Effect of a helical wire on mixed convection heat transfer to carbon dioxide in a vertical circular tube at supercritical pressures

Reactor core of a SCWR (supercritical water-cooled reactor) employs a tight lattice in order to efficiently remove heat from nuclear fuels. In the narrow sub-channels of a tight lattice reactor core, a helical wire instead of a complicated conventional spacer has been used as a turbulence generator and a space-keeper between the fuel rods.A series of experiments were performed in order to investigate an effect of a helical wire on heat transfer to upwardly flowing CO₂ in a electrically-heated circular tube with an inner diameter of 6.32 mm, where a helical wire with an outer diameter of 1.3 mm was tightly inserted inside the tube. The tube inner diameter corresponds to the equivalent hydraulic diameter of a sub-channel of a KAERI’s fuel assembly concept. The mass fluxes ranged from 400 to 1200 kg/m² s; the heat fluxes ranged from 30 to 90 kW/m²; and the pressures were 7.75 and 8.12 MPa. The corresponding Reynolds numbers at the test section inlet ranged from 1.8 × 10⁴ to 7.5 × 10⁴. The heat transfer rate reached almost twice the value obtained from the experiment with a plain tube of the same size near the pseudocritical temperature and the effect of a wire was attenuated as the temperature moved away from the pseudocritical temperature. The wall temperature distribution along the span between the contact points was a concave downward parabola. Near the pseudocritical temperature, the wall temperature showed relatively higher values, indicating a stagnant fluid around the wire. On the other hand, the wall temperature at the contact point showed a relatively lower value, indicating a fin function of a wire.     

水电站蜗壳垫层平面铺设范围的确定原则

目前工程界对如何合理确定水电站蜗壳垫层平面铺设范围尚无统一认识.本文采用三维有限元方法,从座环位移变形、座环抗剪性能、机墩结构位移变形、流道结构承受的扭转力比例四个方面讨论了垫层平面铺设范围的确定原则.研究结果表明,若蜗壳结构问题的主要矛盾是座环和机墩位移变形过大,则平面上垫层末端宜设置在蜗壳135°～180°断面之间;但从改善座环抗剪性能和流道结构受力条件的角度来讲,垫层末端宜设置在蜗壳0°～90°断面之间或270°断面之后.考虑到座环抗剪性能和流道结构受力条件可以通过局部的工程措施予以改善,因此应该优先考虑座环和机墩结构的不均匀变形问题,据此确定蜗壳垫层平面铺设范围.     

基于涡流发生器的翼型失速流动控制及雷诺数效应影响研究

针对所设计的三角形涡流发生器开展用于翼型失速流动控制的风洞实验研究,重点讨论涡流发生器几何参数、方向角、安装位置及实验雷诺数等因素对翼型失速流动控制的影响。实验结果表明:涡流发生器作用下,在干净翼失速迎角后能够形成一个升力几乎不随迎角变化的相对稳定的高升力状态,抑制了失速流动的发生,与此同时阻力大幅下降;本文所设计的涡流发生器方向角过大时会削弱翼型失速流动控制的效果;同一涡流发生器作用下雷诺数过大其失速流动控制效果会急剧恶化,第一种涡流发生器控制翼型失速的雷诺数有效范围略宽于第二种涡流发生器。     

长脉冲高功率无箔二极管动力学模拟

 从二极管设计基础出发,对高功率无箔二极管动力学特征进行了模拟分析。结果表明：电子回轰必须被隔断,不仅不能让其轰击支撑绝缘体,也不能轰击二极管管壁。在直线变压器长脉冲功率源二极管实验研究中,通过合理设计阴极屏蔽座,获得了重复频率25 Hz、功率约5 GW、功率传输系数超过95%的环形电子束输出。     

低磁场过模慢波结构型高功率毫米波发生器的改进

 利用粒子模拟的方法设计了一个高功率毫米波发生器,并对其进行了实验研究及改进。采用过模慢波结构以增大束波作用空间,从而提高功率容量;为实现过模慢波器件的单模、单频工作,选择TM01模的π模作为工作模式。采用过模慢波结构,结合合理的器件结构设计,可降低器件工作所需的导引磁场。实验在TORCH-01加速器平台进行,产生的微波频率由色散线法测量,其功率由远场积分法得到。最初的器件采用矩形波纹慢波结构,得到频率为33.56 GHz、功率约110 MW的微波输出,但功率难以进一步提高,脉宽仅为7~8 ns,且在慢波结构边沿发现击穿痕迹。对矩形慢波结构进行倒圆角处理后,借助数值模拟,发现其TM01模的π模频率变化不大。改进后的器件在0.8 T导引磁场下,当电压和电流分别为590 kV与5.2 kA时,实验得到频率33.56 GHz、功率320 MW的毫米波输出,微波模式为准TM01模,效率约10%,脉宽延长至约13 ns,器件内表面无明显击穿痕迹。     

一种紧凑型宽谱辐射源

 采用快前沿Marx发生器直接驱动辐射天线,设计了一种紧凑型宽谱辐射源。Marx发生器采用3 300 pF低电感陶瓷电容器作为储能电容,采用螺旋形空芯电感作为充电电感,通过各级气体火花开关迅速放电,在负载上建立了陡化前沿的输出电压波形。系统设计为同轴一体化结构,整个Marx发生器放置在一个密封的金属圆筒内,通过充氮气或者六氟化硫气体来绝缘。辐射系统包括振荡器及辐射天线两部分,系统辐射场中心频率为206 MHz,辐射因子40 kV,可重复频率10 Hz运行。     

低抖动快前沿高电压重复率触发器

 介绍了一种低抖动、快前沿高电压重复率触发器,输出参数为：重复率可达100 pulse/s,输出时延约225 ns,抖动约1 ns,前沿约26 ns,脉宽约70 ns,高阻负载上电脉冲的峰值可达-40 kV,重复率为50 pulse/s时,峰值可达-51 kV,单次工作时的峰值可达-60 kV。该触发器主要由控制单元、高压供电单元与脉冲形成单元构成,脉冲形成单元采用了低电感电容对负载快放电的结构,建立开关为氢闸流管。实验发现,氢闸流管存在微导通状态,开关的通道电阻及维持的时间与开关极间的电势差有关;电势差越高,通道电阻越小,微导通状态维持的时间越长。此外,氢闸流管的导通性能受灯丝加热电源的影响明显,当加热电压较低时,氢闸流管导通缓慢,延时与抖动较大,当加热电压过高时,氢闸流管易于发生自击穿。     

Thermoelectric generator based on a bismuth-telluride alloy fabricated by addition of ethylene glycol

This paper introduces a new method to selectively fabricate n-type and p-type bismuth (Bi)-telluride (Te) thermoelectric materials by the rate of addition of ethylene glycol (EG) in the Bi–Te co-electrodeposition solution. As the amount of added EG is increased, the atomic ratio of Bi in the deposited Bi–Te alloy reached a slope of 0.463 (at.% of Bi/vol.% of EG), and increased in a linear manner. When the EG content reached approximately 20%v/v, the n-type material changed into a p-type. This change implies that adjusting the EG content in the electrodeposition solution affords simple control of the Bi–Te composition. To demonstrate the applicability of the developed thermoelectric materials, thermoelectric generators (TEGs) were fabricated using electrodeposited n-type (using solution without EG) and p-type (using solution with 30%v/v EG) Bi–Te alloys. The Seebeck voltage of the pair of n-type and p-type thermoelectric materials was 140 mV and the power generated from the pair was 24.36 nW at a 10 °C temperature difference.     

An exclusive event generator for e＋e- scan experiments

An exclusive event generator is designed for e＋e- scan experiments, including initial state radiation effects up to the second order correction. The generator is coded within the framework of BesEvtGen. There are seventy hadronic decay modes available, with effective center-of-mass energy coverage from the two pion mass threshold up to about 6 GeV. The accuracy achieved for the initial state radiation correction reaches the level achieved by the KKMC generator. The uncertainty associated with the calculation of the correction factor to the initial state radiation is dominated by the measurements of the energy-dependent Born cross section.     

Study of the performance of a thermoelectric generator transformation of the thermal energy conveyed by a heat transfer fluid into electrical energy

A mathematical model to predict the maximum energy conversion efficiency of the thermoelectric generator is developed to improve the performance and maximize the energy conversion efficiency of the thermoelectric power generator. The studied device corresponds to an original configuration of thermoelectric modules mounted on the peripheral surfaces of two channels, one of the channels is crossed by hot fluid and the other by a cold fluid. First, the effect of the flow rate was studied to choose the flow rate adapted to our study for three different configurations of the thermopile, the co-current configuration, the counter-current configuration, and the sandwich configuration. Then a comparison was made to choose the best configuration between these three studied configurations by addressing their thermoelectric performances. The results revealed that the sandwich configuration is much better than the co-current and counter-current configurations and reduces the surface area occupied by the TEG by half while generating more power than a solar panel.