铅铋冷却绕丝燃料组件横流特性分析

准确预测绕丝棒束通道内的横向流动特性是开展铅铋冷却快堆热工水力安全分析的基础。本文采用数值模拟的方法分析了液态铅铋工质下单绕丝和多绕丝燃料组件内的横流特性。分析结果表明,单绕丝组件的中心子通道横流流速最大不超过主流流速的19%,且横流方向和二次流中心随着高度周期性变化;单绕丝组件中,当绕丝与子通道交界面重合或垂直时,中心子通道界面横向流量和横流交混指数趋于零或达到峰值;在单绕丝组件结构一定的情况下,横流交混指数在湍流区对Re不敏感,而与组件结构参数存在较大相关性;多绕丝组件中心子通道界面上的横流存在两个相反的流向。     

液态铅铋合金湍流普朗特数及RANS模型优选

工程上常采用RANS湍流模型进行热工水力相关的数值模拟,然而液态铅铋合金（LBE）具有独特的热物性,常规湍流普朗特数模型和RANS湍流模型对其流动与传热模拟的适用性有待研究。为更准确地描述绕丝燃料组件内LBE的流动与换热过程,本文基于大涡模拟对湍流普朗特数模型和RANS湍流模型进行优选。首先,采用四种湍流普朗特数模型对绕丝燃料组件内LBE的流动与传热过程进行大涡模拟,对比分析实验数据和模拟结果并进行模型优选。基于优选的湍流普朗特数模型,评价RANS湍流模型对LBE数值模拟的适用性和准确性。结果表明,Cheng湍流普朗特数模型和SST k-ω模型对LBE流动与传热模拟的准确性和适用性最高。     

快堆燃料组件棒束通道内流动和传热现象分析与研究

利用三维计算流体力学软件CFX 12.0对由7根带螺旋状定位绕丝的燃料棒组成的快堆燃料组件典型棒束通道内的流动和传热现象进行了数值模拟。模拟得到不同Re下的压降系数曲线与Nu曲线,并将计算结果与经验公式的计算结果进行了比较,两者符合较好。研究了组件内3类典型子通道的横向流交混效应,分析了3类典型子通道的横向流分布特点,发现角子通道横向流交混强度沿轴向波动较大,而3类子通道的横向流交混强度均存在周期性。研究了中心燃料棒壁面上3个截面的局部换热效应,发现在燃料棒与绕丝接触处传热效果最差,在事故分析时应重点关注。     

铅铋冷却快堆含绕丝燃料组件子通道程序开发与验证

由于铅铋冷却剂流动传热现象的复杂性,准确计算铅铋冷却含绕丝燃料组件的冷却剂和包壳温度是液态金属冷却快堆燃料组件热工分析的重点。本文基于集总参数法对守恒方程进行求解,开发了适用于铅铋冷却快堆的子通道分析程序,对液态铅铋在棒束燃料组件中的摩擦阻力模型、湍流交混模型和对流换热模型进行了适用性分析,并对7棒束大涡模拟和19棒束含绕丝传热实验进行了对比验证。结果表明：包壳和冷却剂温度的最大相对误差低于5%。程序能较好完成铅铋冷却含绕丝燃料组件的热工水力计算,可为铅铋冷却快堆设计提供支持。     

方形子通道内超临界流体流动传热CFD分析

国际上对超临界水冷堆进行了大量的研究,但对其堆芯内超临界流体流动传热特征的认识还十分欠缺.本研究采用CFX软件对典型超临界反应堆燃料组件子通道内的超临界热工水力特征进行了数值分析.研究了流动参数、边界条件和节径比(P/D)对子通道间交混现象和传热特性的影响.计算结果表明:燃料组件外围壁面子通道比内部子通道的湍流交混强烈;稠密栅格的湍流交混比宽栅格的湍流交混小.当P/D>1.2后,P/D比对湍流交混影响不再明显.研究还发现,在拟临界点附近区域,出现湍流交混系数的突变.     

钠冷快堆燃料组件热工水力特性数值模拟与分析

利用CFD程序CFX,分别对7、19、37、61根棒组成的三角形排列螺旋绕丝定位的钠冷快堆燃料组件棒束通道进行了热工水力特性的分析研究,并将结果与子通道程序SuperEnergy进行了对比验证。重点考察了棒束通道轴向流动分布、横向流交混效应及子通道轴向温升,分析了定位绕丝的影响。结果表明,绕丝对棒束通道的横向流交混效应、轴向流动分布及子通道温升有着重要影响,且随棒束的增多,通道内的流动趋向复杂化,轴向流动不均匀性有升高趋势。     

基于CFD方法的铅铋冷却燃料棒束的热工水力特性分析

铅铋冷却快堆作为第4代反应堆候选之一具有安全性高等特点,研究其在正常工况下的热工水力特性具有重要意义。本文基于商用计算流体力学（CFD）软件STAR-CCM+,使用流固耦合的方法对带有绕丝结构的19棒束铅铋组件进行数值分析,探究了质量流量、功率等边界条件对组件内部流动传热特性的影响。模拟计算结果表明：CFD方法在子通道中心温度和壁面温度预测上与实验结果取得了较好的一致。同时,绕丝结构的存在使得子通道之间存在周期性的横向交混,并使得棒束表面温度呈现震荡。随质量流量的增加,子通道间横向交混增大。功率变化对通道间的横向交混速度的影响较小,冷却剂温度的横向分布无明显差异。     

基于CFD方法的铅铋冷却燃料棒束的热工水力特性分析

铅铋冷却快堆作为第4代反应堆候选之一具有安全性高等特点,研究其在正常工况下的热工水力特性具有重要意义。本文基于商用计算流体力学(CFD)软件STAR-CCM+,使用流固耦合的方法对带有绕丝结构的19棒束铅铋组件进行数值分析,探究了质量流量、功率等边界条件对组件内部流动传热特性的影响。模拟计算结果表明:CFD方法在子通道中心温度和壁面温度预测上与实验结果取得了较好的一致。同时,绕丝结构的存在使得子通道之间存在周期性的横向交混,并使得棒束表面温度呈现震荡。随质量流量的增加,子通道间横向交混增大。功率变化对通道间的横向交混速度的影响较小,冷却剂温度的横向分布无明显差异。     

紧密排列燃料组件交混系数试验研究

单相及两相工况下的交混系数是燃料组件热工分析、特别是子通道分析的一个关键参数。本文介绍19根棒束绕丝结构紧密排列燃料组件交混系数单相试验的试验本体结构、试验内容、试验方法及试验结果。试验研究获得了燃料组件出口温度分布及紧密排列燃料组件交混系数,最后对试验结果、交混系数值以及热工参数对交混系数的影响等进行分析。     

中国铅基研究实验堆绕丝燃料组件热工水力分析

在铅基研究反应堆燃料组件设计中,燃料棒之间的绕丝可减少燃料棒在运行过程的机械振动,并使冷却剂在各子通道间有效混合,对绕丝燃料组件内冷却剂的热工水力分析将对燃料组件的设计与优化具有重要意义。本文通过CFD方法对中国铅基研究实验堆(CLEAR-Ⅰ)燃料组件参考设计内的冷却剂流动换热过程进行数值模拟,并分析绕丝组件的速度场、温度场等流场特征量的分布规律。结果表明:绕丝在流场中起着搅混冷却剂的作用,内通道搅混较外通道相对均匀;组件内横向流强度、摩擦系数在入口段先迅速变化,后在充分发展区呈波浪状在其平均值上下波动,努塞尔数变化规律与之类似;包壳最高温度满足安全设计限值。     

SA508钢表面临界热流密度强化试验研究

利用"冷喷涂"多孔涂层制备技术,在反应堆压力容器真实材料SA508Gr3碳钢试验件表面制备了微米尺度多孔涂层。通过可旋转实验装置,在常压下开展了下朝向不同角度条件下池沸腾SA508钢试验件光表面、冷喷涂涂层表面的临界热流密度(CHF)试验研究,获得了2种表面在不同倾角下的沸腾冷却曲线。试验结果表明,随着倾角的增加,CHF增加;采用涂层表面的CHF始终高于光表面的CHF,CHF强化至少在25%以上;在多次加热和冷却循环后,多孔涂层表面保持足够的强度和稳定性。     

CHF enhancement by vessel coating for external reactor vessel cooling

In-vessel retention (IVR) is a key severe accident management (SAM) strategy that has been adopted by some operating nuclear power plants and proposed for some advanced light water reactors (ALWRs). One viable means for IVR is the method of external reactor vessel cooling (ERVC) by flooding the reactor cavity during a severe accident. As part of a joint Korean–United States International Nuclear Energy Research Initiative (K-INERI), an experimental study has been conducted to investigate the viability of using an appropriate vessel coating to enhance the critical heat flux (CHF) limits during ERVC. Toward this end, transient quenching and steady-state boiling experiments were performed in the subscale boundary layer boiling (SBLB) facility at the Pennsylvania State University using test vessels with micro-porous aluminum coatings. Local boiling curves and CHF limits were obtained in these experiments. When compared to the corresponding data without coatings, substantial enhancement in the local CHF limits for the case with surface coatings was observed. Results of the steady-state boiling experiments showed that micro-porous aluminum coatings were very durable. Even after many cycles of steady-state boiling, the vessel coatings remained rather intact, with no apparent changes in color or structure. Moreover, the heat transfer performance of the coatings was found to be highly desirable with an appreciable CHF enhancement in all locations on the vessel outer surface but with very little effect of aging.     

Steady-state Experimental Study of Critical Boiling Heat Transfer on Downward Facing Surface with Pin-fin Coating Structure

Enhancing the critical heat flux (CHF) of boiling heat transfer to achieve in-vessel retention (IVR) strategy has become an urgent requirement of commercial PWR nuclear power plants’ security. A new kind of millimeter-micro multi-scale structure surface was fabricated on the surface of copper substrates by cold spraying technology, which combined pin-fin structures with porous coating structures. Steady-state pool boiling experiment was conducted on a plain copper surface and the pin-fin coating structure surface under different inclination angles. The experimental results show that the CHF increases with the inclination angles on downward facing surface, compared with the plain surface, the pin-fin coating structure enhances the CHF more than 63%, which testifies its superior engineering application prospects.     

朝下针翅结构表面稳态临界沸腾换热实验研究

针对商用压水堆核电站堆内熔融物滞留(IVR)策略对提高压力容器外表面沸腾换热临界热流密度(CHF)的迫切需求,本文采用冷喷涂技术在铜基体表面制备了一种由针翅凸起结构与多孔涂层相结合的毫米-微米双尺度结构表面,运用稳态池沸腾实验研究了铜光表面和针翅涂层结构表面在朝下不同倾角下的沸腾换热性能。结果表明：朝下表面的CHF随倾角的增加而增大,与铜光表面相比,针翅涂层结构表面CHF至少提高了63%,具有较好的工程应用前景。     

Development of a critical heat flux mapping method for fin-structured surfaces

In this study, we performed critical heat flux (CHF) experiments using structured surfaces to validate the parameter effects and understand their physical meanings. Experimental results showed that the CHF has a peak value as the fin geometry changes. Fins with height of 0.5 mm produced the largest CHF, 1.7 MW/m², and fins longer than 2 mm reduced the CHF values. To explain the results, a CHF mapping method was developed describing the liquid supply-side and demand-side limits. The liquid demand-side limit is governed by the heat removal capability, mainly the nucleate boiling, calculated using the hot spot model. We consider three liquid supply-side limits restricting the liquid supply to the heating surface: capillary limit and counter-current flow limitations (CCFLs). The capillary limit is determined by balancing the capillary pressure and viscous dissipation in the liquid film on the fin side. The CCFL in the structure is calculated using the Wallis correlation and the CCFL in the free volume limits the liquid downward flow by the vapor jetting from the heating surface. The CHF map for our experimental results successfully describes the CHF trend of the structured surfaces. As a result, we concluded that CHF mapping method is an effective means of explaining CHF in pool boiling.     

超亲水特性传热面上水喷流冷却时的沸腾换热特性实验研究

研究了在纳米材料涂层形成的超亲水材料传热表面上水喷流冷却时的沸腾换热特性,并与普通金属面上的喷流沸腾特性进行了比较.介绍了流动条件、加热方式、加热条件、超亲水材料涂层等条件对高温沸腾换热、临界热流密度的定量影响和一些基本换热规律.实验发现,超亲水传热表面对沸腾换热特性有十分显著的影响,超亲水传热面强化了喷流沸腾临界热流密度.     

Critical Heat Flux and Near-Wall Boiling Behaviors in Saturated and Subcooled Pool Boiling on Vertical and Inclined Surfaces

The mechanism of the critical heat flux (CHF) where the departure from nucleate boiling (DNB)-type boiling transition takes place has not been fully elucidated. In this paper, we examine the trigger mechanism of the CHF for saturated and subcooled pool boiling on vertical and inclined surfaces based on measurements of the liquid-vapor behaviors near heating surfaces by using a conductance probe. The angle of inclination was varied from 90° (vertical) to 170° (facing almost horizontally downwards). The probe signals and the void fraction distributions showed that a liquid layer remains beneath the vapor masses moving upward along the heating surface at high heat fluxes near the CHF. The thickness of the liquid layer was determined from the location where the probe signals corresponding to the vapor masses disappeared. The thickness of the liquid layer formed on the vertical surface increased with increasing degree of subcooling, which may be the cause of the increases in CHF with increasing degree of subcooling. The measurements of saturated boiling on the inclined surface confirmed that the orientation of the heating surface greatly affects the period it takes for vapor masses to pass, but it negligibly affects the liquid layer thickness. This suggests that the decrease in CHF with increasing angle of inclination is primarily caused by the lengthening of the duration of vapor mass passage.     

Bubble Dynamic Behavior Study on Pool Boiling with Downward Facing Heated Surface

Based on the Matlab software, a program for automatic identification of vapor liquid two-phase flow interface was developed. The program can obtain such characteristics as vapor liquid interface change, vapor film thickness, vapor film departure period and normal velocity. The dynamic data of bubbles on the downward facing heated grooved surface with different inclination angles and heat fluxes were processed and analyzed by this program. The results show that when the downward facing heated surface under the nucleate boiling, the vapor film thickness increases with the heat flux, and the bubble departure period decreases with the increase of the heat flux firstly and then maintains a stable value. The vapor film departure period decreases with the increase of inclination angle, and is about 0.27 s when the inclination angle is 5°. When the boiling crisis occurs, the vapor film thickness decreases rapidly, which can be used as the basis for dynamically monitoring the boiling state of heated surface.     

加热面朝下的池沸腾汽泡动态行为研究

基于Matlab软件开发了自动识别气液两相流界面程序,程序可获得气液界面变化、汽膜厚度、汽膜脱离周期和汽膜法向速度等特征。利用该程序对沟槽结构加热表面朝下布置时,在不同倾角、不同热流密度下的汽泡动态数据进行了处理和分析。结果表明：加热表面朝下发生核态沸腾时,汽膜厚度随热流密度的增大而增大,汽泡脱离周期随热流密度的增大先减小,而后维持在一稳定值;汽膜脱离周期随倾角的增大而减小,倾角为5°时的汽膜脱离周期稳定在0.27 s左右。当发生沸腾危机时,汽膜厚度迅速减小,这可作为动态监测加热表面沸腾状态的依据。     

One-dimensional critical heat flux concerning surface orientation and gap size effects

Tests were conducted to examine the critical heat flux (CHF) on a one-dimensional downward heating rectangular channel having a narrow gap by changing the orientation of the copper test heater assembly in a pool of saturated water under atmospheric pressure. The test parameters include both the gap sizes of 1, 2, 5 and 10 mm, and the surface orientation angles from the downward-facing position (180°) to the vertical position (90°), respectively. Also, the CHF experiments were performed for pool boiling with varying heater surface orientations in the unconfined space at atmospheric pressure using the rectangular test section. It was observed that the CHF generally decreases as the surface inclination angle increases and as the gap size decreases. In consistency with several studies reported in the literature, it was found that there exists a transition angle at which the CHF changes with a rapid slope. An engineering correlation is developed for the CHF during natural convective boiling in the inclined, confined rectangular channels with the aid of dimensional analysis. This correlation agrees with the experimental data of this study within ±20%.