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Such estimates were carried out in [5, 6], where it has been shown that there exists a certain intensity flux q*, above which surface evaporation is modified by bulk boiling.


Effect of viscosity of liquid phase on loss of hydrodynamic stability in nucleate bulk boiling


It is found that, in the case of intensive bulk boiling in a jet of superheated liquid, the fluctuation power spectrum has a lowfrequency component (flicker noise) diverging as 1/f.


Two modes of bulk boiling of superheated liquid on a wire




 The investigations were performed on the Thermohydraulic Experimental system HRTL5 which is a fullscale and fullparameter simulator to the primary loop of the lowtemperature heating reactor at Institute of Nuclear Energy Technology, Tsinghua University. The method of visual observation under pressurized operation conditions combined with data recording and analyzing was adopted. The features of hydrodynamic stability of the natural circulation system were investigated with varying system pressure, varying... The investigations were performed on the Thermohydraulic Experimental system HRTL5 which is a fullscale and fullparameter simulator to the primary loop of the lowtemperature heating reactor at Institute of Nuclear Energy Technology, Tsinghua University. The method of visual observation under pressurized operation conditions combined with data recording and analyzing was adopted. The features of hydrodynamic stability of the natural circulation system were investigated with varying system pressure, varying inlet subcooling and in a wide range including singlephase flow, subcold boiling flow and low quality bulk boiling flow at the exit of the test section. Some new hydrodynamic instability phenomena induced by subcold boiling in a natural circulation system with low pressure were discovered in this investigation. Several different mode of mass flow osillation was observed. Under certain conditions, static mass flow drift occured in the natural circulation system. The results of the investigation are of great importance for thermalhydraulic design, safety analysis and start procedure design of a pressurized natural circulation system with low pressure, such as pooltype low temperature heating reactor and integrated vesseltype low temperature heating reactor.  报道了低压压水运行工况下自然循环系统中过冷沸腾引起的两相流流动稳定性研究结果。研究工作是在清华大学核能技术研究所的低温堆全尺寸、全参数热工水力学实验系统HRTL5上进行的,采用了可视化研究与数据记录分析相结合的研究方法,研究了不同系统压力、不同进口过冷度条件下,加热段出口从单相流动、过冷沸腾,到低干度容积沸腾整个范围内自然循环系统的稳定性特征。研究发现了低压过冷沸腾自然循环不稳定现象。在较宽的过冷度范围内存在着多种不同模式的流量振荡,在特定条件下存在着自然循环流量静态漂移。研究结果对低压压水运行的自然循环系统,例如,壳式一体化自然循环供热堆和池式低温供热堆的热工设计和安全分析论证及启动方式研究都具有重要意义。  The investigations were performed on the Thermohydraulic Experimental system HRTL5 which is a fullscale and fullparameter simulator to the primary loop of the lowtemperature heating reactor at Institute of Nuclear Energy Technology, Tsinghua University. The method of visual observation under pressurized operation conditions combined with data recording and analyzing was adopted. The features of hydrodynamic stability of the natural circulation system were investigated with varying system pressure, varying... The investigations were performed on the Thermohydraulic Experimental system HRTL5 which is a fullscale and fullparameter simulator to the primary loop of the lowtemperature heating reactor at Institute of Nuclear Energy Technology, Tsinghua University. The method of visual observation under pressurized operation conditions combined with data recording and analyzing was adopted. The features of hydrodynamic stability of the natural circulation system were investigated with varying system pressure, varying inlet subcooling and in a wide range including singlephase flow, subcold boiling flow and low quality bulk boiling flow at the exit of the test section. Some new hydrodynamic instability phenomena induced by subcold boiling in a natural circulation system with low pressure were discovered in this investigation. Several different mode of mass flow osillation was observed. Under certain conditions, static mass flow drift occurred in the natural circulation system. The results of the investigation are of great importance for thermalhydraulic design, safety analysis and start procedure design of a pressurized natural circulation system with low pressure, such as pooltype low temperature heating reactor and integrated vesseltype low temperature heating reactor.  报道了低压压水运行工况下自然循环系统中过冷沸腾引起的两相流流动稳定性研究结果。研究工作是在清华大学核能技术设计研究院的低温堆全尺寸、全参数热工水力学实验系统HRTL5上进行的,采用了可视化研究与数据记录分析相结合的研究方法,研究了不同系统压力、不同进口过冷度条件下,加热段出口从单相流动、过冷沸腾,到低干度容积沸腾整个范围内自然循环系统的稳定性特征。研究发现了低压过冷沸腾自然循环不稳定现象。在较宽的过冷度范围内存在着多种不同模式的流量振荡,在特定条件下存在着自然循环流量静态漂移。研究结果对低压压水运行的自然循环系统,例如,壳式一体化自然循环供热堆和池式低温供热堆的热工设计和安全分析论证及启动方式研究都具有重要意义。  The experiment was carried out on the test loop HRTL5,which simulates the geometry and system design of a 5 MW Nuclear heating reactor. The analysis was based on a onedimensional twophase flow drift model with conservation equations for mass, steam mass, energy and momentum. ClausiusClapeyron equation was used for the calculation of flashing front in the riser. A set of ordinary equation, which describes the behavior of twophase flow in the natural circulation system, was derived through integration of... The experiment was carried out on the test loop HRTL5,which simulates the geometry and system design of a 5 MW Nuclear heating reactor. The analysis was based on a onedimensional twophase flow drift model with conservation equations for mass, steam mass, energy and momentum. ClausiusClapeyron equation was used for the calculation of flashing front in the riser. A set of ordinary equation, which describes the behavior of twophase flow in the natural circulation system, was derived through integration of the above conservation equations in subcooled boiling region,bulk boiling region in the heated section and in the riser. The method of timedomain was used for the calculation. Both static and dynamic results are presented. System pressure, inlet subcooling and heat flux are varied as input parameters. The results show that, firstly, subcooled boiling in the heated section and void flashing in the riser have significant influence on the distribution of the void fraction, mass flow rate and stability of the system, especially at lower pressure, secondly , in a wide range of twophase flow conditions, only subcooled boiling occurs in the heated section. For the designed twophase regime operation of the 5 MW nuclear heating reactor, the temperature at the core exit has not reaches its saturation value. Thirdly, the mechanism of twophase flow oscillation, namely," zeropressuredrop" , is described. In the wide range of inlet subcooling (0 Kbulk and subcooled boiling unstable flow, (3) subcooled boiling and single phase stable flow. The response of mass flow rate, after a small disturbance in the heat flux, is showed in the above inlet subcooling range, and based on it the instability map of the system is given through experiment and calculation.  实验研究在5MW核供热反应堆模拟热工水力学实验回路HRTL5上进行。分析计算基于带有质量,蒸汽质量,能量及动量守恒方程的一维两相流漂移模型。给出了在不同系统压力,进口过冷度及热流密度条件下的稳态和动态分析结果。研究结果表明:加热段中的过冷沸腾及上升段中的闪蒸对空泡份额分布及流动稳定性有重要影响,特别是在低压条件下;在相当宽的两相流条件下,加热段中只发生过冷沸腾;对于沸水设计工况的5MW低温堆,其堆芯出口温度尚未达到饱和。描述了两相流振荡机理,即“零阻降”机理。在进口过冷度相当宽范围内(OK<ΔT<28K),对系统流条件,存在3个区域,即稳定的两相流,整体和过冷沸腾不稳定流和过冷沸腾以及单相稳定流。给出了系统流量在小热流密度扰动下的响应特性。在此基础上给出了稳定边界图的计算和实验值。  
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