Modeling of Hydrogen Blending on the Leakage and Diffusion of Urban Buried Hydrogen-Enriched Natural Gas Pipeline

With the introduction of various carbon reduction policies around the world,hydrogen energy,as a kind of clean energy with zero carbon emission,has attracted much attention.The safe and economical transportation of hydrogen is of great significance to the development of hydrogen energy industries.Utilizing natural gas pipelines to transport hydrogen is considered to be an efficient and economical way.However,hydrogen has a higher risk of leakage due to its strong diffusion capacity and lower explosive limit than conventional natural gas.Therefore,it is of great significance to study the leakage and diffusion law of hydrogen-enriched natural gas(HENG)pipelines for the safe transportation of hydrogen energy.In this study,the leakage and diffusion characteristics of urban buried HENG pipelines are investigated numerically,and the dangerous degree of leakage is analyzed based on the time and area when the gas concentration reaches the lower explosive limit.The influences of hydrogen blending ratio(HBR),operating pressure,leakage hole size and direction,as well as soil type on the leakage and diffusion law of HENG are analyzed.Results show that the hydrogen mixing is not the key factor in increasing the degree of risk after gas leakage for urban buried HENG pipelines.When the HBR is 5%,10%,15% and 20%,the corresponding first dangerous time is 1053,1041,1019 and 998 s,respectively.Thiswork is expected to provide a valuable reference for the safe operation and risk prevention of HENG pipelines in the future.

Catalyzing the polysulfide conversion for promoting lithium sulfur battery performances:A review

Lithium-sulfur batteries(LSBs)are being recognized as potential successor to ubiquitous LIBs in daily life due to their higher theoretical energy density and lower cost effectiveness.However,the development of the LSB is beset with some tenacious issues,mainly including the insulation nature of the S or Li_(2)S(the discharged product),the unavoidable dissolution of the reaction intermediate products(mainly as lithium polysulfides(LiPSs)),and the subsequent LiPSs shuttling across the separator,resulting in the continuous loss of active material,anode passivation,and low coulombic efficiency.Containment methods by introducing the high-electrical conductivity host are commonly used in improving the electrochemical performances of LSBs.However,such prevalent technologies are in the price of reduced energy density since they require more addition of amount of host materials.Adding trace of catalysts that catalyze the redox reaction between S/Li_(2)S and Li_(2)Sn(3<n≤8),shows ingenious design,which not only accelerates the conversion reaction between the solid S species and dissolved S species,alleviating the shuttle effect,but also expedites the electron transport thus reducing the polarization of the electrode.In this review,the redox reaction process during Li-S chemistry are firstly highlighted.Recent developed catalysts,including transitionmetal oxides,chalcogenides,phosphides,nitrides,and carbides/borides are then outlined to better understand the role of catalyst additives during the polysulfide conversion.Finally,the critical issues,challenges,and perspectives are discussed to demonstrate the potential development of LSBs.

Hybridized S cathode with N719 dye for a photo-assisted charging Li-S battery

Nowadays,huge consumption of fossil fuels brings about serious energy crisis and environmental problems,which urge researchers to explore novel sustainable energy sources and storage systems[1,2].

Introduction to the Special Issue on Advances in Modeling and Simulation of Complex Heat Transfer and Fluid Flow

Heat transfer and fluid flow are fundamental phenomena in nature and engineering.Modeling and simulation of heat transfer and fluid flow are significant for a wide range of scientific and industrial applications.Along with the development of computer industry and the advancement of numerical methods,significant progresses have been witnessed in modeling and simulation of heat transfer and fluid flow.Solid foundation in both hardware and software has been established to study the heat transfer and fluid flow processes because of its importance in reducing production costs,discovering new phenomena and developing new technologies,etc.However,the accurate modeling and efficient,robust simulation of complex heat transfer and fluid flow still remain challenging.And multi-disciplinary research effort has been a clear and general trend.To highlight the recent advances and challenges in numerical modeling,algorithm,and computation of complex heat transfer and fluid flow,the guest editors organized a special issue on“Advances in Modeling and Simulation of Complex Heat Transfer and Fluid Flow”within Computer Modeling in Engineering&Sciences.

Nitrogen-doped carbon dots-modified Prussian blue with sandwichlike structure as a high-performance electrochromic material

Prussian blue(PB),as a promising inorganic electrochromic material(ECM),has been widely used in smart windows,displays,sensors,etc.However,there are still many challenges for PB to achieve high electrochromic performance.Herein,we synthesized nitrogen-doped carbon dots-modified PB film(defined as PB@N-CDs)with a sandwich-like structure by a simple stepwise electrodeposition method.The carbon dots show an obvious advantage in ultrafast electron transfer ability,which can reduce charge loss during the transfer process,improve the electrochemical activity on both sides of PB,and thus facilitate a rapid electrochromic response.Furthermore,the surface of nitrogen-doped carbon dots contains multiple organic functional groups,which widen the movement path of K+ions under electrostatic adsorption.Impressively,the PB@N-CDs film exhibits a short bleaching/coloring time(0.5/0.9 s)and a superior optical modulation range(78.6%).Particularly,the coloring efficiency has been significantly improved to 137.71 cm^(2)/C(at 700 nm).All of these results open up new avenues for developing highperformance PB-based ECMs and promoting their applications in corresponding electrochromic devices(ECDs)and smart windows.

LES Investigation of Drag-Reducing Mechanism of Turbulent Channel Flow with Surfactant Additives

In this work,the drag-reducing mechanism of high-Reynoldsnumber turbulent channel flow with surfactant additives is investigated by using large eddy simulation(LES)method.An N-parallel finitely extensible nonlinear elastic model with Peterlin’s approximation(FENE-P)is used to describe the rheological behaviors of non-Newtonian fluid with surfactant.To close the filtered LES equations,a hybrid subgrid scale(SGS)model coupling the spatial filter and temporal filter is applied to compute the subgrid stress and other subfilter terms.The finite difference method and projection algorithm are adopted to solve the LES governing equations.To validate the correctness of our LES method and in-house code,the particle image velocimetry(PIV)experiment is carried out and representative measured results are compared with LES results in detail.Then the flow characteristics and drag-reducing mechanism of turbulent channel flow with surfactant are investigated from the perspective of drag reduction rate,mean velocity,fluctuation of deformation rate,shear stress,transport and dissipation of turbulent kinetic energy,and turbulent coherent structures.This research can shed a light on the application of turbulent drag reduction technique in district heating,petroleum transport,etc.

有限容积法离散方程截断误差本质及其来源

本文从有限容积法的原理出发,指出有限容积法离散方程截断误差的本质为离散表达式与守恒型积分方程的近似程度.基于该思想,推导了有限容积法离散方程截断误差表达式,该表达式与有限差分法截差表达式有显著的不同;并指出有限容积法中涉及的截断误差主要包含3个层次,分别为由界面上值的近似、界面通量的近似和离散方程的近似带来的截断误差.有限容积法界面通量截断误差包含法向和切向两部分,有限差分法不存在界面未知值近似和切向截断误差,因而即使对于常物性二维/三维问题,两者截差表达式也不相同.与有限差分法相比,有限容积法误差来源较多,单纯提高待求变量的离散精度并不能有效地提高离散方程的整体精度.此外,通过理论推导和数值试验证明了对于规则区域正交非均分网格,计算区域采用内节点法离散的计算精度总体上优于外节点法.

Promoting the Na^(+)-storage of NiCo_(2)S_(4) hollow nanospheres by surfacing Ni-B nanoflakes

Sodium ion battery(SIB)is considered as the potential alternative for next generation energy system to succeed the lithium ion battery(LIB)due to the low price and vast abundance of Na resource.Ternary metal sulfide is identified as an impo rtant redox conversion type of negative electrode for SIB.In this study,amorphous nickel boride(Ni-B)nanoflakes are introduced into the hollow Ni-Co sulfide nanospheres by a facile in situ solution growth route to promote the electrochemical performance of Na^(+)-storage.Electrochemical measurements demonstrate that the Ni-B component could effectively improve the redox kinetics of the conversion reaction and structural stability during long-term Na^(+)insertion/extraction.For example,the NiCo_(2)S_(4)@Ni-B composites display a high reversible capacity of 251.9 mA h g^(-1)at the current density of 1.0 A g^(-1)after 200 cycles,much higher than that of bare NiCo_(2)S_(4)(37.4 mA h g^(-1)at 1.0 A g^(-1)after 200 cycles).As a consequence,these results demonstrate a new sight to explore heterostructures of mixed metal-sulfides electrode materials with superior Na^(+)-storage performances.