International Journal of Thermophysics最新文献

Novel nano-enhanced phase change materials (NEPCMs) for vaccine storage applications have been developed for vaccine transportation. Phase change materials (PCMs) are highly regarded due to their excellent heat storage capacities and their ability to operate within a limited temperature range. Nonetheless, their low thermal conductivity restricts their applicability. A binary mixture of caprylic acid (CL) and capric acid (CA) with a weight fraction of 58:42 was developed for the passive cooling application. The CL–CA binary mixture exhibits a melting enthalpy (H_m) of 119.07 Jg⁻¹ and a melting temperature (T_m) of 7.66 °C. Boron nitride (BN) was used as a thermal conductivity enhancer for the above binary mixture. BN was added in various weight percentages of 0.5 %, 1 %, 1.5 %, and 2 % in the binary mixture to develop NEPCMs. There was an improvement of 12.1 % in thermal conductivity for 2 % BN from the base binary mixture. Furthermore, thermal cycling has been done and the samples have maintained stability and phase change characteristics as confirmed using FTIR (Fourier transform infrared spectroscopy), thermal conductivity, and DSC (differential scanning calorimetry).

Carbon dioxide (CO₂), as a natural working fluid, is blended with hydrofluorocarbons (HFCs) or hydrofluoroolefins (HFOs) that exhibit favorable thermodynamic properties. By modifying the mixture composition, the performance of the refrigeration system can be optimized in terms of efficiency and operational conditions. However, comprehensively evaluating the thermodynamic properties of CO₂-based mixtures through experimental measurements alone remains challenging due to the complexity, expense, and time involved. This highlights the critical necessity for advanced computational methods to enhance and extend experimental research. In this study, molecular dynamics (MD) simulations were employed to comprehensively investigate the vapor–liquid phase behaviors and surface tension properties of CO₂, R32, and R134a in their pure, binary, and ternary components, respectively. The MD results show good agreement with our previous Gibbs Ensemble Monte Carlo (GEMC) simulations and the experiment-derived correlations from REFPROP program, demonstrating the precision and dependability of the employed force field and molecular methodology. These findings validate that molecular simulation, when coupled with a well-parameterized potential energy function, can effectively characterize essential thermophysical properties and fill data gaps where experimental measurements are limited. The methodology provides a solid foundation for subsequent research on refrigerant mixture behavior and offers valuable insights for the optimization and design of thermal cycle systems.

By the measurement of frequency and damping time of surface oscillations, excited by a short pulse on a freely floating liquid droplet, the surface tension and viscosity of the liquid can under certain conditions contactlessly be determined. The conventional physical models connecting these material properties with the corresponding measurement quantities are the well-known Rayleigh and Lamb formula. However, the use of these formulas in oscillating drop experiments does not always deliver physically reasonable results especially in the case of thin fluid liquids. Among others, this is due to the fact that both equations result from calculations of the fluid flow inside the oscillating liquid droplet which are based on the simplified linearized Navier–Stokes equation neglecting its substantially appertaining nonlinear convective term. In the following, the theoretical basis of the Rayleigh and Lamb formulae is investigated in more detail. Furthermore, criteria are derived to provide limits for the reasonable application of these equations.

Clathrate-hydrate-based tritium separation from isotope water is a promising process for removing tritium that is not effectively separated by conventional methods. Clathrate hydrates (hereafter hydrates) are crystalline compounds composed of water and guest molecules. Hydrate-based tritium separation utilizes the property that heavy water (D₂O) forms hydrates under milder temperatures than light water (H₂O). Efficient industrial operation requires a guest compound that forms hydrates at high temperatures and low pressures and has a large difference in phase equilibrium temperature between H₂O and D₂O hydrates (ΔT_DH). In this study, we measured the phase equilibrium conditions of D₂O hydrates formed with HFC-134a, HFC-32, and HFC-23. The formation of D₂O hydrates with these guests can be a route to tritium separation through co-precipitation of T₂O. HFC-134a formed hydrates under the mildest conditions, with ΔT_DH values of 2.8 K, 1.8 K, and 2.4 K for HFC-134a, HFC-32, and HFC-23. In addition to the three investigated guests, the potentials of propane, cyclopentane, and cyclopentane + CO₂ hydrate systems for hydrogen isotope separations were also compared, suggesting that HFC-134a and cyclopentane may be suitable guests for tritium separation. Present and previous studies have also shown a strong positive correlation between the hydration number and ΔT_DH (correlation coefficient = 0.76). This trend may be ascribed to the fact that a higher proportion of water molecules in the hydrate amplifies the effect of replacing H₂O with D₂O. These results indicate that the equilibrium conditions of D₂O hydrates may be approximately predicted to identify suitable guests for tritium separation.

This article main aim is to propose new heat transfer fluids having polyethylene glycol mixtures or PEG 200 as a base fluid. Polyethylene glycols were lately studied as possible heat transfer fluids and several encouraging results were highlighted in the open literature. One of the main concerns is related to their relatively low thermal conductivity (i.e., around 0.2 W·m⁻¹·K⁻¹) and this study aims to give a good referential in terms of thermal conductivity and effusivity at experimental level on a number of polyethylene glycol mixtures enhanced with two kinds of nanoparticles: MWCNT and MgO. The experiment was performed on 28 samples with different concentrations of nanoparticles and the results showed an increase in thermal conductivity when nanoparticles are added, upsurge that is correlated with the nanoparticle type, concentration, as well as the base fluid type. Nevertheless, the host fluid properties influence was found to be relevant when small fractions of nanoparticles are employed, regardless of the nanoparticle type. Both the thermal conductivity and effusivity augmentation were noticed to linearly depend with nanoparticle loading, while the temperature influence was a second-degree polynomial one.

For long-term sustainability, governments and industries worldwide are actively implementing innovative strategies to meet the growing energy demands across the globe simultaneously mitigating environmental impact. Effective energy storage offers a viable solution for supporting renewable resources and addressing the rising energy needs. The thermal storage capabilities of phase change materials (PCMs) for temperature regulation have garnered considerable attention from researchers. Yet, the practical use of PCMs is hindered by their poor thermal conductivity and leakage issue. Addressing this limitation through innovative enhancement methods can substantially improve heat transfer rates and overall system performance. This review article begins with a comprehensive examination and effect of the thermophysical properties of various PCMs. The different methods of heat transfer enhancement techniques of PCMs are explored broadly highlighting the importance of nano-enhanced PCMs (NePCMs) and shape-stabilized PCMs. This review aims to explore the current state of research and discuss future trends by offering readers valuable insights into Artificial Intelligence regarding the fundamental aspects of PCM heat transfer and applications. Finally, enhancing the properties of PCMs has a direct influence on temperature regulation and energy storage, thus promoting sustainable energy use. This review thoughtfully integrates both foundational concepts and practical applications, making it an excellent starting point for newcomers while also providing seasoned experts with a current and critical overview of the field.

Heat carrier fluids are becoming increasingly important in modern energy systems, enabling improved efficiency and functionality in applications such as 5th generation district heating, district cooling, geothermal systems and data centre cooling. These fluids, often glycol- or ethanol-based, play a critical role in heat transfer processes, where the accurate determination of their specific heat capacity is essential. Specific heat capacity not only influences the design and operation of such systems but is also a key parameter for the reliable calculation of heat quantities, particularly in monetary billing. However, while the specific heat capacity of water can be measured with low uncertainty, the determination of this property for other heat carrier fluids often involves greater uncertainties. This paper presents the results of an interlaboratory comparison to evaluate the uncertainty with which the specific heat capacity of common heat carrier liquids can be measured under typical laboratory conditions. The findings aim to highlight the achievable uncertainty, identify potential sources of uncertainty, and provide guidance for improving measurement reliability in routine laboratory practice.

Phase-change materials (PCMs) with crystalline structures and high latent heat of fusion have gained significant attention for thermal management and energy storage applications. In this study, PCM microcapsules were synthesized via interfacial polymerization combined with a solvent–nonsolvent technique, using paraffin wax with the melting point of 46–48 °C, as the core material and a room-temperature vulcanized silicone rubber as the shell. The microcapsules were embedded into flexible high-temperature-vulcanizing silicone rubber to fabricate a surface-adaptable thermal regulation system. Characterization using Fourier-transform infrared spectroscopy, attenuated total reflection, and field emission scanning electron microscopy confirmed successful paraffin wax microencapsulation, with a dominant particle size around 2 µm. Thermal performance evaluations showed that incorporating 30 wt.% paraffin wax microcapsules enhanced thermal stability and achieved an energy absorption efficiency of approximately 50% in a single thermal cycle. Kinetic analysis of the melting and crystallization processes revealed key characteristics of the phase transition behavior in the encapsulated state. The system also exhibited a specific heat capacity of up to 6500 J·kg⁻¹·K⁻¹ during melting. When applied to an electronic circuit board, the fabricated PCM system delayed the temperature increment by more than 75% compared to the control, demonstrating strong potential for electronic thermal management.

The increasing demand for sustainable construction materials has motivated research on recycled fiber (RF) insulation derived from textile and banner waste. In this study, RF insulation panels were fabricated by thermal compression without chemical binders at two target densities (150 and 200 kg·m⁻³). Their fundamental thermophysical properties—including bulk density, porosity, thermal conductivity, and vapor resistance—were experimentally characterized. The measured thermal conductivity ranged from 0.037 W·m⁻¹·K⁻¹ to 0.062 W·m⁻¹·K⁻¹, depending on fiber type and density, confirming the sensitivity of thermal transport to moisture-related sorption behavior. Long-term hygrothermal simulations using WUFI (Wärme Und Feuchte Instationär) were conducted to evaluate moisture accumulation, mold risk, and heat transfer dynamics under the hot-humid summers and cold-dry winters of Seoul, South Korea. Results revealed that RF insulation exhibited strong moisture buffering capacity, with mold indices decreasing below critical thresholds within three years. Compared with expanded polystyrene (EPS), RF insulation required a minimum thickness of 0.15 m to achieve equivalent thermal resistance. To further enhance sustainability, a hybrid wall assembly combining cross-laminated timber (CLT) with RF insulation (CLT_RF) was proposed. Life-cycle analysis indicated a reduction of approximately 17.47 tCO₂-eq in embodied carbon compared to reinforced concrete. Among the tested samples, mixed-fiber insulation (M40) achieved the best balance of thermal performance, hygrothermal safety, and environmental benefits. This work highlights the potential of recycled fiber insulation as a thermophysically reliable and environmentally viable material for low-carbon building envelopes.