垂直向上流动通道内环状流干涸点的理论研究

本文基于分离流模型,建立了垂直向上流动环形通道内环状流的三流体模型,并对干涸点进行了数值模拟.比较计算结果和实验结果,发现两者符合较好.结果显示:当干涸点发生在内管并且外管热流密度不变时,临界含汽率随曲率和间隙的减小而增大,当干涸点发生在外管且内管热流密度不变时,情况相反;对于固定的间隙,当外管内径大于20 mm时,或间隙小于0.5 mm时,压力和质量流速对临界含汽率的影响非常微弱.     

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。     

垂直向上圆管环状流临界热流密度研究

预测高含汽量下的临界热流密度对于直流蒸汽发生器和事故工况下反应堆堆芯的安全性具有工程价值.本文基于液滴夹带、沉积和液膜蒸发理论,对垂直向上的均匀加热圆管内环状流的液膜厚度和液膜质量流速沿轴向的变化进行了预测.结果表明,当液膜蒸干时,干涸发生,此时的热流密度即为临界热流密度.将理论计算的临界热流密度值与实测值相比较,实验数据偏高,偏差在30%以内.     

液钠沸腾两相流流型与临界热流密度(CHF)机理实验研究

通过大量的液态金属钠临界热流密度 (CHF)的实验研究 ,结合液钠两相传热流动特性及液钠的物性特点 ,分析了起始沸腾流型 ,泡状流 ,块状流 ,环状流和双向环状流的热工水力特性 ;并从实验结果出发 ,深入分析了液钠发生临界热流密度时的气泡爆炸和液膜撕裂或局部蒸干的两种传热恶化机理     

自然循环临界热流密度实验现象及分析

对自然循环系统矩形通道内临界热流密度进行实验研究。研究发现:实验本体增加功率后,环状流液膜蒸干,壁温出现持续快速上升,实验本体出口发生沸腾临界。根据壁温的上升趋势和出口处流体的临界含汽率可以判断自然循环系统出现的临界热流密度(CHF)类型为干涸(Dryout)型。当自然循环系统沸腾临界出现时,自然循环流量出现明显的上升。根据理论分析可知:沸腾临界发生时导致自然循环流量上升的主要原因是环状流转变成弥散流,附在加热壁面的液膜消失,摩擦压降迅速减小。     

竖直环形狭缝通道内环状流的预测模型

对竖直环形狭缝通道内环状流流动沸腾传热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，结合汽芯动量方程建立了竖直环形狭缝通道内环状流的数学物理模型。对该模型进行数值求解，得出了液膜厚度、液膜内的速度分布和温度分布、内—外管的换热系数以及通道内压降值，并与实验值进行了比较。     

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。     

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     

底部封闭矩形通道临界热流密度的理论研究

分析研究了在底部封闭矩形通道内逆流汽液两相流条件下的临界热流密度的发生机理。研究表明,临界热流密度与流入矩形通道内的最大下降液体流量相对应,并且临界热流密度可通过求解动量方程、包络线和能量方程得到。通过与日本数土幸夫建立的模型、经验关联式和实验数据比较,该模型可在精度±30 %范围内预测底部封闭矩形通道条件下的临界热流密度。     

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。     

An investigation of flow characteristics and critical heat flux in vertical upward round tube

Prediction of critical heat flux （CHF） in annular flow is important for the safety of once - through steam generator and the reactor core under accident conditions. The dryout in annular flow occurs at the point where the film is depleted due to entrainment, deposition, and evaporation. The film thickness, film mass flow rate along axial distribution, and CHF are calculated in vertical upward round tube on the basis of a separated flow modcl of annular flow. The theoretical CHF values are higher than those derived from experimental data, with error being within 30%.     

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.     

Experimental research on dryout point of flow boiling in narrow annular channels

1 Introduction There are basically two classes of critical heat flux (CHF) situations: departure from nucleate boiling (DNB) and dryout (DO) [1]. DO is also sometimes known as burnout or departure from forced convective boiling in vapor-continuous flow. From the point of view of engineering, the CHF caused by the DO mechanism is of particular importance since boiling annular flow is one of the most common flow patterns in gas–liquid two-phase flow and occurs in a wide range of vapor qua…     

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.