环形狭缝通道内环状流模型的数值分析

对环形狭缝通道内的环状流建立了分离流模型。应用质量、动量和能量守恒方程 ,加上相应的边界条件和使方程组封闭的经验关系式 ,对环形狭缝通道的内、外液膜厚度、液膜内的速度分布和温度分布 ,以及内、外管的换热系数进行了数值计算求解     

曲率对竖直向上环形狭窄通道内环状流特性的影响

基于三流体分离流模型,以液膜质量、动量和能量守恒方程为基础,结合汽芯动量方程,对双面加热垂直向上流动环形狭窄通道内环状流特性进行数值模拟。将计算结果与实验结果相比较,两者符合较好。通过数值模拟,分析了曲率对环状流特性的影响,得到了曲率对液膜厚度、液膜内温度、液膜内速度、临界热流密度等的影响曲线。曲率越大,内液膜越薄,而外液膜越厚。内管干涸时,临界热流密度随曲率的减小而增大;外管干涸时,则反之。     

均匀加热窄通道内环状流液膜厚度和换热系数的预测模型

为探究窄矩形通道内环状流的流动传热特性,根据液膜的质量、动量和能量方程以及汽芯的动量方程建立了环状流的预测模型。对该模型进行数值求解,得出了窄矩形通道内环状流区域的沸腾换热系数,并分析了热流密度、质量流速和矩形通道尺寸对液膜厚度的影响。结果表明:该模型能很好地预测沸腾换热系数,其误差在±30%以内,且热流密度和矩形通道的尺寸对液膜厚度的影响效果比较大。     

环形窄缝通道内干涸型临界热流密度的理论研究

在双面加热的垂直环形窄缝通道内,对向上流动环状流的临界热流密度(CHF)进行理论研究,以质量、动量和能量守恒方程为基础建立数学物理模型。对该模型进行数值求解,得到了不同窄缝间隙通道内的CHF和临界含汽率的关系曲线,分析得出压力对CHF的影响,并将理论计算值与实验值进行比较。     

环形狭缝膜态沸腾弥散两相流动特性研究

在 3种不同间隙的同心竖直环形狭缝膜态沸腾试验段中 ,研究了以去离子水为工质的两相弥散流摩擦压降 ,比较了环形狭缝和圆形通道中两相流动摩擦压降的不同 ,还研究了环形间隙对摩擦压降的影响。结果表明 :不同间隙下的环形狭缝内膜态沸腾弥散流摩擦压降可用修正的Sadatomi方法计算 ,该方法可应用于工程上的环形狭缝膜态弥散流动     

低压下水欠热流动沸腾的两相CFD数值模拟研究

采用两流体(汽相和液相)基本数学模型,结合汽相和液相之间的界面传热、传质和动量交换封闭模型、汽泡平均直径模型、汽泡脱离直径模型、汽泡成核模型、汽泡脱离频率模型、欠热沸腾起始点模型和壁面热流密度分配模型,在CFD软件CFX4.4中采用用户自定义函数将相变引起的传热、传质和动量交换作为源项分别添加到汽相和液相的能量、质量和动量守恒方程中,对低压下内管加热外管绝热的环形通道内的欠热沸腾进行了数值研究,得到了欠热流动沸腾下汽相体积份额、液相速度、汽相速度分布等。采用Lee等的环形通道内低压下欠热沸腾体积份额实验数据对计算结果进行了验证,吻合良好。     

延展表面凝结液膜的动量积分方法

采用动量积分方法分析压水堆发生失水事故时在安全壳的内表面上的液膜凝结、再浸润和蒸发过程。由凝结液膜的质量和动量守恒方程导出了凝结液膜在延展表面的子午线方向平均速度的积分-微分方程。假设液膜以层流的方式流动，把导出的积分-微分方程变成容易进行数值积分的液膜速度的一阶常微分方程，由此求得液膜厚度分布。液膜能量守恒方程的解给出了安全壳内壁面的温度分布。     

环形狭缝通道内干涸后传热研究

以去离子水为工质的高温流体 ,由下向上流过电加热内、外管壁间的环形狭缝 ,对同心竖直环形狭缝进行了干涸后换热试验研究。试验结果表明 :环形缝隙中的干涸后换热 ,与普通环形通道中的换热有着明显不同。试验中发现在相同热流密度下内管换热能力大于外管。应用Groeneveld公式 ,拟给出适合试验数据的换热公式。在试验的基础上 ,对内外管中较大的热流密度 ,与内外管热流密度的平均值的比值建立变量 ,并应用多元线性回归方法 ,建立了适合工程实际应用的环形狭缝通道干涸后传热计算经验关联式。     

水平圆管临界热流密度实验研究

对水平圆管内低质量流速临界热流密度(CHF)进行了实验研究和分析。实验研究发现,水平流动圆管沸腾临界发生在圆管加热壁面顶部。通过对沸腾临界发生时圆管出口的质量含汽率和流型进行分析发现,本文研究的参数范围内沸腾临界时的出口含汽率高,流型为环状流,沸腾临界类型为干涸型(Dryout)。将经验公式预测值与实验结果进行比较发现,Bowring公式和Lookup table的预测值远大于CHF的实验值。导致此现象出现的主要原因为:Bowring公式和Lookup table是基于竖直流动CHF实验数据开发的模型,水平流动时在重力的作用下环状流液膜呈非均匀分布,顶部液膜干涸提前触发沸腾临界造成CHF值降低。     

基于液膜蒸干模型的低压低流量环状流CHF理论研究

为对低压低流量下的环状流临界热流密度（CHF）进行预测,建立了考虑液膜蒸发、液滴沉积和夹带的液膜蒸干模型,并用已有的实验数据对其进行验证。计算结果表明：在实验参数范围内,CHF计算值与实验值相对偏差在25%以内,两者符合较好。以建立的环状流CHF模型为基础,研究了进口焓差、质量流速、管径和加热长度对CHF的影响。该模型能够有效地计算低压低流量环状流CHF和分析CHF随不同参数的变化趋势。     

Heat Transfer to Steam-Water Annular Dispersed Flow in Vertical Annulus

The heat transfer coefficient and slow burnout heat flux were measured for a stream-water annular dispersed upward flow under pressures up to 3.5 ata in an electrically heated vertical annular channel.

An empirical equation was derived for the heat transfer coefficient as function of mass flow rate, steam quality and heat flux. The dominant mechanism of heat transfer to the annular dispersed two-phase flow is forced convection of liquid film on the heater surface even in the region of low steam quality (down to about 0.03). The observed slow burnout heat flux was near the point of intersection of the lines representing liquid film forced convective heat transfer and nucleate boiling heat transfer on the q vs. δT _sat diagram. A dryout mechanism is proposed in which increasingly violent evaporation comes to impede the rewetting of the dry patches generated on the heater surface, which thus spread to cover the whole surface. A maximum value is observed in the slow burnout heat flux plotted against exit steam quality. This can be explained as the effect of heat removal by droplet exchange between liquid film and steam flow.     

基于两相CFD方法的竖直圆管环状流预测研究

基于欧拉-拉格朗日方法,结合壁面液膜模型,模拟圆管环状流中的液滴与连续气相的相互作用、液滴在壁面处的沉积与夹带、液膜的沸腾与蒸发等关键物理现象。通过与瑞典皇家理工学院的环状流实验结果比较,评价欧拉-拉格朗日方法对环状流的预测精度。比较结果表明,数值模拟得到的液膜质量流量与实验测量结果吻合良好,证明所采用欧拉-拉格朗日方法及本构模型能够较准确地模拟环状流动。      

A simple model for vertical annular and horizontal stratified two-phase flows with liquid entrainment and phase transitions: one-dimensional steady state conditions

A simple one-dimensional three-fluid model is presented for the simulation and analyses of vertical annular and stratified horizontal or inclined two-phase flows. The model has been verified for various experimental data: developing annular flow, momentum transfer in an annular flow, plane flow with a hydraulic jump, flooding in a horizontal pipe, and stratified flow with direct steam condensation. Emphasis has been laid upon several mass, momentum and energy interfacial transfer processes. New correlations are proposed for the droplet entrainment intensity in annular flow and for steam direct contact condensation on the liquid film in a stratified flow. The liquid entrainment in the annular flow is correlated with the liquid film thickness. Direct contact condensation is correlated with the turbulent convective heat transfer in the liquid film. It has been shown that the present model is able to predict all dominant processes in both types of flow.     

FIDAS: Detailed subchannel analysis code based on the three-fluid and three-field model

The Film Dryout Analysis Code in Subchannels, FIDAS, has been developed with the main objective of predicting dryout and post-dryout heat transfer in a channel and in rod bundles. In FIDAS, two-phase flow consisting of continuous liquid film, continuous vapor and entrained droplets is modeled by a three-fluid, three-field representation of 12 field equations, i.e. three continuity, three energy and six momentum equations. FIDAS can predict dryout without any empirical CHF correlations by introducing annular flow modeling and the ‘film dryout criterion’. Experiments on film flow characteristics, subchannel flow and enthalpy distributions, dryout and post-dryout heat transfer in tubes and rod bundles were analyzed to demonstrate the performance of FIDAS. The predictions of FIDAS are in close agreement with the experiments.     

两流体模型在环形窄缝内的应用研究

采用EPRI最新开发的Chexal-Harrison相壁相间摩擦模型和简化的相壁相间传热模型,构造了适用于环形窄缝内沸腾传热和流动的两流体模型,并编制了热工水力计算程序——THYME程序.与实验数据比较,分析了环形窄缝套管在不同负荷下Relap5/Mod3.2程序和本文程序的计算结果.计算结果表明,Relap5/Mod3.2低估了环形蒸发管的蒸汽温度,本文计算结果与实验数据较为一致.     

Numerical study on effect of gap width of narrow rectangular channel on critical heat flux enhancement

According to the flow passage characteristic of narrow rectangular channel and liquid film dry-out mechanics of annular flow critical heat flux (CHF), an annular flow CHF analytical model for narrow rectangular channel has been achieved. This model may be used to predict the CHF behavior of boiling two-phase flow in narrow rectangular channel with gap width of not being less than 0.0005 m (the equivalent diameter of this channel is 0.001 m). Through analyzing and calculating, when the inlet dimensionless gap width of narrow rectangular channel is within 30-85, the enhancement of CHF in channel is obvious. At the same time, according to the characteristic of two-phase flow, the new determinant laws of CHF in boiling two-phase flow system have been derived. Through analyzing and calculating, it is substantial that this determinant laws is appropriate. The best dimensionless gap width of heat flux enhancement has been achieved to be 45-75.