International Journal of Thermophysics最新文献

The use of heat transfer improvement methods is crucial for enhancing energy efficiency, minimizing system sizes, lowering costs, and promoting environmental sustainability. In this context, passive (fins, nanoparticles, etc.) and active (ultrasonic, magnetic field) heat transfer improvement methods are applied to the thermal systems. However, relatively few studies have examined the combination of nanofluid and ultrasonic enhancement. Taking advantage of this gap in the literature, this study presents the first systematic experimental investigation of a CuO/water nanofluid in laminar flow regime combined with low-power (P_us = 5 W) ultrasound (US), focusing on the synergistic effects on thermohydraulic performance. For this purpose, a heat flux of q″ = 2250 W·m⁻² was applied to the surface of a smooth tube made of copper, and two different volumetric concentrations (φ = 0.01% and 0.05%) of CuO/water nanofluid were passed through it at four different Reynolds numbers (Re) of 500, 825, 1500, and 1780. In addition, US was applied at a frequency of f = 25.7 kHz at the entry section. The average Nusselt number (Nu) was found to increase with both the increase in Re and the application of US. With the application of US, the average Nu values of the systems containing water, φ = 0.01% and 0.05% CuO/water nanofluids were increased by 11.0 %, 2.0 %, and 4.0 %, respectively. However, when the nanofluid concentration was increased to φ = 0.05%, the average Nu decreased compared to φ = 0.01%, which was considered to be due to increased viscosity and particle agglomeration. The average friction coefficient (ff) increased with both nanofluid use and US. In experiments with water, an average of 20% increase was obtained with the US application, while increases of 15% and 10% were observed with φ = 0.01% and 0.05%, respectively. In measurements performed under NUS (non-ultrasonic) conditions, it was determined that φ = 0.01% and 0.05 % CuO/water nanofluids increased the friction in the system by 11.0% and 15.7 %, respectively. In terms of Performance Evaluation Criteria (PEC) analyses, the use of φ = 0.01% CuO/water nanofluid was more favorable than φ = 0.05%. Although PEC was higher in US conditions at low Re, NUS conditions were found to be more advantageous, as the average PEC values obtained under NUS conditions were 3.0% higher compared to US conditions. These findings demonstrate that the use of low-concentration nanofluid and optimal US application is critical to efficiency in heat transfer systems.

This study investigates thermal energy transport in a microscale heterogeneous thermoelectric system. It is common knowledge that a finite time is needed to complete any physical interactions in materials. The two most essential factors in thermal sciences are the heat flux vector and temperature gradient, which occur at different times during the transport process. This leads to the concept of thermal lagging. The dual-phase-lag model is utilized to determine the interaction of these two factors, as mentioned earlier, by using two relaxation constants, ({tau }_{T}) and ({tau }_{q}), to explore the lagging behavior. The magnitudes of these two constants play an essential role in energy transport in microscale and nanoscale thermal systems. A high-order hyperbolic partial differential equation is utilized to determine the cause-and-effect interaction for a particular pair of relaxation constants. Ultimately, one needs to solve a coupled, but moderately simple, system of finite difference equations that involves the temperature and heat flux simultaneously. The effects of relaxation constants and temperature-dependent material properties in semiconductor thermoelements are thoroughly examined. The microscale heat transport phenomenon plays a significant role in thermal management technology. The study confirmed that the dual-phase-lag model is an appropriate design tool for engineers in the thermoelectric industry.

The thermophysical properties of choline salicylate ([Ch][Sal]), an active pharmaceutical ingredient ionic liquid (API-IL), in (0.1, 0.2, and 0.3) mol‧kg⁻¹ aqueous amino acids (_L-alanine, _L-proline, _L-arginine) solutions have been measured at 298.15 K. Density, speed of sound, viscosity, refractive index, and electrical conductivity of [Ch][Sal] in these solutions at varying concentrations were measured. The standard partial molar volumes, (mathop Vnolimits_{varphi }^{0})  , partial molar isentropic compressibility’s, (kappa_{varphi }^{0}) , viscosity B-coefficients, molar refractions, (mathop Rnolimits_{D}), ion association constants, K_A, and limiting molar conductivities, Λ⁰, were derived. The values of (mathop Vnolimits_{varphi }^{0}) for [Ch][Sal] increased from 196.76 cm³‧mol⁻¹ to 200.56 cm³‧mol⁻¹ in _L-alanine solutions but decreased to 192.03 cm³‧mol⁻¹ in _L-arginine solutions, indicating stronger ion-polar interactions with _L-alanine. Similarly, (kappa_{varphi }^{0}), shifted from negative in water to positive values for _L-alanine and remained positive for _L-proline and _L-arginine, suggesting hydrophobic effects in longer alkyl chains. The viscosity B-coefficients showed an increasing trend in _L-arginine solutions, indicating stronger solute–solvent interactions. To further investigating the interactions in the studied systems, COSMO-based analysis was employed. Results indicate the presence of strong ion-polar interactions between [Ch][Sal] and _L-alanine. These results provide crucial insights into the physicochemical behavior of API-ILs in biologically relevant systems.

Trombe walls represent an effective passive solar heating strategy that can significantly improve indoor thermal comfort and building energy efficiency. However, their overall performance strongly depends on geometric configuration and heat transfer enhancement techniques, which remain under continuous optimization. This study investigates how the integration of V-shaped fins influences the thermal behavior and energy performance of a Trombe wall system. Four fin configurations: 6, 8, 10, and 12 fins were examined experimentally and numerically under controlled conditions (ambient temperature of 16 °C and solar radiation of 750 W m^–2). A three-dimensional CFD model was developed and validated using ANSYS FLUENT based on the finite-volume approach, while experimental data were used for verification. The results demonstrate that increasing the number of fins enhances both convective heat transfer and airflow circulation inside the wall. The thermal efficiency increased from 18.20 % for the unfinned configuration to 26.46 % for the 12-fin case, corresponding to a 45.38 % improvement. Numerical and experimental results showed close agreement, with deviations ranging from 1 to 3 °C. The findings confirm that incorporating V-shaped fins substantially improves the thermal performance and temperature uniformity of Trombe walls, providing an effective design pathway for sustainable and energy-efficient buildings.

A wide-ranging model for the viscosity surface of methane (CH₄) was developed with a range of validity from the triple-point temperature to 625 K and pressures up to 1000 MPa. An extensive literature survey was undertaken and all available experimental data, to the extent of our knowledge, were considered in the development of the model. The correlation incorporates recent ab initio results for the dilute-gas contribution, Rainwater–Friend theory for the initial density dependence, and an empirical contribution for higher densities obtained using recently developed open-source symbolic regression software. The estimated uncertainty of the correlation (at k = 2) varies from a low of 0.13 % for the gas at pressures below 1 MPa over temperatures from 210 K to 392 K, to 0.8 % to 2 % depending on the temperature for the mid-pressure range of 1 MPa < p < 50 MPa, and is 4 % for pressures from 50 MPa to 1000 MPa for temperatures from 223 K to 625 K. In the liquid region at pressures up to 33 MPa, the estimated uncertainty is 3 %.

In the present study, hemoglobin calibration curves were developed by photoacoustic spectroscopy (PAS) using hemoglobin solutions with controlled concentrations. Two types of samples exhibiting different optical properties were obtained: optically opaque (20–180 mg/mL concentrations) and optically transparent (0.0312–2 mg/ml concentrations). Optical absorption spectra were recorded in the wavelength range of 250–750 nm. From these spectra, the Soret band absorption peak at 412 nm and a secondary absorption at 450 nm were identified, and their ratio was determined. The ratios, plotted as a function of hemoglobin concentration, were fitted to the most suitable mathematical model, enabling the estimation of unknown hemoglobin concentrations in various biological samples, both optically opaque (e.g., blood and organs) and optically transparent (e.g., urine and plasma). The results show a strong correlation between the photoacoustic signal and hemoglobin concentration, validating the applicability of this technique to complex biological systems. Accurate quantification of hemoglobin in biological media is essential for the diagnosis and monitoring of numerous diseases. PAS proves to be a reliable tool for clinical and biomedical research applications, offering advantages in sensitivity, specificity, and minimal sample volume requirements.

Synthetic hydroxyapatite is a biomaterial widely used for the production of medical ceramics and coatings, but its thermophysical properties have not been sufficiently studied. In this work, a comprehensive study of the thermal conductivity and the thermal diffusivity of ceramic samples sintered at different temperatures was carried out for the first time. The thermal diffusivity was measured over a wide temperature range (up to 1325 K) using the laser flash method. The isobaric heat capacity of hydroxyapatite was studied using the method of differential scanning calorimetry. Based on the obtained experimental results, the thermal conductivity was calculated. It was shown that with increase in the sintering temperature of green body up to 1473 K, its density increases (from 1955 kg·m^–3 to 2844 kg·m^–3), which leads to an increase in thermal diffusivity (from 0.196 m²·s^–1 to 0.460 m²·s^–1) and thermal conductivity (from 0.281 W·(m·K)^–1 to 0.963 W·(m·K)^–1) for a material having a temperature close to room temperature (293 K). Measurements at high temperatures indicate that the thermal diffusivity and the thermal conductivity of hydroxyapatite depend not only on the material density and temperature, but also on the concentration of hydroxyl groups in the hydroxyapatite crystal lattice. Increasing the material density shifts the thermal diffusivity and the thermal conductivity curves to higher values. The complete absence of hydroxyl groups, which is characteristic of the oxyapatite state, significantly changes the shape of the curve. The investigation indicates the importance of taking into account the degree of hydroxylation of apatite as it changes thermal properties of the material, which is very important and can be crucial in the manufacture of ceramic products.

In the pig houses with mist cooling systems, the layout design of airflow and spray is the important factor affecting the cooling effect of pigs. However, there is currently insufficient understanding of heat and mass transfer characteristics of pig-water-wet air (PWWA) under different design parameters. In order to guide the structural design of systems, the heat and mass transfer characteristics are analyzed for PWWA in a developed model based on heat–mass transfer theory and multi-model coupling method. The model is validated based on experimental data from literature. The results show that the maximum uncertainty between simulation and literature data is 9.1 %. Meanwhile, the influences of different design parameters are analyzed for the heat and mass transfer characteristics of PWWA. It can be found that when the spray height is 800–1200 mm and the spray angle is 40–80°, compared with other three nozzle shapes, the cooling performance between pigs and spray water can be improved when using solid-shaped nozzles. Further, this effect can be strengthened at lower spray heights. Through scheme comparison, the optimal structural design scheme is obtained for the mist cooling system. It is recommended to use a design scheme with s-shaped nozzles, a spray angle of 20° and a spray height of 700 mm. This is because compared with other schemes designed to obtain the optimal heat transfer rate and unit length pressure drop, the disturbance can be significantly increased for wet air around pigs and the mass transfer rate is not significantly changed for water-wet air under the recommended scheme. Although compared with the scheme designed to obtain optimal mass transfer rate, the mass transfer coefficient between spray water and wet air under the recommended scheme decreases by about 10 %, its heat transfer coefficient and unit length pressure drop increase by at most 42.7 % and 13.4 %, respectively. This study can provide a forward-looking theoretical guidance for the pre-design and application evaluation of mist cooling systems in pig houses.

Deep eutectic solvents (DESs) have been the subject of interest in literature with a focus on replacing traditional solvents due to their green solvent’s characteristics. This study presents the experimental data on preparation and physicochemical properties of choline chloride and propionic acid deep eutectic solvent (CC:PA DES) and their aqueous binary mixtures in (298.15 to 353.15) K temperature range. The experimental density ((rho)) data are fitted well by second degree polynomial equation in T. Molar entropy (({S}^{0})) and Lattice energy (({U}_{pot})) are also calculated to explain the behavior of thermodynamic properties. Excess molar volume (({V}^{E})) is showing positive deviation from ideal behavior and the minimum of ({V}^{E}) vs. ({x}_{1}) lies at ({x}_{1}=0.5) (({x}_{1}) = mole fraction of CC:PA DES in binary mixture). Plot of ({overline{V} }_{i}^{E}) vs. ({x}_{1}) also cross each other at ({x}_{1}=0.5). which supports the dominance of specific interactions. Viscosity deviation ((Delta eta)) is observed at ({x}_{1}=0.8), supporting the interstitial accommodation of components molecules into each other. Comparison of Vogel–Fulcher–Tammann (VFT) equation and Arrhenius equation to investigate the temperature dependence of viscosity ((eta)) for ({x}_{1}=0-1.0) shows that VFT is better fitted model in studied temperature range T = (298.15 to 353.15) K. We demonstrated that the PC-SAFT equation of state can reliably predict the density of the pseudobinary CC:PA DES + water system. In addition, PC-SAFT was capable of correctly capture the qualitative behavior of the excess molar volume.

As a direct way to obtain energy for hydrogen fuel cell vehicles, the hydrogen filling has been of great concern for its filling rate, quality and safety. However, there is a lack of indicators to scientifically evaluate the comprehensive performance of different filling strategies. To solve the above problem, a numerical model of hydrogen storage tank (HST) filling with fluid–solid coupling on the inner wall surface is established, and a comprehensive evaluation indicator is determined by using the analytic hierarchy process and entropy method in this study. The results show that the surface temperature of the outer wall of the HST and the maximum temperature difference between the hydrogen zone and the inner wall surface are the key indicators for evaluating the safety of the filling process. Moreover, the comprehensive evaluation indicator has five sub-indicators, with filling time having the greatest influence (59.06%) and state of charge having the least (0.66%). More importantly, the identified comprehensive evaluation indicator can be carefully and accurately evaluated according to user preferences while ensuring a certain degree of objective evaluation. These findings provide new ideas and important references for the evaluation study of the HST filling process.