升沉条件下矩形窄缝通道单相等温流动摩擦阻力特性研究

采用实验和理论分析相结合的方法研究升沉条件下矩形窄缝通道以水为介质的单相等温流动摩擦阻力特性.结果表明,矩形窄缝通道的几何效应体现在层流区；影响升沉条件下矩形窄缝通道摩擦阻力特性的因素是通道入口和出口边界条件；当入口和出口均给定速度边界时,升沉运动对等温流动没有影响,在静止状态获得的摩擦系数计算公式在升沉条件下仍然适用...     

矩形窄缝通道内单相水流动特性研究

通过理论分析,得到了计算矩形窄缝通道单相层流摩阻系数的公式。对小高宽比矩形窄缝通道内的流动特性进行了实验研究,结果表明：矩形窄缝通道内单相摩阻系数随Re变化的曲线和圆管有相同的趋势,但圆管流动摩阻公式不适用于矩形窄缝通道。矩形通道内摩阻系数与Re和通道截面高宽比有关,通道高宽比越小,摩阻系数越大。实验结果和理论推导结论一致。从截面湿周和切向应力两方面解释了高宽比对矩形窄缝通道内单相水层流摩阻特性的影响机理。     

矩形窄缝通道内湍流充分发展区流动边界层探析

从宏观特性比较分析的角度出发,通过计算流体动力学(CFD)微观结果来探析矩形窄缝通道内湍流充分发展区边界层分布的特性.研究结果表明,从宏观角度看,一些适用于常规通道的经典公式仍然通用于矩形窄缝通道;现有的实验结果基本支持湍流充分发展区矩形窄缝通道内的流动和传热规律符合常规通道内特点的结论.对多种湍流模型模拟的结果与经典...     

窄间隙矩形通道单相水纵向涡强化传热实验

在窄间隙矩形通道内设置4对周期性分布的矩形块纵向涡发事器(LVG),研究该类通道和光通道内单相水介质流动阻力特性和对流传热特性.在雷诺数Re为310-4220范围内,纵向涡(LV)使得通道内流动提前由层流向紊流转化.在层流区,LV强化传热可达100.9%,摩擦阻力增大仅11.4%;在紊流区,LV强化传热可超过87.1%...     

环形窄缝通道单相流动特性研究

对环形窄缝通道内单相流动特性进行了分析，提出了理论模型预测环形窄缝通道内单相流动阻力特性。根据该模型，对窄缝宽度分别为1.0、1.5、2.0mm环形通道内单相湍流流动摩擦阻力系数进行了理论计算，并与实验结果进行了比较。理论预测值与实验结果符合较好，且窄缝间隙大小对环形窄缝通道内流动特性有着重要影响，随着间隙的减小，摩擦阻力系数相应减小。间隙对流动阻力系数的影响还依赖于Re大小，其影响随Re的减小而降低。     

摇摆条件下矩形窄缝通道单相等温流动摩擦阻力特性研究

通过实验研究和数值计算相结合的方法研究摇摆条件下矩形窄缝通道单相等温流动摩擦阻力特性。研究发现:受摇摆附加惯性力的影响,流道内的微观流场出现变化,但在本实验参数范围内,流场的微观变化较小,摇摆对摩擦阻力特性的影响可以忽略,由流道静止状态获得的摩擦阻力系数计算公式在摇摆条件下仍然适用。     

竖直矩形窄缝通道内过冷沸腾传热特性的实验研究

以去离子水为工质,在进口压力为0.1~0.3 MPa、质量流速为200~1400 kg?m-2?s-1、热流密度为20~320 kW?m-2的参数范围内,对截面参数为50 mm×2 mm的竖直矩形窄缝通道展开了传热实验研究。实验获得通道内部工质由单相状态到过冷沸腾状态的传热过程曲线,将过冷沸腾段实验值与8个经验公式提供的预测值进行了对比与分析,采用相似原理以及回归分析法,建立了适用于竖直矩形窄缝通道的过冷沸腾准则关系式。研究结果表明,在竖直矩形窄缝通道内,热流密度对过冷沸腾传热具有主导作用;对于本实验的窄缝通道,Bertsch传热公式对于过冷沸腾段的预测效果相较于其他公式更好,本研究所建立的准则关系式与实验数据符合良好。因此,本研究建立的公式能够用于竖直矩形窄缝通道过冷沸腾传热系数的预测。      

矩形窄缝流道角部结构对流动和传热的影响

为了深入了解矩形窄缝通道角部结构对流动和传热的影响,文中采用CFD程序CFX10.0对矩形窄缝通道的流场和温度场进行了数值模拟.研究结果表明,采用削薄角部金属固体,并且在发热固体总量基本相同的条件下,直角型和圆角型结构下的内壁面温度分布与原型结构相差不大,可以反映原型结构中的传热特性.在雷诺数相同的条件下,角部圆角型结构和直角型结构下的二次流分布和摩擦压降基本相同,表明了完全可以采用圆角型结构来模拟原型结构.     

起泡条件下矩形窄缝通道内压力场和温度场数值模拟

当矩形窄缝通道由于辐照肿胀产生形变出现起泡结构时,通道内流动传热特性会发生改变。本文采用数值计算方法分析了起泡条件下矩形窄缝通道内流体压力场和温度场分布。结果表明,起泡对流体的阻碍作用会导致流体在第一个起泡前出现压力高点。经过每一个起泡,局部压降均会先飞升后突降,起泡处流体温度上升,壁面温度下降。通过模型计算分析获得了起泡条件对压力场和温度场的影响规律。     

环形窄缝通道湍流流动换热特性分析

对双面加热环形窄缝通道内单相流动换热进行分析研究,提出了理论预测模型.基于该模型,对窄缝宽度分别为1.0、1.5、2.0 mm的环形通道单相湍流流动换热系数进行了理论计算,并与实验结果进行了对比,理论预测值与实验结果符合较好.研究表明:内外加热热流密度比对环形窄缝通道内的湍流流动换热过程有显著影响,在双面加热情况下,窄缝对流动换热过程强化与否,取决于内外管加热热流密度比及流动状态,即Re大小.     

Experimental investigations on single-phase heat transfer enhancement with longitudinal vortices in narrow rectangular channel

Four pairs of rectangular block as longitudinal vortex generators (LVG) were mounted periodically in a narrow rectangular channel to investigate fluid flow and convective heat transfer respectively in the narrow rectangular channel with LVG and without LVG. Both the channels have the same narrow gap (d) = 3 mm, the same hydraulic diameter (D_h) = 5.58 mm and the same length to diameter ratio (L/D_h) = 80.65. The experiments were performed with the channels oriented uprightly and uniform heat fluxes applied at the one side of the heating plate and single-phase water was used as test fluid. The parameters that were varied during the experiments included the mass flow rate, inlet liquid temperature, system pressure, and heat flux.In each of the experiments conducted, the temperature of both the liquid and the wall was measured at various locations along the flow direction. Based on the measured temperatures and the overall energy balance across the test section, the heat transfer coefficients for single-phase forced convection have been calculated. At the same time, in these experiments, the single-phase pressure drop across the channels was also measured. The correlations have been developed for mean Nusselt numbers and friction factors. Additionally, the visual experiments of infrared thermo-image recording the temperature on the outer wall of the heating plate have been conducted for validating the effects of LV.In these experimental investigations, both laminar regime and turbulent regime were under the thermo-hydraulic developing conditions, laminar-to-turbulent transition occurred in advance with the help of LV when Reynolds numbers vary between 310 and 4220. In laminar regime, LV causes heat transfer enhancement of about 100.9% and flow resistance increase of only 11.4%. And in turbulent regime, LV causes heat transfer enhancement of above 87.1% and flow resistance increase of 100.3%. As a result, LV can obviously enhance heat transfer of single-phase water, and increase flow resistance mildly.     

Steady-state performances and scaling analyses for an open flashing-driven natural circulation system

Simulating investigations are carried out to study the steady-state performances, the pressure resistance distributions and the scaling methods of the single-phase and flashing-induced two-phase flow in the open natural circulation system, which is designed for the passive containment cooling system. The results show that the steady-state mass flow rate changes with the heat transfer regularly both in the single-phase and flashing-induced two-phase flow under a certain inlet subcooling. From the sensitivity analysis, it can be found that the riser height only has impact on the single-phase flow but has little influence on the flashing-driven two-phase flow. Both increasing the diameters of the riser and downcomer can enhance the flow and heat transfer in sing-phase and two-phase flow when keeping the structure of the heat exchanger unchanged, but the influence degree for each flow type is different. The flow resistance distributions of the loops under different flow modes have been studied to provide the foundation for improving the heat transfer capacity by choosing the structural parameters reasonably. The pressure resistance distribution of the steady single-phase flow only relates to the geometrical, but the pressure resistance distribution of the two-phase flow relates both to the pipe diameters and to the external conditions. The acceleration pressure resistance in the riser section is the main resistance under the higher-quality two-phase conditions. Therefore, the influence of the riser diameter on the flashing-induced two-phase flow is far greater than that of downcomer diameter and the most effective method to improve the two-phase flow and heat transfer is to increase the diameter of the riser. Finally, the scaling analysis is performed for the penetration and economy considerations after selecting the optimal dimensions. The scaling of the cold and hot sections is considered separately to insure the driven force of the system unchanged, and different scaling criterions are given for the single-phase and flashing-induced two-phase flow according to the analyses of the pressure resistance distributions. The results show that the scaling criterion of the two-phase flow can deal with the scaling problem accurately both in the single-phase and two-phase flow. However, the scaling criterion of the single-phase flow only can solve the single-phase scaling problem, but it will overestimate the operating results in the scaling model.     

矩形窄缝通道内水稳态和瞬态流动换热特性实验

以去离子水为工质,在压力0.5～5.0 MPa的范围内,对矩形窄缝通道内水稳态及瞬态流动换热特性进行了实验研究。结果表明:矩形窄缝通道在水平和竖直放置以及稳态和瞬态条件下,水的流动换热特性呈现出基本相同的规律。层流向紊流过渡区域的雷诺数(Re)为900Re1300,比常规通道提前,单相摩擦阻力系数比常规通道大;采用Dittus-Boelter公式的形式拟合得到了新的换热实验关联式,其系数较Dittus-Boelter公式的系数约小11.3%。在稳态条件下,紊流区换热系数随质量流速的增加而增大,增大趋势比较明显;换热系数随热流密度的变化不明显;压力对单相强迫对流换热特性基本没有影响。     

扁管单相对流换热实验研究

本文以单相水为介质,对结构尺寸不同的3种扁管的换热与阻力特性进行了实验研究。并根据工程实际的需要,选用适当的方法对扁管在实验范围内的强化换热效率指标进行评价,确定了扁管的最佳工作区域。结果表明,扁管的管内换热系数明显高于光圆管的,换热系数最高可达光圆管的2.62倍,在换热面积和泵功率相同情况下,扁管最佳工作区域的换热量最高可达光圆管的2.2倍。     

倾斜条件下强迫流动的传热特性研究

对倾斜条件下圆管内强迫流动的传热特性进行实验研究及数值分析。实验结果表明,对于单相流动,在浮力的作用下圆管内的传热呈现非对称状态;圆管上侧传热减弱,壁温升高,而圆管下侧传热增强,壁温降低。数值模拟的结果也是如此。以此为基础,提出引入倾斜条件下传热的修正因子,可以较好地预测倾斜条件下单相对流传热的变化幅度。对两相流动中的汽泡进行受力分析,揭示倾斜条件对两相传热影响不大的原因。     

斜微肋扁管单相对流换热实验研究

以单相水为介质,对肋高或结构尺寸不同的4种斜微肋扁管的换热与阻力特性进行了实验研究,并根据工程实际需要,选用适当的方法对斜微肋扁管在实验范围内的强化换热效率指标进行评价,确定了斜微肋扁管的最佳工作区域。结果表明：斜微肋扁管的管内换热系数明显高于光管,换热系数最高可达光管的5.9倍,在换热面积和泵功率相同的情况下,斜微肋扁管最佳工作区域的平均换热量均可达光管的3倍以上。     

重水堆停堆工况下单相自然循环流动与传热分析

使用RELAP5程序建立CANDU 6型重水堆模型,对停堆工况下主热传输系统环路内的单相自然循环进行了分析研究,并推导出重水堆单相自然循环流量模型。对Vijayan模型与RELAP5程序的自然对流传热模型（Churchill-Chu和McAdams模型）进行比较计算,结果表明,Vijayan模型计算的水平壁面传热系数低于程序模型,造成包壳温度略高,而竖直壁面传热系数则无明显差别。     

Heat transfer model of single-phase natural circulation flow under a rolling motion condition

Experimental studies on heat transfer characteristics for single-phase natural circulation flow under a rolling motion condition are performed. Experiments with and without rolling motions are conducted so that the effects of rolling motion on natural circulation heat transfer are obtained. The experimental results show rolling motion enhances the heat transfer. The heat transfer coefficient of natural circulation flow increases with the rolling amplitude and frequency. A modified Reynolds number that considers the influence of the acceleration is employed to express the effect of heat capacity. Using experimental data, an empirical equation for the heat transfer coefficient under a rolling motion condition is obtained. The calculated results agree with the experimental data.     

Experimental study on friction and heat transfer characteristics of pulsating flow in rectangular channel under rolling motion

Friction and heat transfer characteristics of pulsating flow induced by rolling motion are experimentally studied. A series of single-phase forced circulation flow experiments are conducted in a vertical narrow channel. In the present study the flow rate is adjusted through control the impeller rotator speed of the pump. The results show that the flow rate pulsation simultaneously with the rolling motion and the relative amplitude of the flow rate pulsation decreases with the increasing flow rate. Accordingly, the relationships between the relative pulsation amplitude of friction factor, heat transfer coefficient and flow rate are classified. Therefore, the correlations have been developed to calculate the friction and heat transfer coefficient based on the relative pulsation amplitude of the flow rate.     

CFD methodology and validation for single-phase flow in PWR fuel assemblies

This paper presents the CFD modeling methodology and validation for steady-state, normal operation in a PWR fuel assembly. This work is part of a program that is developing a CFD methodology for modeling and predicting single-phase and two-phase flow conditions downstream of structural grids that have mixing devices. The purpose of the mixing devices (mixing vanes in this case) is to increase turbulence and improve heat transfer characteristics of the fuel assembly. The detailed CFD modeling methodology for single-phase flow conditions in PWR fuel assemblies was developed using the STAR-CD CFD code. This methodology includes the details of the computational mesh, the turbulence model used, and the boundary conditions applied to the model. The methodology was developed by benchmarking CFD results versus small-scale experiments. The experiments use PIV to measure the lateral flow field downstream of the grid, and thermal testing to determine the heat transfer characteristics of the rods downstream of the grid. The CFD results and experimental data presented in the paper provide validation of the single-phase flow modeling methodology. Two-phase flow CFD models are being developed to investigate two-phase conditions in PWR fuel assemblies, and these can be presented at a future CFD Workshop.