摇摆对自然循环传热特性影响的实验研究

对摇摆情况下单相自然循环流动的传热特性进行了实验研究.试验结果表明,摇摆运动下,自然循环的换热能力得到了加强,摇摆的频率和振幅增加,换热系数也相应增加.针对摇摆运动下换热系数经验公式的适用性进行了分析,并通过实验数据的拟合得出了适用于摇摆运动下的自然循环换热经验关系式.     

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。     

The modeling and validation of the flow and heat transfer models of pulsating flow in channels in rolling motion

The flow and heat transfer models of laminar flow and turbulent flow in rolling motion are established theoretically and modified with CFD results and experimental data. The correlations of frictional resistance coefficient and Nusselt number in pipes in rolling motion are obtained. The effect of rolling motion on the flow and heat transfer is mainly affected by the Reynolds number, angular acceleration and channel diameter. As the channel diameter is small, the effect of rolling motion on the flow and heat transfer is weak. The modified correlations of frictional resistance coefficient and Nusselt number in rolling motion could predict the flow and heat transfer in pipes in rolling motion correctly. The average discrepancy between theoretical correlations and experimental data is about 15%.     

摇摆运动下自然循环高含汽率流动特性研究

针对摇摆运动下自然循环高含汽率流动特性进行了理论研究。与摇摆运动下的自然循环单相流动波动不同,摇摆运动下的自然循环高含汽率流动波动幅度很小,流动相对稳定。通过构建数学模型,对摇摆运动下自然循环单相流动和高含汽率流动的流动特性进行了计算,计算结果与实验结果符合良好。对两种流动状态下各项压降及摩擦阻力系数进行了分析。分析结果表明,驱动压头和阻力系数的增加是摇摆运动下自然循环高含汽率流动相对稳定的原因。     

摇摆对自然循环核热耦合平均功率的影响

通过对摇摆条件下单相自然循环核热耦合的模拟计算,分析研究了摇摆条件下自然循环核热耦合系统平均功率的影响因素。分析结果表明：摇摆条件下,考虑核反馈后的系统平均功率与系统的平均质量流量、系统的平均传热系数成正比,与慢化剂与燃料的温度反馈系数比成反比。摇摆参数对系统平均功率的影响和慢化剂与燃料的温度反馈系数比有关。当系统平均传热系数的变化对反应性的影响起主导作用时,摇摆越剧烈,系统平均功率越大;当平均阻力系数的变化对反应性的影响起主导作用时,摇摆越剧烈,系统平均功率越小。     

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%.     

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.     

摇摆条件下两环路自然循环回路特性分析

在海上小型堆设计中,需要考虑海洋运动条件对热工水力特性的影响。本文建立了海洋运动条件下的附加惯性力模型,并将该模型应用于RELAP/SCDAP程序中,得到了适用于海洋运动条件下的系统分析程序,利用修改后的RELAP5程序,分析了在摇摆条件下自然循环回路的热工水力特性。分析结果表明,摇摆条件下,自然循环回路的平均流量小于静止条件下的自然循环流量,环路流量波动滞后于横摇运动,冷却水温波动滞后于环路流量波动,摇摆幅值越大,频率越高,流量波动幅值越大。当摇摆较剧烈时,环路上出现倒流现象。增加加热功率或提高冷热源之间高度差可增加系统的自然循环驱动力,减小横摇运动对自然循环的影响。     

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。     

摇摆条件下竖直圆管内干涸型临界沸腾的数值研究

针对摇摆条件下竖直圆管内干涸型临界热流密度（Dryout CHF）进行了三维数值计算,研究了摇摆条件下竖直圆管内相态分布特性、圆管内临界热流密度（CHF）的位置以及最高壁面温度,同时对管壁沿程换热系数特性进行了分析。结果表明:在摇摆条件下,圆管内相分布呈现周期性变化,CHF的位置也会发生周期性变化;同时发现摇摆运动会导致壁面最高温度更高,因此摇摆条件会使沸腾临界现象更严重。随着流型转变和沸腾传热机制的变化,管壁换热系数沿流动方向也会显著变化。本研究可以为摇摆条件下Dryout CHF的数值预测提供参考。      

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.     

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.     

非能动余热排出系统数学模型研究与运行特性分析

利用某型核动力装置非能动余热排出系统1:10原理性试验的8个稳态工况、6个启动工况的试验数据,验证RELAP5/MOD3.2程序对本类型非能动余热排出系统的适用性。结果表明:垂直管内蒸汽凝结换热系数对两相流自然循环的流动与传热影响大;RELAP5/MOD3.2程序过低估算了垂直管内蒸汽流速对蒸汽凝结换热系数的影响,计算结果与试验结果偏差大。对RELAP5/MOD3.2程序垂直管内的蒸汽凝结换热模型进行修正,修正后的计算结果与试验值基本吻合;采用RELAP5程序对垂直管内两相流自然循环传热进行计算,须选择热前沿跟踪模型。对非能动余热排出系统的稳态与瞬态运行特性进行分析,理论计算与试验结果均表明:稳态工况下,系统可以实现稳定的两相流自然循环,系统排热能力受蒸汽发生器水位的影响大,冷却水入口温度与系统压力的影响相对较小;系统的启动特性良好,可快速地建立环路的自然循环,带走反应堆的衰变热。     

摇摆运动下单相自然循环流动特点

针对摇摆工况下单相自然循环流动的特点进行实验研究。实验结果表明,流体在摇摆作用下产生波动;波动频率与摇摆频率一致。理论分析表明,摇摆对自然循环的影响主要有两个方面,一方面摇摆引起回路空间位置的改变导致自然循环驱动压头发生变化;另一方面,摇摆引起的附加加速度使回路产生附加压降。通过建立简化模型,得出了摇摆周期、摇摆振幅和其他参数对单相自然循环流动影响的规律。     

Thermal-hydraulic behavior of a marine reactor during oscillations

The effect of ship motion, such as heaving and rolling, on the thermal-hydraulic behavior of marine reactors was investigated. The COBRA-IV-I CODE was modified to analyse the thermal-hydraulic performance on the critical heat flux under oscillating acceleration conditions. The critical heat flux in the code was verified experimentally using freon as a comparison. The Critical Heat Flux Ratio (CHFR) at the hottest channel of the PWR subchannel was analysed using the same code. A system code RETRAN-02/MOD2-GRAV was developed by improving RETRAN-02/MOD2 to simulate the thermal hydraulic transient under ship motion. It was verified by comparison using the experimental results of both two-phase natural circulation flow under heaving motion and single-phase natural circulation flow at an inclined attitude. The code was used to analyse reactor plant behavior in the nuclear ship Mutsu. Natural circulation flow during rolling motion was investigated experimentally. The characteristics of loop flow and core flow rates were clarified. The core flow rate correlated well with the Reynolds number of rolling motion.     

Experimental study on two-phase flow instability of natural circulation under rolling motion condition

Two-phase flow instability of natural circulation under a rolling motion condition is experimentally studied. The experimental results show the rolling motion induces a fluid flow fluctuation. At the trough point of the flow fluctuation, rolling motion can cause the early occurrence of natural circulation two-phase flow instability, and this case is defined as trough-type flow oscillation. The system stability decreases with increasing rolling amplitude and effect of rolling frequency is nonlinear. The complex overlap effect of trough-type flow oscillation and density wave oscillation can enhance the system coolant fluctuation; this case is defined as complex flow oscillation. Complex flow oscillation may be divided into two types: regular and irregular complex flow oscillations. Irregular complex flow oscillation is a transition type from trough-type flow oscillation to regular complex flow oscillation. Under the same thermal hydraulic conditions, the marginal stability boundary (MSB) of regular complex flow oscillation is similar to that of density wave oscillation without rolling motion, and the influences of rolling parameters on the MSB are slight.     

零功率摇摆条件下自然循环试验回路中流动规律实验研究

以清华大学研发的多用途小型堆NHR为基础,建立全尺寸、全参数1∶1自然循环试验回路研究零功率摇摆条件下自然循环的流动规律。通过分析几组不同摇摆运动下的实验结果,探讨了单自由度摇摆运动摆角幅值ψ_m和摇摆周期T对自然循环速度的影响,并给出自然循环流速波幅V_o和摇摆运动参数ψ_m与T之间的线性关系。研究结果表明：ψ_m对加热段两侧流速影响最为显著,V_o随ψ_m的变大而增大且两侧流速波动相位相差90°;V_o随T的增大而减小,流速波动相位差与T无关;在零功率摇摆条件下,流速波幅的平方V²_o与ψ_m、频率平方w²_d及当量摇摆半径R_eq的乘积呈线性关系。     

摇摆运动条件下自然循环温度波动特性

1.西安交通大学动力工程多相流国家重点实验室,陕西西安 710049;2.哈尔滨工程大学核科学与技术学院,黑龙江哈尔滨 150001     

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。     

摇摆运动对自然循环流动不稳定性的影响

分析研究了摇摆运动下的自然循环流动不稳定性和摇摆对不稳定性的类型以及不稳定性起始点的影响.结果表明,摇摆使流动不稳定性提前发生,改变了不稳定性的类型,摇摆引起的波动和密度波型脉动发生叠加.摇摆运动下自然循环存在两个稳定区域,在这两个区域中间包含着不稳定区域.