Search Results (1,009)

Phase change materials (PCMs) have the advantage of using the latent thermal heat as energy storage. Coconut oil (CO) has attracted much attention as PCM due to its high stability against oxidation. Although the viscosity of CO-based dispersions has extensively been studied, little research has been performed on time-dependent flow behaviors. In this work, the rheological properties of fumed silica dispersed in CO at fractions of 1, 2, 3, and 4 vol.% were investigated. All suspensions showed shear-thinning behavior, which became more Newtonian at temperatures above the phase change. The 3 and 4 vol.% suspensions showed gel-like microstructures. The thixotropic properties of the 3 vol.% suspension at 30 °C and 35 °C were mainly studied through stepwise changes in the shear rate. The results were consistent with thixotropic behavior, with a complete recovery of the microstructure. The sweep frequency of this sample demonstrated the dominance of the elastic modulus at both temperatures. Therefore, a thixoelastic nature of this gel could be inferred. This gel-like material flowed under high stress, providing superior thermal damping capabilities compared to conventional fluids. A reduction of 8.65 °C was confirmed after 30 min. of the laptop power supply operation. Full article

The new passive phase change thermal storage window integrates advanced energy-saving materials and technologies to provide efficient insulation and mechanical properties. It is suitable for green buildings. Through on-site experiments and simulations in summer, autumn, and winter in Jilin City, the cyclic use function of summer insulation and winter heating has been verified. This article establishes a numerical model and compares it with measured data to verify the accuracy of the model. In order to further verify the practicality of the new window, it was applied and tested at the Yichun substation in the cold winter region. The results showed that the new window can significantly reduce energy consumption while increasing indoor temperature. This article used a refined model established by Green Building Saville and Airpak3.0 software to deeply analyze the energy consumption and temperature field distribution of the window, and verified the reliability of numerical analysis in performance prediction. This study not only proves the effectiveness of the new phase change thermal storage window but also provides a new solution for the energy-saving design of green buildings. Full article

The low thermal conductivity of phase change materials (PCMs) limits their widespread application in practical energy storage systems. The integration of fins has emerged as an effective approach to enhance PCM melting rates. This study numerically investigates the effects of fin length and tilt angle variations on PCM melting processes through two-dimensional modeling. A rectangular container with vertical constant-power heating was simulated, which incorporated natural convection effects. Initially, the analysis of equal-length fins with varying dimensions revealed that longer fins and appropriate tilt angles could significantly accelerate the PCM melting. Subsequent investigation under constant total fin lengths demonstrated that two factors enhanced the heat transfer and reduced the melting duration: large fin length differences and the enclosed regions between the fins and the container bottom. Studies of extreme tilt angles during angular variation indicated that the configuration with a 30 mm length difference with limit angles could positively affect the melting performance. The findings offer valuable insights for the optimal design of phase change energy storage systems. Full article

In this study, fumed silica (FS) was used as a support material and infused with the hydrated salt sodium hydrogen phosphate dodecahydrate (DHPD) to create shape-stabilized constant phase change materials (CPCMs). These CPCMs were integrated into a polyurethane matrix as a functional filler, resulting in low-exothermic polyurethane composite foams (CPCM-RPUFs) that demonstrate thermoregulation and flame-retardant properties. Recent findings show that CPCM-RPUF excels in thermal stability compared to pure polyurethane, with a melt phase transition enthalpy of 115.8 J/g. The use of fumed silica allows for the encapsulation of hydrated salts up to 87%, ensuring the structural integrity of the vesicles. As FS content in CPCMs increased, the internal temperature of the composite foam significantly decreased, showing excellent thermal regulation. Thermogravimetric analysis showed that the synergistic effect of DHPD and FS improved the thermal stability and flame retardancy of the composites. By monitoring the internal and surface temperature changes in the foam, it was verified that CPCMs can effectively alleviate heat accumulation during the curing process and reduce the core temperature (56.9 °C) and surface warming rate, thus realizing the thermal buffering effect. With the increase in FS content in CPCMs, the compressive strength of CPCM-RPUF can be maintained or even enhanced. This study provides a theoretical basis and technical support for the development of polyurethane composite foams with integrated thermal regulation and flame-retardant properties, which can have broad application prospects in the fields of building energy conservation, energy storage equipment, and thermal mine insulation. Full article

Phase change material (PCM) concrete walls represent a new type of energy storage wall. It is of great significance to study the fire resistance of PCM concrete walls to ensure the safety of these kinds of components in service. For this reason, fire resistance tests on eight PCM concrete partition wall specimens under the conditions of the ISO-834 standard fire curve were carried out. The tested wall structures included a solid wall and a double-layer wall with an air gap. The PCM used was paraffin phase change microcapsules, which were replaced with a fine aggregate according to the principle of equal volumes, at replacement proportions of 0%, 7%, 10%, and 14%. The test results showed that explosive spalling of the PCM concrete occurred when the double-layer wall specimen with a 10% replacement proportion was heated for 31 min, and the other seven specimens met the integrity requirements after heating for 90 min. The 100 mm thick ordinary concrete solid partition wall specimen did not meet the thermal insulation requirements after 90 min. The addition of PCM and the use of a double-layer structure with an air gap can both improve the wall’s thermal insulation performance; however, it is not the case that, the greater the amount of PCM used, the better the thermal insulation performance of the wall. The reasons that the PCM concrete spalled in the double-layer wall specimen with a 10% replacement proportion are discussed. This study provides critical insights into optimizing the PCM content and wall design for fire-safe energy-efficient buildings, offering practical guidance for sustainable construction practices. Full article

Faced with the current challenges of the energy transition and the quest for sustainable materials, biobased materials are attracting growing interest for their environmental and thermal properties. Cob is well known for regulating humidity and improving thermal comfort in buildings. A building’s thermal inertia can be increased by integrating phase-change materials (PCMs), enabling energy storage. This study explores the integration of microencapsulated PCMs into biobased materials considering realistic environmental conditions during experimental tests. The results show a homogeneous thermal distribution with low temperature variation at different locations. The relative humidity results confirm a one-dimensional thermal and hygroscopic distribution. The material with PCMs exhibits better thermal regulation. It retains more heat on the outside and reduces indoor temperature variations, improving thermal insulation. Measurements show that PCM integration contributes to reducing wall thermal conductivity and increases its thermal capacity, reaching 2.6 times during phase transition. The simulation is conducted with real 96 h Normandy climate data (January and August) for conventional and biobased walls incorporating PCMs. The results show that winter heat losses are highest for conventional walls (−44.08 kWh/m²), low for cob walls (−24.17 kWh/m²), and lowest for cob walls with PCMs (−13.17 kWh/m²). In summer, all walls exhibit the lowest heat gain, while adding PCMs stabilizes heat flux, reducing peak summer heat flux from 150 W/m² to 50 W/m². The results show that the addition of PCMs significantly improves thermal and hygroscopic performance. Full article

Dielectric capacitors with a high density of recoverable energy storage are extremely desirable for a variety of uses. However, these capacitors often exhibit lower breakdown strengths and energy efficiency compared to other materials, which poses significant challenges for their practical use. We report on a novel antiferroelectric ceramic system in the present study, (1 − x){0.97[0.985(0.93Bi_0.5Na_0.5TiO₃–0.07BaTiO₃)–0.015Er)]–0.03AlN}–xNaNbO₃ (x = 0, 10 wt%, 20 wt%, 30 wt%, and 40 wt%), synthesized via a conventional solid-state reaction approach. Here, (Bi_0.5Na_0.5TiO₃–BaTiO₃) is denoted as BNT–BT. We observed that varying the NaNbO₃ (NN) content gradually refined the grain size of the ceramics, narrowed their hysteresis loops, and transformed their phase structure from antiferroelectric to relaxor ferroelectric. These changes enhanced breakdown strength (E_b), thus increasing the performance of energy storage. Specifically, the recoverable energy density (W_rec) and energy storage efficiency (η), respectively, reached 0.67–1.06 J/cm³ and 44–88% at electric fields of 110–155 kV/cm, with the highest performance observed at 30 wt% NN doping. Additionally, over a broad range of temperature and frequency, the 70 wt% {0.97[0.985(BNT–BT)–0.015Er]–0.03AlN}–30 wt% NN ceramic demonstrated exceptional stability in energy storage. These results demonstrate the significant potential of lead-free(1 − x)({0.97[0.985(BNT–BT)–0.015Er]–0.03AlN}–xNN ceramics for the applications of high-performance energy storage. Full article

Over the past few years, the combination of solar power with refrigeration technology has matured, providing a promising solution for sustainable cooling. However, a key challenge remains, namely the inherent intermittency of solar energy. Due to its uneven temporal distribution, it is difficult to ensure continuous 24 h operation when relying solely on solar energy. To address this issue, thermal energy storage technology has emerged as a viable solution. This paper presents a comprehensive systematic review of phase-change material (PCM) applications in solar refrigeration systems. It systematically categorizes solar energy conversion methodologies and refrigeration system configurations while elucidating the fundamental operational principles of each solar refrigeration system. A detailed examination of system components is provided, encompassing photovoltaic panels, condensers, evaporators, solar collectors, absorbers, and generators. The analysis further investigates PCM integration strategies with these components, evaluating integration effectiveness and criteria for PCM selection. The critical physical parameters of PCMs are comparatively analyzed, including phase transition temperature, latent heat capacity, specific heat, density, and thermal conductivity. Through conducting a critical analysis of existing studies, this review comprehensively evaluates current research progress within PCM integration techniques, methodological classification frameworks, performance enhancement approaches, and system-level implementation within solar refrigeration systems. The investigation concludes by presenting strategic recommendations for future research priorities based on a comprehensive systematic evaluation of technological challenges and knowledge gaps within the domain. Full article

Geothermal energy is typically produced from underground reservoirs using water as the working fluid to transfer heat energy to surface and eventually to the delivery point. CO₂ has been proposed as an alternative working fluid due to its improved mobility, density and its supercritical phase state, leading thus to so-called CPG (CO₂ Plume Geothermal) systems. As a positive side effect, the injected CO₂ mass circulation in the reservoir can be considered a CO₂ storage mechanism, which, depending on the size of the porous medium, may account for few millions of CO₂ tons. Moreover, the thermosiphon effect, owned to the significant change of fluid density between the injection (cold) and the production wells (hot) as well as to its change along the wells, significantly reduces the need for pumping, hence the operating costs. In this work, we setup a mathematical model that fully describes flow in the production/injection wells doublet as well as in the geothermal reservoir. Subsequently, the model is used to evaluate the sensitivity of the beneficial effects of circulating CO₂ rather than water. Parameters such as reservoir properties, injection temperature and thermal effects, are tweaked to demonstrate the sensitivity of each one to the system performance. The results can be utilized as a guideline to the design of such systems and to the emphasis needed to be paid by the engineers. Full article

This study employs the effective heat capacity method within the COMSOL simulation framework to analyze the thermal performance of double-layer phase-change walls under typical summer climatic conditions in Zhengzhou, Henan Province. The model considers a wall structure with a total thickness of 100 mm and a height of 300 mm, where the exterior surface represents the outdoor environment, the interior surface represents the indoor environment, and the top and bottom boundaries are assumed to be adiabatic. A highly refined triangular mesh ensures numerical stability and solution accuracy. Special attention is given to the influence of Micro-PCM content on thermal storage characteristics. Simulation results demonstrate that increasing the Micro-PCM content substantially enhances the thermal regulation capacity of the double-layer phase-change walls. At a Micro-PCM volume fraction of 15%, the peak temperature of the double-layer phase-change wall is reduced by 4.33 °C compared to a conventional wall, while the attenuation factor increases to 16.88. Furthermore, the mean thermal delay extends to 440 min, the temperature amplitude decreases to 1.13 °C, and the peak instantaneous heat flux is reduced to 13.24 W/m². These findings highlight the significant latent heat storage capacity and superior thermal modulation performance of double-layer phase-change walls, offering a valuable technical reference for the design of energy-efficient building envelope systems. Full article

Energy savings issues are important in the context of building operation. An interesting solution for the southern external walls of the building envelope is the thermal storage wall (TSW), also known as the Trombe wall. The article considers four variants of the wall structure, including three containing phase change material (PCM). The purpose of this study was to determine the influence of the amount and location of phase change material in the masonry layer on the storage and flow of heat through the barrier. Each wall is equipped with a double-glazed external collector system with identical physical parameters. The research was carried out in specially dedicated testing stations in the form of external solar energy chambers, subjected to real climatic loads. The distribution of the heat flux density values was determined using experimental tests and was subjected to comparative analysis for the various variants considered using statistical analytical methods. A comparative analysis was performed between the heat flux density values obtained for each barrier in the assumed time interval from the one-year research period. The Kruskal–Wallis test and the median test were used for analyses performed in the Statistica 13.3 programme. The purpose of these analyses was to determine the occurrence of significant differences between individual heat flux flows through the barriers tested. The results obtained indicate that the use of PCM in thermal storage walls extends the time required to transfer the accumulated heat in the barrier to the internal environment while reducing the amplitude of the internal air temperature. Full article

Mobilized thermal energy storage (M-TES) systems present a viable alternative to traditional heating systems to meet the heat demands of dispersed consumers. This report uses a case study in Lebanon to provide a techno-economic evaluation of the M-TES system. The compatibility of M-TES with current heating systems was assessed by investigating the design specifications of the heating system. The results show that underfloor heating systems and fan coil heating systems are compatible with M-TES. Several operating schedules for M-TES were also developed, considering various transit methods. The study calculated the payback period (PBP) and net present value (NPV) for each case while estimating the costs and revenues for M-TES. Additionally, this study computed the quantity of CO₂ emissions reduction for different M-TES configurations. The optimal operating strategy involves using two containers and three transportation cycles per day, achieving the highest NPV, a PBP of 3 years, and a yearly CO₂ emissions reduction of 44,787.9 kg. Full article

Correlations between material properties are useful in engineering, and in addition, the underlying common mechanisms allow for a better understanding of the origins of the properties. Properties related to phase changes are an example, being important, e.g., in thermodynamic applications. For n-alkanes used, e.g., as phase change materials for thermal energy storage, linear correlations between enthalpy changes and entropy changes in phase transitions, as well as the number of carbon atoms n, have been observed and described by many researchers. Different correlations for odd and even n were found, though still with significant outliers. In this work, data from high-accuracy and high-resolution calorimetry were used for the analysis of enthalpy and entropy changes for alkanes with n = 14 to 30. The analysis shows more, and different, correlations than described in the previously published literature. Specifically, the ‘outliers’ have a physical and chemical origin, rooted in the phase transitions present in the specific n-alkanes, not just in whether n is odd or even. These detailed findings promise a better understanding of the thermodynamics of phase transitions. Full article

Green building materials refer to environmentally friendly low-consumption construction materials. Their widespread adoption is hindered by high costs, limited technological implementation, and the absence of standardized regulations. This study conducts a bibliometric analysis of 5381 publications from 2003 to 2024, sourced from the Web of Science Core Collection (WoS), applying Sustainability Transitions Theory (STT) to classify research into Niche Innovation (new materials like phase change materials), Regime Adaptation (policies and lifecycle assessments), and Landscape Pressures (climate goals and circular economy integration). The results show rapid growth in research, shifting from basic sustainability concepts to advanced materials, lifecycle analysis, and digital technologies. Key themes include energy conservation, mechanical performance, and environmental impact, with emerging trends like carbon reduction strategies, blockchain applications in circular economies, and the integration of carbon capture and storage (CCS) in construction. Future research should focus on enhancing material durability, standardizing sustainability metrics, and developing cost-effective recycling strategies to promote wider adoption. Full article

This review paper explores the emerging field of conversion cathode materials, which hold significant promises for advancing the performance of lithium-ion (LIBs) and lithium–sulfur batteries (LSBs). Traditional cathode materials of LIBs, such as lithium cobalt oxide, have reached their limits in terms of energy density and capacity, driving the search for alternatives that can meet the increasing demands of modern technology, including electric vehicles and renewable energy systems. Conversion cathodes operate through a mechanism involving complete redox reactions, transforming into different phases, which enables the storage of more lithium ions and results in higher theoretical capacities compared to conventional intercalation materials. This study examines various conversion materials, including metal oxides, sulfides, and fluorides, highlighting their potential to significantly enhance energy density. Despite their advantages, conversion cathodes face numerous challenges, such as poor conductivity, significant volume changes during cycling, and issues with reversibility and stability. This review discusses current nanoengineering strategies employed to address these challenges, including nano structuring, composite formulation, and electrolyte optimization. By assessing recent research and developments in conversion cathode technology, this paper aims to provide a comprehensive overview of their potential to revolutionize lithium-ion batteries and contribute to the future of energy storage solutions. Full article