Search Results (241)

Concrete used in high-risk infrastructures must withstand elevated temperatures and thermal shocks. This study investigated the thermal transfer behavior of explosion-proof concrete exposed to 100–400 °C through a combined experimental and numerical approach. X-ray diffraction (XRD) revealed that the dominant crystalline phases remained identifiable across this range, but peak broadening and intensity reduction indicated partial decomposition of hydration products and microstructural disorder. Thermal conductivity reached its maximum of 1.48 W/(m·K) at 100 °C and decreased at higher temperatures due to porosity growth and microcracking, reflecting detrimental alterations in heat conduction pathways. In contrast, the specific heat capacity increased from 963.89 J/(kg·K) at 100 °C to 1122.22 J/(kg·K) at 400 °C, enhancing the material’s heat absorption. Density initially decreased with temperature but showed a temporary rebound at 300 °C due to secondary hydration, before dropping sharply to 1830 kg/m³ at 400 °C. Numerical simulations confirmed that high temperatures reduce surface–core temperature gradients, leading to more uniform but structurally weakened heat transfer. These findings highlight that explosion-proof concrete retains acceptable thermal stability below 200 °C, while significant degradation occurs beyond 300 °C. The novelty of this work lies in integrating experimental thermophysical tests with finite element simulations to link microstructural changes with macroscopic thermal behavior. Practically, the results provide guidance for optimizing concrete formulations and protective strategies in fire- and explosion-prone facilities such as LNG storage units and petrochemical infrastructures. Full article

Gas coolers play a critical role in CO₂ refrigeration and heat pump systems, where their thermohydraulic characteristics substantially influence the overall system performance. To improve the heat transfer performance of gas coolers, minichannels with aligned or offset fins integrated in the channel sidewalls are proposed to enlarge the heat transfer surface and intensify the flow turbulence. Unlike conventional refrigerants, supercritical CO₂ exhibits significant variations in thermophysical properties with temperature changes, which results in distinct heat transfer behavior. Three-dimensional numerical models are therefore purposely developed by employing the Shear Stress Transport k-ω turbulent model and including the entrance region effect, NIST real-gas thermophysical properties and buoyancy effect. A constant heat flux boundary is employed on the four-side channel walls to ensure that the temperature of CO₂ flowing in the channel exactly decreases from 373.15 K to 308.15 K. The results show that the fins integrated in the channel sidewalls can significantly improve the heat transfer performance, and the heat transfer coefficient significantly increases with increasing mass flux. Compared to the reference smooth channel, the heat transfer performance is enhanced by a factor of 1.85–2.15 with aligned fins and 1.44–1.61 with offset fins. Full article

Solid–liquid phase change materials (PCMs), promising for thermal management, face limited application due to leakage and low thermal conductivity. In this work, a shape-stabilized composite PCM was fabricated using a one-pot in situ process by mixing polyethylene glycol (PEG) with the novel metal–organic network called CFK, which was synthesized from carboxylated multi-walled carbon nanotubes (CMWCNTs), FeCl₃, and Kevlar nanofibers (KNFs). The morphology, composition, and thermophysical characteristics of the composite PCM were assessed. Key properties analyzed to validate its performance included leakage rate, thermal conductivity, latent heat, light absorption, photothermal conversion efficiency, and cycling stability. This composite PCM exhibits reduced leakage while maintaining remarkable thermal energy charge/discharge performance. The study establishes that the composite PCM containing 89.9 wt% PEG has a leakage rate of 0.76% since the PEG molecules are deeply embedded in the pores of CFK. The thermal conductivity of this composite PCM was enhanced by 170.5% relative to pure PEG, and the latent heat was measured as 147.9 J·g⁻¹ for fusion and 143.7 J·g⁻¹ for crystallization. Additionally, this composite PCM reveals excellent light absorption capacity, a photothermal conversion efficiency as high as 83.4%, and outstanding stability in photothermal cycling experiments. In short, this work offers a new strategy for both preparing high-performance composite PCMs and applying them in visible light conversion. Full article

Solid particle thermal energy storage technology demonstrates extraordinary thermal stability across wide temperature ranges and possesses significant cost-effectiveness that meets stringent economic requirements for long-duration energy storage. These distinctive characteristics enable this technology to continuously support increasing decarbonization demands and drive the strategic progression of sustainable energy transformations. This review work conducts a thorough analysis of three representative reactor types: packed beds, moving beds, and fluidized beds, focusing on how particle thermophysical properties affect heat transfer and storage performance. The paper analyzes pressure drop and heat transfer correlations to reveal the coupling effects between particles and working fluids that impact system efficiency. By comparing hydrodynamic behavior across different reactor types, the study identifies optimization strategies and technical challenges. The review paper concludes by outlining future research directions for enhancing system efficiency, supporting industrial deployment, and facilitating integration with next-generation renewable energy technologies. Full article

A series of studies was conducted on the functional and structural characteristics of polymer composite materials (PCMs) based on silicone polymers modified with multi-walled carbon nanotubes (MWCNTs) and metallic particles (CuAl or Al). The influence of the structural parameters of carbon and metallic inclusions in the polymer matrix on the electrophysical and thermophysical properties of the composites was demonstrated. Various conduction mechanisms dominating in the inverse temperature ranges of 50 K^–1–13 K^–1, 13 K^–1–6 K^–1, and 6 K^–1–2 K^–1 were identified. The operational modes of the polymer composites as active materials for thermoregulating coatings were established. The highest temperature of 32.9 °C in operating mode and the shortest warm-up time of 180 s were observed in the composite modified with 4 wt.% CNTs and 10 wt.% bronze particles at a supply voltage of 10 V. The characteristics of the composites under atomic oxygen (AO) exposure with a fluence of 3 × 10²¹ atoms/cm² was evaluated, confirming their functionality, particularly for potential space applications. The composites demonstrated nearly complete retention of their functional characteristics. The aim of this study was to develop electrically conductive functional composites based on silicone polymers containing MWCNTs and metallic particles inclusions for creating electric heating elements with tailored functional characteristics. Full article

This study investigates the thermal dynamics and material behavior involved in the baking process for Lebanese flatbread, focusing on the heat transfer mechanisms, water loss, and dough expansion under high-temperature conditions. Despite previous studies on flatbread baking using impingement or conventional ovens, this work presents the first experimental investigation of the traditional Lebanese flatbread baking process under realistic industrial conditions, specifically using a high-temperature tunnel oven with direct flame heating, extremely short baking times (~10–12 s), and peak temperatures reaching ~650 °C, which are essential to achieving the characteristic pocket formation and texture of Lebanese bread. This experimental study characterizes the baking kinetics of traditional Lebanese flatbread, recording mass loss pre- and post-baking, thermal profiles, and dough expansion through real-time temperature measurements and video recordings, providing insights into the dough’s thermal response and expansion behavior under high-temperature conditions. A custom-designed instrumented oven with a steel conveyor and a direct flame burner was employed. The dough, prepared following a traditional recipe, was analyzed during the baking process using K-type thermocouples and visual monitoring. Results revealed that Lebanese bread undergoes significant water loss due to high baking temperatures (~650 °C), leading to rapid crust formation and pocket development. Empirical equations modeling the relationship between baking time, temperature, and expansion were developed with high predictive accuracy. Additionally, an energy analysis revealed that the total energy required to bake Lebanese bread is approximately 667 kJ/kg, with an overall thermal efficiency of only 21%, dropping to 16% when preheating is included. According to previous CFD (Computational Fluid Dynamics) simulations, most heat loss in similar tunnel ovens occurs via the chimney (50%) and oven walls (29%). These findings contribute to understanding the broader thermophysical principles that can be applied to the development of more efficient baking processes for various types of bread. The empirical models developed in this study can be applied to automating and refining the industrial production of Lebanese flatbread, ensuring consistent product quality across different baking environments. Future studies will extend this work to alternative oven designs and dough formulations. Full article

Ozone is a powerful destructive agent in the oxidative process of polymer composites. The destructive ability of ozone depends primarily on its concentration, duration of exposure, the type of polymer, and its matrix structure. In this work, nonwoven PLA/NR fibers with natural rubber contents of 5, 10, and 15 wt.% were obtained, which were then subjected to ozone oxidation for 800 min. The effect of ozone treatment was estimated using various methods of physicochemical analysis. The visual effect was manifested in the form of a change in the color of PLA/NR fibers. The method of differential scanning calorimetry revealed a change in the thermophysical characteristics. The glass transition and cold crystallization temperatures of polylactide shifted toward lower temperatures, and the degree of crystallinity increased. It was found that in PLA/NR fiber samples, the degradation process predominates over the crosslinking process, as an increase in the melt flow rate by 1.5–1.6 times and a decrease in the correlation time determined by the electron paramagnetic resonance method were observed. The IR Fourier method recorded a change in the chemical structure during ozone oxidation. The intensity of the ether bond bands changed, and new bands appeared at 1640 and 1537 cm⁻¹, which corresponded to the formation of –C=C– bonds. Full article

The IREQ (Insulation REQuired) index is the only reliable and effective model for predicting and evaluating the protection given by a clothing ensemble in cold environments. Even with the growth of studies aimed at assessing the thermophysical characteristics of clothing, IREQ remained unaltered from Holmér’s original formulation four decades prior. This paper focuses on the effect of the evaluation of the clothing area factor and the resultant vapour resistance on the assessment of cold environments via IREQ. Obtained results reveal meaningful variations in the duration limit exposure (up to 5 h), whereas IREQ values remain unchanged. Observed phenomena could be interesting when discussing the revision of the ISO 11079 standard, which prescribes using IREQ for the determination and interpretation of cold stress. Full article

Creating a comfortable microclimate in the premises of buildings is currently becoming one of the priorities in the field of architecture, construction and engineering systems. The increased attention from the scientific community to this topic is due not only to the desire to ensure healthy and favorable conditions for human life but also to the need for the rational use of energy resources. This area is becoming particularly relevant in the context of global challenges related to climate change, rising energy costs and increased environmental requirements. Practice shows that any technical solutions to ensure comfortable temperature, humidity and air exchange in rooms should be closely linked to the concept of energy efficiency. This allows one not only to reduce operating costs but also to significantly reduce greenhouse gas emissions, thereby contributing to sustainable development and environmental safety. In this connection, this study presents a parametric assessment of the influence of climatic and geometric factors on the aerodynamic characteristics of the air cavity, which affect the heat exchange process in the ventilated layer of curtain wall systems. The assessment was carried out using a combined analytical calculation method that provides averaged thermophysical parameters, such as mean air velocity ($V_s$), average internal surface temperature ($t_{in.s}^{av}$), and convective heat transfer coefficient (${\alpha }_s$) within the air cavity. This study resulted in empirical average values, demonstrating that the air velocity within the cavity significantly depends on atmospheric pressure and façade height difference. For instance, a 10-fold increase in façade height leads to a 4.4-fold increase in air velocity. Furthermore, a three-fold variation in local resistance coefficients results in up to a two-fold change in airflow velocity. The cavity thickness, depending on atmospheric pressure, was also found to affect airflow velocity by up to 25%. Similar patterns were observed under ambient temperatures of +20 °C, +30 °C, and +40 °C. The analysis confirmed that airflow velocity is directly affected by cavity height, while the impact of solar radiation is negligible. However, based on the outcomes of the analytical model, it was concluded that the method does not adequately account for the effects of solar radiation and vertical temperature gradients on airflow within ventilated façades. This highlights the need for further full-scale experimental investigations under hot climate conditions in South Kazakhstan. The findings are expected to be applicable internationally to regions with comparable climatic characteristics. Ultimately, a correct understanding of thermophysical processes in such structures will support the advancement of trends such as Lightweight Design, Functionally Graded Design, and Value Engineering in the development of curtain wall systems, through the optimized selection of façade configurations, accounting for temperature loads under specific climatic and design conditions. Full article

The central role of heating and cooling in energy transition has been recognised in recent years, especially with geopolitical developments since February 2022 which demand an acceleration in deploying local energy sources to increase the resilience of the energy sector. Geothermal energy is a promising and vital option to optimize heating and cooling systems, promoting sustainability of urban environments. To this end, a proper design is of paramount importance to guarantee the energy performance of the whole system. This work deals with the optimization of the technical and geometrical characteristics of borehole heat exchangers (BHEs) as part of a shallow geothermal plant that is assumed to be integrated in an already operating gas-fired DH grid. Thermal performances of three different configurations were analysed according to the geological information that revealed an aquifer at −36 m overlying a poorly permeable marly succession. Numerical simulations validated the geological, hydrogeological, and thermo-physical models by back-analysing the experimental results of a thermal response test (TRT) on a pilot 150 m deep BHE. Five-year simulations were then performed to compare 150 m and 36 m polyethylene 2U, and 36 m steel coaxial BHEs. The coaxial configuration shows the best performance both in terms of specific power (74.51 W/m) and borehole thermal resistance (0.02 mK/W). Outcomes of the study confirm that coupling the best geological and technical parameters ensure the best energy performance and economic sustainability. Full article

In response to the growing impact of the climate crisis, many countries are accelerating efforts to develop sustainable and carbon-free energy solutions. This has led to increasing interest in advanced energy storage and conversion technologies, particularly the development of high-temperature molten salt energy systems. Among these, chloride salt-based molten salt systems, which offer excellent thermal properties such as high thermal conductivity, low melting points, and favorable chemical stability, are emerging as strong candidates for thermal energy storage and heat-transfer applications. This study focuses on deriving key thermophysical properties essential for selecting suitable molten salt heat-transfer fluids by examining their eutectic points and thermal stability with respect to various salt compositions. Three chloride mixtures—NaCl-MgCl₂, NaCl-KCl-MgCl₂, and NaCl-KCl-ZnCl₂—were evaluated for potential use in high-temperature molten salt energy systems. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to measure the melting points and thermal stability of molten salts with various compositions near their eutectic regions. Experimental results were compared with predicted eutectic points to assess the thermal performance of each salt mixture. The findings indicate that the NaCl-KCl-MgCl₂ mixture exhibits the most promising characteristics, including a low melting point below 400 °C and superior thermal stability, making it highly suitable as a heat-transfer fluid in high-temperature molten salt energy systems. In contrast, NaCl-KCl-ZnCl₂ was found unsuitable for such applications due to its high hygroscopicity and poor thermal stability. This study provides essential data for selecting optimal molten salt compositions for the efficient and reliable operation of high-temperature molten salt energy systems. Full article

Energy retrofitting of historic buildings presents complex challenges, particularly when using internal insulation strategies. While such interventions can enhance thermal comfort and reduce energy demand, they can also pose risks of condensation and mold formation, thereby reducing usable space. This paper proposes an evaluation methodology for assessing the performance of internal insulating panels within a multicriteria framework to support decision-making during the design phase. The approach, scalable to various contexts, is grounded in a digital workflow that integrates heritage building information modeling (HBIM), visual programming (VP), and building energy modeling (BEM) to create a decision-support tool for renovation designers. The methodology, tested on a building located in Bologna (Italy), allows for assessing internal insulation systems with varying thermophysical properties and performance characteristics, and evaluating how they affect space- and wall-level key performance indicators, including condensation risk, energy efficiency improvement, and usable space reduction. The research was conducted under the Horizon Europe HERIT4AGES project, which aims to develop reversible, innovative insulation panels fabricated from local and recycled materials for historic building retrofitting. Full article

With the development of the agro-processing industry, the efficient cryogenic treatment and resource utilization of porcine bile—a high-value byproduct—has received increasing attention. This study investigates the dynamic behaviour and freezing characteristics of porcine bile droplets upon impact on cold substrates under varying conditions of surface temperature (−10 °C to −20 °C) and impact velocity (0.18–0.59 m/s). The effects of droplet size, dimensionless numbers (Weber, Reynolds, Bond, Ohnesorge, and Prandtl), and thermal gradients were systematically analyzed. A thermoelectric cooling substrate combined with high-speed imaging was used to quantitatively characterize the spreading ratio, retraction ratio, and freezing time of droplets. The results show that the maximum spreading ratio increases with higher impact velocity but decreases with lower substrate temperature. Lower substrate temperatures significantly shorten the freezing time, with a maximum reduction of up to 45%, particularly for smaller droplets. Droplets with high Weber numbers (We > 3) form flattened ice layers with preserved retraction patterns, while those with low Weber numbers (We < 1) generate smooth, hemispherical ice caps. For the first time, the thermophysical properties of porcine bile were incorporated into the framework of droplet impact dynamics on cryogenic surfaces. The findings reveal multiscale freezing mechanisms of biological fluids at low temperatures and provide a theoretical basis for optimizing processes such as freeze-drying and cryogenic sterilization in agro-product processing. Full article

Lead–bismuth eutectic alloy (LBE, Pb_44.5Bi_55.5) has emerged as a promising candidate for use in advanced nuclear and solar energy systems due to its favorable thermophysical characteristics and radiation shielding capabilities. The aim of this research is to assess the applicability of the induction melting technique to synthesize LBE. This paper presents a comprehensive evaluation of the structural, thermophysical, and radiation shielding properties of the obtained LBE sample. Various techniques were employed to investigate the solid-to-liquid eutectic transformation, phase composition, morphology, and homogeneity of the obtained material. Experimental and theoretical determinations on density, void, molar volume, thermal conductivity, heat capacity, thermal diffusivity, and electrical conductivity were performed. Radiation shielding performance over photon energies ranging from 0.015 to 15 MeV was simulated using the Phy-X/PSD program. The results revealed the eutectic structure comprising Pb₇Bi₃ and Bi phases with near-ideal stoichiometry and a melting point of 127.6 °C. The alloy demonstrated a small void that corresponds to a high degree of sample compaction, high specific heat capacity, moderate thermal conductivity, low thermal diffusivity, and effective radiation shielding. These findings confirm that LBE obtained by the induction melting technique possesses the necessary structural stability and functional properties for integration into nuclear reactor and solar thermal technologies. Full article

This study presents numerical analyses of the thermal, metallurgical, and mechanical processes involved in welding. The temperature fields were computed by solving the transient heat transfer equation using the ABAQUS/Standard 2024 finite element solver. Two types of moving heat sources were applied: a surface Gaussian distribution and a volumetric model, both implemented via DFLUX subroutines to simulate welding on butt-jointed plates. The simulation accounted for key welding parameters, including current, voltage, welding speed, and plate dimensions. The thermophysical properties of the INC 738 LC nickel superalloy were used in the model. Solidification characteristics, such as dendritic arm spacing, were estimated based on cooling rates around the weld pool. The model also calculated transverse residual stresses and applied a hot cracking criterion to identify regions vulnerable to cracking. The peak transverse stress, recorded in the heat-affected zone (HAZ), reached 1.1 GPa under Goldak’s heat input model. Additionally, distortions in the welded plates were evaluated for both heat source configurations. Full article