高温小球下落冷池运动机理的实验研究

高温颗粒在粘滞性冷液中沸腾蒸发瞬变运动引发蒸汽爆炸是一个工程安全问题.利用实验室设计建造的高温颗粒下落冷池沸腾可视化实验装置,通过高速摄影记录小球在冷液中的下落全过程,分别进行了单个高温小球在不同粒径、不同温度和不同冷液过冷度条件下的一系列试验,并对实验结果进行了分析和讨论.文章指出,高温小球的温度、直径和冷液过冷度是影响小球运动速度的重要因素.     

冷液中运动高温球传热阻力耦合特性实验研究

高温颗粒与冷液接触会引发剧烈的沸腾蒸发瞬变现象，涉及到工程安全，是一高速瞬变多相传热问题。本实验室设计建立了高温颗粒下落冷液沸腾可视化实验装置，初次实验将1个或有限几个高温球形颗粒坠入水中，利用高速摄像机记录其在冷液中的运动速度，证实了确实存在由周围冷液快速蒸发引起的作用在运动中高温颗粒上的特殊阻力，验证了高温颗粒的蒸发曳力模型。     

高温颗粒下落冷池的沸腾蒸发瞬变阻力特性研究

设计建立了高温颗粒下落冷液沸腾可视化实验装置 ,初次实验将一个或有限几个高温球形颗粒坠入低沸点的冷液中 ,利用高速摄像机记录其在冷液中的运动速度 ,以了解由周围冷液快速蒸发引起的作用在运动中高温颗粒上的特殊阻力 ,验证了高温颗粒的蒸发曳力模型     

高温颗粒下落冷液中沸腾运动过程实验研究

高温颗粒在粘滞性冷液中沸腾蒸发瞬变运动引发蒸汽爆炸的工程安全问题,其流体动力特性与人们熟知的颗粒在粘滞性流体内的运动特性完全不同,是一多相热物理基础问题,涉及的过程和现象十分复杂.利用本实验室设计和建立的研究高温颗粒与冷却剂相互作用的实验装置,通过高速摄影记录小球的下落过程,分别进行了单个、多个粒子在不同温度和不同冷液过冷度条件下的系列试验,获得了下落小球运动过程曲线,从中得出一些有意义的结论,并为进一步研究高速瞬态蒸发传热奠定了实验基础.     

水蒸汽爆炸粗混合阶段机理研究的实验设计

高温颗粒在粘滞性冷液中沸腾蒸发瞬变运动引发蒸汽爆炸的工程安全问题，其流体动力特性与人们熟知的颗粒在粘滞性流体内的运动特性完全不同．是一个多相热物理基础问题．涉及的过程和现象十分复杂。为了验证高温颗粒在粘滞性冷液中下落阻力特性的蒸发曳力模型，设计了高温颗粒下落冷池沸腾可视化实验装置。     

膜态沸腾下高温颗粒热动力特性理论分析

对膜态沸腾条件下冷液中运动高温球传热阻力耦合特性理论模型进行了分析,以液膜质量、动量和能量守恒方程为基础,结合对高温颗粒在冷却剂中运动的详细受力分析,提出了一个基于特殊复合结构的高温颗粒在冷却剂中运动的传热阻力数学物理模型.对该模型进行数值分析求解,得到高温颗粒下落速度的理论计算值,并与实验值进行了比较.     

高温颗粒落入水中瞬态过程的数值模拟

以液膜质量、动量和能量守恒方程为基础提出了一个高温颗粒在冷却剂中运动的瞬态理论模型.由于高温颗粒在冷却剂中运动的瞬态复杂性,利用适合于求解大条件数的Gear算法对该模型进行了数值模拟.求解过程中采用自适应技术处理高温颗粒在冷却剂中运动时周围蒸汽膜不断变动的动边界问题,得到高温颗粒下落速度的理论计算值,并与实验值进行比较,得到了蒸汽膜的温度、厚度以及作用力等瞬态数值模拟结果.     

高温颗粒在液面下运动的蒸发阻力模型

在蒸汽爆炸的粗混合过程中,由于液体的快速蒸发,高温颗粒周围会产生一层很薄的蒸汽膜,此时高温颗粒周围的边界层流动与没有液体蒸发时有很大差别.因此,采用常温情况下颗粒在连续液体中运动时的阻力模型是不适用的.本文通过受力分析,考虑高温颗粒受力的分布及表面蒸发对颗粒运动的影响,提出了单个高温颗粒在液面下运动时的蒸发阻力模型.理论分析表明,蒸汽膜的厚度对阻力大小有很大的影响,在蒸汽膜的生长初期,除了相对速度较高的情况,蒸发阻力要大于一般阻力模型的计算值.计算结果表明,除非初始汽膜厚度或相对速度很大,否则计算高温颗粒在液面下运动的阻力时必须要考虑蒸发阻力.     

膜态沸腾条件下高温颗粒周围流体热动力特性的实验研究

利用已有的实验和理论基础 ,对高温球体与冷液在膜态沸腾条件下的多相混合结构进行详细的小规模实验研究 ,分析了单个高温颗粒在水中阻力受力的情况。发现高温小球在冷却剂中的速度比冷球的低 ,且随球温的升高而减小。目的是利用小规模实验研究单个高温颗粒的传热和阻力特性 ,可以分割各种在膜态高速沸腾条件下干扰换热与运动的影响因素 ,从而从本质上了解该结构条件下的热动力特性。     

基于分子动力学理论界面传质的过冷沸腾汽泡生长特性研究

基于分子动力学理论的准平衡态界面处界面蒸发/冷凝因素,以及汽泡底部微液层传热因素建立综合传热传质相变模型,对窄通道内汽泡过冷流动沸腾条件下的生长情况进行模拟。相变模型体现了汽泡底部微液层蒸发、近壁过热液体传热、汽泡顶部主流冷凝等多方面机制对汽泡生长的影响。模拟结果体现了汽泡底部微液层厚度的变化情况,与实验结果相吻合;微液层蒸发机制在汽泡生长初期对汽泡生长有较大影响,流道壁面效应对汽泡生长有显著影响。     

Improvements of evaporation drag model

A special visible experiment facility has been designed and built, and an observable experiment is performed by pouring one or several high-temperature particles into a water pool in the facility. The experiment result has verified Yang‘s evaporation drag model, which holds that the non-symmetric profile of the local evaporation rate and the local density of vapor would bring about a resultant torce on the hot particle so as to resist its motion. However, in Yang‘s evaporation drag model, radiation heat transfer is taken as the only way to transfer heat from hot particle to the vapor-liquid interface, and all of the radiation energy is deposited on the vapor-liquid interface and contributed to the vaporization rate and mass balance of the vapor film. In improved model heat conduction and heat convection are taken into account. This paper presents calculations of the improved model, putting emphasis on the effect of hot particle‘s temperature on the radiation absorption behavior of water.     

对蒸发曳力模型的修正

建立了一套研究高温小球落水的工程热物理基础实验装置。在此装置上进行了一系列实验,证实了蒸发曳力模型的可信性．同时也发现其局限性：对蒸发曳力模型进行了修正,增加考虑了辐射热在液体内部和汽液交界面的分布及对流换热对小球落水阻力的影响,扩大了蒸发曳力模型的适用性。     

Coupling effect between film boiling heat transfer and evaporation drag around a hot-particle in cold liquid

Extremely rapid evaporation could occur when high-temperature particles contact withlow-temperature liquid. This kind of phenomenon is associated with the engineering safety and the problems in high-transient multi-phase fluid and heat transfer. The aim of our study was to design and build an observable experiment facility. The first series of experiments were performed by pouring one or six high-temperature particles into a low saturated temperature liquid pool. The particle's falling-down speed was recorded by a high-speed camera, thus we can find the special resistant feature of the moving high-temperature particles, which is induced by the high-speed evaporation surrounding the particles. The study has experimentally verified the theory of evaporation drag model.     

高温颗粒下落时水面沸腾的瞬变阻力特性模型和实验验证

建造了高温炉下落小球实验装置，并进行了高温小球落入水中的实验。考虑粒子受力的分布及蒸发对粒子周围力的影响，从阻力的基本机理上分析了蒸发状态下颗粒的运动阻力，给出了蒸发曳力的理论分析模型．该模型已用于分析核电站严重事故时发生高温融熔金属同水相互作用的蒸汽爆炸现象的事故分析程序中结果与实验极其相符.     

Experimental investigation on the bursting of single molten droplet in coolant

An experiment facility for observing low-temperature molten tin alloy droplet into water was es- tablished to investigate mechanisms of vapor explosion occurring in severe accidents of a fission nuclear reactor.The vapor explosion behaviors of the molten material were observed by a high-speed video cam- era and the vapor explosion pressures were recorded by a pressure transducer mounted under the water surface.The results showed that the pressure reached a peak value when the molten metal temperature was 600℃-650℃,and the coolant temperature had an obvious decreasing effect on the droplet breakups.A model for single droplet fuel/coolant interaction is proposed.It considers that in the case of Rayleigh-Taylor instability,the coolant that jets from opposite direction penetrates into the fuel and the vapor explosion occurs because of the rapid evaporation.This model explained the effect of metal droplet temperature and coolant temperature on vapor explosion.     

An evaluation model to predict steam concentration in a BWR reactor building

When there is no power for cooling the spent fuel pool and conditioning the air in a boiling water reactor (BWR) reactor building, water vapor is generated from the pool and it affects the atmosphere in the building. To consider the impact of the steam in preparing emergency operation procedures, the building atmosphere under various conditions is to be evaluated with reasonably low computational cost. A lumped parameter model to predict the transient behavior of the building atmosphere was developed, in which the evaporation from the spent fuel pool and the condensation to the wall were taken into consideration. A transient behavior of temperature and vapor concentration in a BWR operating floor was predicted with the model. The results and the prediction speed were compared to those of a three-dimensional computational fluid dynamic calculation, and it was confirmed that the model could obtain almost the same results about 280,000 times faster. Parameter studies are conducted with the model, and dominant parameters to the evaporation and the condensation were clarified.     

Assessment of the MARS code for design of water pool-type reactor cavity cooling system in HTGR

This paper reports an experimental and numerical study on the assessment of the MARS code as a tool for analyzing the water pool-type reactor cavity cooling system (RCCS), which was developed by Seoul National University (SNU). A series of experiments were performed to determine the heat removal capability of the proposed RCCS and assess the capability of MARS code to predict the forced convective, natural convective and radiative heat transfer under normal operation conditions and boiling heat transfer during accident conditions in the RCCS. In the loss of forced convection (LOFC) accident experiment performed at the integral effect test facility called RCCS-SNU, the MARS code underestimated the vapor generation rate at the inner wall of the water pool. Therefore, the newly developed models of the bubble departure and lift-off diameters were implemented into the MARS code to make a better prediction of the vapor generation rate. The improved MARS code was assessed again using the experimental data of the LOFC accident conditions in the RCCS-SNU facility.