[en] Thermal energy storage is a technology under investigation since the early 1970s. Since then, numerous new applications have been found and much work has been done to bring this technology to the market. Nevertheless, the materials used either for latent or for sensible storage were mostly investigated 30 years ago, and the research has lead to improvement in their performance under different conditions of applications. In those years a significant number of new materials were developed in many fields other than storage and energy, but a great effort to characterize and classify these materials was done. Taking into account the fact that thousands of materials are known and a large number of new materials are developed every year, the authors use the methodology for materials selection developed by Prof. Ashby to give an overview of other materials suitable to be used in thermal energy storage. Sensible heat storage at temperatures between 150 and 200 C is defined as a case study and two different scenarios were considered: long term sensible heat storage and short term sensible heat storage. (author)

[en] Despite the strong request coming from the CSP industry, the design and synthesis of new materials with enhanced heat capacity is still suffering from the lack of a fundamental knowledge on the heat capacity enhancement mechanisms. New materials obtained by adding nanoparticles to nitrates have been investigated, but almost exclusively from the experimental point of view. In this theoretical study we will illustrate, for the first time, the mechanisms generating the variation of heat capacity in nanomaterials (NMs) and, accordingly, we will give indications on the design criteria of new materials with improved thermal properties. Starting from a comprehensive set of molecular dynamics calculations, we analyse the results via ad hoc-developed relations on non-ideal mixtures of nanoparticles in bulky materials. These goals are reached by studying silica nanoparticles in nitrates, which are prototype materials for TES. The density profiles of the atoms at the silica/KNO₃ interface show the formation of liquid like interfaces in the solid phase, and of solid-like interfaces in the liquid phase. These characteristics of the interfaces translate in a cP enhancement of the solid nanomaterial, and in a cP decrease of the liquid nanomaterial with respect to the bulk suspending KNO₃

No abstract available

[en] The phase change materials (PCMs) have ability to store and release energy over a narrow range of temperature making these materials potential aspirants for energy redistribution. Microencapsulation of the PCM overcomes the limitations faced by the direct incorporation of the PCM into the base fluid for cool thermal energy storage applications. In this study, the microencapsulation of the dimethyl adipate as peM using organic melamine formaldehyde as shell material has been carried out through polymerization technique. The as-prepared microencapsulated PCM (MPCM) was characterized using the FESEM, FTIR, DSC and TGA techniques. The microstructural analysis carried out using FESEM as depicted in the article infer that, the MPCM being formed exhibited good surface morphology and the microparticles were almost spherical in shape with an average size of 2.8 μm

[en] Recently, electronic and electrical products have problems how to reduce heat in trend reducing size and increasing speed. heat pipes worked by latent heats can solve problems for effective and quiet electronic applications. Heat Pipes have to be suitably designed for the external conditions due to showing optimum performance. it has influence on efficiency of heat pipes to the exterior structure changed by length, bending angle, diameter. Designing heat pipes has depended on experience from trial and error. this method wasted too many resources, but can't guarantee efficiency. to prevent those wastes, this study aims at making the thermal transfer coefficient predicting efficiency. In this study, the thermal transfer coefficient has been made from experimental results that used variables - lengths between heat source and radiation, bending angles, diameters of heat pipes. variables become non-dimensional in modeling process for making the coefficient

[en] Short communication

[en] Highlights: • An optimal design principle (ODP) and a new design procedure are presented. • Optimization and improvement of helical HTF tube are conducted based on the ODP. • U-shaped double helical tube is determined as the optimal structure of HTF tube. • Improvement of reaction bed achieves reductions of material and energy consumption. - Abstract: Metal hydride (MH) is an attractive alternative for thermochemical heat storage. This study proposes an optimal design methodology for MH heat storage reactors (MHHSRs), integrating the optimal design principle (ODP) and a new design procedure. Based on the optimal design methodology, the design of the powder bed with helical heat transfer fluid (HTF) tube is conducted via numerical simulation. A mathematical model is established for the thermal coupling between the powder bed and the HTF tube. The gravimetric exergy-output rate (GEOR) is adopted to evaluate the overall discharging performance. First, the helical HTF tube is optimized and improved based on the ODP, which increase the GEOR from 198.4 to 255.4 W kg⁻¹. The optimal helical diameter is 30 mm and the optimal improved structure is determined as a U-shaped double helical tube. Then, the structural improvement of the reaction bed is supplemented, achieving reductions of material and energy consumption by 12.2% and 11%, respectively. The final design of the powder bed with helical tube based on optimal design methodology improves the GEOR from 198.4 to 306.1 W kg⁻¹, which constitutes a significant increase of 54.3%. This optimal design methodology is validated and efficiently guides the design of advanced MHHSRs.

[en] A hybrid numerical method is developed to solve one-dimensional phase change problems with the mushy zone. This hybrid numerical method involves the control volume formulation for the space domain and the Laplace transform technique for the time domain. In the present study, nonlinear terms are linearized by using the Taylor series approximation. The growth of the mushy zone is unknown a priori and is predicted by using the least squares concept. To show the efficiency of the present numerical method, various comparative examples are illustrated. It can be seen that excellent agreement is observed between present numerical results and those of early works

[en] TES (Thermal energy storage) can enhance energy systems by reducing environmental impact and increasing efficiency. Thermochemical TES is a promising new type of TES, which permits more compactness storage through greater energy storage densities. In this article, closed and open thermochemical TES is investigated using energy and exergy methods. The latter method enhances assessments of made using the former. Efficiencies based on energy and exergy are determined for the overall storage cycle and its charging, storing and discharging processes. Examples using experimental data are presented to illustrate the analyses of closed and open thermochemical TES. The overall system energy and exergy efficiencies, respectively, are determined to be 50% and 9% for the closed storage, and 69% and 23% for the open storage. The results suggest that there is a significant margin for loss reduction and efficiency improvement for closed and open thermochemical storages, since the exergy efficiencies of both are significantly lower than the energy efficiencies.

[en] Highlights: • This paper analyzes the performance of a building-integrated thermal storage system. • A wall opposing a glazed surface serves as phase change materials thermal storage. • The study is based on both experimental and simulation studies. • Heat is stored and released up to 6–8 h after solar irradiation. • Yearly heating requirements are reduced by 17% in a cold climate. - Abstract: As energy availability and demand often do not match, thermal energy storage plays a crucial role to take advantage of solar radiation in buildings: in particular, latent heat storage via phase-change material is particularly attractive due to its ability to provide high energy storage density. This paper analyzes the performance of a building-integrated thermal storage system to increase the energy performances of solaria in a cold climate. A wall opposing a highly glazed façade (south oriented) is used as thermal storage with phase change materials embedded in the wall. The study is based on both experimental and simulation studies. The concept considered is particularly suited to retrofits in a solarium since the PCM can be added as layers facing the large window on the vertical wall directly opposite. Results indicate that this PCM thermal storage system is effective during the whole year in a cold climate. The thermal storage allows solar radiation to be stored and released up to 6–8 h after solar irradiation: this has effects on both the reduction of daily temperature swings (up to 10 °C) and heating requirements (more than 17% on a yearly base). Coupling of the thermal storage system with natural ventilation is important during mid-seasons and summer to improve the PCM charge-discharge cycles and to reduce overheating. Results also show that cooling is less important than heating, reaching up to 20% of the overall annual energy requirements for the city of Montreal, Canada. Moreover, the phase change temperature range of the material used (18–24 °C) is below typical summer temperature levels in solaria, but the increase in thermal capacity of the room alone can reduce annual cooling requirements by up to 50%.