关于无限棒束间流动和传热特性的数值研究

应用非线性ｋε湍流模式，采用非正交曲线坐标系下求解三维ＮＳ方程的非交错网格有限体积方法，数值模拟了充分发展条件下，三角形排列无限棒束间通道内，不同的几何参数（Ｐ／Ｄ），雷诺数（Ｒｅ）下的流动和传热问题。给出了不同参数下的速度和温度分布以及湍流二次流动，分析了几何参数、雷诺数及二次流对棒束内流动和传热特性的影响，得到了不同参数下通道的摩擦系数和Ｎｕｓｅｌｔ数，并与经验关系式作了比较     

双自由度流致振动恒温圆管热流固耦合特性

针对单根恒温圆管双自由度流致振动-换热耦合特性,分析了结构振动响应以及温度场、平均努塞尔数和最大局部努塞尔数位置的变化规律。结果表明,在雷诺数为100、质量比为1.37和折减速度为5时,圆管振动轨迹为逆时针型式的“8”字形,横流方向振幅远大于顺流方向振幅;旋涡脱落模态为2S,涡脱会引起后驻点附近局部努塞尔数的突增;不同时刻,振动圆管最大局部努塞尔数的位置均不同程度地偏离前驻点;振动圆管的平均努塞尔数明显大于固定圆管,相比固定圆管最大增加5.73%。      

内部带旋转肋片的直流蒸汽发生器传热管热工水力性能实验研究

对一种新型的传热管内部带旋转肋片式的直流蒸汽发生器传热管传热性能进行实验研究,分析不同流量工况下带旋转肋片传热管的换热系数以及螺距对努塞尔数(Nu)的影响规律。研究表明,在高雷诺数(Re)工况下旋转肋片对传热管换热性能影响明显,旋转肋片螺距的减小能够提高传热管换热性能。     

卧式螺旋管内气液两相含气率的试验与理论研究

本文从试验和理论两方面详细地研究了卧式螺旋管内气液两相流截面含汽率的分布与变化规律。在水/空气两相流回路中系统地研究了卧式螺旋管内气液两相全管圈平均截面含汽率随螺旋直径的变化规律;测量了局部截面含汽率沿螺旋径向的分布和平均截面含气率沿螺旋周向的变化规律;依据实验测量结果,木文使用文献[3]中提出的特别适用于弯曲通道的单流体双区域坐标摄动修正变密度模型进行了计算,推出了含汽率特性及相分布、相速度分布的预报公式,同时给出了适合于工程实用的全管圈平均截面含汽率简便计算公式。试验结果与理论公式具有良好的一致性。     

5×5定位格架棒束通道内三维流场研究

采用混合网格技术、SST k-ω湍流模型、改进的速度-压力耦合算法SIMPLEC求解雷诺时均的连续性方程、动量方程,得到格架内各截面的速度场和压力场。计算结果表明：在定位格架的影响下,通道内产生了强烈的横向流动;横向速度呈抛物线分布,轴向速度分布在通道内趋于均匀;阻力系数随进口雷诺数的增大而减小。将速度分布和阻力系数分布的预测值与试验值进行了对比,两者吻合较好。     

基于激光多普勒测量的6×6棒束间湍流流动研究

采用3D激光多普勒测速装置研究了6×6棒束间的流场分布。实验选择了5种工况进行研究,雷诺数范围为6.6×103~7.03×104。其中6×6棒束试验段几何结构模拟相邻组件的布置方式。实验设置两种测量模式,第1种模式选择从试验段侧边测量,获得了距定位格架不同位置处的轴向速度和湍流强度的分布;第2种测量模式选择从试验段出口端面进行测量,获得了出口截面子通道间的三维速度和雷诺应力分布。通过对比不同雷诺数下的实验结果,分析了雷诺数对此次6×6棒束实验的影响。比较发现在雷诺数为6.6×103的情况下,存在低雷诺数效应。     

矩形通道内两相脉动流平均摩擦压降实验研究

通过对截面为40 mm×3 mm窄矩形通道内不同正弦脉动周期、振幅、平均流量工况下氮气 水两相流（平均分液相雷诺数Re_l<10 000,平均分气相雷诺数Re_g<800）进行实验研究,发现两相脉动流与单相水脉动流的规律不同,平均压差对脉动周期、振幅不敏感。应用各经验公式计算的脉动工况下平均摩擦压降的偏差与稳态工况的计算偏差在数值和分布上均无明显差异,且计算值分布在测量值两侧、相对偏差基本小于20%。其中,Mishima-Hibiki方法和Lee-Lee方法的计算结果与测量结果吻合良好,相对偏差在10%以内,说明两相流摩擦压降经验公式同样适用于脉动工况下平均摩擦压降的计算。     

5×5定位格架棒束通道内三维流场研究

采用混合网格技术、SST k-ω湍流模型、改进的速度-压力耦合算法SIMPLEC求解雷诺时均的连续性方程、动量方程,得到格架内各截而的速度场和压力场.计算结果表明:在定位格架的影响下,通道内产生了强烈的横向流动;横向速度呈抛物线分布,轴向速度分布在通道内趋于均匀;阻力系数随进口雷诺数的增大而减小.将速度分布和阻力系数分布的预测值与试验值进行了对比,两者吻合较好.     

带定位格架的类三角形子通道内超临界水流动传热数值研究

针对超临界反应堆类三角形子通道的传热和流动特性,数值研究了不同栅距比定位格架作用下子通道内超临界水的流动传热特性、二次流及流动阻力特性。研究结果表明:定位格架对子通道内超临界水的换热影响显著;不同栅距比下的壁面温度、换热系数的轴向分布都具有相同的趋势,定位格架附近壁面温度下降,换热系数上升;定位格架下游壁面温度分布不均匀,且不均匀程度随栅距比减小而更加明显;定位格架下游截面形成四个对称旋涡,栅距比较小时,二次流强度较大;不同栅距比堆芯子通道流动阻塞率不同,流动阻力随栅距比减小而增大。     

空气-水在垂直非圆截面通道内流型研究

采用可视化方法研究了水力直径分别为15mm和10mm的两种正方形截面、14.43mm的三角形截面以及14mm的圆形截面通道内空气-水垂直上升流动,表观气速0.04～80m/s,表观水速0.001～6m/s.观察到了泡状流、弹状流、块状流、环状流和弥散泡状流等常见流型.此外,在表观气速很大而表观水速很小时,在非圆截面通道内发现了爬动流,证实了非圆截面直通道内存在"二次流"现象,且对气-液两相流动的相分布有较大影响,证明截面形状对两相流流型及其转变具有重要影响.由实验得到了流型转变界限,并首次获得了包括爬动流的两相流流型图.比较本文的实验结果及与前人的研究结果对比发现,水力直径的大小对两相流流型的转变具有一定影响.     

Local heat transfer and hot-spot factors in wire-wrap tube bundle

Heat transfer coefficients and hot-spot factors have been determined from measured local temperatures and calculated local mass flux in seven adjacent tubes and associated subchannels of a 61 wire-wrap tube bundle characteristic of the blanket of a GCFR (Gas Cooled Fast Reactor). The bundle consisted of 2.11 cm OD stainless steel tubes on a triangular array with a pitch/diameter ratio of P/D = 1.05. The helical wire of 0.1067 cm in diameter was coiled on the tube with a respective initial orientation of 0–120–240°C and 30.48 cm helical pitch. The experiment used water at atmospheric pressure and temperature as coolant. The resulting dimensionless correlation for heat transfer is applicable to gases and all non-metal fluids in one phase flow when the fluid properties at subchannel bulk temperature are used. This correlation is based on local subchannel mass flux and is applicable to all wire-wrap configurations. Local subchannel mass fluxes were determined with a computer program COBRA IV and used to correlate the average Nusselt number for each subchannel in terms of local Reynolds number and fluid Prandtl number. The differences of up to 19% between that correlation and the one presented in earlier work are discussed in the text. The hot-spot factors on the convective heat transfer coefficient for tubes and subchannels are given as a function of Reynolds number based on a bundle average mass flux and a local subchannel hydraulic diameter. These factors are specific to the bundle configuration and are also dependent on the wire-wrap configuration.     

Axisymmetric Mirror as a Driver for a Fusion–Fission Hybrid: Physics Issues

The axisymmetric mirror has a number of attractive features as a driver for a fusion-fission hybrid system: geometrical simplicity, inherently steady-state operation, and the presence of natural divertors in the form of end tanks. Operation at Q ~ 1 allows for relatively low electron temperatures, in the range of 4 keV, for the DT injection energy ~80 keV. A simple mirror with the plasma diameter of 1 m and mirror-to-mirror length of 35 m is discussed. A brief qualitative discussion of three groups of physics issues is presented: axial heat loss, MHD stability in the axisymmetric geometry, and the microstability of sloshing ions.     

A lumped parameter dynamic model of the helical coiled once-through steam generator with movable boundaries

A lumped parameter mathematical model of the helical coiled once-through steam generator of the 10 MW high-temperature gas-cooled reactor (HTR-10) is developed based upon the fundamental conservation of fluid mass, energy, and momentum. The steam generator is handled with single tube concept and is divided into three regions as subcooled region, boiling region, and superheater region. And these regions have movable boundaries to simulate the change of the region lengths. A lot of numerical experiments are investigated using the developed model. The steady-state simulation results agree well with the design data. The transient simulation results show that the model can properly predict the steam generator dynamics.     

高温气冷堆螺旋管蒸汽发生器流量漂移不稳定性研究

建立与氦气对流换热的并联螺旋管蒸汽发生器数值模型,分别采用一维飘移流模型和一维可压缩流动模型描述水侧和氦气侧的流动。在此基础上研究了球床模块式高温气冷堆核电站螺旋管蒸汽发生器内的流量漂移不稳定性。动态计算结果表明,在一定条件下蒸汽发生器内有可能发生流量漂移,不同传热管流量可相差几倍,而出口温度则相差几百度。通过对质量流速-压降曲线的分析,发现热负荷对稳定性起主导作用,热负荷越大越易发生流量漂移,且边界质量流量随热负荷呈线性增长。增大入口节流阻力和过冷度可以在一定程度上避免流量飘移。最后给出了蒸汽发生器流量飘移的稳定边界。     

Countercurrent flow limitation in inclined channels with bends

The countercurrent flow limitation phenomenon in an inclined round channel connected to bends at both ends is experimentally studied. The channel inner diameter is 1.9 cm, the bend radius divided by channel diameter is 10, and the channel length divided by channel diameter is varied in the 105–315 range. Countercurrent flow rates are measured with liquid and gas superficial velocities in the 0.015–0.21 m s⁻¹ and 0.1–3.1 m s⁻¹ ranges respectively. Air and water at room temperature and atmospheric pressure are used in the experiments. The liquid injection system is a constant-head plenum, and the channel angle of inclination with respect to the vertical line is varied in the 0°–60° range. The measured liquid and gas flow rates for all the angles of inclination are correlated using Wallis' flooding correlation, with a unique value for each of the two constants in the correlation.     

Numerical investigation on the similarity of developing laminar flows in helical pipes

This paper presents numerical investigations into the similarity of developing laminar flows at the entrance region of helical pipes. It is shown that the new characteristic parameters can be used to represent the flow development in helical pipes. The development of friction factor and flow pattern along with the characteristic parameters is not significantly affected by the variations of Reynolds number, dimensionless pitch, or curvature ratio at a given condition of modified Dean number and inlet velocity profile. The development of the friction factor is investigated in a modified Dean number range of 20–400, and a new correlation for the fully developed angles of laminar flows in helical pipes is proposed.     

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.     

Some Results of an Investigation and Prospects for the Development of a High-Temperature Power Reactor with a Solid Coolant

A validation of the possibility of developing and the basic advantages of a high-temperature nuclear reactor where the first-loop coolant is a solid are presented. The basic requirements for a solid coolant are formulated, a technology for fabricating spherical graphite particles by gas-phase pyrolytic deposition is developed, and three experimental batches are prepared. The experimental facilities for investigating the motion and heat transfer, including coolant flow stability, heat exchange, and durability, are described. The results of a determination of the heat-emission coefficient during the flow of the solid coolant in a 10-mm in diameter circular channel with warming-wall temperatures in the range 373–1073 K and flow velocities 0.1–0.22 m/sec in vacuum, argon, and helium are presented. The requirements for a 500-kW bench model, on which the basic parameters of the nuclear power system with a solid coolant are to be obtained, are formulated. __________ Translated from Atomnaya Energiya, Vol. 99, No. 5, pp. 358–365, November, 2005.     

Structure of air–water two-phase flow in helically coiled tubes

Air–water two-phase flow in helically coiled tubes is investigated experimentally to elucidate the effects of centrifugal acceleration on the flow regime map and the spatial and the temporal flow structure distribution. Three kinds of test tubes with 20 mm inner diameters including a straight tube are used to compare the turbulent flow structure. Superficial velocities up to 6 m/s are tested so that the centrifugal Froude number covers a range from 0 to 3. The interfacial structure is photographed from two directions by a high-speed video system with synchronized measurement of local pressure fluctuations. The results reveal that the flow transition line alters due to centrifugal force acting on the liquid phase in the tube. In particular, the bubbly flow regime is narrowed significantly. The pressure fluctuation amplitude gets large relatively to the average pressure loss as void fraction increases. The frequency spectra of the pressure fluctuation have plural peaks in the case of strong curvature, implying that the periodicity of slugging two-phase flow is collapsed by an internal secondary flow activated inside the liquid phase. Moreover, under large Froude number conditions, the substantial velocity of the gas phase that biases to the inner side of the helical coil is slower than the total superficial velocity because the liquid flow is allowed to pass through the outer side and so resembles a radial stratified flow.     

螺旋管式直流蒸汽发生器的准稳态数学模型

为了满足模拟机实时仿真核电站一、二回路工况的需要,根据流体的质量、动量和能量守恒原理,建立了适合模拟机要求的螺旋管式直流蒸汽发生器的准稳态数学模型.该模型将蒸汽发生器作为单管模型处理,并根据水的状态将蒸汽发生器分为单相水段、两相段和过热段三大段,每大段又细分若干小段.该数学模型方程采用变步长四阶龙格库塔法联立求解一、二...