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[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] 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] 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%.
[en] During seismic wave propagation on a free surface, a strong material contrast boundary develops in response to interference by P- and S- waves to create a surfacewave phenomenon. To accurately determine the effects of this interface on surface-wave propagation, the boundary conditions must be accurately modeled. In this paper, we present a numerical approach based on the dynamic poroelasticity for a space–time-domain staggeredgrid finite-difference simulation in porous media that contain a free-surface boundary. We propose a generalized stess mirror formulation of the free-surface boundary for solids and fluids in porous media for the grid mesh on which lays the free-surface plane. Its analog is that used for elastic media, which is suitable for precise and stable Rayleigh-type surface-wave modeling. The results of our analysis of first kind of Rayleigh (R1) waves obtained by this model demonstrate that the discretization of the mesh in a similar way to that for elastic media can realize stable numerical solutions with acceptable precision. We present numerical examples demonstrating the efficiency and accuracy of our proposed method.
[en] Highlights: • A procedure to design effective thermal energy storage (TES) system. • A guidance for the selection of the working material (PCM) and the heat exchanger development. • Suggestions for heat transfer enhancement techniques for the air-TES system. • Mathematical, computational and experimental methods optimising the air-TES system. - Abstract: The paper seeks to offer a procedure to design an effective short term thermal energy storage (TES) system using phase change materials. The methodology focus on two main aspects: the selection of the working material and the heat exchanger development. The selection of the appropriate PCMs is one of the main keys for any TES therefore their classifications, properties, advantages and disadvantages need to be investigated. Due to the intensive researches using this kind of materials in the recent years, there are a range of commercial PCMs available and supplied by different companies. However, all types of PCM present their specific problems and therefore requirements are defined in order to select the most suitable PCMs. The other main key when designing TES is related to the heat exchanger formed by the PCM and the cold/hot heat sources. For this step, the choice of the appropriate container to encapsulate the PCM and the heat transfer enhancement techniques are analysed. Distinct methodologies such as experimental and numerical study methods and modelling software tools are presented to analyse the thermal energy performance of the system and achieve the optimal design of the TES system