Results 1 - 10 of 1966
Results 1 - 10 of 1966. Search took: 0.025 seconds
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[en] Highlights: • The efficiency of the MNITG at arbitrary power is analytically derived. • A universal bound on the efficiency of the MNITG with broken time-reversal symmetry and the arbitrary power is obtained. • Some system-specific characteristics are discussed and uncovered. • The broken time-reversal symmetry provides the physically allowed degrees of freedom for tuning the performance of heat devices. - Abstract: We investigate the performance at arbitrary power of minimally nonlinear irreversible thermoelectric generators (MNITGs) with broken time-reversal symmetry within linear irreversible thermodynamics, and the efficiency of MNITGs at arbitrary power is analytically derived. Furthermore, a universal bound on the efficiency of thermoelectric generators (TGs) with broken time-reversal symmetry and the arbitrary power is obtained. Some system-specific characteristics are discussed and uncovered. A large efficiency at arbitrary power can also be achieved via the cooperative mechanism between the system parameters. Our results indicate that the broken time-reversal symmetry provides the physically allowed degrees of freedom for tuning the performance of thermoelectric devices, and the physical trade-off region between the efficiency and the power output can also offer the appropriate space for optimizing the performance of TGs.
[en] Highlights: • A new design of solar thermoelectric generator is proposed. • The design combines the segmented materials and asymmetric legs. • The output power is enhanced by 19–21%, as compared with the conventional design. • A simple analytical model is developed to predict the optimal leg length ratio. - Abstract: In this work, a novel solar thermoelectric generator (TEG) design is proposed to enhance its output power and conversion efficiency. It combines segmented thermoelectric materials and asymmetrical legs with variable cross-sectional area along the leg length. A three-dimensional multiphysics thermoelectric model is employed to examine the performance of the new design. The optimal leg length ratio of two segmented materials (P1 and P2 materials) and the optimal cross-sectional area ratio of cold end to hot end are determined. In comparison with using P1 and P2 materials, the results show that the segmented design increases the output power by 14.9% and 16.6%, respectively, when the leg length ratio is optimized. When the asymmetrical legs are introduced to the segmented design, the output power can be additionally increased by 4.21%, as compared with the optimal segmented design. Moreover, a simple analytical model is proposed to predict the optimal leg length ratio of two thermoelectric materials for the present new design. The proposed model can be reduced to the existing models when the leg cross-sectional area ratio of cold end to hot end is equal to 1. Thus, the model can be considered as a generalized model, which can evaluate the optimal leg length ratio for the segmented design with any leg shape. Based on the model, the optimal leg length ratio should make the interface temperature between the two materials equal to the temperature of intersection point of their ZT (figure of merit) curves. Theoretically, this conclusion can be extended to any leg shape with a constant or variable cross-sectional area. The present simulations verify the theoretical prediction of the optimal leg length ratio.
[en] Highlights: • A new design for DCNB with sub-micrometer thickness radiation source, both-side emission and collection. • The energy conversion efficiency of DCNB with this design may reaches over 20% in theory. • This work will establish a theoretical foundation for application of DCNBs in the future. - Abstract: Direct charging nuclear batteries (DCNB) have the potential of being widely used to meet the special requirements in the area of aerospace and ocean. The current application of direct charging nuclear batteries is restricted by the low energy conversion efficiency, commonly less than 10%. This low efficiency is limited mainly by issues of low source efficiency and shunt factor among others, such as collection and geometry factors. Based on a numerical simulation and empirical calculations we here propose a design of DCNB by utilization of a sub-micrometer thickness radiation source to increase the source efficiency, both-side emission, and collection of decay particles to improve the collection and geometry factors, as well as impedance matching of batteries and load to improve the shunt factor, among other various optimizations. The energy conversion efficiency of DCNB with this design reaches over 20%. The successful deployment of the current design should vastly improve the energy conversion efficiency of DCNBs, and also establish a theoretical foundation for extending the scope of applications of DCNBs in the future.
[en] We investigate the design and performance of thin-film micro thermoelectric generators (µTEGs) using human body heat for wearable device applications, in which various module structures using different thermal-isolations are examined. A transverse type of µTEG suitable for a thin-film thermopile is employed for the modules. The thermal and electrical insulation of the interspace between the hot and cold plates of the modules is an important factor to determine the output power of the µTEGs. A module using vacuum thermal-isolation gives the performance limit of the µTEGs. On the other hand, an easy-to-fabricate insulator-based thermal-isolation severely degrades the performance. A new module structure using insulator/vacuum-hybrid thermal-isolation also has a device-process-friendly structure and in addition can exhibit high output power close to the performance limit achieved by the vacuum thermal-isolation module, which would be adaptable to the power source of wearable devices for internet-of-humans. (paper)
[en] Atomic-scale structures of oxygen reduction reaction (ORR) active sites in non-platinum group metal (non-PGM) catalysts, made from pyrolysis of carbon, nitrogen, and transition-metal (TM) precursors have been the subject of continuing discussion in the fuel cell electrocatalysis research community. Quantum chemical modeling is one path forward for understanding of these materials and how they catalyze the ORR. We here demonstrate through literature examples of how such modeling can be used to better understand non-PGM ORR active site relative stability and activity and how such efforts can also aid in the interpretation of experimental signatures produced by these materials.
[en] The paper and presentation describe an alarm and communications device to be used to provide a basic level of protection to Radioisotope Thermoelectric Generators (RTGs) while they are located in remote locations. The effort is to deploy a small, simple, and cost-effective communications device that will provide a basic level of protection to RTGs located in remote areas in Russia. This level of protection is intended to be temporary, covering RTGs while they await removal from the field to more secure locations.
[en] The paper and presentation Problems Connected with Operation and Decommissioning of RTGs Used for Navigation by Alexander Gordienko, described the inventory and the life cycle of 336 RTGs that were in service at the Russian Ministry of Defense. The author explained the main problems of RTG management and decommissioning: the need for constant monitoring of RTG conditions at sites; removal and replacement with alternative power sources; provision of certified transportation means for RTGs removal and means for personnel radiation protection; the need to create secure interim accumulation pads. Case studies of handling damaged RTGs were presented. International partners were invited to join efforts for RTG decommissioning.
[en] The paper/presentation describes the key provisions of the Master Plan for decommissioning, replacement with alternative power sources and disposal of Radioisotope Thermoelectric Generators (RTGs) developed in 2007 under the financial support of Canada. The Master Plan defines strategic approaches to solve the problem of decommissioning of RTGs of the Russian Federation, substantiates different transportation schemes, and RTG and radioactive heat sources handling options; provides an assessment of required funds. • General information on the scope and locations of RTGs, transportation and handling options, and approaches to their implementation. • Assessment of RTG decommissioning options and replacement by alternative energy sources. • Analysis of risks of RTG loss and decommissioning expenses.
[en] Highlights: • Highly electrocatalytic Se/Au/Pd nanoparticles have been developed. • Se/Au/Pd nanoparticles exhibit higher activity than commercial Pd/C catalysts. • Photoelectrochemical effect of Se results in enhanced electrocatalytic activity. • Se/Au/Pd nanoparticles show their critical role in self-powered sensing systems. • A self-powered electrochemical sensing system for glucose detection is developed. Bimetallic nanoparticles (NPs) have received increasing attention for their outstanding catalytic activity which the corresponding monometallic NPs can hardly achieve. In this paper, we developed a facile approach to prepare Se-supported Au/Pd NPs with high and photo-assisted electrocatalytic activity. Cyclic voltammetry (CV) measurements showed that the electrocatalytic activity of the Se-supported Au/Pd NPs was dependent on the Pd content. This result indicates that the interface between Pd and Au plays a vital factor in the electrocatalytic activity, while the individual metal components in the Se/Au/Pd system are of minor relevance for such activity. The Se-supported Au/Pd NPs exhibited mass activities of 4.25 (A/mgPd) and 1.21 (A/mgAu+Pd) toward ethanol oxidation, which were higher than that of the commercial Pd/C catalyst (0.36 A/mgPd). The electrocatalytic activity of Se-supported Au/Pd NPs was further enhanced by 2.4 times under solar light irradiation due to the photoelectrochemical effect of the Se NPs. It was further demonstrated in this paper that the presence of Se-supported Au/Pd NPs is crucial in self-powered electrochemical sensing systems as the overall sensitivity is significantly improved.
[en] The presentation and paper provided a review of the Russian regulatory and supervisory system for management and decommissioning of radioisotope thermoelectric generators (RTG) in 2005. Suggestions to improve the regulatory system are made. • Operational experience of handling Russian RTGs. • Measures to ensure safety of operation and decommissioning RTGs. • Safe management of damaged RTGs. • Suggestions to improve regulatory requirements and rules. • Development of risk and safety assessment tools. • Radiation emergency response planning.