用于堆芯熔融物容器内滞留的堆外冷却两相流动特性研究

来源 :华北电力大学(北京) | 被引量 : 0次 | 上传用户:fsdgvii
下载到本地 , 更方便阅读
声明 : 本文档内容版权归属内容提供方 , 如果您对本文有版权争议 , 可与客服联系进行内容授权或下架
论文部分内容阅读
In-Vessel Retention of corium through External Reactor Vessel Cooling(IVR-ERVC)is an ongoing technique for the extraction of heat out of the reactor pressure vessel.The efficiency of heat transfer and critical heat flux are dependent on the optimal design of the external flow channel,working fluids,and the boiling conditions.The experimental and theoretical study on flow and heat transfer characteristics of boiling DI(deionized)water as a coolant has been executed on ULPU-IV based test facility built at Beijing Key Laboratory of Passive Safety Technology for Nuclear Energy for IVR-ERVC.The water as a coolant is allowed to flow from the reservoir through the extermal 90° curved channel at a flow rate of 0.129m3s-1 under natural circulation with inlet subcooling temperature of 20K and 80K.The heat flux(301.204kWm-2)is supplied perpendicularly to the convex wall of the flow channel owing to the square cross-section with hydraulic diameter and radius of curvature of 0.040m and 0.476m respectively.The two-phase boiling model of computational fluid dynamics(CFD)is incorporated for the execution of numerical results.The increase in the degree of subcooling from 20K to 80K enhanced two folds of heat transfer coefficient(HTC)which consequently embellished heat dissipation out of the surface and reduced heating wall temperature.The flow and heat transfer characteristics of two-phase fluid have been discussed by considering velocity,void fraction and temperature distribution of the heating wall.The bubble departure frequency increased with the increase in the degree of subcooling and the sliding motion of bubbles on the inclined surface played a vital role in the enhancement of heat transfer.The computed results agreed well with the experimental results.The mean percentage error(MPE)is calculated as 29.21%.Insertion of flow field modulators i.e.fins,grooves,etc.within the channel are considered as promising factors for maximizing heat dissipation out of the vessel via flowing fluid,but on the other hand,their insertion may impose excessive back pressure on the channel which may lead it to be ruptured.So,it is necessary to analyze the pressure effect while designing the flow channel in order to overcome associated safety issues.By keeping this in view,the present study has been executed in order to analyze the two-phase pressure gradient through the curved channel.Two-phase(steam-water)pressure gradient calculation through the 90° square,even cross-sectional,curved channel occupying 40mm of hydraulic diameter and 476mm of curvature radius has been deliberated by conferring Homogeneous Flow Model(HFM)as well as Separated Flow Model(SFM)for the computation of combined effect of frictional,acceleration and gravitational pressure gradients.The calculated pressure gradient with respect to exit steam quality(x)was validated by the experimental results conducted at ’ Beijing Key Laboratory of Passive Safety Technology for Nuclear Energy ’.The experimental and calculated results were in good agreement within 0<x<0.030 under ’bubble flow regime’having RMSE of 0.389 and 1.822 with HFM and SFM respectively.As the efficacy of IVR-ERVC is strongly correlated with the CHF on the lower head of the reactor pressure vessel(RPV).The high limit of critical heat flux(CHF)prevents the RPV from failure by extracting much heat out of the vessel through the circulation of working fluid in an external flow channel.In the present study,the deionized water is allowed to flowthrough a curved flow channel having a radius of curvature of368mm and hydraulic diameter of 40mn with a square cross-section.The heat flux of 1500kWm-2 is applied perpendicular to the convex wall of the channel CHF on the wall of the flow channel has been predicted by incorporating CFD based two-phase(liquid-vapor)boiling model The investigations on spatial variation of pressure,temperature,and velocity and heat flux acquired as a result of numerical simulations have been discussed in detail.The CHF and average HTC is predicted as 1.798e+04kWm-2 and 38.98lkWm-2K-1 respectively.The numerical calculations are performed to predict CHF during subcooled boiling of deionized water through 90° curved flow channel with a square cross-section.Two types of flow regimes have been observed at low and high flow velocities.In case of low flow velocities,the continuous accumulation of vapors formed a vapor blanket on the heating surface which consequently reduced heat dissipation out of the surface and triggered CHF due to drying out of liquid between vapor blanket and heating wall.On the other hand,coolant circulation at higher velocities hindered the formation of vapor blanket and allowed subcooled liquid for rewetting.The consistent rewetting led to the formation of small and separate vapor blankets.The enhancement in CHF has been observed with an increased degree of subcooling and by increasing flow velocity in the present study.The three-phase(water-liquid,water-vapor and nanoparticles)numerical simulations have also been done on CFD with the model of ULPU-IV facility of Beijing Key Laboratory by considering water and four water based-nano fluids as a working fluid viz.Graphene-water,Alumina-water,Titania-water,and Silica-water.The supplied heat flux is 1500kWm-2,and the coolant is allowed to flow at 0.02m3s-1 under natural circulation with an inlet temperature of293K.These nanofluids have been analyzed on the basis of thermo-physical properties by incorporating particle diameter of 85nm within the range of volume concentration(1-3 vol.%.).The effeetive thermal conductivity,HTC and heating wall temperature have been examined by taking each nano fluid as a coolant at different volume concentration and the enhancement ratio is evaluated with respect to water(liquid-vapor mixture)alone as a coolant.The stability analysis by comparing sedimentation velocities of the aforementioned nanofluids and cost analysis on the basis of a recent survey are also done.It has been evaluated that the incorporation of nanoparticles in water showed a remarkable result in the enhancement of effective thermal conductivity,HTC and in reducing wall temperature as compared to water coolant.It has been observed that increasing volume concentration imparted negative impact on heat transfer phenomena in case of Alumina-water,Titania-water and Silica-water as a coolant from 1 vol.%to 3 vol.%whereas in case of Graphene-water the enhancement of heat transfer occurred from 1 vol.%to 2 vol.%but at 3 vol.%reduction in heat transfer was observed due to agglomeration and sedimentation of particles.It has been concluded that the water-based graphene nanofluid outperformed other working fluids at an optimum concentration of 2 vol.%due to its high heat extraction efficiency and profound stability but it is not regarded as cost-effective.
其他文献
纳米流体等离激元光热转化是国际前沿课题,也契合国家重大需求,例如纳米流体吸收太阳能实现光热转化在发电、海水淡化、污水处理等方面有巨大应用潜力。此外,在光流控等功能化应用方面,用光控制纳米流体运动有其独到优势,拥有很大的施展空间。纳米流体中的颗粒与入射光耦合发生局域等离激元效应(LSPR)实现光热转化,成为纳米尺度的移动热源。因此,纳米流体光热转化及相变传热中的核心科学问题是“纳米流体中时空分布变换
纵观国内外创新发展经验,很多全球知名创新区均呈现出"廊带"分布特征,科创走廊已成为多个城市跨区域合作的一种重要模式。基于创新链视角,以"128号公路"创新廊道和广深科创走廊为例,探究科创走廊的建设机制,研究发现:第一,科创走廊可视为一个包含核心节点和辅助节点的虚组织,且所有节点不是等量齐观的,核心节点具有核心功能;第二,若核心节点的功能弱化,科创走廊会呈现劣化趋势;第三,科创走廊的建设包含从知识资
日前,能源与环境问题已成为制约人类社会长期发展的瓶颈,回收利用低品位余热能够有效提高能源利用率,缓解当前能源短缺与环境污染问题。有机朗肯循环(ORC)以低沸点有机物代替常规朗肯循环中的水作为循环工质,具有系统结构简单、余热回收效率高、投资成本低和运行可靠等优点,在低品位余热回收利用方面具有良好的应用前景。鉴于ORC技术的重要应用价值,本文对ORC系统及其关键部件向心透平进行了性能优化研究,并搭建了
煤炭是我国的主体能源和重要原料,为中华民族伟大复兴做出了不可磨灭的历史贡献,在今后较长时期内,特别是推动我国能源转型发展中还将发挥不可或缺的兜底保障作用。作为“双碳”目标的主战场,能源产业的减碳、降碳是我国“双碳”工作的重点方向。由于我国以煤为主的能源禀赋现状,在保障能源安全的基础上,降低煤炭消费总量及其消费过程中的碳排放强度是实现“双碳”目标的必然选择。当前,“双碳”目标已对煤炭行业整体技术布局
空化泡在外部声场的作用下会发生泡壁稳定性变化,这种稳定性变化在水力机械、噪声控制、生物医学等领域有重要作用。例如,当空化泡在水轮机叶片表面附近破灭时,其内部产生的微射流会对金属壁面造成冲击、伤害,甚至产生裂痕。而空化泡的表面在不断膨胀、缩小的过程中也会产生压力脉冲,引起局部、甚至全局流动状态的变化,影响水力机械的运行。空化泡的稳定性反映了空化泡自身维持稳定振荡的状态,主要分为四类:球形稳定性、刚度
对流扩散方程是一类基本的运动方程,方程中包含扩散项及对流项,可用来描述河流污染、大气污染、核污染中污染物质的分布,流体的流动和流体中传热等众多物理现象。但对于这类方程,除了极少数简单情形,大部分问题目前还无法求得精确解,所以利用数值方法进行数值模拟是求解这类问题的主要方法,构造精确、稳定和高效的数值方法成为研究这类问题的重要内容。本文提出了一种边界型方法—半边界法用于数值求解线性及非线性对流扩散方
当前,利用流化床装置进行的气化技术是生物质能源利用的重要途径。其中双循环流化床系统采用鼓泡流化床和快速流化床组合的方式,对生物质气化反应涉及到的气化和燃烧过程进行分区强化,可有效提高产气品质和产量。该系统因两床流化状态的不同而存在复杂的颗粒流动规律,且生物质-惰性流化介质混合颗粒的物性差异又会加剧其复杂程度。为此,本文采用石英砂与稻壳所组成的大异重颗粒作为实验床料,分别在鼓泡流化床和双循环流化床冷
随着我国建筑行业的迅猛发展,传统的建筑方式已经逐渐落后于时代,装配式建筑取代其变成了目前市场上最流行的建筑方式,而且装配式建筑凭借其高效的施工效率、良好的施工质量、稳定的施工效益必将成为我国未来建筑行业发展的新方向。
基于对煤炭行业资源综合利用内涵的梳理,通过对煤炭行业资源综合现状、利用方式和途径的细致分析,提炼总结了矿区废弃物资源综合利用发展过程中面临的主要问题。通过对碳达峰、碳中和目标确定后煤炭产业、煤炭行业资源综合利用等受到的具体影响进行分析,详细阐述了"双碳"目标下煤炭行业资源综合利用发展的5个路径,结合提出的问题和发展路径分析,给出了意见和建议。