Study on the formation of arc plasma on the resistive wall liquid metal current limiter

Due to its significant attributes,the liquid metal current limiter(LMCL)is considered a new strategy for limiting short-circuit current in the power grid.A resistive wall liquid metal current limiter(RWLMCL)is designed to advance the starting current-limiting time.Experiments are performed to investigate the dynamic behaviors of liquid metal,and the influence of different currents on the liquid metal self-shrinkage effect is compared and analyzed.Furthermore,the liquid metal self-shrinkage effect is mathematically modeled,and the reason for the formation of arc plasma is obtained by simulation.The laws of arc plasma formation and the current transfer in the cavity are revealed,and the motion mechanisms are explained by physical principles.The simulations are in accordance with the test data.It is demonstrated that the sudden change of the current density at both ends of the wall causes the liquid metal to shrink and depress under the electromagnetic force,and the current starts to transfer from the liquid metal path to the wall resistance path.The RWLMCL can effectively advance the starting current-limiting time.

Test study of high liquid limit clay modified by quick lime used as sub-grade material

Through laboratory test, the relationships among change of compactibility, liquid/plastic limit, free swell, swell ratio without load, california bearing ratio (CBR) and soakage (after being soaked in water), and mix-ratio of quick lime and time were studied. The results show that optimum water content, plastic limit and CBR of high liquid limit clay improved by quick lime increase with the increase of mix-ratio of quick lime, while the maximum dry density, liquid limit, plasticity index, soakage (after being immersed in water), free swell, and swell ratio without load decrease with the increase of mix-ratio of quick lime. Plastic limit of high liquid clay improved by quick lime gradually increases with time, while the liquid limit, plasticity index, free swell and swell ratio without load gradually decrease with time. When the mix-ratio of quick lime exceeds 2%, after 14 d, swell ratio without load of the improved clay is zero, its free swell is about 30% of that of untreated soil, and its plasticity index is less than 26 for sub-grade material, satisfying the requirement by 'Specifications for Design of Highway Subgrade'.

Investigation on the Arc Ignition Characteristics and Energy Absorption of Liquid Metal Current Limiter Based on Self-Pinch Effect

The GaInSn liquid metal current limiter based on the fluid pinch effect has broad application prospects due to its particular properties. However, the limited rated current and abil- ity of power dissipation are the critical problems for its wide application. Firstly, the temperature distribution of the liquid metal current limiter （LMCL） was obtained by experiments with a rated current of 1 kA and the arc ignition phenomenon was observed with 1.5 kA, which indicates that the rated current is mainly limited by the arc rather than the high temperature compared to the traditional switchgears. Furthermore, an improved method is proposed by adding the paralleled pure resistance, impedance or another LMCL element to protect the setup from the fault energy concentration in the setup. The problem of a slower arc voltage increasing rate can be solved by adding a paralleled impedance with suitable parameters. Finally, the current limiting properties based on the improved method were investigated and the alternating oscillating current was found between two paralleled LMCL elements owing to their deviation of arc ignition in reality.

LOW MACH NUMBER LIMIT OF A COMPRESSIBLE NON-ISOTHERMAL NEMATIC LIQUID CRYSTALS MODEL

In this paper, we study the low Mach number limit of a compressible nonisothermal model for nematic liquid crystals in a bounded domain. We establish the uniform estimates with respect to the Mach number, and thus prove the convergence to the solution of the incompressible model for nematic liquid crystals.

Evidence of vapor shielding effect on heat flux loaded on flowing liquid lithium limiter in EAST

A lithium(Li)vapour layer was formed around a flowing liquid Li limiter to shield against the plasma incident power and reduce limiter heat flux in the EAST tokamak.The results revealed that after a plasma operation of a few seconds,the layer became clear,which indicated a strong Li emission with a decrease in the limiter surface temperature.This emission resulted in a dense vapour around the limiter,and Li ions moved along the magnetic fleld to form a green shielding layer on the limiter.The plasma heat flux loaded on the limiter,measured by the probe installed on the limiter,was approximately 52%lower than that detected by a fast-reciprocating probe at the same radial position without the limiter in EAST.Additionally,approximately 42%of the parallel heat flux was dissipated directly with the enhanced Li radiation in the discharge with the liquid metal infused trenches(LIMIT)limiter.This observation revealed that the Li vapour layer exhibited an excellent shielding effect to liquid Li on plasma heat flux,which is a possible beneflt of liquid-plasma-facing components in future fusion devices.

A novel fault current limiter topology design based on liquid metal current limiter

The liquid metal current limiter(LMCL)is regarded as a viable solution for reducing the fault current in a power grid.But demonstrating the liquid metal arc plasma self-pinching process of the resistive wall,and reducing the erosion of the LMCL are challenging,not only theoretically,but also practically.In this work,a novel LMCL is designed with a resistive wall that can be connected to the current-limiting circuit inside the cavity.Specifically,a novel fault current limiter(FCL)topology is put forward where the novel LMCL is combined with a fast switch and current-limiting reactor.Further,the liquid metal self-pinch effect is modeled mathematically in three dimensions,and the gas-liquid two-phase dynamic diagrams under different short-circuit currents are obtained by simulation.The simulation results indicate that with the increase of current,the time for the liquid metal-free surface to begin depressing is reduced,and the position of the depression also changes.Different kinds of bubbles formed by the depressions gradually extend,squeeze,and break.With the increase of current,the liquid metal takes less time to break,but breaks still occur at the edge of the channel,forming arc plasma.Finally,relevant experiments are conducted for the novel FCL topology.The arcing process and current transfer process are analyzed in particular.Comparisons of the peak arc voltage,arcing time,current limiting efficiency,and electrode erosion are presented.The results demonstrate that the arc voltage of the novel FCL topology is reduced by more than 4.5times and the arcing time is reduced by more than 12%.The erosions of the liquid metal and electrodes are reduced.Moreover,the current limiting efficiency of the novel FCL topology is improved by 1%–5%.This work lays a foundation for the topology and optimal design of the LMCL.

A statistical reappraisal of the relationship between liquid limit and specific surface area, cation exchange capacity and activity of clays

More than 500 datasets from the literature have been used to evaluate the relationships of specific surface area (SSA),cation exchange capacity (CEC) and activity versus the liquid limit (LL).The correlations gave R^2 values ranging between 0.71 and 0.92.Independent data were also used to validate the correlations.Estimated SSA values slightly overestimate the measured SSA up to 100 m^2/g.Regarding the estimated CEC values,they overestimated the measured CEC values up to 20 meq/(100 g).A probabilistic approach was performed for the correlations of SSA,CEC and activity versus LL.The analysis shows that the relations of SSA,CEC and activity with LL are robust.Using the LL values,it is possible to assess other basic engineering properties of clays.

Influence of Heating and Water Exposure on Liquid Limit of Bentonite

Bentonite has been considered as the buffer material for embedding canisters with high-level radioactive waste(HLW)in the deep geology repositories. GMZ bentonite deposit which is located in Xinghe County,Inner Mongolia has been proposed as buffer/backfill material for HLW repository in China. Liquid limit of natural Na-bentonite GMZ01 and commercial Na-bentonite MX80 which were previously put in the oven at 80℃and 95℃,and exposed to water for different times were measured.The liquid limit of GMZ01 increased slightly at the beginning, and then decreased as the heating time increased.

NONSMOOTH MODEL FOR PLASTIC LIMIT ANALYSIS AND ITS SMOOTHING ALGORITHM

By means of Lagrange duality of Hill＇s maximum plastic work principle theory of the convex program, a dual problem under Mises＇ yield condition has been derived and whereby a non-differentiable convex optimization model for the limit analysis is developed. With this model, it is not necessary to linearize the yield condition and its discrete form becomes a minimization problem of the sum of Euclidean norms subject to linear constraints. Aimed at resolving the non-differentiability of Euclidean norms, a smoothing algorithm for the limit analysis of perfect-plastic continuum media is proposed. Its efficiency is demonstrated by computing the limit load factor and the collapse state for some plane stress and plain strain problems.

PLASTIC LIMIT ANALYSIS OF INCOMPATIBLE FINITE ELEMENT METHOD

This paper describes an incompatible finite element model satisfying the consistency condition of energy to solve the numerical precision problem of finite element solution in perfectly plastic analysis. In this paper the reason and criterion of the application of the model to plastic limit analysis are discussed, and an algorithm of computing plastic limit load is given.

Influence of heating and water-exposure on the liquid limits of GMZ01 and MX80 bentonites

Bentonite has been considered as a buffer material for embedding canisters with high-level radioactive waste（HLW） in deep geological repositories.GMZ bentonite deposit,located in Xinghe County,Inner Mongolia Autonomous Region,China was proposed as a buffer/backfill material for HLW repository in China.The liquid limits of natural Na-bentonite GMZ01 and commercial Na-bentonite MX80,which are previously heated at 80 ℃ and 95 ℃,respectively,and exposed to water for different times are measured.It is observed that the liquid limit of GMZ01 increases slightly at the beginning,and then decreases as the heating time increases,while the liquid limit of MX80 decreases with the heating time.The liquid limits of both GMZ01 and MX80 decrease with increasing water-exposure time.After the samples are heated at 80℃and 95 ℃ for several months,the mineralogical composition of GMZ01 does not exhibit evident change,whereas MX80 experiences some changes.In addition,the chemical composition,cation exchange capacity（CEC） and exchangeable cation of all the samples do not change significantly.

Optical Limiting and Stabilization Properties of a Liquid Dye on 1064 nm Nanosecond Laser Pulses

A novel liquid dye 2-((2E,5E)-2,5-bis(4-(methyl(2,5, 8,11-tetraoxatridecan-13-yl)amino)benzylidene)cyclopentylidene) malononitrile (TO-BDCM) was synthesized by incorporating two oligo(ethenyl glycol) groups into the backbone of a prototype malononitrile derivative (BDCM) for the purpose of increasing its solubility in organic solvents. The nonlinear absorption properties of this liquid dye on 1064 nm ns pulsed laser were investigated in DMF with remarkably high concentration up to ~1M, showing a superior large nonlinear absorption coefficient of 55.6 cm3/GW2. Fairly good optical limiting and stabilization effects were achieved. Meanwhile, the liquid dye exhibited equivalent stability under laser irradiation compared to its prototype dye BDCM.

PLASTIC LIMIT ANALYSIS OF DISCONTINUOUS LINING UNDERGROUND PRESSURE

Discontinuous lining is a special form of support in underground excavation. Based on the method of plastic limit analysis, it is found the upper and the lower bound solution of the pressure of circular discontinuous lining and discussed support parameter of discontinuous lining and its applicable conditions , which provides theoretical basis for the design and calculation of discontinuous lining.

Techno-Economic Evaluation of Thermal and Catalytic Pyrolysis Plants for the Conversion of Heterogeneous Waste Plastics to Liquid Fuels in Nigeria

Techno-economic potentials of thermal and catalytic pyrolysis plants for the conversion of waste plastics to liquid fuels have been widely studied, but it is not obvious which of the two plants is more profitable, as the existing studies used different assumptions and cost bases in their analyses, thereby making it difficult to compare the economic potentials of the two plants. In this study, industrial-scale thermal and catalytic waste plastics pyrolysis plants were designed and economically analyzed using ASPEN PLUS. Amorphous silica-alumina was considered the optimum catalyst, with 3:1 feed to catalyst ratio. Based on 20,000 tons/year of feed and 20% interest rate, the catalytic plant, having a net present value (NPV) of &#83582208 million, was found to be economically less attractive than the thermal plant, having the NPV of &#83582426.4 million. On the contrary, sensitivity analyses of the two plants at a feed rate of 50,000 tons/year gave rise to a slightly higher NPV for the catalytic plant (&#83589861 million) than the thermal plant having NPV of &#83589838 million, thereby making the former more economically attractive for processing large amounts of waste plastics into liquid fuels. Consequently, as the catalytic plant showed a better scale economy and would produce higher quality liquid fuels than the thermal plant, it is recommended for commercialization in Nigeria.

Mesenchymal Stem Cells Express Low Levels of Cardiomyogenic Genes and Show Limited Plasticity towards Cardiomyogenic Phenotype

Mesenchymal stem cell differentiation towards osteogenic, chondrogenic and adipogenic lineages have been extensively described and reproduced in the literature. In contrast, cardiomyogenic differentiation still remains largely controversial. In this study the authors aim to shed new light into this unclear phenomenon and test whether BMMSC （bone marrow mesenchymal stem cells） and ATMSC （adipose tissue derived mesenchymal stem cells） are able to differentiate into functional cardiomyocytes, investigating two differentiation protocols. AT and BMMSC behaved differently when cultured in differentiation media and presented lower levels of proliferation and alkaline phosphatase production, expression of cardiomyocyte-specific transcription factors such as GATA-4, Nkx2-5 and proteins such as ct and 13 Myosin Heavy Chains. Furthermore, MSC started to express higher levels of Connexin-43 and c~ sarcomeric actinin protein. Unfortunately, though, MSC did not present cardiomyocyte-like electrophysiological properties. In order to analyze a possible explanation for such limited plasticity, the authors decided to address the issue using a quantitative approach. Gene expression was quantified by Real time PCR, and, for the first time, the authors show that a possible explanation for limited plasticity of MSC is that even though differentiated cells presented differential gene expression, the levels of key cardiomyogenic genes did not reach expression levels presented by adult cardiomyocytes, nor were maintained along differentiation, reaching peaks at 4 days of stimulation, and decaying thereafter.

纤维素生物质与废塑料共催化热解制取富烃液体燃料的研究进展

生物质能是国际公认的零碳可再生能源,其高效利用成为缓解能源与环境危机的关键,并对中国实现“碳达峰”和“碳中和”的目标具有重要意义。纤维素生物质与废塑料的共催化热解技术,不仅能制备高附加值的富烃液体燃料,还可达到“以废治废”的目的,进而实现生物质与废塑料的高效资源化利用。本工作从生物质与废塑料高值化利用的角度出发,对生物质和废塑料共催化热解制备富烃液体燃料的研究现状进行了综述,介绍了纤维素生物质和废塑料的基础化学特性差异,论述了废塑料种类、催化剂种类、物料和催化剂比例、催化热解温度等因素对生物质和废塑料共催化热解生物油产率和品质的影响,阐述了生物质和废塑料单独催化热解过程中的化学反应机理,并揭示了共催化热解过程中的协同反应机理,展望了该领域未来的发展方向,为生物质与废塑料的高附加值利用提供参考与思路。

土性对工程泥浆固化强度影响规律及微观机理

本文开展了一系列不同液限高分子吸水树脂固化工程泥浆无侧限抗压强度试验,探讨了泥浆土液限对固化效率的影响规律,对比研究了掺入高岭土对泥浆固化强度的改进程度,最后基于XRD和SEM试验揭示了液限和高岭土对固化泥浆强度影响的微观机理。结果表明:随着泥浆土液限的增大,固化泥浆土强度逐渐降低,固化效率随着泥浆土液限增大显著衰减,当液限增加10%,固化泥浆土强度qu平均减少48.2%。然而高岭土的掺入则显著提升了固化泥浆土的强度,并且强度增长率随着龄期逐渐增大,对于龄期为90天时,增加40%高岭土能够提升固化泥浆土强度qu 1.17倍。微观结构试验表明泥浆土液限变化对水化产物产量的影响较小,固化泥浆土强度随泥浆土液限减小主要是由于固化泥浆土孔隙随着泥浆土液限增大而增多,使得微观结构松散从而导致强度降低。高岭土的掺入则显著提升了固化泥浆土的水化产物产量,增强了固化泥浆土胶结强度,从而提升了固化泥浆土强度。因此,在实际工程中,一方面可以通过调配泥浆土液限来提高固化效率;另一方面可以通过掺入高岭土或者一些高岭土基废弃物(如高岭土尾矿)来提高固化强度,实现“以废制废”绿色环保的理念。

冻融循环下低液限盐渍化粉土力学特性研究

为了研究冻融作用对低液限盐渍化粉土强度的影响,对不同初始含水率低液限盐渍化粉土进行冻融循环试验后,开展不固结不排水(UU)剪切和扫描电镜(SEM)试验,从宏微观角度揭示低液限盐渍化粉土强度的劣化机理。结果表明:未冻融时,含水率的改变不会引起低液限盐渍化粉土应力-应变曲线形态发生变化,均表现为软化型;在冻融作用下,含水率小于14%时试件的曲线形态不会发生改变,呈现软化型,高含水率的试件其应力-应变曲线形态会向着硬化性转变;通过分析冻融和含水率与破坏强度的关系,发现低液限盐渍化粉土破坏强度随含水率的提高呈现线性衰减,破坏强度随冻融循环次数的增加呈现指数型衰减,前3次冻融过程中破坏强度的衰减速率和幅度最大,随后趋于稳定;随着围压的增大,试件的应力-应变曲线会由软化型向硬化型过渡;在微观结构方面,冻融作用会改变土颗粒之间的接触形式,造成孔隙和裂隙的发育,冻融过程中微观结构的变异规律和宏观力学指标的劣化具有一致性。结合土体损伤力学,构建了冻融作用下的低液限盐渍化粉土黏聚力损伤劣化模型,冻融过程中的劣化度符合双曲线关系,最终劣化度A_(c)与含水率呈指数型关系,劣化速率B_(c)与含水率呈线性关系。

基于实验的碳酸盐岩气藏储量计算——以X气藏为例

四川盆地X气藏为碳酸盐岩储层,储层层间及层内都具有较强的非均质性,是气藏储量计算面临的困难之一。针对此问题,本文采用实验方法支撑储量计算,首先通过实验测量得到气藏各小层岩心的孔隙度、渗透率等基础物性参数,将小层渗透率校正为克氏渗透率,并根据物性差异将储层分类为孔隙型储层、孔隙-孔洞型储层,再通过产能模拟实验计算得到气藏工业产能对应的有效储层孔隙度和渗透率等储层物性下限。继而通过液膜厚度实验测得各目标储层的液膜厚度,并结合压汞实验测得的孔径分布曲线,得到有效储层中含烃孔隙体积比例,最后通过地质储量计算公式得到气藏储量。研究结果表明:①利用基础物性测试实验、产能模拟实验、水膜厚度实验等实验方法,确定储层物性下限以及有效孔隙体积比例,为气藏储量计算奠定基础,X气藏有效储层孔隙度下限为1.21%~1.56%;②气藏有效储层中含烃孔隙体积比例范围在42.62%~67.73%,通过地质储量计算公式可得到该气藏的有效储量;③该方法对于非均质性较强的碳酸盐岩储层气藏的储量确定具有理论意义和现场指导意义。

不同种类软土与杂填土互嵌沉降试验研究

为了研究不同种类软土与杂填土互嵌沉降的规律,以下卧的淤泥软土为研究对象,分别开展了不同软土种类在不同荷载及不同液性指数下与上覆杂填土的室内互嵌沉降试验。分析了不同种类软土与杂填土地基在50,100,150 kPa下总沉降、固结沉降及互嵌沉降随时间发展规律,以及不同种类软土分别在液性指数为0.8、1.0、1.2与杂填土地基在100 kPa下总沉降、固结沉降及互嵌沉降随时间发展规律。研究结果表明:三种土样互嵌沉降量与互嵌沉降完成度分别随荷载及液性指数的增大而增大,对于不同土样来说,高液限土的互嵌沉降大于低液限土的互嵌沉降,互嵌沉降完成度在不同的液性指数下具有不同的变化规律。