fluid theory equations of state to estimate the surface tension of (monoethanolamine + water) system for the first time. For each equation of state, three cases of association scheme and two forms of influence parameters have been used. Two forms of influence parameters are also applied to the gradient theory. The second form contains two exponents that lead to the accuracy of surface tension estimations, especially at low mole fractions of monoethanolamine. The highest and lowest AADs% of surface tension are 5.24 and 1.11, respectively. The interfacial density profiles show the enrichment of the surface layer with monoethanolamine. However, the enrichment of the surface layer does not exist at high concentrations of monoethanolamine in the mixture. The overall AADs% of the present model confirm its reliability for description of (monoethanolamine + water) interface.

The stability, safety, and shelf life of various formulations are significantly enhanced by the incorporation of antioxidants and antimicrobial preservatives. This work investigates the molecular interactions and thermodynamic characteristics of ternary mixtures consisting of L-ascorbic acid/Ascorbyl glucoside in aqueous solutions of Potassium sorbate, at temperatures ranging from 288.15 K to 318.15 K and concentrations from (0.0 to 0.7) mol·kg⁻¹. Experimental measurements of density and ultrasonic velocity were used to calculate key thermodynamic parameters, including partial molar volumes ((V_{upphi }^{0})), apparent molar volume (({V}_{phi })), isentropic compression ({(K}_{phi ,s})), and their transfer parameters ((V_{upphi }^{0}), (Delta K_{upphi }^{0})). The results reveal stronger solute -solvent interactions for Ascorbyl glucoside compared to L-ascorbic acid. Additionally, the analysis of relative association (R_a), relaxation strength (r_s) and specific heat ratio (ϒ) provides further insights into the molecular behavior and structural dynamics of these mixtures. The co-sphere overlap theory provides a quantitative framework for interpreting molecular interactions, assessing whether ternary mixtures promote structural organization or disruption. Temperature-dependent behavior is analyzed through the first derivative ((partial {text{E}}_{upphi }^{0}/partial text{T})) _P, offering insights relevant to applications in the cosmetics, chemical, and pharmaceutical industries.

The viscosity of 1-octanol was determined experimentally and modeled using both empirical as well as physical models. The viscosity of liquid 1-octanol was measured using a falling-body viscometer at pressures up to 600 MPa and temperatures between 293.15 K and 373.15 K. For the physics-based modeling, entropy scaling in combination with a molecular-based equation of state, namely SAFT-VR Mie, was used. Also for the evaluation of the viscosity measurements, the SAFT-VR Mie EOS was used for describing the density of the fluid. The new viscosity data significantly extend the available literature data. For the new experimental data, the relative expanded uncertainty is below 10% for most data points. Moreover, an empirical model was developed to represent experimental data from this work. Finally, the entropy scaling model was employed and tested for describing the viscosity of 1-octanol in a wide range of states including gaseous, liquid, supercritical, and metastable states. It describes all available experimental data well and is robust when used for extrapolations.

Transition metal carbides and nitrides (MXenes), a family of two-dimensional materials, exhibit exceptional promise for energy storage applications due to their tunable structural and electrical properties. However, the pronounced adsorption properties inherent to their layered structure complicate the accurate characterization of their thermophysical properties. Here, we systematically investigate the thermal diffusivity of one-dimensional Ti₃C₂T_x MXene fibers using a transient electrothermal method under controlled electrical currents and vacuum environments. Our results reveal a strong correlation between the electrical and thermal responses of Ti₃C₂T_x MXene fibers during heating cycles. As heating progresses, the rate of voltage rise decreases, and the logarithm of the transient voltage response exhibits a robust linear dependence on time, enabling consistent extraction of thermal diffusivity. The thermal diffusivity fluctuates within experimentally determined upper and lower limits, corresponding to the degree of adsorption and desorption of water molecules, quantified at 3.6 × 10⁻⁵ m²·s⁻¹ and 1.0 × 10⁻⁶ m²·s⁻¹, respectively. By refining the understanding of MXene’s thermophysical behavior, this work provides critical insights for optimizing their energy applications and advancing materials with variable physical properties.

This paper presents a new wide-ranging reference correlation for the viscosity of argon, incorporating recent ab initio dilute-gas calculations and critically evaluated experimental data. The correlation is designed to be used with a high-accuracy Helmholtz equation of state that extends from the triple point (83.8058 K) to 700 K, and at pressures up to 1000 MPa. The estimated uncertainty of the correlation based on comparisons with the best experimental data indicate that the uncertainty for the gas at pressures from zero to 0.1 MPa for temperatures from 202 K to 394 K is 0.076% (at k = 2), the uncertainty of the best experimental data, offering a significant improvement over the current reference equation that has an uncertainty in this region of 0.5%. A zero-density correlation based on ab-initio values is incorporated that is valid over a temperature range between 84 K and 10 000 K and has an uncertainty of 0.12% (at the 95% confidence level). The estimated uncertainty for moderate pressures from 1 MPa to 100 MPa is 1% for temperatures from roughly 195 K to 300 K, rising to 2% at 175 K. For the high-pressure region, the estimated uncertainty of the correlation is about 2% for temperatures between 175 K and 308 K at pressures from 100 MPa to 606 MPa. For temperatures from 308 K to 700 K at pressures to 5.2 GPa, the equation has an estimated uncertainty of 10%. The estimated uncertainty in the liquid phase at pressures up to 34 MPa is 3%. The correlation behaves in a physically reasonable manner over the full range of applicability of the EOS, although uncertainties may be higher in regions where data were not available for full validation.