Results 1 - 10 of 678
Results 1 - 10 of 678. Search took: 0.026 seconds
|Sort by: date | relevance|
[en] It is well known that components with dissimilar compatibility factors cannot be combined by segmentation into an efficient thermoelectric generator, since each component needs a unique optimal current density. Based on the complex variable method, the thermal-electric field within a bi-layered thermoelectric composite has been analyzed, and the field distributions have been obtained in closed-form. Our analysis shows that current refraction occurs at the interface, both the refraction angle and current density vary with the incidence angle. Further analysis proves that the current densities in two components can be adjusted independently by adjusting the incidence current density and incidence angle, thus the optimal current density can be matched in both components, and the conversion efficiency can be significantly increased. These results point to a new route for high efficiency thermoelectric composites. (paper)
[en] In this paper we analyze the thermodynamic efficiency expected for a fully dissipative thermoelectric generator (TEG) operating under stationary conditions at a finite rate. Although a finite-time thermodynamic analysis of TEGs has been aimed at since long time, no complete theory is available yet. The state of the art of theory is reviewed, and a simple expression for the maximum achievable efficiency of TEGs operating under fully irreversible conditions is obtained. This also sets a reference efficiency for forthcoming studies of nonstationary operation of TEGs.
[en] We propose four different models of three-terminal quantum dot thermoelectric devices. From general thermodynamic laws, we examine the reversible efficiencies of the four different models. Based on the master equation, the expressions for the efficiency and power output are derived and the corresponding working regions are determined. Moreover, we particularly analyze the performance of a three-terminal hybrid quantum dot refrigerator. The performance characteristic curves and the optimal performance parameters are obtained. Finally, we discuss the influence of the nonradiative effects on the optimal performance parameters in detail. (paper)
[en] Hydrogen energy applications often require that systems are used indoors (e.g., industrial trucks for materials handling in a warehouse facility, fuel cells located in a room, or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons, to isolate them from the end-user and the public, or from weather conditions. Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks, including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture, or can result in jet-fires. Within Hyindoor European Project, carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation, vented deflagrations, jet fires and including under-ventilated flame regimes (e.g., extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified. (authors)
[en] The present work analyses the linear azimuthal stability of a single interface between two cylindrical dielectric fluids. The theoretical model consists of two incompressible rotating electrified fluids throughout the porous media. The system is influenced by a uniform azimuthal electric field. The inner cylinder is filled with a viscous liquid. The outer one is occupied by an inviscid gas. The problem meets its motivation from a geophysics point of view. Therefore, for more convenience, the problem is considered in a planar configuration. Typically, the normal mode analysis is used to facilitate the stability approach. The examination resulted in a stream function,which is governed by a fourth-order ordinary differential equation with complicated variable coefficients. By means of the Mathematica software along with the special functions, the distribution of the stream function is written in terms of the modified Bessel functions. A non-dimensional procedure exposes some non-dimensional numbers, for instance, Weber, Ohnesorg, Taylor, Rossby and Darcy numbers. These numbers are considered with regard to the temporal and spatial increase of both frequency and modulation. The linear stability theory generated a very complicated transcendental dispersion equation. The influences of various physical parameters in the stability profile were studied as well. (author)
[en] The wide-bandgap semiconductors, which have the advantages of radiation resistance and high carrier mobility, have gained increased research attention in recent years for the conversion nuclear battery. Nevertheless, when a wide-bandgap semiconductor is used, the collection efficiency and current are reduced, even though the open circuit voltage is increased. In this research, a heterojunction photovoltaic cell is used to increase collection efficiency and power in the betavoltaic battery. A theoretical investigation of the electrical performance has been carried out on Ni63/GaN and Ni63/GaN-Si betavoltaic cells. The effects of doping concentration and junction depth on the maximum power are examined. By optimizing the doping concentration and junction depth, a high-efficiency heterojunction betavoltaic microbattery can be achieved. The maximum power is calculated as 22.90 nW/cm2 using 1 mCi Ni63 beta source and GaN-Si heterojunction with junction depth of 0.1 μm and doping concentrations of Na = 4 × 1017 cm-3 and Nd = 4 × 1016 cm-3 in the emitter and the base region, respectively. (author)
[en] The presentation and paper describe the status of the Radioisotope Thermoelectric Generators (RTGs) in Russia as of 2012 and the efforts for their recovery and decommissioning. This work was carried out by Russia, the USA and other international partners. The work done in 2012 was presented along with the plans for activities in 2013. As an additional effort, the recovery of four RTGs from the Antarctic was suggested.
[en] This report provides a practical action plan and investment guide for policy makers and investors, to help stimulate economic transition at the speed and scale needed to avoid the worst effects of climate change. With its 55 actionable recommendations for financial support, it targets the utilization of the European Commission's Euro 750 billion recovery fund, and other innovation funding vehicles, to transform Europe's economy and set it on course for climate neutrality by 2050. This report investigates and analyzes existing and future technologies across five core economic domains: energy, building and construction, transportation, food and land use. Capgemini Invent worked with over 100 eminent innovators, entrepreneurs, corporate strategists and policy makers, to identify the 55 high impact climate technologies most likely to deliver transformational results, at speed and scale. These 55 quests provide a balanced mix to energize and engage all areas of the European economy and regions. More than 200 individual projects were examined, each with differing levels of technological maturity, to assess their transformational potential and readiness for investment support and the resulting 55 choices have impacts in the five sectors summarised below. The building sector is one of the most significant sources of CO2e emissions in Europe. 28 billion square meters of floor space generates 1,100 MtCO2e (600 MtCO2e direct emissions, 500 MtCO2e for electricity) that must be cut down over 80% to just 200 MtCO2e by 2050. Of this, 430 MtCO2e in direct emissions come from Europe's 20 billion square meters of residential space. Our Building report looks at how automating and streamlining construction processes to deep renovation can help accelerate our delivery of net-zero emissions. Using fossil fuels has major drawbacks, not least that their combustion emits greenhouse gases. Also a considerable portion of energy is wasted, mostly heat in combustion processes, power plants and due to high-temperatures. Our Energy report looks at the solutions and projects to scale up towards the net-zero target, from new generation solar modules and bifacial panels to large-scale hydrogen production and combined solar generation, storage, and grid. Our report looks at the key challenges and the recommended technologies and projects to reducing the environmental impact of the whole agricultural value chain from farm to fork to cut down emissions by 20% in 2030 and 50% in 2050 to boost systemic change to reach net - zero emissions. Achieving a low carbon industry is of paramount importance, not only to reach the 2050 carbon neutrality target, but also to allow economic growth for EU companies and workers. Our report focuses on solutions for the steel and cement industries, responsible for 30% of emissions. Transportation in its many forms currently produces over 1,200 MtCO2e per year, 30% of total emissions in the EU. Liquid fossil fuels drive most air, marine, road and rail movements. Our Transport report looks at solutions for clean alternatives, supported by giga-scale battery and charging infrastructure from scaling up green c-liquid fuel production for aviation and long distance shipping to ammonia fueled vessels.
[en] Thermoelectric properties of Sb B compounds (B-Se, Te) are acceptable for their practical use as materials for thermocouples. These compounds have p-type conductivity, which allows to consider them as perspective materials for positive branches of thermoelectric devices (thermo generators). A characteristic feature of these compounds is a low coefficient of thermal conductivity - which gives a high value of coefficient of thermoelectric figure of merit as thermoelements. These compounds can be recommended as new materials for the creation of thermocouples. (author)
[en] A novel model of the hot carrier solar cell (HCSC) with double energy selective contacts (ESCs) is established. Expressions of the efficiency and power output are derived analytically. The effects of the cell voltage, extraction energy level, width of the ESCs, band gap energy of the absorber, and energy gap between the two contacts on the performance of the HCSC with double quantum dot (QD)- and quantum well (QW)-ESCs are examined. The results obtained show that the HCSC with double QD- and QW-ESCs can obtain a high efficiency. When the parameters of the HCSC are optimized, the maximum efficiency of the HCSC with double QD-ESCs is higher than that with double QW-ESCs. Moreover, the maximum efficiencies of the HCSC with double QD- and QW-ESCs decrease with the increase of the energy gap between the two contacts. (paper)