Erosion of Pyrolytic Graphite and Ti-doped Graphite due to High Flux Irradiation

The erosion of pyrolytic graphite and titanium doped graphite RG-Ti above 1,780K was investigated by 5keV Ar beam irradiation with the flux from 4x10¹⁹ to 1x10²¹ m^?2·s^?1. The total erosion yields were significantly reduced with the flux. This reduction would be attributed to the reduction of RES (radiation enhanced sublimation) yield, which was observed in the case of isotropic graphite with the flux dependence of RES yield of φ^?0.26 (φ: flux) obtained in our previous work. The yield of pyrolytic graphite was roughly 30% higher than that of isotropic graphite below the flux of 10²⁰ m^?2·s^?1 whereas each yield approached to very close value at the highest flux of 1x10²¹ m^?2·s^?1. This result indicated that the effect of graphite structure on the RES yield, which was apparent in the low flux region, would disappear in the high flux region probably due to the disordering of crystal structure.

In the case of irradiation to RG-Ti at 1,780K, the surface undulations evolved with a mean height of about 3μm at 1.2×10²⁰ m^?2·s^?1, while at higher flux of 8.0×10²⁰ m^?2·s^?1 they were unrecognizable. These phenomena can be explained by the reduction of RES of graphite parts excluding Tic grains.     

Thermal Performance Study of VPS-W Coatings on CuCrZr Under High Heat Flux

Three tungsten coatings with a thickness of 250 μm, 600μm and 220 μm, respectively, were deposited on a CuCrZr substrate by the vacuum plasma spraying technology. In order to study the thermal performance of the coatings, heat load limit, thermal fatigue lifetime and thermal response tests were performed by means of the electron beam irradiation with a heat flux from 0 MW/m^2 to 10 MW/m^2. Experimental results indicated that tungsten coatings on CuCrZr with a titanium or tungsten/copper interlayer could expel heat flux timely and had good thermal fatigue properties, titanium was a promising compliant layer which provided a reliable way to join tungsten onto the CuCrZr heat sink, even suffering from a heat flux of 10 MW/m^2 or withstanding 54 cycles of fatigue tests under 5 MW/m^2. However, the better quality of tungsten coating itself was necessary because its surface temperature was higher than that of the sample with a tungsten/copper interlayer.     

Behavior of Brazed W/Cu Mockup Under High Heat Flux Loads

In order to transfer the heat from the armor to the coolant, tungsten has to be connected with a copper heat sink. The joint technology is the most critical issue for manufacturing plasma facing components. Consequently, the reliability of the joints should be verified by a great number of high-heat-flux （HHF） tests to simulate the real load conditions. W/Cu brazed joint technology with sliver free filler metal CuMnNi has been developed at Southwestern Institute of Physics （SWIP）. Screening and thermal fatigue tests of one small-scale fiat tile W/CuCrZr mockup were performed on a 60 kW electron-beam Material testing scenario （EMS-60） constructed recently at SWIP. The module successfully survived screening test with the absorbed power density （Pabs） of 2 MW/m2 to 10 MW/m2 and the following 1000 cycles at Pabs of 7.2 MW/m2 without hot spots and overheating zones during the whole test campaign. Metallurgy and SEM observations did not find any cracks at both sides and the interface, indicating a good bonding of W and CuCrZr alloy. In addition, finite element simulations by ANSYS 12.0 under experimental load conditions were performed and compared with experimental results.     

高温钠热管传热性能试验研究

为获得高温钠热管传热性能,开展真空条件下钠热管启动性能和等温性能试验,获得了钠热管真空条件下启动速度与等温性能数据;开展强制冷却工况条件下传热性能试验,获得了钠热管声速限特性与试验工况下的最大传热功率。经试验验证,所研制高温钠热管在真空条件下,580 ℃时完全启动,启动用时20 min,轴向壁面温差低于11 ℃,等温性能良好;钠热管传热功率在工作温度为500～650 ℃时受声速极限限制,在650 ℃以上受携带极限限制;在750 ℃和850 ℃时,测得热管最大散热功率分别为4.78 kW与8.02 kW,对应的最大轴向热流密度分别为1.51 kW/cm²与2.53 kW/cm²。试验结果表明,所研制钠热管具有较强传热能力,可满足热管式核反应堆等工程应用需求。     

干道式高温热管的传热性能试验研究

干道式高温热管传热性能试验主要是为了获得干道式热管在不同温度范围的传热极限及重力场对传热极限的影响。在真空条件下启动热管,调节水套气隙氩气和氦气比例来测量声速极限,建立可调角度台架得到不同倾角下热管的极限传热性能。试验得到400～650 ℃工作温度下热管的极限传热功率曲线及不同倾角下热管的极限传热功率。此类热管510 ℃以下传热极限为声速限;±10°范围内重力对传热极限无影响;极限传热功率为2.8 kW。     

Manufacturing and High Heat Flux Testing of Brazed Flat-Type W/CuCrZr Plasma Facing Components

Water-cooled flat-type W/Cu Cr Zr plasma facing components with an interlayer of oxygen-free copper(OFC) have been developed by using vacuum brazing route.The OFC layer for the accommodation of thermal stresses was cast onto the surface of W at a temperature range of 1150oC-1200 oC in a vacuum furnace.The W/OFC cast tiles were vacuum brazed to a Cu Cr Zr heat sink at 940 oC using the silver-free filler material Cu Mn Si Cr.The microstructure,bonding strength,and high heat flux properties of the brazed W/Cu Cr Zr joint samples were investigated.The W/Cu joint exhibits an average tensile strength of 134 MPa,which is about the same strength as pure annealed copper.High heat flux tests were performed in the electron beam facility EMS-60.Experimental results indicated that the brazed W/Cu Cr Zr mock-up experienced screening tests of up to 15 MW/m~2 and cyclic tests of 9 MW/m~2 for 1000 cycles without visible damage.     

Magnetic Influence on Natural and Marangoni Convections in a Zone of Metal Melted by High Heat Flux

In readiness for utilization as material for the first wall of fusion reactors that will simultaneously generate high heat flux and a high magnetic field, the heat transfer and melting behavior of stainless steel has been numerically analyzed applying the finite difference method. Envisaging the application of a heat flux of 2.34 kW/cm² axially on an 8 mm thick, 60 mm diameter stainless steel disk under an axial magnetic field of intensity varied parametrically, the analysis clarifies the effect of differences in applied magnetic field intensity on the configuration of the melted metal zone boundary, on the flow pattern of convective circulation generated within the same zone, and on the radial temperature distribution across the zone. The analysis is performed both for the cases of natural convection alone taken into account and of combination with Marangoni convection. As a result, it is shown that, assuming steady state, the surface flow velocity at the point of interest varies with the applied magnetic field intensity approximately in inverse proportion to the square of Hartmann number in the case of natural convection alone, and that the same applies to the case of combination with Marangoni convection, though with greater deviation from the foregoing analytical result toward higher magnetic field intensities. It is also shown that the assumption of steady state (adopted in deriving the above relation between surface flow velocity and Hartmann number) becomes valid after the lapse of a short time after the start of heat flux application.     

控制棒驱动机构传热机理与隔热套性能研究

控制棒驱动机构(CRDM)依靠强制冷却措施维持工作温度。本文针对CRDM复杂的轴向传热机理,基于冷热侧流动的假设建立热虹吸自然对流分析模型,计算得到轴向温度分布及隔热套内径与热虹吸传热量之间的关系曲线;同时进行验证试验,测量不同情况下CRDM内外轴向温度分布和总散热量。通过分析和试验对比证明:基于假设的分析模型能模拟实际情况,热虹吸传质传热是CRDM轴向传热的主要途径,设置隔热套能有效抑制热虹吸、减少散热量。     

高温、高流速氢气在圆管内流动换热特性研究

为探究工质在核热推进反应堆冷却剂通道内的热工水力行为,基于数值计算方法,开展了圆管内高温、高流速氢气流动换热特性研究。通过与实验数据对比发现,采用压力基耦合算法、SST k-ω湍流模型以及物性模型进行高温、高流速氢气流动换热特性数值模拟是合理可行的,计算值与实验值符合较好,计算模型选择正确。在分析基础工况流场与温度场的基础上,还研究了热工参数对氢气管内流动换热特性的影响,结果表明,随质量流量的增大换热效果增强,随热流密度的增大换热效果变差。研究方法与结果可为高温、高热流密度环境下气体工质流动换热特性研究、核热推进反应堆的热工设计与仿真模拟提供参考。     

Heat Transfer Performance of High Temperature and High Velocity Hydrogen Flow inside Circle Tube

In order to investigate the thermo-hydraulic characteristics of working fluids in the coolant channel of nuclear thermal propulsion reactors, the flow and heat transfer performance of high temperature and high velocity hydrogen in the circle tube was studied by the numerical calculation method. Comparing with the experimental data, it is found that the pressure-based coupled algorithm, SST k-ω turbulence model and hydrogen property model are reasonable and feasible to simulate the flow and heat transfer performance of hydrogen at high temperature and high velocity. The calculated values agree well with the experimental data, and the numerical simulation model is correct. Based on the analysis of flow and temperature field of the base case, the effects of thermal parameters on the flow and heat transfer performance of hydrogen were also studied. The increasing inlet mass flow rate enhances heat transfer performance and the increasing heat flux weakens it. The methods and results can provide some references and guidance for the study of the flow and heat transfer performance of gaseous fluid under high temperature and high heat flux, and thermal design and simulation of nuclear thermal propulsion reactor.