螺旋型波纹管流阻测量系统研制及液氮压降测量

超导电缆芯通常内嵌于真空绝热波纹管并被管内低温流动介质冷却和保护。螺旋型波纹管因一次成型制作长度上的优势更适合于大长度超导电缆应用。设计并搭建了螺旋型波纹管液氮流动压降特性实验台,不仅可以方便地更换被测波纹管样品,而且允许插入不同规格的线芯模拟物。利用该实验台测量了液氮流量1～9 L/min区间内不同规格(通径11～15 mm)螺旋型波纹管插入4 mm线芯后的流动压降特性。实验结果验证了三维波纹管压降损失数值模型的准确性。同时,通过进行不同尺寸波纹管实验,发现尺寸变化对摩擦因子变化规律的影响不明显,这为通过该实验台获得小管径实验数据用于指导大管径实际应用波纹管设计提供了理论基础。     

波纹管内流动特性的实验研究

随着超导技术的发展,高温超导电缆在电力输运中逐渐得到重视并进行了广泛的研究.由于波纹管具有良好的柔韧性和收缩性,在高温超导电缆中得到应用.波纹管内的流动压力损失参数是高温超导电缆低温系统重要的设计参数,因而研究波纹管内的流动特性具有重要的意义.对通径为6 mm,8 mm和10 mm的波纹管内液氮和氮气的流动特性进行了实验研究.液氮实验结果表明:液氮在波纹管内的流动具有波动性.在4000～40000的雷诺数范围内,测量了氮气的质量流量和压力损失,计算得到流动摩擦系数.分析表明:压力损失随雷诺数的增大而增大;波纹管的摩擦系数要高于光管,摩擦系数随雷诺数的增大而减小,摩擦系数随t/d的减小而减小.     

高温超导电缆波纹管内液氮流动阻力特性实验平台搭建与分析

介绍了搭建高温超导电缆用波纹管内液氮流动阻力特性实验平台的搭建过程及其工作方式与原理。给出液氮的流动阻力特性实验测试,并与数值计算结果进行了对比分析。实验结果表明压力损失随着液氮流量的增大逐渐增大,出压差大致与流速的平方成正比。     

结构参数对波纹管内液氮流动与能量损失的影响

高温超导电缆通常浸泡在采用真空多层绝热保护的双层波纹管内程管的液氮中。液氮在超导电缆内流动的压力损失和冷却效果是其运行系统设计的重要参数。对不同直径的波纹管进行了不同流量下的CFD仿真计算,结果表明流量越大、直径越小,压降越大;波高直径比与波高波距比不变时,波纹管的达西流动阻力系数与波纹管的直径基本无关;波纹管直径对超导电缆的沿程温升几乎没有影响;增大波纹管的直径能够大幅降低超导电缆的沿程能量损耗。该文结果为超导电缆设计过程中波纹管的选取提供了理论依据。     

倾斜角度对管内液氮流动阻力系数的影响

高温超导电缆大都采用带真空多层绝热保护的双层波纹管作为冷却电缆的液氮套管。波纹管内含有超导电缆时液氮的流动压力损失是其低温系统设计的重要参数。超导电缆根据实际布置需要,存在按一定角度倾斜排布的情况。对倾斜角度的波纹管进行了液氮流动实验,考察倾斜角度和流动阻力系数的关系。同时,也对光滑圆管进行不同倾斜角度的CFD仿真,考察光滑圆管内液氮流动受到不同角度下重力作用的影响。通过上述两方面的研究,得出结论认为在超导电缆实际应用中,电缆的倾斜不会对液氮的流动压力损失造成明显影响。     

铋系高温超导直流电缆的研制

6m长,2000A的铋系高温超导直流电缆在中国科学院电工研究所研制并试验成功,电缆的导体由8层共238根Bi-2223/Ag带材在不锈钢波纹管骨架上螺旋绕制而成,导体的内径为41．5mm,导体层间绝缘,导体层外侧有低温电绝缘,电缆芯的外径为48mm,它安装在低温容器内,并与两个终端相连,电缆的直流耐压大于2．5kV,在液氮下的实验表明,电缆的临界电流为2480A（1uV/cm判据）,n值为7．7,接头总电阻为0．1mΩ,均超过设计指标,在1h传输2kA电流的运行中,电缆的传输特性稳定,经4次热循环,电缆的临界电流没有降低。     

高温超导电缆用波纹管内液氮流动特性的数值研究

随着超导技术的发展,高温超导电缆在电力输运中逐渐得到重视并进行了广泛的研究。由于波纹管具有良好的柔韧性和收缩性,在高温超导电缆中作为杜瓦放置电缆,冷却超导体用的液氮需流经波纹管。在系统设计中,需要对液氮在波纹管中的流动特性加以了解。为了研究液氮在波纹管内的流动特性,对其进行了数值计算及理论分析。分析表明:压力损失随入口速度的增大而增大;在波纹内形成了涡旋流;在所考察的雷诺数范围内,雷诺数对摩擦系数的影响不大,而波纹尺寸对摩擦系数具有主要的影响。摩擦系数随s/t的增大而减小。。     

1kA级铋系高温超导模型电缆的研制

我们研制了一根１０００Ａ级铋系高温超导模型电缆。电缆由不锈钢波纹管骨架、导体层、层间绝缘和外绝缘绑扎带组成。电缆的导体层由６层共１７１根Ｂｉ－２２２３／Ａｇ多芯带材绕制而成，电缆外径为４５．２ｍｍ，长度为１ｍ。在液氮下的通电实验表明，电缆的临界电流超过１１８０Ａ（１μＶ／ｃｍ判据），接头总电阻小于０．０６μΩ，均超过设计指标。经两次热循环实验，电缆的临界电流仅退化２．７％，在半小时传输电流１ｋＡ的     

高温超导大电流导体临界电流特性研究

YBCO带材在高磁场下仍有好的通流性能,可以用多根高温超导带材构成大电流导体用于高场磁体。为减小导体的交流损耗,大电流导体有多种结构形式,缠绕型和扭转堆叠是其中的两种结构形式。临界电流是高温超导大电流导体的重要指标之一。文中采用四引线法对这两种导体结构在液氮、自场环境下的临界电流特性进行了实验测量,分析并总结了其临界电流特性与结构的关系。     

CFETR CS模型线圈NbTi导体的管内压降分析

CICC导体的压降是设计及应用过程中的重要问题。为了研究CFETR CS模型线圈NbTi的管内流体阻力性能,对模型线圈的NbTi导体进行了实验和理论的分析。压降实验采用氮气作为流体工质,测试不同流量下,导体的进出口压降。理论分析采用一种一维模型描述双通道流体,引用电缆区域及中心孔区域的摩擦因数描述流道阻力进行计算,并与测试结果作分析比较,为实际应用中的氦流体在导体中的稳态流动阻力计算提供了一种理论方法。     

A soft EOS from flow and elliptic flow

We find that results for flow and elliptic flow from Au+Au collision at 20–60 AMeV and Ar+Sc from 45 to 105 AMeV are best explained using transport models incorporating a soft equation of state.     

Force-coupling method for particulate two-phase flow: Stokes flow

In this paper we describe a force-coupling method for particle dynamics in fluid flows. The general principles of the model are described and it is tested on three different Stokes flow problems; a single isolated sphere, a pair of otherwise isolated spheres, and a single sphere in a channel. For sphere to sphere or sphere to wall distances larger than 1/4 of the sphere radius the force-coupling results compared well with analytical and accurate numerical values. For smaller distances the results agree qualitatively, but lubrication effects are not included and this leads to a quantitative discrepancy.     

The flow noise level at microphones in flow ducts

When sound measurements are made in flow ducts one has to insure that the signal-to-noise ratio of the sound signal to the flow noise, which is produced by the turbulent flow at the microphone, is sufficiently high. To accomplish this, knowledge of the flow noise level under the specific given flow conditions is required. In this paper two procedures for determining the flow noise level are described. For the first method, the mean flow velocity and the turbulence level have to be known to estimate the flow noise level as a function of duct diameter and frequency. For the second method knowledge of only the mean flow velocity is required. The procedure involves two measurements: one with a microphone fitted with a conventional nose cone and one with a microphone fitted with a slit-tube. The slit-tube is a special device for reducing the flow noise level. Finally, guidelines are given for sound measurements in the presence of flow and for the use of a microphone with a slit-tube under unusual temperature conditions or in gases other than air.     

Degeneration of flow pattern in acousto-elastic flow through sharp-edge microchannels

Acoustic streaming (AS) is the steady time-averaged flow generated by acoustic field, which has been widely used in enhancing mixing and particle manipulation. Current researches on acoustic streaming mainly focus on Newtonian fluids, while many biological and chemical solutions exhibit non-Newtonian properties. The acoustic streaming in viscoelastic fluids has been studied experimentally for the first time in this paper. We found that the addition of polyethylene oxide (PEO) polymer to the Newtonian fluid significantly altered the flow characteristics in the microchannel. The resulting acousto-elastic flow showed two modes: positive mode and negative mode. Specifically, the viscoelastic fluids under acousto-elastic flow exhibit mixing hysteresis features at low flow rates, and degeneration of flow pattern at high flow rates. Through quantitative analysis, the degeneration of flow pattern is further summarized as time fluctuation and spatial disturbance range reduction. The positive mode in acousto-elastic flow can be used for the mixing enhancement of viscoelastic fluids in the micromixer, while the negative mode provides a potential method for particle/cell manipulation in viscoelastic body fluids such as saliva by suppressing unstable flow.     

Charge inversion and flow reversal in a nanochannel electro-osmotic flow

Ion distribution and velocity profiles for electro-osmotic flow in a 3.49 nm wide slit channel with a surface charge density of -0.285 C/m(2) are studied using molecular dynamics simulations. Simulation results indicate that the concentration of the co-ion exceeds that of the counterion in the region 0.53 nm away from the channel wall, and the electro-osmotic flow is in the opposite direction to that predicted by the classical continuum theory. The charge inversion is mainly caused by the molecular nature of water and ions. The flow reversal is caused by the immobilization of counterions adsorbed on the channel wall and due to the charge inversion phenomena.     

Time-of-flight flow imaging of two-component flow inside a microfluidic chip

Here we report on using NMR imaging and spectroscopy in conjunction with time-of-flight tracking to noninvasively tag and monitor nuclear spins as they flow through the channels of a microfluidic chip. Any species with resolvable chemical-shift signatures can be separately monitored in a single experiment, irrespective of the optical properties of the fluids, thereby eliminating the need for foreign tracers. This is demonstrated on a chip with a mixing geometry in which two fluids converge from separate channels, and is generally applicable to any microfluidic device through which fluid flows within the nuclear spin-lattice relaxation time.