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为了研究竖直圆管中高含汽率泡状流的含汽率径向分布,设计了一种测量含汽率径向分布的方法.该方法通过统计投影视图中的像素信息得到泡状流的投影含汽率,根据汽泡投影重叠概率计算出截面含汽率在投影面上的边缘分布;再基于竖直圆管中含汽率分布轴对称的假设,使用改进的傅里叶级数展开方法求解Abel逆变换,计算出含汽率沿圆管径向的分布.为验证该方法的有效性,测量了较低含汽率时的泡状流径向含汽率,并与匹配方法的测量结果进行比较.实验结果表明:此方法能得到高含汽率或含汽率近壁分布等其他方法难以测量的含汽率分布. 相似文献
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矩形通道几何尺寸偏差对热工水力特性的影响 总被引:3,自引:1,他引:2
与圆管和棒束几何通道相比,板型元件窄边的几何尺寸偏差对流道流通截面积影响较大。本文以某一尺寸为例,定量评估了矩形通道窄尺寸偏差对热工水力特性(流动压降和CHF)的影响。通道尺寸对压降的影响主要表现在当造成热通道含汽后,即使含汽量只有1%,从单相压降向两相压降变化造成的流量偏离仍可达11%。在单相区,窄边偏差0.1mm对流量的影响一般不超过4.0%。对CHF的影响则与所使用的公式有关,对于本文所选C 相似文献
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神经网络在CHF预测中的应用 总被引:2,自引:0,他引:2
利用人工神经网络理论对均匀加热垂直上升圆管内的临界热流密度(CHF)进行预测和参数趋势分析。本研究采用局部条件假设,并选用Croenevld的CHF查询表数据为本文神经网络训练的样本,采用训练成功的网络预测CHF值可以得到比常规方法更好的效果,其均方差为14.9%。 相似文献
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在中压强迫循环工况下开展了低流速过冷沸腾压降实验.实验中同时对过冷沸腾空泡率进行了测量基于得到的实验数据,对低流速过冷沸腾压降计算方法进行了研究.研究表明.过冷沸腾工况下的流动压降与重力压降亦即空泡率密切相关.选用合理的空泡率计算模型对于低流速过冷沸腾压降的准确计算极为重要由于目前普遍采用的Saha模型.Levy模型难以得出准确的低流速过冷沸腾真实含汽率与空泡率预测结果,应用于低流速过冷沸腾压降计算时会产生较大偏差.笔者提出的真实含汽率模型和净蒸汽产生点(NVG)空泡率模型可用于蒸汽-水强迫循环低流速过冷沸腾压降计算通过本文研究、最终得出蒸汽-水强迫循环低流速过冷沸腾压降的推荐计算方法。 相似文献
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利用人工神经网络分析了水在上升流均匀加热垂直圆管条件下的临界热流密度(CHF)实验数据的参数趋势。以三种观点,即固定入口条件、固定出口条件或以局部条件假设为基础进行了上述分析。采用Katto和Groeneveld等的无量纲参数和CHF实验数据来一文的ANNs;训练成功的ANNs预测的CHF结果比任何其它传统的关系式都好。其远距离监测系统(RMS)误差在固定人口条件、固定出口条件和局部条件假设下分别 相似文献
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《中国原子能科学研究院年报》2017,(0)
正在直径为8.2mm、加热长度为2.4m的均匀加热圆管上对欠热和含汽强迫流动沸腾工况下的临界热流密度(CHF)进行了实验,覆盖的参数范围为:压力为3~21MPa,质量流速为963~3 883kg/(m~2·s),出口含汽率为-0.87~0.78。系统参数研究表明:CHF随进口欠热度和质量流速的增加而呈线性增加,随进口含汽率的增加而迅速减小。在次临界压力区域,CHF随压力的增加而减小,欠热度对CHF的影响减弱。不同含汽量的工况下,CHF 相似文献
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《核动力工程》2015,(1):168-172
基于欧拉两流体模型和非平衡过冷沸腾模型,完成过冷沸腾数值模型的构建,并通过与Bartolomei单管过冷沸腾实验进行对比,验证模型的正确性。利用该模型计算得到圆管的沸腾曲线,将进入"临界区"后的第一个点作为偏离泡核沸腾(DNB)判定的标准,对高压、高流量下圆管内的DNB型临界热流密度(CHF)进行数值模拟,CHF数据取自最新(2006年)的查询表;计算中考虑质量流量、平衡含汽率和压力对CHF的影响,最终预测值与实际值符合良好,误差在15%以内。预测CHF出现的位置也与实际相符,表明本文提出的方法能够很好地模拟高压、高流量下圆管内的DNB型CHF。 相似文献
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A mechanistic modeling of critical heat flux (CHF) in upflow boiling at low qualities is performed. The developed model is based on a physical criterion of CHF occurrence and a mechanism limiting the thermal transport between a stagnant bubbly layer and bulk stream. The mechanism can be mathematically formulated by coupling the equation of limiting mixing mass flux, which is derived from momentum balance equations in two regions, with local mass and energy balance equations on the bubbly layer. The resulting form of the model is represented by a general and straightforward CHF formula involving two empirical constants related to the void fraction and the thickness of the bubbly layer. The predictions agree well with the extensive CHF data of water in uniformly heated tubes. 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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A mechanistic model to predict a critical heat flux (CHF) over a wide operating range in the subcooled and low quality flow boiling has been proposed based on a concept of the bubble coalescence in the wall bubbly layer. The conservation equations of mass, energy and momentum, together with appropriate constitutive relations, are solved analytically to derive the CHF formula. The model is characterized by an introduction of the drag force due to wall-attached bubbles roughness in the momentum balance, which determines the limiting transverse interchange of mass flux crossing the interface of the wall bubbly layer and core. Comparison between the predictions by the proposed model and the experimental CHF data shows good agreement over a wide range of parameters for both light water and fusion reactors operating conditions. The model correctly accounts for the effects of flow variables such as pressure, mass flux and inlet subcooling as well as geometry parameters. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(11):1038-1048
The mechanism of the critical heat flux (CHF) where the departure from nucleate boiling (DNB)-type boiling transition takes place has not been fully elucidated. In this paper, we examine the trigger mechanism of the CHF for saturated and subcooled pool boiling on vertical and inclined surfaces based on measurements of the liquid-vapor behaviors near heating surfaces by using a conductance probe. The angle of inclination was varied from 90° (vertical) to 170° (facing almost horizontally downwards). The probe signals and the void fraction distributions showed that a liquid layer remains beneath the vapor masses moving upward along the heating surface at high heat fluxes near the CHF. The thickness of the liquid layer was determined from the location where the probe signals corresponding to the vapor masses disappeared. The thickness of the liquid layer formed on the vertical surface increased with increasing degree of subcooling, which may be the cause of the increases in CHF with increasing degree of subcooling. The measurements of saturated boiling on the inclined surface confirmed that the orientation of the heating surface greatly affects the period it takes for vapor masses to pass, but it negligibly affects the liquid layer thickness. This suggests that the decrease in CHF with increasing angle of inclination is primarily caused by the lengthening of the duration of vapor mass passage. 相似文献
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An integral equation model for critical heat flux at subcooled and low quality flow boiling 总被引:1,自引:0,他引:1
A new theoretical model of critical heat flux (CHF) is developed for the flow boiling condition from bubble-detached to low quality range. The CHF condition is postulated to occur when the superheated liquid layer on the heated wall, which is formed under the bubbly layer from the point of the onset of significant void generation, is depleted due to the evaporation along the heated length. The model shows a very promising agreement with the uniformly heated round tube data for both water and refrigerants by simply applying well-known constitutive relationships without any tuning constant for the CHF data. The significance of the proposed model in unifying the existing models is also discussed. 相似文献
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《Journal of Nuclear Science and Technology》2012,49(12):1141-1156
ABSTRACTDue to the important role critical heat flux (CHF) plays in the boiling field, it is of great significance to study CHF, especially the mechanism of CHF in the nucleate boiling. In this study, a new model to predict CHF both in pool boiling and flow boiling of downward-face was proposed and the relationship between CHF and nucleation site density (NSD) was studied. The model was based on the bubble interaction theory, which assumed that CHF happened due to the coalescing of the bubbles generated on the heating surface and prevented liquid to be supplied. The relationship between NSD and CHF was derived from previous observations in the experiments and simulations. To validate the relationship between NSD and CHF, several experiments with CHF and NSD were chosen and they all showed good agreement with our assumptions. Due to the rarity of experimental data on NSD and CHF, the numerical method was also used to validate. The results also showed an inverse relationship between CHF and NSD. 相似文献
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池沸腾临界热通量是沸腾相变传热的重要参数,决定了相变换热器件的推广应用。表面粗糙度和饱和压力对沸腾传热边界层分布、表面铺展润湿及工质动力学特性具有重要影响,进而对临界热通量作用显著。本文对HFE-7100工质在4种不同粗糙度的铜基表面(0.019、0.205、0.311和0.587 μm)条件及在不同饱和压力(0.07、0.10、0.15及0.20 MPa)工况下的池沸腾稳态临界状态下的传热及可视化实验进行了研究。对表面粗糙度及饱和压力对稳态临界沸腾的影响机制进行了分析,并考察了临界热通量预测模型对临界热通量的预测准确性。可视化研究表明,临界状态下的沸腾气液两相工质由小气泡、大气泡、气柱及蘑菇状气团组成,而在过渡状态下,沸腾表面会形成非平滑气膜,并不断分离出气泡。同时传热数据表明,表面粗糙度及饱和压力的增加能使表面临界热通量得到提升。相比而言,Bailey等建立的临界热通量预测模型能相对准确地预测HFE-7100工质沸腾临界热通量数据。为进一步提升预测准确度,建立了临界热通量无因次参数K预测经验关联式,其预测值与本实验及文献实验数据吻合较好。 相似文献
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在核电事故中当堆芯熔融物落入反应堆压力容器(RPV)下封头时,如果实际热流密度超过RPV的临界热流密度(CHF),RPV将会被熔穿,造成事故的进一步扩大。为研究RPV在氧化条件下和有添加剂的工质中的CHF特性,采用池沸腾实验方法,以去离子水为工质,研究了RPV常用材料SA508钢经高温预氧化、7次池沸腾传热实验氧化后的CHF特性以及工质中添加剂对其CHF的影响。结果表明:在625 ℃下预氧化8 h后,SA508钢表面产生的较薄氧化层能增加传热面积、表面粗糙度和亲水性,从而提高CHF;随着池沸腾实验次数的增加,SA508钢表面的氧化腐蚀和颗粒沉积程度增加,CHF先增加后降低;0.4%硼酸(BA)、0.5%磷酸三钠(TSP)溶液和两者的混合溶液均有利于CHF的提升,但强化机理有所不同:BA会加速SA508钢表面的腐蚀并改善亲水性;TSP可降低表面张力使表面获得超亲水性;BA和TSP的混合溶液会形成一层沉积物使表面获得超亲水性。 相似文献