共查询到19条相似文献,搜索用时 171 毫秒
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板状燃料元件中的矩形窄缝通道具有宽高比大的几何特征,高度方向速度梯度大、分布陡峭,发生过冷沸腾时,近壁面汽泡运动行为将受其影响而改变,其中汽泡滑移现象对沸腾换热影响较大。本文针对矩形窄缝通道中的汽泡滑移行为,构建了包含滑移热流的壁面热流分配模型,并建立机理性的汽泡受力模型和滑移模型计算汽泡脱离直径、浮升直径和滑移距离等辅助参数,开发了一套适用于矩形窄缝通道内向上流动沸腾的壁面沸腾模型。选用Nuthel窄缝通道沸腾实验进行数值模拟验证,结果表明:本文模型可以较好地预测1~4 MPa中低压工况窄缝通道向上流动沸腾的壁面过热度,最大误差相比RPI模型由80%降低至17%;蒸发热流份额和近壁面空泡份额相比RPI模型更低。 相似文献
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采用高速摄像仪对矩形窄缝通道内垂直上升流过冷流动沸腾区域汽泡脱离频率进行可视化实验研究。结果表明,汽泡脱离频率随质量流速的增大而减小,随入口过冷度的增大而减小,随热流密度的增大而增大。将实验数据与文献中汽泡脱离频率计算模型进行比较,发现基于池式沸腾和饱和流动沸腾开发的计算模型不能准确预测过冷沸腾区域汽泡脱离频率。本文以无量纲参数的形式,分别用液相雷诺数、过冷雅各布数和核态沸腾热流密度表示质量流速、主流过冷度和热流密度对汽泡脱离频率的影响,获得矩形窄缝通道内过冷沸腾区域汽泡脱离频率预测关系式,关系式的平均预测误差为±17.1%。 相似文献
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基于壁面汽泡壅塞理论,针对近临界压力区两相流动沸腾的偏离泡核沸腾(DNB)现象,对垂直上升内螺纹管的DNB型临界热流密度(CHF)进行了数值计算研究。以内螺纹管为分析对象改进已有的汽泡壅塞模型,计算了汽泡层区与主流区的极限传递质量流量、湍流速度分布、汽泡层区临界截面含气率等本构关系,汽泡脱离直径的计算考虑了汽泡接触角的影响。本文模型还根据大量CHF实验数据拟合得到了新的αb关联式。最后,基于Fortran语言编制了CHF的理论预测数值模型程序,研究分析了压力、质量流速、热平衡干度及进口欠焓对CHF的影响,并根据CHF查表值对本文模型进行评估,同时将实验得到的内螺纹管CHF数据与采用Bowring模型、Katto模型、Shah模型和本文模型计算的CHF进行比较,发现本文模型的误差最小,与实验值吻合结果较好,说明本文模型能较好地对垂直上升内螺纹管DNB型CHF进行预测。 相似文献
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通过汽泡受力分析,构建窄缝通道内汽泡脱离直径预测模型。基于可视化实验获得的汽泡轴心倾斜角、前后接触角以及底部接触直径等数据,评价分析汽泡界面参数对脱离直径预测的影响,进而确定适用于本实验工况下窄缝通道内汽泡受力模型求解的界面输入参数,获得了窄缝通道汽泡脱离直径的预测值。利用竖直和倾斜条件下可视化实验获得的58个数据对汽泡脱离直径预测模型进行了验证,预测值和实验值符合较好。基于验证的汽泡脱离直径模型评估了各个力的地位和作用,应用分析了热工参数对汽泡脱离直径的影响。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(8):604-618
Experiments were carried out on DNB (Departure from Nucleate Boiling) heat flux for both upflow and downflow in a rectangular vertical channel simulating a subchannel in the fuel element of the research reactor JRR-3, which is scheduled to be upgraded at 20MWt with 20% low enriched uranium (LEU) fuel. The experiments were carried out for the conditions of pressure and velocity which are important for the safety design of the JRR-3. With the investigation of the data of the present experiment along with already existing data for both rectangular channels and other channels, a scheme of DNB heat flux correlations was obtained for upflow and downflow. With the all available data, the errors of the correlations adopted in this scheme were so evaluated as to utilize these results in the safety analysis of the JRR-3. This scheme includes a new correlation of DNB heat flux for upflow and the identification of a region of high coolant flow rate where no remarkable differences in the DNB heat flux are observed between upflow and downflow. This scheme is considered to be applicable not only to the rectangular channels of the JRR-3 but also to other channels. 相似文献
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常压下,以空气和水为工质,对宽高比不同的两个矩形通道内两相流动摩擦阻力特性进行了研究,并对常规通道和微小通道内两相压降的计算模型进行了验证和评价。结果表明:传统的常规通道经验关系式并不适用于窄矩形通道中的压降计算;基于微小通道的计算方法中,Lee-Lee模型与实验值符合程度较好,但在一定的参数范围内仍存在较大误差。提出基于Chen模型的Chisholm C系数方法的修正关系式,式中综合考虑了矩形通道宽高比、全液相雷诺数和L-M参数对Chisholm C系数的影响,修正关系式与实验值符合较好。 相似文献
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Flow regime transition criteria for upward two-phase flow in vertical narrow rectangular channels 总被引:1,自引:0,他引:1
In relation to the cooling system of high performance microelectronics, a high power research reactor with plate type fuels and plasma facing components of a fusion reactor, study of two-phase flow in a narrow rectangular channel has been paid considerable attention, recently. For the two-fluid model, direct geometrical parameters such as the void fraction should be used in flow-regime criteria. From this point of view, flow-regime transition criteria for vertical upward flows in narrow rectangular channels have been developed considering the mechanisms of flow-regime transitions. The basic concept of the present modeling followed the Mishima and Ishii model for vertical upward two-phase flows in round tubes. Newly developed criteria have been compared with the existing experimental data for air–water flows in narrow rectangular channels with the gaps of 0.3–17 mm. The present criteria showed satisfactory agreements with those data. Further comparisons with data for steam–water in a rectangular channel at relatively high system pressures have been made. The results confirmed that the present flow-regime transition criteria could be applied over wide ranges of parameters as well as to boiling flow. 相似文献
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在中国核动力研究设计院热工试验回路上进行了矩形双通道管间脉动试验.对各种热工水力参数的试验研究后得出结论:随着进口过冷度的增加,界限热流密度增大,脉动振幅增大,脉动周期变长,进口过冷度对界限含汽率的影响表现出一定程度的非单值性;随着进口质量流速的增大,界限热流密度增加,界限含汽率减小,脉动振幅增大,脉动周期变短;随着系统压力的升高,界限热流密度和界限含汽率增加,脉动振幅减小,系统压力对脉动周期的影响表现出一定程度的非单值性;根据进口过冷度数Nsub和相变数Npch绘制出的脉动界限图,拟合出判断管间脉动界限的准则关系式:Npch=3.1419 Nsub 10.014. 相似文献
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窄矩形通道因具有结构紧凑、换热面积大等优点而被广泛应用于各个领域。通过完善窄矩形通道中临界热流密度(CHF)的预测方法,建立CHF机理模型,可以提高反应堆的安全性和经济性。本文对窄矩形通道内竖直向上流动CHF进行了可视化实验研究,在此基础上开发了一种基于加热壁面能量平衡的CHF机理模型,并提供一组本构关系用于封闭所开发的新模型,同时使用实验数据对新模型进行对比评价,对比结果发现,新模型在窄矩形通道中模拟结果良好,偏差基本都在±20%之间。 相似文献
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矩形窄缝通道内水稳态和瞬态流动换热特性实验 总被引:1,自引:0,他引:1
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。 相似文献
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This paper focuses on the unsteady numerical simulation of the turbulent flow in two types of geometry containing a narrow gap with the explicit algebraic Reynolds stress model. The model was first validated through the comparison of simulation results inside a rectangular channel containing a cylinder and the corresponding experimental data. The structures of the oscillation were correctly reproduced. Simulation of turbulent mixing between circular channels connected by a narrow gap was carried out with the validated model. Because of the influence of the strong anisotropic turbulent flow in the gap region, the mixing rate was dramatically enhanced by the cyclic and almost periodic flow pulsation. The calculation results of the turbulent mixing rate showed good agreement with the experiment and the maximum error was less than 15%. 相似文献
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空泡份额和界面浓度是两相流动中重要的相界面参数,准确获取窄矩形通道内搅混流和环状流工况下空泡份额和界面浓度是构建和完善两流体模型的关键。本文针对横截面为65 mm×2 mm的矩形通道开展了气液两相流动特性可视化实验研究,气相折算速度jg=1~9 m/s,液相折算速度jf=0.1~1.5 m/s,流型包含搅混流和环状流。提出了基于高速摄像法获取搅混流和环状流下空泡份额和界面浓度的分析计算方法,利用该方法所得空泡份额与窄矩形通道内经验关系式计算值的相对偏差约在10%以内。此计算方法可为研究复杂流型下窄矩形通道内的相界面参数提供理论依据。 相似文献