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The inlet/outlet is an important part of a water conveyance system in a pumped storage power station (PSPS). Its hydraulic characteristics are directly related to the operation and economic benefit of the PSPS. Frequent changes between inflow and outflow operations pose significant challenges in the design of the inlet/outlet diffusion segment shape. In this study, an effective optimization method, including three-dimensional parametric modelling, computational fluid dynamics and a genetic algorithm, is introduced and coupled to the design of the diffusion segment shape. The hydraulic characteristics of bi-directional flow, including the head loss, velocity uneven distribution and uneven discharge distribution, are selected as the objective function in the optimization method. Using this method, the recommended shape of the inlet/outlet is studied and its hydraulic characteristics are discussed. The results indicate that the optimized inlet/outlet has better performance. [ABSTRACT FROM AUTHOR]

Frequent changes between inflow and outflow operations pose significant challenges in the design of bidirectional flow passage components with high efficiency and stability. In this study, hydraulic optimization of the inlet/outlet diffusion segment of a pumped storage power station was performed. First, a 3D-optimization platform was established for the inlet/outlet diffusion segment, and consists of parametric modelling, automatic mesh generation, CFD numerical calculation, and an optimization strategy. Three objective functions; the head loss, velocity uneven distribution, and discharge uneven distribution; were adopted to evaluate the overall performance of the inlet/outlet diffusion segment. Both dual- and triple-objective optimizations were adopted to optimize the shape of the inlet/outlet diffusion segment, the response surface methodology (RSM) was used to generate approximate functions relating to the objectives and design parameters, and the non-dominated sorting genetic algorithm (NSGA-II) was selected to conduct the optimizations. The objective of the present study was to use a numerical optimization method to determine the optimal inlet/outlet structure configurations yielding better hydraulic performance with bidirectional flow conditions. The results show that with triple-objective optimization, the head loss decreased by 2.71%, velocity uneven distribution decreased by 21.05%, and discharge uneven distribution decreased by 2.24%. [ABSTRACT FROM AUTHOR]

The discharge channel of the pumped storage power station has bidirectional flow characteristics. When the water flow from the conveyance tunnel diffuses to the reservoir through the discharge channel, the instantaneous velocity at the trash rack section varies greatly, and the fluctuation value exceeds twice the time-averaged value. As previously reported, only the time-averaged velocity parameter cannot fully represent instant flow effects. In this paper, the improved delayed detached eddy simulation (IDDES) is proposed to numerically simulate the velocity field inside the discharge channel. The laser doppler velocimetry (LDV) is used to measure the velocity along the segment inside the discharge channel. It is found that the instantaneous velocity of the trash rack section varies significantly with time, the fluctuating velocity is close to or even more than twice the time-averaged velocity, and the average turbulence intensity is 0.72. The probability density distribution of fluctuating velocity is found to be close to normal distribution. During the flow from the conveyance tunnel segment to the reservoir through the diffusion segment and the adjustment segment, the turbulence intensity initially increases and then decreases along the process. The fluctuating velocity in the conveyance tunnel segment is minor, and the average turbulence intensity is 0.27. The turbulence intensity of water flow at the diffusion segment increases by 4.55 times to 1.23, which explains the large fluctuation velocity and high turbulence intensity at the trash rack section. The research results could help to understand the flow characteristics of the discharge channel, optimize the shape parameters of the discharge channel, and analyze the cause of fatigue failure of the trash rack. • The fluctuating velocity characteristics at the trash rack section are demonstrated detailed. • The large fluctuating velocity and the turbulent intensity of the trash rack section are explained. • The improved delayed detached eddy simulation is used to simulate the field inside the discharge channel. • The laser doppler velocimetry is used to measure the velocity along the segment inside the discharge channel. [ABSTRACT FROM AUTHOR]

Transition metal oxides are a class of promising host materials of sulfur for lithium-sulfur (Li-S) batteries due to their robust polysulfide adsorption, and catalytic effect on sulfur redox reaction. It is proven that the adsorption-catalysis property can benefit a lot from incorporating multiple metal elements, and high-entropy oxides (HEOs) show good competitive potential for durable Li-S batteries. Herein, HEO nanofibers are designed as bidirectional catalytic host of sulfur to promote both the reduction of soluble intermediates and the re-oxidation of insoluble products. Specifically, the high-entropy perovskite oxide La 0.8 Sr 0.2 (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2)O 3 (HE-LSMO) nanofibers prepared via an electrospinning-calcination method show a unique porous fibrous structure for incorporation with sulfur. The introduced multiple metal elements can effectively modulate the binding strength of soluble polysulfides, and HE-LSMO nanofibers act as bidirectional electrocatalyst for the liquid-solid conversion processes between soluble polysulfides and insoluble Li 2 S, which is enabled by the high entropic contribution. As a result, the S/HE-LSMO cathode with a sulfur loading of 8.4 mg cm−2 shows a high areal capacity of 6.6 mAh cm−2 at low electrolyte/sulfur ratio of 5.3 μL mg−1, as well as good cycle stability. This work provides a foundation understanding of the bidirectional catalytic role of HEOs toward practical Li-S batteries. [Display omitted] • Porous La 0.8 Sr 0.2 (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2)O 3 nanofibers were prepared via an electrospinning-calcination method. • High configuration entropy contributes to the formation of a single perovskite phase. • The multiple metal elements effectively modulate the binding strength of polysulfides. • The oxide acts as a bidirectional catalyst to promote the reduction of polysulfides and the oxidation of Li 2 S. • High areal capacity of 6.6 mAh cm−2 is realized at a sulfur loading of 8.4 mg cm−2 and an E/S ratio of 5.3 μL mg−1. [ABSTRACT FROM AUTHOR]

Rechargeable lithium–sulfur batteries operate based on the interconversion between sulfur and Li2S. Due to its insoluble and insulated nature, Li2S deposition is kinetically sluggish, which has an important effect on performance of lithium–sulfur batteries. In this work, cobalt‐edged nickel alloy is designed and used as host material of sulfur cathodes to manipulate the behavior and morphology of Li2S deposition. It is found that Co and Ni have different catalytic kinetic characteristics for Li2S deposition reactions, and the difference in nucleation and growth rates of Li2S and geometrical effect of Co‐edged Ni alloy can cause a well‐spaced morphology to prevent premature surface passivation, thereby improving sulfur utilization and rate capability of the cathodes. As a result, the thick sulfur cathode using cobalt‐edged nickel as host material with a sulfur loading of 4.0 mg cm−2 shows an initial capacity of 1229.3 mA h g−1 at electrolyte/sulfur ratio of 8 µL mg−1, as well as high capacity retention of 92.2% at 0.2 C during 100 cycles. These results provide an alternative perspective not only for developing new mixed host materials for lithium–sulfur batteries, and also for further understanding the existing works using composite host materials. [ABSTRACT FROM AUTHOR]

• The impact of sediment layer characteristics on flow-vegetation interactions was investigated. • The bed permeability has a threshold effect on the hydrodynamic characteristics of channels with vegetation patches. • The permeability Reynolds number is suitable for characterizing the bed permeability and its threshold effect. Vegetation patches grow on permeable beds, but the effects of bed permeability on the hydrodynamic characteristics of channels with vegetation patches are rarely discussed. In this study, emergent rigid cylinders are used to represent a vegetation patch, and porous media are utilized to represent the sediment. Multiple groups of conditions with various bed permeabilities are simulated. The results show that when the bed permeability is high, a jet flow forms downstream of the patch. With increasing bed permeability, the velocity distribution of the Karman vortex block is closer to the level in front of the patch, and the peak value of the turbulent kinetic energy increases and extends downstream. However, when the bed permeability is low, the hydrodynamic characteristics in a channel with a vegetation patch (HCCVPs) change negligibly with the bed permeability. The bed permeability has a threshold effect on the HCCVPs. A further discussion suggests that the permeability Reynolds number Re k is suitable for characterizing the bed permeability and its threshold effect. The magnitude of the Re k threshold that corresponds to the change in hydrodynamic characteristics is 1. These new results also explain the process differences in sediment transport and patch expansion under different bed permeability conditions. [ABSTRACT FROM AUTHOR]

We developed a facile infiltration route for synthesizing hollow-structured SnO2 with an adjustable Ti doping content using SiO2 microspheres as hard templates via an improved Stober method. The microstructures of as-prepared Ti-doped SnO2 samples were characterized using XRD, SEM, TEM, XPS, and N2 adsorption and desorption techniques. The photocatalytic activity of hollow-structured Ti-doped SnO2 photocatalysts was investigated via the decomposition of methylene blue (MB) under UV and visible-light illumination in a photochemical reactor. It was revealed that hollow-structured Ti-doped SnO2 spherical specimens display enhanced photocatalytic activity for decomposing MB compared with a pure SnO2 sample. In comparison with pure SnO2 hollow spherical sample, Ti-doped SnO2 with a doping content of 20 mol% displays the highest photocatalytic activity, with 92% MB photocatalytically decomposed under UV light irradiation, with 54% MB photocatalytically decomposed under visible light irradiation, within a degradation time of 135 min, respectively. The relation between microstructure, optical response, and photocatalytic performance is discussed and analyzed. The enhancement in photocatalytic performance of Ti-doped SnO2 can be attributed to the following reasons. Homogeneous doping of Ti into the lattice of SnO2 prevents the recombination of electron–hole pairs and expands the range of usable excitation light to the visible-light region. In addition, the highly crystalline state, large surface area, and large pore size of Ti-doped SnO2 also contribute to the improved photocatalytic activity of the Ti-doped SnO2 samples. [ABSTRACT FROM AUTHOR]