Evaluation of The Thermal Performance of Multi—Element Doped Graphite under Steady—State High Heat Flux

Multi-element doped graphite,GBST1308 has been developed as a plasma facing material(PFM) for high heat flux components of the HT-7U device.The thermal performance of the material under steady-state(SS) high heat flux was evaluated under actively cooling conditions,the specimens were mechanically joined to copper heat sink with supercarbon sheet as a compliant layer between the interfaces.The experiments have been performed in a facility of ACT (actively cooling test stand) with a 100kW electron gun in order to test the suitability and the loading limit of such materials.The surface temperature and bulk temperature distribtuion of the specimens were investigated.The experimental results are very encouraging that when heat flux is not more than 6 MW/m^2,the surface temperature of GBST1308 is less than 1000℃,which is the lowest,compared with IG-430U and even with CX-2002U(CFC),The primary results indicate that the mechanically-joined material system by such a proper design as thin tile.Super compliant layer,GBST as PFM and copper-alloy heat sink,can be used as divertor plater for HT-7U in the first phase.     

高热流密度电加热元件

本文论述了用于液态金属钠热工水力性能研究的高热流密度模拟电加热元件的结构特点、材料选择、热电偶设置及其他与棒束传热实验研究有关的问题。     

Temperature Distribution and Heat Flux on the EAST Divertor Targets in H-Mode

An infrared camera (IR) has been put into operation in the Experimental Advanced Superconducting Tokamak (EAST), which is used to measure the temperature distribution on the surface of lower divertor target plates. With a finite di®erence method, the heat flux onto the divertor target plates is calculated from the surface temperature profile. The high confinement mode (H-mode) with type-III edge localized modes (ELMs) has been obtained with about 1 MW lower-hybrid wave power on the EAST in the autumn experiment in 2010. The analyzed H-mode discharges were lower single null X-point diverted discharges with a density range of < ne > (1~ 4)x 10¹⁹ m^-3. The surface temperature of the inner target plate increases with heating power. The peak temperature on the surface of target plates is lower than 200 oC with about 2.4 MW heating power. Comparison among the heat flux profiles occurring in di fferent phases in the same discharge has been erformed. It indicates that the heatflux profile obviously changes from the ohmic phase to the H-mode phase, and the full width at half maximum (FWHM) of the heat flux pro file is the narrowest during the ELM-free H-phase. On the outer target plate, the peak heat flux exceeds 2 MW/m2 during the ELMy H-mode phase, whereas it is only about 0.8 MW/m2 during the ELM-free phase in the same discharge.     

偏滤器高热负荷材料研究

用热等静压焊接的方法对两种性能差异很大的金属材料钨和铜进行了成功的焊接。用SEM对断口和焊接界面在各种不同条件下焊接的性能作了对比分析。给出了两种样品的断裂特征和焊接过程中元素的扩散特点。钨和铜合金的结合主要是物理结合 ,是在高温高压下 ,材料表面微观的凹凸不平而产生的犬齿交合结合在一起的 ,扩散结合只占很少的部分。偏滤器靶板的寿命主要决定于靶板材料的热疲劳性能。在真空室中用大功率电子束作为热源进行了热疲劳试验。电子束的功率密度选为 9MW/m2 ,循环周期为 4 0s,冷却水流量为 80mL/s。用直径为 0 .3mm的NiCr NiSi热电偶测量了下材料表面的温度分布。结果发现 ,在冷却充分的情况下 ,表面最高温度约 4 0 0℃ ,钨铜焊缝处的平均最高温度约1 5 0℃。经过 1 0 0 0次的循环加热后 ,没有发现靶板材料出现破坏现象。对试验条件下的材料表面温度分布进行了计算机模拟计算。计算结果和试验测得的结果是相吻合的 ,表明试验结果是真实可靠的     

不对称加热矩形窄缝通道临界热流密度研究

以氟利昂12为冷却介质,对4种加热比条件下的矩形窄缝通道双面不对称加热工况下的临界热流密度(CHF)进行实验分析,获得各种工况下CHF与冷却剂质量流速、入口过冷度、出口含汽率的关系。实验结果表明:低含汽率下,CHF随加热比的增加而增加,随着含汽率的增加,不同加热比的实验通道内CHF差异减小;高含汽率下,CHF随加热比变化趋势与低含汽率的相反。     

Correction to: Flow Boiling Burnout in a Hypervapotron Channel Under High Heat Flux and High Sub-Cooling Conditions

Journal of Fusion Energy - We develop a rapid simulation code for neutral beam injection (NBI) heating analysis, FIT3D-RC, to evaluate the power deposition in NBI-heated plasmas of the Large...     

Study of Striated Heat Flux on EAST Divertor Plates Induced by LHW Using Infrared Camera

An upgraded infrared （IR） imaging system which provides a wide field of view （FOV） has been installed on the Experimental Advanced Superconducting Tokamak （EAST） to monitor the surface temperatures on plasma facing components. Modified magnetic topology induced by lower hybrid wave （LHW） can lead to the formation of striated heat flux （SHF} on divertor plates which can be clearly observed by IR camera. In this paper, LHW power modulation is applied to analyze the appearance of SHF. It is also demonstrated that deuterium （D） pellet injection and supersonic molecular beam injection （SMBI） can to some extent reduce the heat flux on the outer strike point （OSP）, but enhance the SHF on lower outer plates （LOP） of divertor. This may provide an optional approach to actively control the distribution of heat flux on diveror plates, which can protect materials from long duration high-heat flux.     

Design Comparison of Coated Structures for High Heat Flux Components in Fusion Reactor

High heat flux components in fusion reactors are examined from a viewpoint of structural design. Maximum admissible steady heat flux, which can be absorbed and removed by coated structures, was determined by one-dimensional numerical analysis basing on ASME code Sec. HI. Comparison of the current candidate materials is made in order to make heat flux as high as possible. The following conclusions were obtained. (1) Be-Cu structure can be used in order to remove high heat flux beyond 10 MW/m², however, the strong chemical activity of Be gives rise to a problem. (2) SiC-HT-9 and SiC-V alloy structures are promising in case of high heat flux less than 2 MW/m². (3) From thermal stress analysis tungsten and graphite are excellent coating materials and are available for many structural materials. The study of thermal shock resistance and thermal fatigue of these materials is now a problem to be solved.     

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.     

Erosion and Modifications of Tungsten-Coated Carbon and Copper Under High Heat Flux

Tungsten-coated carbon and copper was prepared by vacuum plasma spraying (VPS) and inert gas plasma spraying (IPS), respectively. W/CFC (Tungsten/Carbon Fiber-Enhanced material) coating has a diffusion barrier that consists of W and Re multi-layers pre-deposited by physical vapor deposition on carbon fiber-enhanced materials, while W/Cu coating has a graded transition interface. Different grain growth processes of tungsten coatings under stable and transient heat loads were observed, their experimental results indicated that the recrystallizing temperature of VPS-W coating was about 1400℃ and a recrystallized columnar layer of about 30μm thickness was formed by cyclic heat loads of 4 ms pulse duration. Erosion and modifications of W/CFC and W/Cu coatings under high heat load, such as microstructure changes of interface,surface plastic deformations and cracks, were investigated, and the erosion mechanism (erosion products) of these two kinds of tungsten coatings under high heat flux was also studied.     

密度锁内流体稳态传热模型的建立

根据温度场的特点,将密度锁分为混合区、导热区和恒温区,并分别进行建模。用该模型对密度锁进行稳态传热计算,并与实验结果进行对比。结果表明:本工作建立的稳态传热模型能较好地计算出密度锁内的温度场。研究建立了密度锁的热损失量计算式,并对热损失量最小值的情况进行了讨论。     

Ablation of Fusion Materials Exposed to High Heat Flux in an Electrothermal Plasma Discharge as a Simulation for Hard Disruption

Electrothermal plasma sources operating in the confined controlled arc discharge regime produce heat fluxes in the range expected for hard disruptions in future large tokamaks. The radiative heat flux produced inside of the capillary discharge channel is from the formed high density (10²³–10²⁷/m³) plasma with heat fluxes of up to 125 GW/m² over a period of 100 μs, making such sources excellent simulators for ablation studies of plasma-facing materials in tokamaks during hard disruptions. Graphite, beryllium, lithium, stainless steel, tungsten, copper, and molybdenum are among the materials proposed for use in fusion reactors. Computational experiments with the ETFLOW code using heat fluxes between 10 and 125 GW/m² have shown low total erosion for the low-z materials Li, Be and C and higher erosion for high-z materials Fe, Cu, Mo and W. The time rate of material erosion for various ranges of heat fluxes shows increased erosion with time evolution over the 150 μs pulse length of the simulated disruption event. At the highest values of simulated heat flux, low-z materials were found to ablate almost identically. At all simulated values of heat flux, the ablation of high-z materials correlated positively with the z-number.     

Measurement of Neutron Flux at the Initial Phase of Discharge in EAST

Neutron emission in EAST was investigated by a time-resolved monitor systems which consist of four 3He proportion counters and a 235U fission chamber. The D-D neutron flux increased approximately an order of magnitude during the 27 MHz Ion-cyclotron resonance frequency (ICRF) heating, demonstrating that the ICRF wave heated the plasma effectively. In addition in LHW experiment with higher plasma parameters D-D neutrons were also detected. However, a mass of photoneutrons were generated in ohmic discharges with low plasma density. Effect of plasma density on the production of photoneutrons was studied, and it is found that LHW can suppress the runaway electrons and reduce the photoneutrons effectively.     

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.     

Numerical Study of High Heat Flux Performances of Flat-Tile Divertor Mock-ups with Hypervapotron Cooling Concept

The hypervapotron (HV), as an enhanced heat transfer technique, will be used for ITER divertor components in the dome region as well as the enhanced heat flux first wall panels. W-Cu brazing technology has been developed at SWIP (Southwestern Institute of Physics), and one W/CuCrZr/316LN component of 450 mm×52 mm×166 mm with HV cooling channels will be fabricated for high heat flux (HHF) tests. Before that a relevant analysis was carried out to optimize the structure of divertor component elements. ANSYS-CFX was used in CFD analysis and ABAQUS was adopted for thermal–mechanical calculations. Commercial code FE-SAFE was adopted to compute the fatigue life of the component. The tile size, thickness of tungsten tiles and the slit width among tungsten tiles were optimized and its HHF performances under International Thermonuclear Experimental Reactor (ITER) loading conditions were simulated. One brand new tokamak HL-2M with advanced divertor con?guration is under construction in SWIP, where ITER-like ?at-tile divertor components are adopted. This optimized design is expected to supply valuable data for HL-2M tokamak.     

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.     

Orientation Effects on Critical Heat Flux due to Flooding in Thin Rectangular Channel

Forced convective critical heat flux (CHF) in a rectangular channel that depended on an inclination angle was investigated. The experiment has been performed with a one side-heated thin rectangular channel under the atmospheric pressure with the inclination angle varying from 10° to 90° and mass flux from 0 to 400 kg/m²·s. The CHF was found to decrease with the inclination angle remarkably at low mass flux. Flooding CHF analysis was carried out based on the result of flow visualization in the channel, and the incorporation of inclination angle into a model was proposed. A comparison of the model prediction with experimental results showed good agreement between the measured and predicted CHF with varying inclination angle. The model was combined with a conventional CHF correlation for evaluation of mass flux, and finally a forced convective CHF correlation for an inclined thin rectangular channel was proposed.     

EAST阻性换热器多物理场耦合模拟计算

阻性换热器是EAST高温超导(HTS)电流引线的重要组成部分,目前有三头螺旋翅片和叠片两种结构形式,为了比较这两种阻性换热器的优劣,对它们的热工水力性能进行了多物理场耦合模拟计算,计算结果表明:两种阻性换热器在换热性能方面基本相当,均可满足快速换热的要求,但叠片换热器的流动阻力远小于三头螺旋翅片换热器的。实际运行过程中,三头螺旋翅片换热器中氮冷却回路的压力控制较为困难,经常需人工调节控制阀阀门,而叠片换热器中氮冷却回路的压力控制则较为简单,不需经常调节。因此,叠片式结构较三头螺旋翅片式结构更适合应用在EAST阻性换热器中。     

Heat Transfer and Critical Heat Flux in Transient Boiling, (I)

Heat transfer and critical heat flux in saturated pool boiling were experimentally studied under transient power condition. The heating elements were flat plates of nickel submerged facing vertically in stagnant water. The heat generation rate in the test section was increased linearly in time, upon which, under certain conditions, the heat flux was found to reach a maximum point located in the nucleate boiling regime. The heat flux of this critical point increased with mounting sharpness of the transient, and the mechanism that occurs such a high critical heat flux may be the rapid formation and evaporation of thin liquid film at the bases of vapor bubbles. Examination of high speed motion pictures reveals that all bubbles on the heating surface are still in the phase of the first generation until the critical condition is reached. Compared to the case of steady boiling, the effect of differences in the heat capacity of the test section upon the critical heat flux was found to be less marked under the present experimental conditions.