倾角变化的窄缝通道内CHF理论模型

对倾角变化的矩形窄缝通道的临界热流密度(CHF)进行分析,基于逆向对流限制(CCFL)机理建立相应的理论分析模型,并将该理论模型的预测结果与已有的实验结果进行对比。结果表明:当矩形窄缝通道尺寸为1 mm和2 mm,且倾角在范围在15°~90°时,预测结果与实验值符合得比较好;在倾角小于15°时,理论模型对CHF的预测明显小于实验值;修正的Katto-Kosho关系式可以比较准确地预测倾角小于15°时的CHF值;当通道尺寸为5 mm和10 mm时,预测值比实验值大,这表明基于CCFL机理的CHF预测理论模型仅适用于通道尺寸小于等于2 mm的窄缝通道。     

基于机器学习的螺旋流动过冷沸腾CHF预测研究

过冷沸腾广泛应用于以国际热核聚变实验堆（ITER）为代表的高热流冷却场合。本文聚焦高热流、螺旋流动条件下水的过冷沸腾临界热流密度（CHF）的预测方法,建立了该类工况下的过冷沸腾CHF实验数据库。选用了4种典型机器学习模型：反向传播（BP）神经网络、遗传算法( GA )-BP神经网络、 径向基函数（RBF）神经网络和极限学习机（ELM）;利用传统的经验关联式和新兴的机器学习方法对螺旋流动过冷沸腾CHF进行预测研究。经与实验数据库对比,结果表明,相关机器学习模型能够有效预测螺旋流动过冷沸腾CHF,其预测性能相较于传统的经验关联式有大幅提升,其中ELM模型预测效果最优,平均绝对误差和均方根误差分别为2.79%和4.22%。研究成果为高热流螺旋流动过冷沸腾CHF的准确预测提供了新途径。     

氧化铝纳米流体增强球形下封头IVR能力边际研究

为评价氧化铝纳米流体相对于纯水工质对球形下封头熔融物滞留（IVR）能力边际的拓展程度,采用基于气泡力平衡的氧化铝纳米流体临界热流密度（CHF）机理模型和壁面热通量拆分CHF模型计算球形下封头外表面纳米流体CHF。利用熔融物堆内滞留分析软件CISER开展衰变热分布抽样计算,得到下封头壁面CHF随倾角变化的随机分布,并将其与纳米流体CHF模型的理论值相比,以CHF比值小于1作为IVR成功准则,研判纳米流体对IVR能力边际拓展的影响程度。研究结果表明,若不对下封头内外传热构成采取任何优化措施,仅采用纳米流体替代纯水工质,压水堆核电厂的IVR能力边际能够拓展至1300 MW额定电功率水平。     

池沸腾下朝向曲面加热面临界热通量分析模型

堆内熔融物滞留（IVR）策略得以实施的关键在于压力容器下封头外部冷却（ERVC）能力,即压力容器下封头外部临界热通量（CHF）高于下封头壁面对应的热通量。通过结合Helmholtz不稳定性与液膜蒸发,提出了池沸腾下朝向曲面加热面临界热通量的分析模型。由于表面张力作用,内部嵌有汽柱的薄液膜附着在下封头壁面外,Helmholtz 不稳定性作用于薄液膜与汽柱的交界面;随着加热表面热通量的增大,汽柱与液膜之间相对速度达到一定时,在Helmholtz 不稳定性的作用下,汽液交界面产生畸变,并形成汽膜,阻碍主流液到达加热表面;当加热热通量接近CHF时,液膜逐渐蒸发直至CHF触发。通过该模型计算得到了不同过冷度下,CHF随加热曲面方位角的变化,计算结果与现有的大量实验数据一致性较好。     

单棒垂直方形通道临界热流密度实验研究

采用R134a作为流体工质,对单棒垂直方形通道临界热流密度（CHF）进行了实验研究。流道横截面为19 mm×19 mm的方形通道,内置外径为9.5 mm的单根加热棒,用来模拟压水堆中典型栅元通道。实验工况通过流体模化方法覆盖了压水堆典型运行工况。实验结果表明,R134a在方形通道内的CHF参数趋势与圆管中水的CHF参数趋势相同,R134a可以替代水作为模化工质;通过对圆管Bowring关系式和Katto &; Ohno关系式进行冷壁因子修正,可用于预测带有冷壁的方形通道的CHF;Katto的流体模化方法适用于带有冷壁的方形通道。     

CF3I气相催化合成机理研究

CHF3分别进行了空管裂解及活性炭催化裂解,并对反应后的活性炭进行XPS分析。实验结果表明：CHF3在催化剂作用下热解生成CF2卡宾,并在活性炭表面形成稳定结合,为CF3I气相催化合成的CF2卡宾机理提供了有力证据。     

Steady state boiling crisis in a helium vertically heated natural circulation loop – Part 1: Critical heat flux,boiling crisis onset and hysteresis

Experiments were conducted on a 2-m high two-phase helium natural circulation loop operating at 4.2 K and 1 atm. The same loop was used in two experiments with different heated section internal diameter (10 and 6 mm). The power applied on the heated section wall was controlled in increasing and decreasing sequences, and temperature along the section, mass flow rate and pressure drop evolutions were recorded. The values of critical heat flux (CHF) were found at different positions of the test section, and the post-CHF regime was studied. The predictions of CHF by existing correlations were good in the downstream portion of the section, however CHF anomalies have been observed near the entrance, in the low quality region. In resonance with this, the re-wetting of the surface has distinct hysteresis behavior in each of the two CHF regions. Furthermore, hydraulics effects of crisis, namely on friction, were studied (Part 2). This research is the starting point to future works addressing transients conducing to boiling crisis in helium natural circulation loops.     

Wettability of heated surfaces under pool boiling using surfactant solutions and nano-fluids

The wettability of the heated surface under pool boiling of surfactant solutions and nano-fluids has been investigated. Tri-sodium phosphate (TSP, Na₃PO₄) solutions (0.01, 0.05, 0.1, 0.3, 0.5, 0.8 wt.%) and Aluminum oxide (Al₂O₃) nano-fluids (NF) (0.5, 1, 2, 4 vol.%) were prepared for experiments. Stainless steel (SUS 304) strips (30 × 30 × 3 mm) were heated by an alcohol lamp and quenched in the prepared solutions. Before complete quenching, when the surface temperature was 150 ± 10 °C (nucleate boiling region), the strip was taken out and excessive liquid on the surface was removed. Contact angles of pure water and the solutions on the quenched surface and fresh surface were measured. Contact angles of pure water on the quenched surfaces (5°–25°) were much smaller than those on the fresh surface (65°–70°). The solutions (TSP, NF) on the quenched surface shows the smallest contact angle (5°–15°). Surfaces deposited TSP and nano-particle could affect surface energy of the strips and enhance hydrophilicity of the surfaces. Several implications of the experimental results on the pool boiling CHF model and CHF enhancement using TSP and NF were discussed.     

不同流道间隙下矩形通道临界热流密度的实验研究

在氟利昂工质条件下,进行1~3 mm间隙的矩形通道临界热流密度(CHF)的实验研究。研究发现,在1~3 mm间隙的矩形通道内,随着压力的升高,CHF稍有下降;质量流速对CHF的影响呈非单调关系,在低含汽率区随着质量流速的增大,CHF增大;在高含汽率区,随着质量流速的增大,CHF减小;临界含汽量的增加导致CHF明显降低。综合分析表明,在本实验工况参数范围内,流道间隙范围为1~3 mm的矩形通道在相同的工况参数条件下,其CHF基本不受流道间隙的影响。     

Analytical model for CHF in narrow gaps with surface orientation effects

The CHF in rectangular narrow gaps has been investigated to develop a reasonable predictive model for CHF, accounting for the surface orientation effects. The model was based on Wallis formulation of the counter current flow limitation (CCFL) for flooding of the flow entrance gap. The results by the predictive model were compared with the experimental data by Kim and Suh (2003), and a good agreement was obtained for gap sizes of 1 mm and 2 mm with surface inclination angles ranging from 15° to 90°. However, when the surface inclination angle was less than 15° (nearly downward-facing position), the predictive model underestimated the CHF. A modified Katto–Kosho correlation based on Kutateladze approach was further proposed and it could predict the CHF well for inclination angles less than 15°, due to the surface tension effects. For the gap sizes of 5 mm and 10 mm, the predictive results were far larger than experimental data by Kim and Suh. And the large differences between the predictive results and experimental data were attributed to the fact that the mechanism of CHF in large gap is quite different from a narrow gap. It indicated that the validity of the model based on CCFL was limited to gaps of less than 5 mm. The present work is instructive for the safety analysis of the lower head of PWR in case of core meltdown during severe accident.