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[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
[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] 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] The purpose of this review leads to use of energy conservation technologies. There are so many systems which are used for energy saving among them thermal storage system with Phase Change Material (PCM) is well known. In this review majority focuses on the human comforts. It was observed that maintaining the human comfort is the challenging task for living spaces like room, offices etc. such type of required energy which is satisfied by thermal storage PCM based system. If the phase change materials are applied to building applications they can be used for peak load shifting in cool storage system. Development of the new techniques for getting thermal comfort for building (lowering the heating and cooling demand is required. Also it includes the expenses behind development, maintenance and installation. Moreover this review finds the effective phase change materials. Such thermal storage system has a potential to replace the conventional methods but the effectiveness or efficiency of that system is less. So it is required improvement in the selection of thermal storage system and phase change material. Also this review presents the potential of the phase change material system
[en] Highlights: • Comprehensive review of the main types of electrospun ultrafine PCFs since 2006. • Review relationship between fiber morphology, composition and thermal properties. • Discuss future challenges and opportunities of electrospun ultrafine PCFs. - Abstract: Over the last 30 years, phase change fibers (PCFs) have been extensively investigated and applied as high-performance nonwoven fabrics and coatings. As a prospective renewable and clean material, PCFs with micro-scale have been successfully prepared by melt/wet spinning for applications in thermal energy storage (TES) and temperature regulation. With the development of fiber manufacturing techniques, e.g. electrospinning, ultrafine PCFs have been exploited and investigated in the last decade. This paper considers the state of investigations and developments in ultrafine (submicro-scale) PCFs by electrospinning technique since 2006. Electrospun ultrafine PCFs individually using long-chain aliphatic hydrocarbons (and paraffin waxes), polyethylene glycol, fatty acids (and their eutectics), and other solid-liquid phase change materials (PCMs) as latent heat storage (LHS) component are reviewed. The relationship between morphology, composition, and thermal properties are discussed for providing guidance for fabricating appropriate ultrafine PCFs with desired thermophysical properties for various applications. The further challenges and opportunities of electrospun ultrafine PCFs for TES and other applications are also discussed.
[en] Electric energy storage is considered to become a key element of the future electricity infrastructure. PTES (Pumped thermal electricity storage) represents an emerging thermo mechanical storage technology based on the transformation of low temperature heat by surplus electricity. After transformation, the high enthalpy heat is stored. During the discharge process, this heat is used to drive a thermodynamic cycle generating electricity. This concept allows storage of energy in the multi-MW range for several hours without any specific geographical requirements. Various combinations of thermodynamic cycles and storage types have been suggested for implementation using either low temperature storage (<200 °C) or high temperature storage (>500 °C). In contrast to these PTES concepts, the Compressed Heat Energy STorage (CHEST) concept presented in this paper is based on a medium temperature conventional Rankine cycle combined with a latent heat storage unit according to the current state of the art. This concept attains an efficiency of 70% while the maximum temperature is below 400 °C. The integration of heat provided by low temperature sources during the charging process represents an additional option of the CHEST concept; losses can be compensated, the electric work delivered during the discharge process might even outweigh the work needed during the charging process. - Highlights: • New concept for storage of electrical energy in the multi-MWh range is presented. • State of the art medium temperature storage technology is applied. • Maximum temperature is below 400 °C. • Roundtrip efficiency in the range of 70% is calculated. • Integration of low temperature heat sources allows compensation of losses
[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] Spin casting is being used widely in the prototyping industry as a secondary process to convert a master model into a functional metal or plastic part. The main problem of the spin-casting process is the poor thermal conductivity of silicone rubber as mould material--which leads to a long cooling time between casting processes, a short lifespan of the mould and therefore quality problems with respect to the final product. In order to address these problems different cooling methods, such as the λ-ρC method and latent heat storage method, have been developed, investigated experimentally and described in this paper. Experimental results show that some metals--such as plain carbon steel--can be used to control the thermal process in spin casting effectively
[en] Advancement in thermal management system which can be adopted to absorb heat generated in Li-ion battery pack for hybrid vehicle during charge and discharge cycles, by keeping the battery pack in optimum range of 15°C-25°C. Factors such as parasitic power, additional weight of cooling unit, temperature rise and cell temperature dierence play a vital role. PCM (Phase Change Material) are compounds having high thermal conductivity and latent heat storage. They go through phase change when they absorb or release heat. The basic design is to manufacture a cooling jacket using phase change material which absorbs heat during the day and rejects it at night. The result show decreases in temperature by 1.5°C, additional increase in weight of battery pack by 17.5%, no parasitic power consumption, increase in safety and compactness to applications. (paper)
[en] The present study is an experimental investigation of nucleate boiling heat transfer mechanism in pool boiling from wire heaters immersed in saturated FC-72 coolant and water. The vapor volume flow rate departing from a wire during nucleate boiling was determined by measuring the volume of bubbles, varying 25 μm, 75 μm, and 390 μm, from a wire utilizing the consecutive-photo method. The effects of the wire size on heat transfer mechanism during a nucleate boiling were investigated by measuring vapor volume flow rate and the frequency of bubbles departing from a wire immersed in saturated FC-72. One wire diameter of 390 μm was selected and tested in saturated water to investigate the fluid effect on the nucleate boiling heat transfer mechanism. Results of the study showed that an increase in nucleate boiling heat transfer coefficients with reductions in wire diameter was related to the decreased latent heat contribution. The latent heat contribution of boiling heat transfer for the water test was found to be higher than that of FC-72. The frequency of departing bubbles was correlated as a function of bubble diameters