Effects on the crystallite growth behavior of LaPO4 nanopowders and its mechanical properties

The effects of pH of the reaction solution and the concentration of phosphoric acid on the crystal growth behavior of LaPO₄ crystallites were investigated and the mechanical properties of rare-earth phosphates were compared. As a result, the concentration of phosphoric acid of 10% was beneficial to the crystal growth of LaPO₄ nanocrystalline. When the pH value of the reaction solution was 2, the size of LaPO₄ crystallites increased gradually with the increasing reaction temperature, and the smallest crystallite size of 43.27 nm was obtained after heat-treatment at 1000 °C. Simultaneously, the activation energy for crystal growth of LaPO₄ nanocrystalline was relatively lower (26.82 kJ mol⁻¹). With the decreasing radii of rare-earth ions, the hardness, Young's modulus and fracture toughness of the bulk rare-earth phosphates exhibited a reduced tendency, resulted from the increase of porosity under the same preparation process.     

A robust model-free controller for a three-phase grid-connected photovoltaic system based on ultra-local model

In this paper, a robust model-free controller for a grid-connected photovoltaic (PV) system is designed. The system consists of a PV generator connected to a three-phase grid by a DC/AC converter. The control objectives of the overall system are to extract maximum power from the PV source, to control reactive power exchange and to improve the quality of the current injected into the grid. The model-free control technique is based on the use of an ultra-local model instead of the dynamic model of the overall system. The local model is continuously updated based on a numerical differentiator using only the input–output behavior of the controlled system. The model-free controller consists of a classical feedback controller and a compensator for the effects of internal parameter changes and external disturbances. Simulation results illustrate the efficiency of the controller for grid-connected PV systems.     

Strong tribocatalytic dye degradation by tungsten bronze Ba4Nd2Fe2Nb8O30

The triboelectric effect has recently demonstrated its great potential in environmental remediation and even new energy applications for triggering a number of catalytic reactions by utilizing trivial mechanical energy. In this study, Ba₄Nd₂Fe₂Nb₈O₃₀ (BNFN) submicron powders were used to degrade organic dyes via the tribocatalytic effect. Under the frictional excitation of three PTFE stirring rods in a 5 mg/L RhB dye solution, BNFN demonstrates a high tribocatalytic degradation efficiency of 97% in 2 h. Hydroxyl radicals (?OH) and superoxide radicals (?O₂－) were also detected during the catalysis process, which proves that triboelectric energy stimulates BNFN to generate electron-hole pairs. The tribocatalysis of tungsten bronze BNFN submicron powders provides a novel and efficient method for the degradation of wastewater dye by utilizing trivial mechanical energy.     

粉体含能材料生产与储运中的静电安全及防护

分析了静电产生的原因,阐述了粉体含能材料生产中的静电起电现象、静电的危害、静电安全性评估标准以及建立在此标准基础上的静电放电危险的评价办法,提出了粉体含能材料在生产、运输中所需要采取的静电防护措施。     

A new signal processing-based islanding detection method using pyramidal algorithm with undecimated wavelet transform for distributed generators of hydrogen energy

Machine learning-based fault detection methods are frequently combined with wavelet transform (WT) to detect an unintentional islanding condition. In contrast to this condition, these methods have long detection and computation time. Thus, selecting a useful signal processing-based approach is required for reliable islanding detection, especially in real-time applications. This paper presents a new modified signal processing-based islanding detection method (IDM) for real-time applications of hydrogen energy-based distributed generators. In the study, a new IDM using a modified pyramidal algorithm approach with an undecimated wavelet transform (UWT) is presented. The proposed method is performed with different grid conditions with the presence of electric noise in real-time. Experimental results show that oscillations in the acquired signal can be reduced by the UWT, and noise sensitivity is lower than other WT-based methods. The non-detection zone is zero and the maximum detection and computational time is also 75 ms at a close power match.     

基于概率法的电力系统安全分析

为应对电力系统安全分析中的停机问题，基于概率法的方式，将常用的确定停机计算与加入了概率法的概率停机进行比较，研究了二者的区别与其在长期投资方向的不同。在进行电力系统停机分析时，通常会分别从确定停机与概率停机的角度出发，对其应急状态下的潮流进行计算。但前者的方法可能导致极低概率的停机事件被忽略，进而影响长期的资金投资。通过加入概率法的计算，使得对单个停机事件的判定由其具体的频率来确定，增加了系统运行的稳定性。     

Efficient Visible-to-UV Photon Upconversion Systems Based on CdS Nanocrystals Modified with Triplet Energy Mediators

Developing high-performance visible-to-UV photon upconversion systems based on triplet–triplet annihilation photon upconversion (TTA-UC) is highly desired, as it provides a potential approach for UV light-induced photosynthesis and photocatalysis. However, the quantum yield and spectral range of visible-to-UV TTA-UC based on nanocrystals (NCs) are still far from satisfactory. Here, three different sized CdS NCs are systematically investigated with triplet energy transfer to four mediators and four annihilators, thus substantially expanding the available materials for visible-to-UV TTA-UC. By improving the quality of CdS NCs, introducing the mediator via a direct mixing fashion, and matching the energy levels, a high TTA-UC quantum yield of 10.4% (out of a 50% maximum) is achieved in one case, which represents a record performance in TTA-UC based on NCs without doping. In another case, TTA-UC photons approaching 4 eV are observed, which is on par with the highest energies observed in optimized organic systems. Importantly, the in-depth investigation reveals that the direct mixing approach to introduce the mediator is a key factor that leads to close to unity efficiencies of triplet energy transfer, which ultimately governs the performance of NC-based TTA-UC systems. These findings provide guidelines for the design of high-performance TTA-UC systems toward solar energy harvesting.     

Hydrogen supply scenarios for a climate neutral energy system in Germany

A climate neutral energy system in Germany will most likely require green hydrogen. Two important factors, that determine whether the hydrogen will be imported or produced locally from renewable energy are still uncertain though - the import price for green hydrogen and the upper limit for photovoltaic installations. To investigate the impact of these two factors, the authors calculate cost optimized climate neutral energy systems while varying the import price from 1.25 €/kg to 5 €/kg with unlimited import volume and the photovoltaic limit from 300 GW to unlimited. In all scenarios, hydrogen plays a significant role. At a medium import price of 3.75 €/kg and photovoltaic limits of 300–900 GW the hydrogen supply is around 1200 to 1300 TWh with import shares varying from 60 to 85%. In most scenarios the electrolysis profile is highly correlated with the photovoltaic power, which leads to full load hours of 1870 h–2770 h.     

Hybrid hydrate processes for CO2/H2 mixture purification: A techno-economic analysis

In this work, hydrate based separation technique was combined with membrane separation and amine-absorption separation technologies to design hybrid processes for separation of CO₂/H₂ mixture. Hybrid processes are designed in the presence of different types of hydrate promoters. The conceptual processes have been developed using Aspen HYSYS. Proposed processes were simulated at different flow rates for the feed stream. A comprehensive cost model was developed for economic analysis of novel processes proposed in this study. Based on the results from process simulation and equipment sizing, the amount of total energy consumption, fixed cost, variable cost, and total cost were calculated per unit weight of captured CO₂ for various flow rates of feed stream and in the presence of different hydrate promoters. Results showed that combination of hydrate formation separation technique with membrane separation technology results in a CO₂ capture process with lowest energy consumption and total cost per unit weight of captured CO₂. As split fraction and heat of hydrate formation increases, the share of hydrate formation section in total energy consumption increases. When TBAB is applied as hydrate promoter, due to its higher hydrate separation efficiency, more amount of CO₂ is captured in hydrate formation section and consequently the total cost for process decreases considerably. Hybrid hydrate-membrane process in the presence of TBAB as hydrate promoter with 29.47 US$/ton CO₂ total cost is the best scheme for hybrid hydrate CO₂ capture process. Total cost for this process is lower than total cost for single MDEA-based absorption process as the mature technology for CO₂ capture.     

Charge source and the charging mechanism of the contact electrification of polymer powder

The charge sources, as well as the charging mechanism of the contact electrification (CE) of polymers, are still debatable. Since CE is accompanied by destruction, it is considered that “hard contacting” via ball milling can induce covalent bond scission and produce naked-activated-charge sources. Regarding “soft contacting” via nano-scale sliding, which does not induce covalent bond scission, a frontier-electron, “f-electron,” of the naked-activated-charge source is crucial to electron transfer among the naked-activated-charge sources. Here, we configure naked-activated-charge-source models, naked-activated-mechano-anion, and naked-activated-mechano-cation, which are produced by mechanical energy induced heterogeneous covalent bond scission, as well as naked-activated-mechano-radicals that are produced by homogeneous covalent bond scission. Regarding “soft contacting” among naked-activated-charge sources in a vacuum, f-electron can be transferred from a donor to an acceptor if the energy level of the donor is higher than that of the acceptor. The net amount of the normalized transferred-f-electrons is obtained by adopting settings in which the average energy level of the naked-activated-charge sources (as the donors) is higher than that of the sources employed as acceptors. Thus, the surfaces comprising the donors and acceptors will exhibit positive and negative net surface charges, respectively. We conclude that net surface charges depend on the average energy level of naked-activated-charge sources. Further, we observe that the alignment of polyethylene (PE)-polyvinyl chloride (PVC)-polytetrafluoroethylene (PTFE) to the average energy level is identical to that of the triboelectric series.