International Journal of Thermophysics最新文献

The present work reports experimental data on the thermal conductivity of the four hydrocarbons cyclohexane, n-decane, n-hexadecane, and squalane in the liquid state at ambient pressure up to temperatures of 353.15 K. Absolute measurements were performed with a steady-state guarded parallel-plate instrument (GPPI) with an average expanded (coverage factor k = 2) measurement uncertainty of 2 %. For the linear alkanes n-decane and n-hexadecane as well as the cyclic compound cyclohexane, the measured thermal conductivities agree with reference correlations in the literature, indicating the reliability of the technique used for the study of fluids with relatively low thermal conductivities and weak absorption of radiation. For the first time, experimental data are determined for the long-branched alkane squalane between (278 and 353) K, which cannot be accurately represented with estimation methods commonly used in the literature. In summary, the present measurement results confirm the existing database for representative linear and cyclic hydrocarbons and provide first experimental thermal conductivities for squalane.

A thorough evaluation of the thermophysical properties of ethylcyclohexane (ECH) mixed with 2-alkanols (2-propanol to 2-hexanol) is presented across the temperature range of 293.15 to 323.15 K. The focus of this study is on the density and viscosity behavior of these systems. The experimental results demonstrate positive deviations from ideality in excess molar volume, while viscosity deviations are negative for all examined mixtures. This observation suggests the presence of weak intermolecular interactions between ECH and the 2-alkanol. These findings are consistent with the self-association behavior of 2-alkanol and the nonpolar nature of ECH, which disrupts the associated structures of the alcohols. Furthermore, the Friction theory (f-theory) was employed to model the viscosity of the binary mixtures. The f-theory exhibits excellent agreement with the experimental data, with a maximum deviation of only 2.24% observed in the ECH + 2-butanol system. This minimal discrepancy underscores the f-theory's efficacy in accurately correlating the viscosity measurements.

A suite of measurements of refractive index (n(p, T_{90})) is reported for gas phase ordinary water H(_2)O and heavy water D(_2)O. The methodology is optical refractive index gas metrology, operating at laser wavelength (633 text {nm}) and covering the range ((293< T_{90} < 433) text {K}) and (p < 2 text {kPa}). A key output of the work is the determination of molar polarizabilities (A_{text {R}} = 3.7466(18) cdot [1 + 1.5(6) times 10^{-6} (T/text {K} - 303) ] text{cm}^3 cdot text{mol}^{-1}) for ordinary water, and (A_{text {R}} = 3.7135(18) cdot [1 + 4.4(10) times 10^{-6} (T/text {K} - 303) ] text{cm}^3 cdot text{mol}^{-1}) for heavy water, with the numbers in parentheses expressing standard uncertainty. For heavy water, this work appears to be only the second gas phase measurement to date. For both ordinary and heavy water, this work agrees within (0.15 %) with recent ab initio theoretical results for (A_{text {R}}), but the comparison is affected by imperfect knowledge of dispersion. For ordinary water, the close agreement between the present work and theory suggests problems at the (2 %) level in the low density limit of the reference formulation for refractivity.

Numerous attempts have been made to measure the viscosity of liquids under high pressure by analyzing the response of a quartz crystal resonator. However, because the response of the resonator yields the product of density and viscosity, separating each value is necessary. A procedure was devised to measure the density changes of a liquid under high pressure by considering the fact that the response of a TiO₂-coated quartz crystal resonator is correlated with density. The resonance frequency shift of the TiO₂-coated quartz crystal resonator is the sum of terms that depend on (rho ) and (sqrt{eta rho }). Each effect can be separated using plane equation fitting. By applying ethyl laurate, densities up to 300 MPa were obtained at 313 K and 333 K. These values agreed with previously reported values within ± 1 %, thereby demonstrating the effectiveness of this method. Since the pressure dependence of (sqrt{eta rho }) is also obtained in the process of obtaining density data, the pressure dependence of the viscosity (eta ) can be estimated. The viscosities of ethyl laurate at 313 K and 333 K were calculated. Although the viscosity values differed significantly from the reported values and the measurements are still inaccurate, the possibility of using this method as a density measurement method under high pressure was demonstrated. Therefore, this study introduces a method with the potential to conveniently measure high-pressure physical properties.

Passive daytime radiative coolers (PDRCs) with exceptionally high solar reflectance and emissivity in the atmospheric window can provide sub-ambient cooling while reducing buildings’ cooling energy demand. However, glare and esthetic issues limit their application to high-rise buildings while may increase the building’s heating energy needs. Passive colored radiative coolers (PCRCs), based on fluorescent materials, convert part of the absorbed UV and visible solar radiation into emitted light, providing color and reducing the thermal balance of the materials and the potential visual annoyance. This article investigates the state of the art on the PCRC based on fluorescent technologies. Seven articles presenting different combinations of PDRC technologies with fluorescent components to create PCRCs of various colors are presented and analyzed in detail. Quantum dots and phosphors embedded in polymer matrices and combined with reflecting and emitting layers were used as the fluorescent layer of the seven developed green, red, yellow, and yellow–green films. The proposed PCRCs are characterized by very significant differences in cooling performance, although most presented sub-ambient surface temperatures. Their cooling potential is comparatively investigated in terms of the testing climatic conditions and their optical characteristics. The potential increase of their surface temperature, caused by the addition of the fluorescent component, is analyzed through comparisons between the proposed PCRCs and the corresponding white PDRCs without the fluorescent component. The average temperature difference of the green, red, yellow, and yellow–green films against the reference PDRCs is found to be 0.66 °C, 2.6 °C, 1.7 °C and 1.4 °C, respectively. A relevant decreasing trend, but not statistically significant, is observed between the temperature increase caused by the fluorescent additives and the corresponding photoluminescence quantum yield.

Densities and refractive indices of the three following ternary mixtures (glycerol + water + methanol), (glycerol + water + ethanol) or (glycerol + water + 2-propanol) and the corresponding binary mixtures were measured over the entire composition range at three temperatures from 298.15 to 318.15 K and atmospheric pressure. Excess molar volumes,({V}_{123}^{E}), and changes of refractive index on mixing,(Delta{n}_{D, 123}), for the ternary systems were calculated and compared with the results obtained with some semi-empirical methods for the estimation of ternary properties from binary results. Furthermore, Perturbed Chain Statistical Associating Fluid Theory was applied to model the density for the binary and ternary mixtures. On the other hand, four mixing rules (Lorentz–Lorenz, Gladstone–Dale, Laplace, and Eykman) were used to compute predictively the refractive index of the mixtures. The fitting parameters of all equations and their respective standard deviations are reported and the results are discussed in terms of molecular interactions.

High-temperature equations of state (EoSs) for solid magnesium with hexagonal close-packing (hcp) and for liquid magnesium were formulated herein by using experimental data on the thermodynamic properties, thermal expansion, compressibility, temperature-dependent bulk compression modulus, and melting curve. The totality of experimental data was co-optimized using the temperature-dependent Tait EoS over a pressure range of 0–500 kbar at temperatures of 20–923 K for solid Mg and at 923–2000 K for liquid Mg. The temperature dependence of thermodynamic and thermophysical parameters was described by the extended Einstein model. The resultant EoSs give a good fit to the whole set of experimental data within measurement errors of individual quantities. The high prediction accuracy was achieved by estimating the thermodynamic and thermophysical properties of solid Mg. For liquid Mg, the suggested model adequately describes and, in some cases, averages the existing experimental data.

We present a new wide-range correlation for the viscosity of ethene based on critically evaluated experimental data. The viscosity correlation is valid from the triple point to 450 K and up to 195 MPa. The average absolute percentage deviation of the fit for the primary data (including the critical region) is 1%, with a bias of 0.2%, The estimated uncertainty of the correlation in the gas and supercritical phases at pressures up to 195 MPa is 2.5% (at the 95% confidence level). For the dilute gas (pressures up to 0.1 MPa) in the temperature range 296 K to 450 K, the uncertainty is 0.5%. For the liquid phase at pressures up to 5.5 MPa the estimated uncertainty is 5.3%. The correlation includes a term for the critical enhancement that is significant only in a very narrow region very close to the critical point. It is less than 1% outside of the region around the critical point from 279.80 K ≤ T ≤ 290.27 K to 140.79 kg⋅m⁻³ ≤ ρ ≤ 293.08 kg⋅m⁻³.

This study focuses on utilizing a novel method, the droplet generation method (DGM), to prepare hybrid nanofluids. The aim is to compare thermophysical properties, including thermal conductivity (TC) and viscosity, and magnetic properties between the DGM and two-step method (TSM). To prepare a bio-nanofluid, both fluid and nanoparticles must be biocompatible. Therefore, simulated body fluid (SBF) and olive oil were used to prepare this hybrid bio-nanofluid, and for the magnetic particle, iron oxide (Fe₃O₄) was used. Phase and microstructural examinations were conducted using XRD, FTIR, and FE-SEM. The KD2 Pro and DV2 Pro devices were employed to measure the thermal conductivity and viscosity of the samples, respectively. For both samples prepared using DGM and TSM, different volume fractions ranging from 0.01% to 1.00% and temperatures varying from 20°C to 40°C were measured individually. In TSM, from 20°C to 40°C, for 0.10% and 1.00% v.v, TC increased by 6.31% and 10.14%, respectively, while in DGM, it decreased by 0.48% and 1.23%, respectively. At a shear rate of 12.23 s⁻¹, from 20°C to 40°C, for 0.10% and 1.00% v.v, in the TSM, the viscosity decreased by 31.39% and 34.99%, respectively, while in DGM, it decreased by 25.11% and 28.83%, respectively. At a shear rate of 122.3 s⁻¹, from 20°C to 40°C, for 0.10% and 1.00% v.v, in the TSM, the viscosity decreased by 22.92% and 29.25%, respectively, while in DGM, it decreased by 17.42% and 23.85%, respectively. The results of this study contribute to understanding the effect of DGM on altering thermophysical properties of bio-nanofluids.