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。     

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.     

单棒通道流动振荡诱发沸腾临界可视化实验研究

为深入分析沸腾两相流动振荡诱发沸腾临界的影响特性,本文以去离子水为工质,横截面19 mm×19 mm、中心为外径9.5 mm的单棒通道为研究对象,通过在不同热工参数下开展沸腾两相流动特性可视化实验研究,结合汽泡行为和汽-液界面特性,分析流动振荡诱发沸腾临界的影响特性。研究结果表明,低压力、低质量流速和低入口过冷度下,极易出现流动振荡,并导致沸腾临界提前发生,此时的临界热流密度与稳定工况下相比明显偏低;随着壁面热流密度不断增加,流道中两相流型先后出现泡状流、弹状流、合并弹状流、搅混流、剧烈搅混流、不稳定环状流;当流动出现剧烈振荡时,流道存在回流;发生沸腾临界时流道压降波动最大,对应的流型为不稳定环状流。因此,单棒通道内流动振荡可能会导致沸腾临界提前发生。      

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。     

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。     

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。     

流量波动作用下临界热流密度特性理论模型开发与验证

基于微液层蒸干机理和均匀流两相流场瞬态特性模型,建立能够预测通道入口流量波动条件下的瞬态临界热流密度的机理模型并开发了相应的计算程序,采用入口流量稳定和流量波动条件下实验数据对模型进行了验证,表明所开发模型能够较好地预测入口流量波动条件下瞬态临界热流密度,并具有较好的计算精度。     

管束外垂直上升汽液两相流沸腾传热特性的数值模拟

以唐琦琳的管束外垂直上升汽液两相流沸腾传热试验台为原型,进行基于CFX的管束外垂直上升汽液两相流沸腾传热特性数值模拟,得出了不同入口温度、热流密度、质量流速下管束外狭窄通道的热工水力特性。沿管束高度流体温度的模拟结果与实验结果的最大相对偏差为3.5%,从而证明了数值计算的有效性和正确性。在此基础上,探讨了汽液两相流速度分布、沸腾压降与含汽率及其影响因素。     

窄间隙矩形通道间隙厚度对传热强化影响研究

根据窄间隙矩形通道的流道结构特点，参考圆管环状流临界热流密度（CHF）预测解析模型，得到了可以预测间隙厚度不小于0．5mm的窄间隙矩形通道内发生沸腾两相流环状流时的CHF解析模型。计算表明，当窄间隙矩形通道的进口截面宽度与间隙厚度比为25～85时，通道内的CHF值强化比较明显。根据汽-液两相介质的特点，推导出了在沸腾两相流系统中发生CHF时的传热强化判定准则。分析计算表明，这个判定准则是合理的，传热强化较好的进口截面宽度与间隙厚度比为45～75。综合两者的计算结果，窄间隙矩形通道内传热强化的参考进口截面宽度与间隙厚度比为45～75。     

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。     

当量直径对超临界水流动传热特性的影响

以CFD商业软件FLUENT为计算平台,对圆管和圆环通道内超临界水流动传热特性进行数值模拟。通过对几种湍流模型的对比,选取在超临界条件下适用性相对较好的SST模型进行计算,分别比较不同热力当量直径和不同水力当量直径下圆管与圆环通道加热面壁温、边界层温度及速度的分布,研究热力当量直径和水力当量直径对超临界水流动传热特性的影响。结果表明,正常传热工况下,水力当量直径对超临界水流动传热特性有很大影响,而热力当量直径几乎无影响。圆环通道内流动传热关系式可基于圆管进行拟合,超临界水流动传热特性的其他影响因素还需进一步研究。     

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.     

Experimental investigation of pebble beds thermal hydraulic characteristics

The purpose of this paper is to present the results of the experimental investigation of the thermal hydraulic characteristics for two types of test sections—thin annular pebble beds (i.e. spheres dumped in thin annular slots) and pebble beds placed between cylinders. The experimental results of heat transfer from the spheres and from a cylinder, as well as hydraulic drag for both types of test sections are presented in this paper. The results of performed experiments in the case of thin annular pebble beds demonstrated that maximum heat transfer and hydraulic drag is at the relative width of the annular slot K equal to 1.07 and 1.75 of spheres diameter. The heat transfer in internal layers at these values of K is equal to the heat transfer in the internal layers of large (unlimited) rhombic packing. The results of the experimental investigation of pebble beds between cylinders demonstrated that the randomly arranged pebble bed is preferable to the regular rhombic structure from the point of view of design simplicity, heat transfer from the cylinder and drag coefficient.     

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.     

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。      

Thermal hydraulic investigations of intermediate heat exchanger in a pool-type fast breeder reactor

Intermediate heat exchanger (IHX) in a pool-type liquid metal cooled fast breeder reactor is an important heat exchanging component as it forms an intermediate boundary between the radioactive primary sodium in the pool and the non-radioactive secondary sodium in the steam generator (SG). The thermal loads during steady state and transient conditions impose thermal stresses on the heat exchanger tubes and on the shells which hold the tube bundle. Estimation of these thermal loads and achieving uniform temperature distribution in the tubes and shells by having uniform flow distributions are the major tasks of thermal hydraulic investigations of IHX. Through multi-dimensional thermal hydraulic investigations performed using commercially available computer codes such as PHOENICS, the flow and temperature distributions in the tubes and shells and in its secondary sodium inlet and outlet headers are obtained with and with out provisions of flow distribution devices. The effectiveness of these devices in achieving acceptably uniform flow and temperature distributions has been assessed and thermal loads on the tubes and shells for thermo mechanical analysis of the IHX have been defined. The predictions of the computational studies have been validated against simulated experiments.     

Evaluation of Cooling Capability in a Heated Narrow Flow Passage

A numerical method for the thermal hydraulic phenomena in a narrow flow passage is developed to evaluate the gap cooling capability. Based on a drift flux model, the two-dimensional gas-liquid two-phase flow in the annular and hemispherical heated narrow flow passages is modeled. The drift velocity correlation is combined with the flooding correlation, which describes physical phenomena under cooling limits. Experiment on thermal hydraulic phenomena in the heated narrow flow passage is performed. Boiling two-phase flow behavior and dryout phenomena are observed. The critical heat flux data is obtained from measurement of the heating surface temperature. Counter-current two-phase flow, which is a key phenomenon in the gap cooling mechanism, is reproduced by the numerical analysis appropriately. The critical heat flux is predicted by assuming that deficiency of the liquid supply against the gas upward flow leads to occurrence of dryout. Validity of the newly developed numerical method is demonstrated through comparison of the predicted critical heat flux with the present and existing data in the gap width range from 0.5 to 5 mm and the pressure range from 1 to 50 bar.     

同心环形管内沸腾两相流动与传热实验研究

对窄缝为2．1mm的同心环形管,试验研究了外管加热条件下水的沸腾两相流动阻力与传热特性,得到了以下结果：窄缝环形管内两相流动的阻力较普通圆管内大,沸腾换热得到了较明显的强化,换热系数弓压力、热平衡干度、工质流量、加热负荷均有关系,且与缝隙宽度和加热方式有关;提出了环形管强化传热的微液膜蒸发机理与汽泡扰动机理的物理解释;得到了环形管内流动摩擦阻力系数与传热系数的实验关联式。     

Experimental Study of Liquid Sodium Flow and Heat Transfer Characteristics Along Hexagonal 7-rod Bundle Channel

The flow and heat transfer characteristics of single-phase liquid sodium were experimentally investigated in a hexagonal 7-rod bundle channel with the velocity of 0-4 m/s, the heat flux of 0-120 kW/m² and the absolute pressure of 1.5-200 kPa. The corresponding Reynolds number ranges from 4 000 to 60 000, and the Peclet number varies from 0 to 340. The influence of some thermal parameters on the heat transfer characteristics of liquid sodium flow in a hexagonal 7-rod bundle channel was analyzed in depth. Empirical correlations of liquid sodium flow and heat transfer in a hexagonal 7-rod bundle channel were obtained by nonlinear regression analysis for experimental data. The results show that these correlations can accurately predict the friction coefficient and Nu in a hexagonal 7-rod bundle channel. The prediction error for flow and heat transfer is less than 5% and 6%, respectively. The new equation was compared with other results, and the error is within 30%. It is shown that the new empirical correlation is suitable for the flow heat transfer of liquid sodium in a hexagonal 7-rod bundle channel.     

六边形排列的7棒束通道内液态钠流动换热特性试验研究

以液态钠作为试验工质,对六边形排列的7棒束通道内液态钠流动换热特性进行了试验研究。试验流速为0~4 m·s^-1,热流密度为0~120 kW·m^-2,系统压力为1.5~200 kPa,对应的雷诺数和佩克莱数分别为4 000~60 000和0~340。深入分析了部分热工参数对7棒束通道内液态钠流动换热特性的影响,通过对7棒束通道内液态钠流动换热的试验数据的非线性拟合,得到适用于7棒束通道内液态钠流动换热的经验关系式。结果表明：拟合得到的摩擦系数关系式和努塞尔数关系式能准确地预测7棒束通道内的试验数据,其预测误差分别小于5%和6%。将获得的努塞尔数关系式与其他研究者的试验数据进行比较,与其他研究者985%的试验数据误差在30%以内,表明获得的关系式适用于7棒束通道内液态钠流动换热。