液态金属内单个气泡上升行为的MPS法数值模拟

液态金属冷却核反应堆采用气泡泵的概念设计来提升堆芯自然循环能力。液态金属内气液两相流动特征将直接影响核反应系统一回路的自然循环能力及堆芯安全。本研究通过采用移动粒子半隐式（MPS）方法,对液态金属中单个上升气泡的气泡动力学行为进行数值模拟。分析了铅铋合金中3种初始直径不同的单个氮气泡在上升过程中的气泡形状和速度的变化趋势;对比了初始直径相同的单个氮气泡在液钾、液钠、铅铋合金、钾钠合金和锂铅合金5种液态金属中的上升行为;同时将模拟得到的气泡形状与Grace经验关系图进行了对比,验证了MPS方法数值模拟结果的正确性。     

液态金属螺旋管式直流蒸汽发生器数值模拟研究

螺旋管式直流蒸汽发生器(HCOTSG)是一种蒸汽发生器常用形式。得益于其特殊的优势,HCOTSG被广泛用于各类反应堆动力系统中。本文提出了利用计算流体力学软件（FLUENT）对液态金属HCOTSG的壳侧液态铅铋、管侧两相流体进行耦合流动传热计算的CFD方法,并通过与相关实验研究结果的对比验证了数值模拟方法的正确性。在此基础上,本文对HCOTSG在典型工况下开展了数值模拟计算,得到蒸汽发生器内部的热工水力参数分布情况,并对其内部的流动换热特性进行分析。本研究为液态金属HCOTSG流动换热特性研究及结构设计优化提供新的思路方法。     

液态金属与冷却剂相互作用机械能释放模型分析

基于熔融金属与冷却剂相互作用蒸汽爆炸粗混合理论分析,本文对高化学活性液态金属与冷却剂相互作用过程的化学反应及金属液滴细粒化过程进行了分析,建立了液态金属与冷却剂相互作用爆炸的机械能释放模型及爆炸压力峰值模型,研究表明溶解在金属液滴表面热边界层的氢气快速释放将导致熔融金属液滴表面细粒化,使高化学活性液态金属与冷却剂相互作用面积瞬间增大,快速释放的化学反应热使能量释放量级增加,模型计算结果与实验结果符合较好,能够分析不同液态金属初始温度和液态金属初始质量对能量释放及爆炸强度的影响。     

液态金属与冷却剂相互作用机械能释放模型分析

基于熔融金属与冷却剂相互作用蒸汽爆炸粗混合理论分析,本文对高化学活性液态金属与冷却剂相互作用过程的化学反应及金属液滴细粒化过程进行了分析,建立了液态金属与冷却剂相互作用爆炸的机械能释放模型及爆炸压力峰值模型,研究表明溶解在金属液滴表面热边界层的氢气快速释放将导致熔融金属液滴表面细粒化,使高化学活性液态金属与冷却剂相互作用面积瞬间增大,快速释放的化学反应热使能量释放量级增加,模型计算结果与实验结果符合较好,能够分析不同液态金属初始温度和液态金属初始质量对能量释放及爆炸强度的影响。     

涡流扩散率及其对湍流放热的影响

一、前言目前还没有一精确计算湍流流体放热的公式,特别是对液态金属。虽然液态金属是牛顿流体,但它有非常高的导热系数和低的粘性。因此,普朗特数Pr是极低的,约10~(-2)级。在湍流流动里,低Pr数的影响是:分子热传导不仅在粘性底层重要,而且在过渡层,甚至在流体核心区也重要。现在计算一般流体的放热准则—N_α数,可用熟知的雷蓓(Reynibs)比拟,普朗特(Pramdtl)比拟,卡门(Karman)比拟和马丁耐里(Martinelli)比拟等等。在这些比拟中,或没考虑涡流热扩散率,或假设了涡流热扩散率C_H“等于涡流动量扩散率ε。如果把这些比拟用于液态金属的放热计算就必须加以修正。鲁比辛(Rubesin)曾修正了卡门比拟式,德赖斯别(Van Driest)也修正了卡门比     

ITER中国液态锂铅实验包层模块液态金属流动MHD效应数值模拟

为研究国际热核聚变实验堆(ITER)的中国双功能锂铅实验包层模块(DFLL-TBM)中液态金属磁流体动力学(MHD)效应,对在强磁场环境下磁流体动力学效应对液态金属LiPb流动和传热的影响进行数值模拟和分析.主要包括三部分:(1) 建立模拟液态金属磁流体的磁感应方程数学模型和程序简介;(2) 对液态LiPb MHD流体在全模块内流动的数值模拟,给出了速度场和压力场分布,重点考察和分析局部的流动特点和对传热的影响;(3) LiPb在进口供给联箱内的流场的数值模拟,对供给联箱的分流作用给出了初步的估算和评价.     

基于OpenFOAM的液态金属铅铋三维流动换热特性数值模拟研究

铅铋快堆是第4代核能系统的主要堆型之一,但由于液态金属铅铋的热物性与传统工质如水、空气等有很大不同,假设流动边界层与热边界层相似的雷诺比拟原理已不再适用。本文在开源程序OpenFOAM中开发了基于k-ε-k_θ-ε_θ四因子模型的自定义求解器,考虑热边界层与流动边界层的差异性,对带绕丝棒束通道中液态金属铅铋的流动换热现象进行数值模拟,得到了速度、温度等重要热工水力参数的三维分布,揭示了绕丝对冷却剂流动传热过程的影响规律,并将计算结果与经典实验关联式进行对比,结果符合良好,证明了所用模型和程序的正确性。本研究可为在OpenFOAM中添加新模型、开发自定义求解器以及开展针对液态金属流动换热问题的计算流体动力学（CFD）模拟提供参考。     

钠冷快堆分析程序ATHAS-LMR的子通道模型

以子通道模型和绕丝分布式阻力模型为基础,研发了液态金属快中子增殖堆热工水力子通道分析程序ATHAS-LMR,以对液态金属快中子增殖堆燃料组件中的热工水力现象进行分析。与国外知名实验和类似子通道分析程序比较,结果表明：ATHAS-LMR与实验结果及其他子通道分析程序的结果相近,能够完成包括堵流工况的各种工况下液态金属快中子增殖堆组件的热工水力性能分析。     

液态金属镓回路搭建及无窗靶实验研究

液态金属回路是开展液态金属散裂靶关键技术与实验验证的必备实验平台。镓具有较低的熔点、非常高的沸点,且无毒性,可在液态金属回路实验中作为模拟介质使用。本文介绍了一套小型液态金属镓回路的设计思路、结构组件、基本功能及使用流程,给出了液态镓在变频离心泵驱动下强制对流的流量、压力、压差及无窗靶自由液面位置和形态的实验测量结果,并分析了压力、压差及自由液面位置随流量的变化关系。结果表明,无窗靶自由液面位置主要由流体压力和流速决定。     

聚变发电反应堆双冷锂铅包层液态金属流动MHD效应计算与分析

对液态金属LiPb流体在规则直管和异形管内流动的磁流体动力学(MHD)效应问题进行了理论分析和数值模拟,并给出这两种情况下的压降和功耗比。在此基础上,对FDS-Ⅱ的双冷液态锂铅(DLL)包层模块的MHD压降和功耗进行计算分析,并给出关键流道(直管和典型异形管)和全模块的数值模拟结果,为包层的结构和热工水力设计提供参考。     

水平管内含空气蒸汽强制对流冷凝换热模型研究

为研究含空气蒸汽在水平管内强制对流冷凝换热特性,基于对传热传质过程的分析,建立了管内为环状流与波状流条件下的流动冷凝换热模型。从潜热、显热和液膜3个环节对整个换热过程进行建模,最终得到计算局部冷凝换热系数的理论关系式。模型预测结果与实验数据的对比表明,二者相对偏差在±20%以内,验证了该换热模型的准确性与适用性。通过进一步的研究发现：从换热管入口至出口,随着冷凝的进行,管内换热主要热阻由液膜热阻向气液界面的凝结热阻转变;主流气体对流换热过程基本可忽略。     

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。     

Experimental research on heat transfer to liquid sodium and its incipient boiling wall superheat in an annulus

Liquid sodium is mainly used as a cooling fluid in the liquid metal fast breeder reactor （LMFBR）, whose heat transfer, whether convective heat transfer or boiling heat transfer, is different from that of water. So it is important for both normal and accidental operations of LMFBR to perform experimental research on heat transfer to liquid sodium and its boiling heat transfer. This study deals with heat transfer with high temperature （300-700℃） and low Pe number （20-70） and heat transfer with low temperature （250-270℃） and high Pe number （125-860）, and its incipient boiling wall superheat in an annulus. Research on heat transfer involves theoretical research and experiments on heat transfer to liquid sodium. It also focuses on the theoretical analysis and experimental research on its incipient boiling wall superheat at positive pressure in an annulus. Semiempirical correlations were obtained and they were well coincident with the experimental data.     

Investigation of forced convection heat transfer of supercritical pressure water in a vertically upward internally ribbed tube

In the present paper, the forced convection heat transfer characteristics of water in a vertically upward internally ribbed tube at supercritical pressures were investigated experimentally. The six-head internally ribbed tube is made of SA-213T12 steel with an outer diameter of 31.8 mm and a wall thickness of 6 mm and the mean inside diameter of the tube is measured to be 17.6 mm. The experimental parameters were as follows. The pressure at the inlet of the test section varied from 25.0 to 29.0 MPa, and the mass flux was from 800 to 1200 kg/(m² s), and the inside wall heat flux ranged from 260 to 660 kW/m². According to experimental data, the effects of heat flux and pressure on heat transfer of supercritical pressure water in the vertically upward internally ribbed tube were analyzed, and the characteristics and mechanisms of heat transfer enhancement, and also that of heat transfer deterioration, were also discussed in the so-called large specific heat region. The drastic changes in thermophysical properties near the pseudocritical points, especially the sudden rise in the specific heat of water at supercritical pressures, may result in the occurrence of the heat transfer enhancement, while the covering of the heat transfer surface by fluids lighter and hotter than the bulk fluid makes the heat transfer deteriorated eventually and explains how this lighter fluid layer forms. It was found that the heat transfer characteristics of water at supercritical pressures were greatly different from the single-phase convection heat transfer at subcritical pressures. There are three heat transfer modes of water at supercritical pressures: (1) normal heat transfer, (2) deteriorated heat transfer with low HTC but high wall temperatures in comparison to the normal heat transfer, and (3) enhanced heat transfer with high HTC and low wall temperatures in comparison to the normal heat transfer. It was also found that the heat transfer deterioration at supercritical pressures was similar to the DNB at subcritical pressures.     

Experimental heat transfer in supercritical water flowing inside channels (survey)

This literature survey is for heat transfer to supercritical water flowing in channels. The objectives are to assess the work that was done and to understand the specifics of heat transfer at these conditions. Our exhaustive literature search, which included over 450 papers, showed that the majority of experimental data were obtained in vertical tubes, some data in horizontal tubes and just a few in other flow geometries including bundles. In general, the experiments showed that there are three heat transfer modes in fluids at supercritical pressures: (1) normal heat transfer, (2) deteriorated heat transfer with lower values of the heat transfer coefficient (HTC) and hence higher values of wall temperature within some part of a test section compared to those of normal heat transfer and (3) improved heat transfer with higher values of the HTC and hence lower values of wall temperature within some part of a test section compared to those of normal heat transfer. The deteriorated heat transfer usually appears at high heat fluxes and lower mass fluxes. Also, a peak in HTC near the critical and pseudo-critical points was recorded. Due to the limited number of publications that are devoted to heat transfer in bundles cooled with water at supercritical pressures, more work is definitely needed to provide the additional information for design purposes.     

超临界水冷堆类三角形子通道传热不均匀性研究

基于类三角形堆芯子通道超临界水传热不均匀性试验,建立棒径为8 mm、栅距比为1.2~1.4的超临界水冷堆（SCWR）类三角形堆芯子通道物理模型,研究通道内超临界水传热不均匀性,分析超临界压力区子通道传热轴向与周向不均匀性。试验研究表明类三角形子通道轴向传热强度不均,沿轴向传热强度存在峰值区,大比热区传热强度大,而远离大比热区传热强度低;试验与数值模拟对比表明 (Spezlale, Sarkar and Gatski Model) 湍流模型可准确预测SCWR类三角形子通道超临界水传热特性;子通道周向传热严重不均,在垂直于主流方向横截面,流体和管壁之间的局部传热系数随着周向角的增大先升高后降低,其值在中心主流区处最大,在窄缝区位置最小,并且在不同的主流焓值区内周向传热不均程度不同;栅距比对子通道传热有影响,随着栅距比的增大,在整个主流焓值区内,平均壁温升高,换热系数降低,周向传热不均匀性显著减小。      

液态金属高温热管传热极限研究

热管作为一种高效可靠、可进行长距离传热的非能动设备,在核能领域有着广泛的应用。本文针对工质为钠、充液量为158 g与208 g的毛细驱动热管,对其传热极限开展实验和理论研究。实验方面,设计搭建了高温热管传热极限测试分析实验平台,研究了液态金属高温热管在不同水平倾角和不同加热功率下传热功率的变化。理论方面,验证了连续流动极限与夹带极限理论模型的正确性,总结了两种极限的发生规律。研究发现,热管连续流动极限影响热管的启动;由于水平夹角较大时转变温度较高,因此大角度下的热管更容易发生连续流动极限,小角度下经验模型的预测误差在6.58%以内,大角度下误差超过28%。夹带极限发生时热管蒸发段温度骤升且冷凝段温度出现波动,热管倾角越大夹带极限越容易发生,经验模型在不同角度下均存在误差,大角度下误差超过100%。本文总结了连续流动极限与夹带极限的发生规律,为先进核反应堆系统中热管的设计提供参考。     

肋片对圆环通道内超临界水传热特性影响的数值分析

以计算流体力学(CFD)商业软件CFX为计算平台,对圆环通道内超临界水(SCW)的传热特性进行数值模拟。通过对几种湍流模型的对比,选取对超临界条件适用性相对较好的SST模型进行计算;比较光滑圆环通道与带肋片圆环通道内的壁温分布及传热系数的变化;研究肋片形状、高度、间距及宽度等因素对传热特性的影响。结果表明:圆环通道内肋片的存在会导致局部传热强化;在本文计算的尺寸范围内,肋片形状和宽度对传热的影响很小;一定范围内,增加肋片高度以及减小肋片间距都有利于传热强化。     

复合换热管过冷沸腾换热实验与关联式评价

以去离子水为实验介质,在单面受热流密度条件下,开展了聚变装置偏滤器的过冷流动沸腾强化换热特性实验研究,将内肋强化换热技术与内插扭带结构相结合,利用两者的协同强化传热效应,设计出一种复合换热管。实验参数为：质量流速,992～4 960 kg/(m2·s);压力,04～2 MPa;入口过冷度,8701～11921 ℃;热流密度,1～163 MW/m2。对4种强化换热管（光管、内插扭带管、内螺纹肋管和复合换热管）的管内过冷流动沸腾换热特性和综合性能评价指标（PEC）进行了对比实验。结果表明：与其他3种管道相比,复合换热管的对流换热系数和PEC最高,传热特性最好。研究了复合换热管的扭带扰动比、螺距、压力和质量流速对管内两相流动对流换热系数的影响规律,发现对流换热系数与螺距、质量流速呈正比,与扭带扰动比、压力呈反比。最后对比了4个现有的过冷流动沸腾换热经验公式,并在无量纲模型基础上,增加了扰动比和螺径比（t/Dh）进行修正,利用非线性拟合方法提出了适合复合换热管过冷流动沸腾的努塞尔数新公式。     

Pool boiling heat transfer enhancement on porous surface tube

The passive residual heat removal exchanger (PRHR HX),which is a key equipment of the passive residual heat removal system,is installed in an elevated pool.Its heat transfer performance affects security and economics of the reactor,and boiling heat transfer in the liquid surrounding the exchanger occurs when the liquid saturation temperature exceeded.The smooth tubes,which are widely used as heat transfer tubes in PRHR HX,can be replaced by some enhanced tubes to improve the boiling heat transfer capability.In this paper,the pool boiling heat transfer characteristics of smooth tube and a machined porous surface tube are investigated by using high-pressure steam condensing inside tube as heating source.Compared with smooth tube,the porous surface tube considerably enhances the boiling heat transfer,and shortens the time significantly before reaching the liquid saturation temperature.Its boiling heat transfer coefficient increases from 68% to 75%,and the wall superheat decreases by 1.5oC.Combining effect of condensation inside tube with boiling outside tube,the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution.Based on these investigations,enhance mechanism of the porous surface tube is analyzed.