International Journal of Thermophysics最新文献

This study conducts an examination of the thermophysical properties of 3-methyl-3-pentanol alongside a series of short-chain alcohols, ranging from C₃ to C₆ alcohols (1-propanol through 1-hexanol), across a temperature spectrum from 293.15 K to 323.15 K. The focus of this investigation lies on the assessment of excess molar volumes and deviations in viscosity, uncovering a systematic enhancement in negative excess molar volumes as the length of the alkyl chain increases. Concurrently, viscosity analyses indicate deviations from ideality, showcasing a positive trend that diminishes with the extension of the alkyl chain. This suggests significant molecular interactions occurring between 3-methyl-3-pentanol and the examined alcohols. Further, this research incorporates the free volume theory (FVT) to draw correlations between the viscosities of both pure substances and their binary mixtures. Remarkably, the FVT demonstrates a close congruence with the experimental findings, exhibiting a maximum deviation of 2.23 % in the mixture of 3-methyl-3-pentanol and 1-hexanol. Such findings underscore the precision and utility of the FVT in elucidating the thermophysical behaviors of these mixtures, thus advancing our comprehension of their intricate molecular interactions.

We present a new extended parametric equation-of-state model for thermodynamic properties and the correlation length for a simple fluid near its liquid–gas critical point. The model involves 16 universal parameters to perfectly match 10 leading universal amplitudes of the asymptotic Ising-like limit of the critical-to-classical crossover functions calculated by Garrabos and Bervillier [Phys. Rev. E 74,021113 (2006)] from the massive renormalization scheme. The universal values of 8 Ising-like amplitude combinations are then matched exactly. The closure of the construction of parameters is determined after a careful analysis of the intrinsic limitation of parametric equations to describe the universal features at the first order of the confluent corrections-to-scaling. In the asymptotic mean-field limit, the crossover master model also reproduces the mean-field amplitude combinations except for the susceptibility case. The new model is compared with the crossover parametric model previously developed by Agayan et. al [Phys. Rev. E 64, 02615 (2001)]. The residuals from comparison with the mean crossover functions of Garrabos and Bervillier are reported to define the application range of the crossover master model to any simple fluid for which the generalized critical coordinates of the liquid–gas critical point are known.

Brown’s characteristic curves of polar fluids were studied using molecular simulation and molecular-based equation of state. The focus was on elucidating the influence of dipole interactions and the molecule elongation on the characteristic curves. This was studied using the symmetric two-center Lennard–Jones plus point dipole (2CLJD) model fluid class. This model class has two parameters (using Lennard–Jones reduced units), namely the elongation and the dipole moment. These parameters were varied in the range relevant for real substance models that are based on the 2CLJD model class. In total, 43 model fluids were studied. Interestingly, the elongation is found to have a stronger influence on the characteristic curves compared to the dipole moment. Most importantly, the characteristic curve results for the 2CLJD fluid are fully conform with Brown’s postulates (which were originally derived for simple spherical dispersive fluids). The independent predictions from the computer experiments and the theory are found to be in reasonable agreement. From the molecular simulation results, an empirical correlation for the characteristic curves of the 2CLJD model as a function of the model parameters was developed and also applied for modeling real substances. Additionally, the intersection points of the Charles and Boyle curve with the vapor-liquid equilibrium binodal and spinodal, respectively, were studied.

The heat storage system (HHS) still faces the problem of void formation as a result of the supercooling phenomenon caused by the use of paraffin. This study was conducted to analyze the effect of HTF discharge variation in the HHS system on the increase of heat storage efficiency in both the charging and discharging processes. The prototype helical coil heat exchanger is designed, fabricated, and experimentally analyzed on 4 types of helical coils with different models of fin designs: finless helical coil, straight fin, branched fin, and crossed fin. The phase change material (PCM) used is 9 kg of commercial paraffin type. The heat transfer fluid (HTF) is SAE 20W40 oil which is heated to a temperature of 210 °C with the heat source coming from the heating element. The pump is used to circulate the HTF with an output of 10 mL·s⁻¹, 11 mL·s⁻¹, and 12 mL·s⁻¹. The experimental results show that the variation of the HTF flow rate affects the melting temperature, the paraffin freezing temperature, and the power efficiency of the LHS. The highest temperature absorption by paraffin was achieved by the branch fin model at 124 °C with a discharge of 11 mL·s⁻¹, and the highest temperature release in the Branch Fin at 90 °C with a discharge of 12 mL·s⁻¹. The highest effective power achieved by the branched fin model with effective power of 73 % charge and 53 % discharge occurred at a discharge of 12 mL·s⁻¹. Varying the HTF discharge makes a positive contribution to the charge/discharge pattern, so it can be used as a reference for latent heat storage models.

The present study aimed to evaluate the heat transfer performance of three different mixtures of propylene glycol and De ionized water-based nanofluids in a mini hexagonal tube heat sink (MHTHS), as well as the influences of particle volume fraction and temperature on the thermo physical properties of nanofluids. The three different nanoparticles such as MgO, ZnO, and Al₂O₃ were dispersed in a mixture of Propylene Glycol (PG) and De ionized water (DIW) at four different volume fractions of 0.01, 0.02, 0.03, and 0.04 respectively. In colder regions, propylene Glycol was used as a better heat transfer fluid in miniature devices due to its anti-freezing properties. In this study, the experiment was conducted under two conditions First, the flow rate of DIW was maintained at 20L/h and the flow rate of three different nanofluids varied from 20 L/h to 50 L/h. Secondly, mixture proportions of 20%(PG)/80% (DIW) and 40% (PG)/60% (DIW) were taken as base fluids. The measurements of thermal conductivity and viscosity were also investigated. Experiments were performed to determine the heat transfer coefficient, Nusselt number, friction factor, and pressure drop of three different nanofluids flowing in an MHTHS were also investigated. Experimental results indicate that heat transfer coefficients and Nusselt number intensify with an increase in Volume fractions and Reynolds number. Consequently, friction factor and pressure drop were also investigated. The results revealed MgO-PG (20%)/DIW (80%) with 0.04VF results in a 36.6% enhancement in heat transfer rate compared to the base fluid. The Nusselt number for MgO-PG (20%)/DIW (80%) at 0.04VF showed an enhancement of 25.6% compared to the base fluid. ZnO-PG (40%)/DIW (60%) had a higher friction factor and pressure drop than the base fluid. Finally, the Reynolds number of nanofluids for selected velocity and contour escalated with increasing temperature and decreased with higher volume fraction. By optimizing the volume fraction of MgO-PG (20%)/DIW (80%) based nanofluids, the performance and longevity of miniature devices in colder regions can be effectively enhanced by providing an efficient cooling solution.

In this research, we explored the thermophysical characteristics of 3-ethyl-3-pentanol in combination with a selection of short-chain alcohols, specifically from C₃ to C₆ (1-propanol to 1-hexanol), over a range of temperatures from 293.15 K to 323.15 K. The exploration primarily focuses on examining both the excess molar volumes and viscosity deviations, revealing a consistent increase in negative excess molar volumes with the elongation of the alkyl chain. At the same time, an examination of viscosity presents deviations from expected ideals, displaying a positive pattern that lessens as the alkyl chain lengthens. This points to notable molecular interactions taking place among 3-ethyl-3-pentanol and the alcohols under study. Moreover, the study employed Free Volume Theory (FVT) to establish connections between the viscosities of both the individual substances and their combined mixtures. Notably, FVT closely matches our experimental data, with the largest difference seen being a 1.94% deviation in the mixture of 3-ethyl-3-pentanol and 1-pentanol. These results highlight the accuracy and relevance of FVT in providing insight into the viscosity of these mixtures, thereby deepening our understanding of their complex molecular dynamics.

A systematic study of Brown’s characteristic curves of the two center Lennard–Jones plus point quadrupole (2CLJQ) fluid was carried out using molecular simulation and molecular-based equation of state (EOS) modeling. The model parameters (elongation and quadrupole moment) were varied systematically covering the range relevant for real fluid models. In total, 36 model fluids were studied. The independent predictions from the EOS and the computer experiments are found to be in very good agreement. Based on these results, the influence of the quadrupole moment on the fluid behavior at extreme conditions is elucidated. The quadrupole interactions are found to have a surprisingly minor influence on the extreme state fluid behavior. In particular, for the Amagat curve, the quadrupole moment is found to have an almost negligible influence in a wide temperature range. The results also provide new insights into the applicability of the corresponding states principle, which is compared to other molecular property features. Interestingly, for a wide range of quadrupole moments, the fluid behavior at extreme conditions is conform with the corresponding states principle—opposite to the influence of other molecular features. This is attributed to the symmetry of the quadrupole interactions. Moreover, an empirical correlation for the characteristic curves was developed as a global function of the model parameters and tested on real substance models. Additionally, the applicability of Batschinski’s linearity law for the Zeno curve was assessed using the results for the 2CLJQ fluid.

A high-pressure vibrating tube densimeter, specified by the manufacturer for temperatures from (263 to 473) K at pressures up to 140 MPa, was tested at temperatures down to 100 K and from vacuum to pressures up to 10 MPa. To verify the functionality and overall performance under these conditions, the densimeter was calibrated with measurements under vacuum as well as methane and propane as reference fluids. The calibration range is T = (120 to 200) K at pressures from (2.0 to 10.0) MPa. To evaluate the recorded data, two established calibration models were used to describe the dependence of the densimeter's oscillation period on the investigated reference fluids' temperature, pressure, and density. The experiments showed that the vibrating tube densimeter is operational even at temperatures down to 100 K, but exhibits a shift of its vacuum resonance when subjected to thermal cycling at temperatures below 180 K. Accordingly, the calibration models were modified with respect to how the vacuum resonance is considered. Then, the determined calibration parameters reproduce the densities of the reference fluids within ± 0.10 kg·m⁻³ for the calibration model that performed better for the present study. Measurements on pure ethane and argon validate the calibration of the densimeter. Here, the densities are within (− 0.47 to 0.16) kg·m⁻³ of values calculated with the respective reference equation of state. The estimated combined expanded uncertainty (k = 2) in density for the validation measurements ranges from (0.52 to 1.13) kg·m⁻³ or is less than 0.1 % for liquid densities.

This paper focuses on falling-cylinder viscometry, a commonly used method for measuring viscosity due to its simplicity and versatility. The review explores the development of falling-cylinder viscometers, with an emphasis on their adaptability to high-pressure environment. The theoretical foundation for an ideal falling cylinder in a fluid within a rigid tube is discussed, addressing limitations arising from geometry, eccentricity, non-verticality, and entrance/exit effects. Critical Reynolds number and transient regime, are also examined. Practical aspects, including sinker design, working equations, calibration, as well as temperature and pressure influences on the constant apparatus, are discussed. By critically assessing these aspects, this review provides insights and recommendations for the effective application of falling-cylinder viscometry in both scientific and industrial contexts.

Over the past few years, eutectic solvents (ESs) have drawn the scientific community's attention because they are usually more environmentally friendly than traditional organic solvents. One of the applications of ESs is in the gas capture field, where they are considered promising absorbers to replace amine- (MEA, DEA, or MDEA processes), methanol- (Rectisol process), dimethyl ethers of polyethylene glycol- (Selexol process), N-methyl-2-pyrrolidone- (Purisol process), propylene carbonate- (Fluor solvent process), or morpholine-based (Morphysorb process) solvents on CO₂ capture from the atmosphere. Although several studies have reported experimental gas solubility data in ESs, especially for CO₂, only a few existing options are covered. In fact, resorting to experimental methods to obtain the solubility data seems unfeasible considering the vast number of possible eutectic mixtures. Therewith, theoretical predictions of gas solubility in ESs are valuable for the fast pre-screening of prospective solvents. In this work, the ability of the thermodynamic model COSMO-RS to represent solubility data of CO₂, CH₄, and H₂S in 17 choline chloride-based (ChCl) ESs was evaluated. The experimental data were collected from the literature at different molar ratios, at 298.15 K or 313.15 K, and in the pressure range from 1 to 125 bar. COSMO-RS offers a qualitative description of these gases' solubility, which was expected due to the model's fully predictive character. To improve the CO₂ and CH₄ solubility data description, a temperature–pressure-dependent correction was applied to the COSMO-RS predictions for these gases, offering a global average relative deviation of 15%.