Effect of rolling on the flowing and heat transfer characteristic of turbulent flow in sub-channels

The flowing and heat transfer of turbulent flow in typical 4 rod bundles in rolling motion is investigated with LES and URANS. As the rolling period decreases, the average wall shear stress increases, and the frictional resistance increases. The wall shear stress solved by LES is not good enough, while that of URANS is consistent with experiments. The variation of frictional resistance coefficient, Nusselt number and Reynolds stress with rolling amplitude is very weak. In rolling motion, the biggest frictional resistance coefficient is not located in a constant time.     

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.     

摇摆条件下热工水力程序的研制与验证

在RELAP5/MOD3.3程序的基础上,通过添加计算摇摆因素的模块和引入新的流动传热模型以对原程序进行修正,从而建立了摇摆条件下的热工水力分析程序。利用实验结果对理论模型和程序计算结果进行了校核和验证。结果表明：本文采用的流动传热模型可准确计算出摇摆条件下的摩擦阻力系数和传热系数,建立的热工水力分析程序也可对摇摆条件下的热工水力系统进行模拟。     

摇摆条件下子通道内湍流流体的数值分析

利用FLUENT软件分析了摇摆条件对典型四棒束间的湍流流体流动和传热特性的影响机理。摇摆运动会对棒束间流体的流动传热特性产生一定影响。RSM模型可以很好地描述摇摆条件下子通道内的参数分布。摇摆周期变化带来的径向附加力的变化不会对摩擦阻力系数、传热系数和Reynolds应力产生影响。在摇摆条件下,摩擦阻力系数、传热系数和Reynolds应力呈周期性变化,但最大摩擦阻力系数所在时刻并不固定,而最大传热系数却始终是在流速最大的时刻。     

The development and validation of a thermal hydraulic code in rolling motion

An advanced thermal hydraulic code is established on the basis of RELAP5/MOD3.3 code for the investigation of the thermal hydraulic behavior of nuclear power systems. The RELAP5 code is modified by adding a module calculating the effect of rolling motion and introducing new flow and heat transfer models. The experimental data are used to validate the theoretical models and calculation results. It is shown that the advanced flow and heat transfer models could correctly predict the frictional resistance and heat transfer coefficients in rolling motion. The thermal hydraulic code is used to simulate the operation of a natural circulation system in rolling motion. The calculation results are in good agreement with experimental data. The relative discrepancies between calculation results and experimental data are less than 5%.     

CFD analysis of flow and heat transfer of turbulent pulsating flow in a tube in rolling motion

The investigation of flow and heat transfer of turbulent pulsating flow is of vital importance to the nuclear reactor thermal hydraulic analysis in ocean environment. In this paper, the flow and heat transfer of turbulent pulsating flow is analyzed. The calculation results are firstly verified with experimental data. The agreement between them is satisfactory. The effect of spanwise and wall-normal additional forces is significant in small Reynolds number, and decreases with Reynolds number increasing. The rolling axis and rolling radius contribute slight to the flow and heat transfer. The effect of velocity oscillation period on the heat transfer is limited than that of Reynolds number and oscillating velocity Reynolds number. The traditional empirical correlations could not predict the flow and heat transfer of turbulent pulsating flow in rolling motion.     

自然循环系统摇摆条件下棒束通道内传热特性研究

棒束燃料元件子通道间流体存在搅混与横向二次流,流动及阻力特性相较矩形通道、圆管等简单通道更为复杂。核动力舰船、船舶、小型浮动核电站等会受到海浪影响,经常处于倾斜、摇摆、垂荡等瞬变运动下。目前的相关研究多集中在低压工况的研究领域,高温高压自然循环运动条件下的研究较少。本文采用实验研究方法,对自然循环系统摇摆条件下棒束通道内流动传热特性进行了研究,获得了过冷沸腾和饱和沸腾两种条件下摇摆角度和摇摆周期对棒束壁面温度变化和传热系数的影响,并获得了摇摆周期内棒束通道内的传热系数计算关系式。结果表明,饱和沸腾传热系数变化比过冷沸腾的剧烈;在本文实验工况范围内,棒表面传热系数波动幅值随着摇摆幅度的增大而增大;摇摆条件下棒束通道过冷沸腾和饱和沸腾工况时均传热系数基本不变。     

Research on operational characteristics of passive residual heat removal system under rolling motion

The operational characteristics of passive residual heat removal system under rolling motion were investigated experimentally. The passive residual heat removal system under rolling motion was simulated with the advanced RELAP5 code. The results are consistent with experiments. The relative discrepancy between calculating and experimental results is less than 10%. The modified condensation heat transfer model can also be used to calculate the condensation heat transfer coefficient with droplet carryover precisely. The fluctuation of condensate temperature and steam pressure is not noticeable. As the power becomes larger for the same rolling motion, the oscillation amplitude of condensate flow rate becomes larger. The effect of rolling motion upon heat transfer coefficient and flow resistance was investigated with experimental results. Rolling motion can increase the flow resistance in a great extent. The more serious the rolling is, the more the flow resistance is. Additional pressure drop does not effect on average flow velocity. The decreasing of average flow velocity is due to the decreasing average gravity pressure drop and the increasing of flow resistance. The contribution of gravity pressure drop on the decrement of average flow velocity is less than 20%. The other is due to the increasing flow resistance. In the present paper, the experimental results are listed first, and then the simulation results comparing with the experimental results are listed in the second part. At last, the effect of rolling motion is investigated theoretically.     

摇摆运动下矩形窄通道内流动沸腾阻力特性

本工作对摇摆运动下水在矩形窄通道内流动沸腾阻力特性进行实验研究分析。一方面利用竖直静止实验数据对已有两相压降的计算方法进行评价,结果表明,应用于常规通道的关系式已不适用于窄通道中流动沸腾压降的计算,基于窄通道的Zhang-Mishima及Sun-Mishima关系式预测结果与实验值符合较好;另一方面得出了摇摆运动下流动沸腾阻力特性,摇摆运动使两相压降周期性波动,但摇摆角度和摇摆周期对压降的波动幅度、两相平均摩擦压降几乎无影响。     

环形通道内液态铅铋合金流动换热特性实验研究

通过对环形通道内液态铅铋合金的流动换热特性进行实验研究,得到了气泡泵注气对液态金属流动的影响,并拟合出环形通道内液态铅铋合金的摩擦系数关系式和换热特性关系式。结果表明：采用气泡泵注气能有效提升铅铋合金的质量流速;相同Reynolds数下环形通道内液态铅铋合金的摩擦系数大于由布拉休斯公式计算得到的摩擦系数;液态铅铋合金对流换热过程中,导热项占主导地位,并且Nusselt数随Peclet数的增大而增大。     

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.     

The model of laminar pulsatile flow in tubes in rolling motion

The laminar pulsatile flow in tubes in rolling motion is investigated theoretically. The theoretical model of laminar flow in rolling motion is developed and the velocity correlation is also derived. The effect of rolling motion on velocity and frictional resistance factor is analyzed. The rolling motion mainly affects on the laminar flow by the tangential force. The centrifugal force does not affect on the flow. The tangential force affects on the flow in axial direction, its radial effect is very weak and could be omitted. There are two critical rolling points in rolling motion. After the first critical rolling point, the flowing velocity next to the wall reverses. Moreover, the flow rate at the tube cross-section becomes negative after the second critical rolling point. The buoyancy force is only one part of the effects that affects on the average velocity of a natural circulation system in rolling motion. The effect of Womersley number on the velocity is significant, which can not only affect on the average velocity but also on the oscillating period and velocity amplitude. The rolling motion does not affect on the average frictional resistance of laminar pulsatile flow. If the rolling motion is very serious, the flow is at a transitional or turbulent flow state, in this case the effect of rolling motion on the average frictional resistance is considerable.     

摇摆条件对湍流流动特性的影响

利用Fluent软件对摇摆条件下矩形管内的湍流流体进行理论分析,分析了多种湍流模型和多个参数对流动特性的影响。在摇摆条件下,矩形管中心区域速度分布趋于均匀化,但壁面附近的速度梯度增大,从而使摩擦阻力系数增加。壁面会对摇摆条件对湍流流体的影响产生抑制作用。在纵摇条件下,小长宽比矩形管内速度等高线成哑铃状分布。对于本文的计算流体,摇摆条件下的湍流摩擦阻力系数与Re的0.47次方成反比。     

Experimental study on convective heat transfer of water flow in a heated tube under natural circulation

This paper reports on an experimental study on transitional heat transfer of water flow in a heated vertical tube under natural circulation conditions. In the experiments the local and average heat transfer coefficients were obtained. The experimental data were compared with the predictions by a forced flow correlation available in the literature. The comparisons show that the Nusselt number value in the fully developed region is about 30% lower than the predictions by the forced flow correlation due to flow laminarization in the layer induced by co-current bulk natural circulation and free convection. By using the Rayleigh number Ra to represent the influence of free convection on heat transfer, the empirical correlations for the calculation of local and average heat transfer behavior in the tube at natural circulation have been developed. The empirical correlations are in good agreement with the experimental data. Based on the experimental results, the effect of the thermal entry-length behavior on heat transfer design in the tube under natural circulation was evaluated.     

摇摆条件下窄矩形通道内两相流动瞬态阻力特性研究

摇摆条件下的气液两相流动受摇摆引起的附加惯性力的影响,致使其摩擦阻力特性发生改变。本工作在摇摆周期为8、12、16 s和摇摆振幅为10°、15°、30°的条件下,对窄矩形通道（40 mm×1.6 mm）内空气-水两相流动的瞬态阻力特性进行了研究。结果表明：摇摆时瞬态摩阻系数的变化呈明显周期性;气相质量含气率越大,摩擦压降的波动幅度越大;摇摆周期越小,振幅越大,摩擦压降的波动幅度越大。给出1个用于计算摇摆条件下两相摩阻系数的关联式,92.5%的计算值的相对误差在±20%以内     

骨架发热多孔介质内单相水流动传热实验研究

针对骨架发热多孔介质内单相水流动阻力和传热特性开展了实验研究,拟合获得骨架发热多孔介质内热态流动阻力和对流换热关系式。实验参数范围是:雷诺数Re取127～394,表面热流密度12～62 kW/m2。实验结果表明:在本文研究的孔隙有效雷诺数范围内,惯性项阻力系数Rf受流动参数影响;基于骨架发热条件下获得的阻力关系式具有较好的扩展性,可以较好地预测骨架不发热条件下多种几何结构的多孔介质通道内单相水、单相蒸汽流动阻力;随着表面热流密度增大,对流换热系数不断降低;在相同热流密度条件下,随着质量流速的增大,对流换热系数也会随之增大。     

Investigation on condensation in presence of a noncondensable gas for a wide range of Reynolds number

A theoretical model has been developed to study the local heat transfer coefficient of a condensing vapour in the presence of a noncondensable gas, where the gas/vapour mixture is flowing downward inside a vertical tube. The two-phase heat transfer is analysed using an annular flow pattern with a liquid film at the tube wall and a turbulent gas/vapour core. The gas/vapour core is modeled using the analogy between heat and mass transfer. The model incorporates Nusselt equation with McAdams modifier and Blangetti model for calculating the film heat transfer coefficient, Moody and Wallis correlations to account for film waviness effect on gas/vapour boundary layer. The suction effect due to condensation, developing flow and property variation of the gas phase is also considered. A comparative study of heat transfer coefficient and vapour mass flow rate has been made with various models to account for condensate film resistance and condensate film roughness. Results show that for very high Reynolds number, the condensation heat transfer coefficient is higher than the film heat transfer coefficient.     

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。     

Numerical analysis of flowing characteristics of turbulent flow in rectangular channels in ocean environment

Because of the periodic effects of ocean waves, there are great discrepancies between the operational characteristics of nuclear power systems in ocean environment and that of land-based nuclear power systems. In some special operational status, like natural circulation, the additional forces due to ocean environment may impose so great disturbance on the coolant flow that theatres the safety operation of the systems. In the present paper, the turbulent flow in rectangular channels in ocean environments is investigated theoretically with CFD code FLUENT. The effects of several parameters on turbulent flow are analyzed. The effects of rolling motion includes two parts, the first part is the additional force parallel to flowing direction, which can affect on the pressure drop of the flow and change the flowing velocity, and the other part is the additional force perpendicular to flowing direction. In ocean environments, the flowing characteristics of turbulent flow are dominated by the additional force parallel to flowing direction. The effect of additional force perpendicular to flowing direction is very limited. In rolling and heaving motions, if the flowing velocity is the same, the flowing characteristics of turbulent flow are nearly the same, too. The bigger the Reynolds number is, the more serious the oscillation of turbulent kinetic energy and frictional resistance coefficient is, and the more the oscillation of turbulent flow is. The relationship between average frictional resistance coefficient and velocity oscillating amplitude is quadratic. And the oscillating amplitude of frictional resistance coefficient is in direct ratio with velocity oscillating amplitude.     

摇摆条件对矩形通道内泡状流摩阻特性影响

摇摆运动作为一种典型海洋条件,对管内的气液两相流动过程产生较大影响。本工作通过摇摆条件下空气 水泡状流在矩形通道内流动阻力特性的实验,研究摇摆运动对两相流动过程的影响。实验在常温、常压下进行,通道尺寸为40 mm×10 mm,摇摆角度为10°、15°和30°,摇摆周期为8、12和16 s。结果表明,摇摆条件下瞬态摩擦压降的变化具有明显周期性,随着两相雷诺数变大,瞬态摩阻系数的波动幅度和平均水平均变小;摇摆周期越小,摇摆振幅越大,即摇摆运动越剧烈,摩擦压降的波动幅度也越大。