Potential Thermal Energy Research Articles

COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF NEW CONCEPT HEAT EXCHANGER FOR OTEC APPLICATION

This paper presents a comprehensive analysis of a new concept of heat exchanger for Ocean Thermal Energy Conversion (OTEC) applications. The study utilizes Computational Fluid Dynamics (CFD) simulations to evaluate the performance of different heat exchanger designs for extracting thermal energy from oceanic sources, specifically using water and R717 liquid. Key performance parameters including cold vapor fraction, temperature difference, and pressure drop are evaluated through a combination of numerical simulations and experimental validations. The analysis of the cold vapor fraction provides insights into evaporation rates and their distribution across multiple prototypes, highlighting the impact of the wetted area on heat transfer effectiveness. The evaluation of temperature differences reveals variations in discharge fluid temperatures, with some prototypes deviating from thermodynamic principles at a default evaporation frequency of 0.1. Various evaporation frequencies are simulated and compared with experimental data to select the optimal frequency for each prototype. The simulations and experiments, conducted under similar conditions, ensure accurate validation despite inconsistencies arising from variations in heat exchanger design and boundary conditions. The performance evaluation demonstrates the effectiveness of the three prototypes, with Prototype 2 achieving the highest effectiveness up to 59% for OTEC applications. The findings contribute to a better understanding of heat exchanger performance in OTEC and provide valuable insights for design optimization and future application development. This paper emphasizes the significance of efficient heat transfer and highlights the potential of ocean thermal energy as a renewable and sustainable resource.

Assessment of Geothermal Energy in Aluto‐Langano and Tulu‐Moye, Central Ethiopia

ABSTRACTThis study aims to identify the primary issues leading to the pause in geothermal energy development at Aluto‐Langano and Tulu‐Moye sites, while also exploring opportunities in new drilling wells and assessing compliance with occupational safety, health and environmental standards. The geothermal energy development status was evaluated through focus group discussions, site visits and field data collection. The Tulu‐Moye Geothermal Operation (TMGO) project is underway to establish a power plant, with a phased development spanning 6 years targeting a total capacity of 150 MW, comprising 50 MW for Phase 1 and 100 MW for Phase 2, though with some constraints. The Aluto‐I Geothermal Pilot Plant marked the initial efforts to produce electricity from geothermal sources but faced shutdown due to declining thermal energy in some wells, turbine corrosion, pentane leakage, frequent in efficiency of fans and instability of foundations. Consequently, Phase 2 of the project aims to integrate with Phase 1 wells to mitigate potential thermal energy losses. Geothermal energy development demands substantial initial investment but entails minimal ongoing costs and workforce requirements. Its eco‐friendliness benefits communities, offering higher efficiency and lower maintenance compared to hydroelectricity. Leveraging Ethiopia's geothermal potential is crucial for electricity generation, mineral extraction, and water supply, with plans involving nationwide field expansion to enhance renewable energy capacity.

A thermal flexible rotor dynamic modelling for rapid prediction of thermo-elastic coupling vibration characteristics in non-uniform temperature fields

The flexible rotors within aero-engines operate in complex thermal environments, where temperature influences both the vibration frequency and amplitude. This study establishes a simple thermal flexible rotor dynamics model to rapidly and precisely predict thermo-elastic coupling vibration characteristics within a non-uniform temperature field. The thermal potential energy of the thermal rotor element is derived for any temperature field, and the motion equation is obtained using the Euler-Lagrange equation. Specifically, the generalized vector of an arbitrary point and cross-sectional non-uniform thermal stress of the thermal rotor element are considered in the thermal potential energy. The model's frequency error is <1 % under identical boundary conditions. Numerical findings indicate that thermal stress, temperature-dependent material properties, and the coupling effect collectively reduce the natural frequency (NF), with thermal stress having a more pronounced impact under axial constraint. Additionally, thermal stress and material decrease the amplitude across a broad range of rotation speeds, contrasting with thermal bending. This model will play a key role in the iterative calculation of thermo-elastic coupling vibration control due to its accuracy and simplicity.

Geophysical modeling of the middle Bogotá River Basin with support from interpretation of electrical resistivity, gravity, seismic and borehole data to evaluate potential deep aquifers

The main objective of this research was to develop a geological and geophysical modeling to infer the geometry and thickness in the sedimentary sequence of the middle basin of the Bogotá River with emphasis on the Guadalupe Group, reconstructing the stratigraphic sequence, structural setting, hydrogeological modeling, and potential geothermal uses. Various geophysical methods were applied, including vertical electrical soundings (VES), and magneto telluric soundings (MT-VES), whose results were complemented with the interpretation of seismic lines, regional and local gravity anomaly maps, and borehole data, among others, which allowed to model the subsurface from the surface to depths beyond 3000 meters, with emphasis on the interval between 500m to 1000m depth. Integrated models were developed from interpretations of electrical resistivity data, gravity and magnetic data, reflection seismic and borehole data. Based on the results, potential deep aquifers have been proposed to be confirmed by drilling. These deep aquifers can contribute to satisfy the need for water, which historically has been explored and overexploited from shallower aquifers in this sector of the basin. A recommendation was also made to consider the potential of low enthalpy thermal energy for agro-industrial purposes associated with groundwater’s temperature at the depth of this research. As a result, the modeled sedimentary sequence is characterized by a thick quaternary overburden overlying an intensively folded and faulted Neogene, Paleogene, and upper Cretaceous formations, mainly composed of siltstone, sandstones, and shale sequences of fluvial and marine environment, including facies of marine regressions and transgressions near the coastline. The penetration obtained allows establishing a high hydrogeological potential in the first 2000m depth, especially associated with the Guadalupe group, where the Labor and Tierna and Arenisca Dura formations have the highest hydrogeological potential. In addition, the preliminary estimation of thermal gradients suggest that low enthalpy geothermal energy potential is feasible to be used for the agro-industrial demand of energy of the study area.

The role of pit lake thermal dynamics on the thermal performance of ground heat exchangers

The addition of ground heat exchangers (GHEs) to a pit lake’s basin has the potential for abundant, clean and renewable geothermal energy extraction using shallow geothermal systems. Basin-embedded GHEs avoid direct interaction with mine water, which has been shown to impact efficiency and longevity in mine open-loop geothermal systems negatively. The now accelerated closure of open-pit coal mines presents itself as an opportunity to use this technology. However, no guidelines currently exist for designing or operating GHEs embedded in the sediment of water bodies. Furthermore, the two-way coupling between the complex annual thermal fluid dynamics that lakes are naturally subjected to and heat fluxes on the sediments and the GHE system has not been explored. In this study, we develop and validate finite element models to assess the relevance of lake thermal stratification in the performance of a geothermal system embedded in water bodies basins, e.g., on open-pit mine closures, under temperate residential thermal loads. The results show that the pit lake’s role as a thermal sink improves significantly when the lake’s thermal dynamics are accounted for, with an increase of up to 292% in the lake’s available energy budget. A minor variation in energy budget (~8%) was found whether the lake is modelled explicitly or simplified as a transient Dirichlet temperature boundary condition. This small difference vanishes if horizontal circulation along the lake is considered, highlighting the lake’s thermal energy potential. Finally, the impact on the GHE Coefficient of Performance (COP) is evaluated, with a maximum of ~15% difference among all cases.

Experimental investigation of tailoring functionalized carbon-based nano additives infused phase change material for enhanced thermal energy storage

The advancement of phase change materials (PCMs) as potential thermal energy storage (TES) materials for building envelopes holds promise for efficient energy utilization. However, the PCMs have a major drawback during energy storage, which is lower thermal conductivity, leading to inadequate heat transfer performance and energy storage density. The foremost objective is to formulate a nanocomposite by dispersing functionalized multi-walled carbon nanotubes in salt hydrate PCM with the presence of surfactant. A two-step technique is employed to formulate the nanocomposites with different weight concentrations (0.2, 0.4, 0.6 and 0.8 %) of carbon-based nanoparticles and these nanocomposites are thoroughly characterized to explore the thermophysical properties. Resulting the nanocomposite demonstrates a significant improvement in thermal conductivity, increasing by 91.45 %, which can be attributed to the well-developed thermal networks with the PCM matrix. The nanocomposite samples exhibit extreme thermal stability up to 477 °C with a slight enhancement of 4.6 %. Optical investigations further confirmed that the transmissibility of PCM decreased to 8.3 % from 62.8 %, indicating an enhanced absorption capability due to the dark color nature of the nanoparticles. Moreover, the formulated nanocomposite demonstrated both chemical and thermal stability, with negligible changes in melting enthalpy even after 300 cycles of heating and cooling operations. Additionally, a numerical simulation analysis of 2D heat transfer was performed using Energy 2D software to demonstrate the efficacy of thermal conductivity in heat transfer. The thermally energized nanocomposite is suitable for medium-temperature TES applications such as photovoltaic thermal systems, building applications, textiles, electronic cooling, and desalination systems.

High thermal conductivity composite phase change material with Zn2+ metal organic gel and expanded graphite for battery thermal management

Phase change materials (PCMs) with promising potential thermal energy is stored and released much thermal energy during phase change process, which has greatly prospect in building energy conservation, waste heat recovery, energy storage, electrical vehicles (EVs) and other fields. Nevertheless, the low thermal conductivity and easy leakage of PCM is still a challenge to restrict its fasting development. Traditional supporting material is hard to reconcile antileakage and thermal conductivity of composite PCM (CPCM). Herein, the polyethylene glycol (PEG) with three-dimensional Zn2+ metal–organic gel (ZnHGL) as high-thermal conductivity support framework, styrene–butadiene–styrene block copolymer (SBS) and expanded graphite (EG) has been designed and prepared PZSE with high thermal conductivity, accompany with double transferring heat and supporting network structure. In contrast with pure PEG, the thermal conductivity of PZSE2 is increased by obvious 8.7 times when Zn2+ metal–organic gel and SBS with the proportion of 1:1, the mass maintenance rate and latent heat storage capacity are increased to 99.5 % and 103.64 J/g, respectively. Further, the thermal imaging camera indicate that PZSE2 exhibit a stable temperature-regulation property, which is benefited to extend the time to adjust the temperature. Additionally, the maximum temperature and temperature differential of the battery module with PZSE2 can be maintained within 60 °C and 6 °C, respectively, even at 1.5C discharge rate after ten cycling process. It indicates that the battery module with PZSE2 has optimum thermal management effect. Therefore, PZSE with metal–organic gel and EG can provide a promising candidate utilization in thermal regulation of EVs and energy storage.

Thermoelectric Energy Harvesting from the Roof and Attics of a Building

Globally people are faced with difficulties in environmental pollution, increasing power costs, and global warming. As such researchers are focusing on enhancing energy-harvesting using thermoelectric generators for power generation to lessen the difficulties. Through the Seebeck effect, thermoelectric generators (TEGs) have proven their ability to convert thermal energy into electric power. Given the unique benefits they present, thermoelectric generators have arisen in the recent decade as a possible alternative to other green power generation technologies. A thermoelectric generator (TEG) is a solid-state device that converts thermal energy into electrical energy. TEG consists of elements of p and n-type semiconductors, connected thermally in parallel and electrically in series. In this paper, one hundred and ninety-two thermoelectric generators connected in series and parallel were used to investigate the thermal energy potential at the roof and attic area for domestic application for 20 days from the falling solar radiation on a residential prototype in Bashar, Wase Local government area of Plateau State. A theoretical analysis was used in determining the average output power (P) due to the delta T across the thermoelectric generator module junction. The load resistance value of the thermoelectric generator configuration was evaluated. The results show that the TEG generated power output ranging from 217 mW to 1.99 W throughout the day, 5.97 mW to 13.8 mW in the morning, and 6.8 mW to 36.9 mW in the evening. Furthermore, The finding also reveals that the attic side has the capacity to store thermal energy, which can be harnessed owing to the fast heat transfer to the surroundings during the convection process. In conclusion, solar irradiance has a major impact on the system.

Evaluation of the Thermal Energy Potential of Waste Products from Fruit Preparation and Processing Industry

In the context of a changing climate and increasing efforts to use renewable energy sources and waste materials and to green the environment, new sources and technologies for energy recovery from waste are being sought. This study evaluates the possibilities of energy generation potential from waste products of fruit species used in the food processing industry. The results indicate good potential for energy use of materials from fruit processing due to low input moisture content of around 15 wt. %, an average energy lower heating value (LHV) of 16.5 MJ·kg−1, an average low ash content of 4.9% and meeting most of the emission limits of similar biofuels. Elemental analysis and combustion residue studies indicate safe operation within existing standards. The results of our analyses and experience from similar studies allow us to recommend most of the studied waste materials for energy generation use directly in processing plants at the local level.

Numerical modelling of flow and heat transport in closed mines. Case study Walsum drainage province in the Ruhr coal-mining area

High geothermal potential and multiple mine-water-based geothermal installations in Germany and other countries improve the relevance of detailed studies and modeling of promising sites. In this context, we developed a numerical model of water flow and heat transport in the Walsum mine drainage province in the west of the Ruhr coalmining area using the available data on geology, mining, water levels, pumping, and the temperatures of deep rocks and mine water. The model was validated by varying the parameters of groundwater recharge and hydraulic conductivity to achieve sufficient consistency with measured inflows and pumping rates from the central pumping facility located in the Walsum 2 shaft. The calculated mine water temperature of 30.3 ºC is close to the average of the measured temperature varied within the range of 29 – 33 ºC during the last years of mine maintenance. Using the numerical model, we evaluated the expected thermal capacity of a hypothetical open-loop circulation system and two closed-loop geothermal systems within the study area. The installation and operation of these systems would enable the generation of a thermal capacity from a few dozen kW to 1 MW sufficient for small-size to mid-size heat consumers with insignificant impact on the high thermal energy potential of the Walsum mine drainage province.

Strengths, Weaknesses, Opportunities, and Threats Analysis for the Strengthening of Solar Thermal Energy in Colombia

Colombia has made different efforts to contribute to fulfilling its international commitments to curb climate change by reducing emissions and promoting technological development and project financing. However, the existing policies and regulatory framework primarily focus on promoting the photovoltaic industry for electricity production. Likewise, the energy sector has neglected the potential of solar thermal energy as a heat source. In this sense, it is necessary to redouble efforts through new public policies that integrate solar thermal energy in the residential and productive sectors. Using solar thermal energy for heating can contribute to the energy transition and meet its sustainable development goals. Therefore, the main objective of this work was to analyze Strengths, Weaknesses, Opportunities, and Threats to determine the potential application of thermal solar heat in Colombia while considering the local context. Factors such as their environmental conditions, policies, and regulations; the existence of international agreements; and their political status in general were analyzed. The analysis revealed Colombia’s significant solar heat potential, enabling over 1.3 million cold-climate households to access hot water or reduce firewood use. Industrially, applying solar heat in 5% of the current industry could decrease fossil fuel consumption by 13 PJ. The findings highlight that Colombia’s potential in thermal solar energy necessitates collaborative efforts, legislative reinforcement, climate-adaptive measures, and the resolution of political and social challenges.

Polydopamine based silver coated cenosphere microcapsule for thermal energy storage

In the present work, low-cost and eco-friendly metallic multi-shell wall microcapsules having paraffin wax were synthesized by encapsulating them with industrial waste cenosphere. Acid etching of the cenosphere shell wall was carried out to create multiple pores through which liquefied paraffin was vacuum infiltrated. Later, metallic coating of Ag was done through surface functionalizing the microcapsule with bio-polymer polydopamine (PD). The metallic coating is adapted to provide a dual function in terms of sealing the pores as well as increasing the thermal conductivity of the microcapsules. Further, the coating also provides additional mechanical strength of the microcapsule. Scanning electron microscopy (SEM) images showed that the mean diameter of the cenospheres was ∼67 µm and the pore diameter was ∼2 µm. The thickness of the Ag coating was ∼773 nm. The Fourier transform infrared (FTIR) Spectroscopy and X-ray photoelectron spectroscopy (XPS) results of the functionalized microcapsules showed additional peaks attributing to functional groups introduced after PD polymerization. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) results inferred that the thermal storage capacity of the microcapsule was 99.92% with high thermal reliability. Furthermore, silver coated microcapsules showed ∼33% enhanced heat transfer performance than uncoated microcapsules as evidenced by TT-curve. The metallic coating at the outer shell and PCM at the inner core of the cenosphere enable it to be a potential thermal energy storage (TES) material for versatile engineering applications.

Alternative Use of the Waste from Ground Olive Stones in Doping Mortar Bricks for Sustainable Façades

The aim of achieving sustainability in construction is a reality. A useful strategy to achieve this is the use of waste from agricultural activities. This waste could reduce the environmental impacts associated with the production of raw materials such as natural aggregate, reducing energy consumption from fossil fuels and therefore CO2 emissions. This study examines the thermal conductivity of mortars doped with ground olive stones, a residual by-product of industrial processes. The objective is to evaluate the potential of ground olive stones to improve thermal insulation in construction. Ground olive stones are used as a partial replacement for the aggregates used in mortar bricks. The methodology followed herein to quantify the benefits of this product involves creating several types of mortar with a different percentage of ground olive stones in each sample (between 0% and 30%). Thermal conductivity was determined according to UNE-EN12939:2001. Finally, a case study is conducted performing an energy simulation of a residential building to determine the energy savings derived from reducing the combined thermal demands of heating and cooling and to analyse the feasibility of the alternative use of ground olive stone residue doped in mortar bricks for new sustainable façades. The results show a saving in energy demand (heating and cooling) of 0.938 kWh/m2·year when using 30% GOS-doped mortar bricks compared to the reference bricks. This is equivalent to a decrease in energy demand of 2.23% per square meter of façade. In addition, these annual energy savings are compared to the potential thermal energy created from the combustion of ground olive stones in a biomass boiler, which is the main traditional use of this waste today. It reveals that for a doping range of 5–15%, the recovery time ranges between 30 and 75 yeas, which is within the lifetime of a building. The results demonstrate the great viability of using ground olive stones as fine aggregates in mortars and their possible application in sustainable construction, in particular in more sustainable façades that allow energy savings in buildings and therefore a lower consumption of fossil, which will make it possible to reduce greenhouse gas emissions and the excessive consumption of resources.

A new evaluation framework for the assessment of wastewater heat recovery potential coupled with wastewater reuse

Abstract The integration of wastewater heat recovery (WWHR) and wastewater reuse offers a numerous advantage, making its application possible in various sectors. Nevertheless, this concept faced challenges to the identification of appropriate location. Existing research lacks comprehensive evaluation methods that encompass a various factor for effective decision-making. This study introduces a new evaluation framework that involves different aspects, including thermal energy potential and spatial distribution analysis. The novelty of this research lies in its unique focus on the combination of WWHR and wastewater reuse. Moreover, it introduces a structured evaluation framework that considers multiple criteria and expert opinions, enhancing decision-making precision. Multi-criteria decision analysis (MCDA) was applied to select assessment criteria, which were categorized into three aspects: water–energy supplier, water–energy consumers, and water–energy station. The relative importance of criteria was determined using the analytical hierarchical process (AHP). The results of the AHP highlight significance of factors: treated wastewater flow rate; treated wastewater temperature; water–energy supply distance, and type of water–energy consumer. These factors were assigned weight values of 0.297, 0.186, 0.123, and 0.096, respectively. It is emphasizing their influence in the decision-making process that potential locations depend on the water–energy supplier and water–energy consumer as supply and demand sources.

Thermal conductivity of Portlandite: Molecular dynamics based approach

Energy storage provides a greener path of efficient energy utilization. Recent trends of research suggest concrete as a potential thermal energy storage (TES) material. Its cheap commercial availability makes it one of the most deserving candidates. Cement paste is the key glue of concrete, hence performance of its major components in thermal conduction seeks thorough scientific study. Portlandite or calcium hydroxide is the second major component of cement paste, microscopically visible at a scale length of <10−4 m. Molecular dynamics (MD) simulation has been utilized to investigate the thermal transport mechanism of portlandite at an atomistic scale. The thermal conductivity of this component has been computed using three major force fields which are compared with the experimental outcome using modulated differential scanning calorimetry (MDSC). It has been observed that the simulation outcomes are in order with the experimental value but the results are sensitive to the choice of force fields. Excitation of molecules during thermal transport is predominantly governed by lower-frequency molecular vibration indicating the existence of Boson Peaks. This manuscript presents the full thermal conductivity tensor of portlandite along with the possible mechanism associated with thermal transport.

Stability assessment of alumina and SiC based refractories in a high temperature steam environment as potential thermal energy storage materials

Solar energy can be utilized not only for electricity generation but also for synthetic fuel production, making it a versatile option in the transition to a low-carbon and sustainable energy system. However, to enable economically viable solar fuel production, the development of efficient thermal energy storage (TES) materials is crucial. Ceramic materials have been identified as a potential solution for high-temperature TES applications. In this study, two commercially available refractories, alumina coated recrystallized silicon carbide and alumina-based refractory were investigated for their stability under long-term steam corrosion tests to evaluate their suitability as TES materials for a potential TES unit. X-ray diffraction (XRD) revealed that recrystallized silicon carbide is composed of two different SiC polytypes (moissanite 6H and moissanite 4H) while alumina-based refractory contained corundum and mullite. Upon being exposed to steam, both materials exhibited distinct characteristics. SiC experienced significant mass gain, a subtle lightning of its surface color and erosion of a porous alumina coating on the SiC. Amorphous silica phases were detected as an indication of oxidation of SiC from X-ray diffractrograms. These remarkable changes clearly indicate that SiC is unsuitable for use in a potential thermal energy storage (TES) unit. On the other hand, there was no significant visual changes in the alumina-based refractory and the weight change was only marginal after corrosion tests. However, XRD indicated mullite completely disappeared after steam corrosion tests possibly due to its decomposition into Al2O3 and Si(OH)4.

Ocean thermal energy conversion (OTEC) system driven with solar-wind energy and thermoelectric based on thermo-economic analysis using multi-objective optimization technique

In the present study, we investigated a multiple energy generation system based on the use of solar, wind and ocean thermal energy for the study area with high renewable energy potential. In this study, all existing capacities in coastal areas (wind, sun, ocean temperature difference) are used to design a renewable system. The present system consists of subsystems including organic Rankin cycle (ORC), wind turbine, thermoelectric, heat exchanger and flat panel solar collector. EES thermodynamic software has been used to model the system and obtain thermodynamic results. The system designed for the city of Bushehr, which has good ocean thermal energy, wind energy and solar radiation potential, has been studied. The most important effective and practical parameters in the proposed system are collector area, solar radiation, and wind turbine speed. The results of the investigation of the system in Bushehr City showed that the production power of the system is 4,840,913.8 and 1,138,957.02 kWh compared to the climate changes. Also, the amount of freshwater produced by the system is 103,495.99 and 429,080.51 m3/h compared to the climate changes. Finally, in order to optimize the designed system, the response level multi-objective optimization method has been used to find the best set of objective functions and decision variables. The two objective functions of this optimization included the exergy efficiency of the whole system and the system cost rate. The most optimal value of exergy efficiency was 13.25% and the cost rate was 72.17 $/hour.

A Study on the Drivers of Carbon Emissions in China’s Power Industry Based on an Improved PDA Method

The power industry is a major source of carbon emissions in China. In order to better explore the driving factors of carbon emissions in China’s power industry and assist the Chinese government in formulating emission reduction strategies for the power industry, this study applies the improved production-theoretical decomposition analysis (PDA) method to analyze the carbon emission drivers of China’s power industry. This study investigates the impact of energy intensity, per capita GDP, population density, power generation structure, and environmental climate on carbon emissions in China’s power industry in 30 provinces from 2005 to 2020. It was found that the carbon emission ratios of the power sector in all provinces and cities are basically greater than 1, which indicates that carbon emissions in most of the power sectors in the country are still increasing as of 2020. Overall, the effects of potential thermal fuel carbon emission efficiency, potential thermal energy consumption efficiency, the carbon emission efficiency of thermal power generation, economic scale, population density, and annual rainfall change are mostly greater than 1 and will promote the growth of carbon emissions in the power sector. Moreover, the effects of thermal power generation energy efficiency technology, thermal power generation emission reduction technology, power generation structure, and power generation per unit GDP are mostly less than 1 and will inhibit the growth of carbon emissions in the power sector. However, each of these drivers does not have the same degree of influence and impact effect for each province and city. Based on the research results, some policy recommendations are proposed.

Preparation of novel hollow metal organic framework for enhancing flame retardancy of paraffin/EP thermal energy storage materials

AbstractParaffin is a potential thermal energy storage material, but leakage and flammability are the two major problems affecting its storage and safe use. Here, a novel flame retarded paraffin/epoxy resin composite was developed by using paraffin, epoxy resin and hollow metal organic framework (W‐UiO66‐PPA) as thermal energy storage material, supporting material and flame retardant, respectively. The thermal energy storage and flame retardancy performances were examined with differential scanning calorimetry, vertical burning, limiting oxygen index and cone calorimeter tests. The results show that the paraffin/epoxy resin retains intact without leakage when the content of paraffin reaches 40 wt%, and this material exhibits high melting latent heat and remarkable thermal recycling property. In addition, the flame retarded paraffin/epoxy resin shows excellent flame retardancy, which is attributed to the following three aspects: (1) the hollow structure with open vertices of W‐UiO66 is capable of absorbing and collecting the combustible gasses produced by the combustion of epoxy resin; (2) the Zr and W elements of W‐UiO66 can facilitate catalytic charring and form a dense char layer; (3) phosphorous‐containing free radicals are able to capture OH· and O· free radicals during the combustion of paraffin and epoxy resin, thus interrupting the combustion chain reaction. On the whole, the flame retarded paraffin/EP possesses excellent thermal energy storage, thermal recycling, and flame retardancy properties. Our work provides a fantastic inspiration for the rational design of other flame retarded form‐stable phase change materials.

Realizing an Optical Micro‐Cavity in a CuCo2O4‐W‐CuCo2O4 Thin Film Stack for Spectrally Selective Solar Absorbers

AbstractTapping the potential of solar thermal energy requires spectrally selective solar absorber coatings, which lead to high photothermal efficiency. Micro‐cavities are known to dramatically enhance or suppress light absorption and emission in a directional manner and are used in nanophotonics, photodetectors, lasing, etc. Here, a dielectric‐metal‐dielectric multilayer stack with an optical micro‐cavity of a 12 nm tungsten layer formed between two dielectric layers of transition metal oxide CuCo2O4 (CCO) is designed. The CCO‐W‐CCO thin film multilayers deposited on stainless steel substrate by DC‐radio frequency magnetron sputtering achieve a 90% solar absorptance for the entire solar spectrum and a thermal emittance of 19% for the infrared spectrum. Optimization of thicknesses of individual layers is achieved by numerical simulations done in COMSOL Multiphysics, thereby reproducing the optical properties of each layer. The simulation results satisfactorily reproduce the experimental reflectance and demonstrate maximum power dissipation in the metallic layer in visible as well as NIR regions. Nevertheless, CCO material characterizations reveal that the enhanced absorption over the entire solar spectrum could be attributed to the underlying spinel crystal structure and the nanostructure film morphology.