环形通道内液态金属钠沸腾两相传热特性实验研究

对环形通道内液态金属钠沸腾两相流动特性进行了实验研究。实验中,系统压力为3.6~110.0kPa,热流密度为11~600kW·m~(-2),流速为0.02~0.45m·s~(-1)。实验结果表明,液态金属钠沸腾传热系数与壁面热流密度和系统压力有强烈关系,而与入口过冷度和质量流速无关。在本文实验数据基础上,拟合得到了计算液态金属钠沸腾两相传热系数的关系式,通过与各组实验数据间的比较,证明本文关系式适用于计算环形通道内液态金属钠沸腾两相传热系数。     

大宽高比矩形窄缝通道沸腾起始点实验研究

矩形窄缝通道中的泡核沸腾起始点（ONB）预测对反应堆安全设计十分重要。针对通道尺寸为50 mm×3 mm×1000 mm的竖直矩形窄通道,以去离子水为介质,通过监测壁面温度变化确认ONB的位置,研究了热流密度、质量流速、压力、入口过冷度等参数对ONB发生位置和壁面过热度的影响。收集并评价了已有的8个ONB预测模型,结合实验数据分析得到结论：基于池沸腾的ONB预测模型及其改进模型不能很好的适用于矩形窄通道内,尤其是针对质量流速带来的影响。一些针对矩形通道ONB预测开发的模型可以一定程度上反映ONB点壁面过热度随不同参数变化的发展趋势,但由于实验参数范围不够宽,适用范围和预测精度仍受到限制。结合影响矩形窄缝通道ONB发生的主要因素,推导了适用于计算宽谱参数工况下矩形窄通道中ONB点壁面过热度的解析解形式,并利用实验数据进行了拟合,新关系式超过95%的预测结果与实验结果偏差小于±20%。同时新关系式对其他相关公开文献的ONB数据预测仍在较好的误差范围内。     

过冷沸腾起始点预测关系式研究

本文认为过冷沸腾起始点为一个流程段,起于气泡开始汽化点,终于气泡脱离气穴点。基于这一假设建立了更为符合实际的过冷沸腾起始点气泡模型,在此基础上,用唯象方法获得了气泡半径公式及壁面过热度与热流密度关系式,并与实验数据进行了比对,其误差分布更加合理。     

强制对流过冷沸腾流体中汽泡脱离频率

在垂直上升环形通道内进行强制对流过冷沸腾实验。实验工质为水，实验压力为大气压力。由一台高速摄像仪对汽泡核化的动力学过程进行图像捕捉。通过影像获取总共58个工况下的汽泡脱离频率。对本实验的数据和从文献中获取的数据进行无量纲分析。将已有的模型和关系式与汽泡等待时间、生长时间以及脱离频率等实验数据进行比较。由池式沸腾改进的关系式未能很好地应用于强制对流过冷沸腾，同时，由过冷沸腾提出的模型也不能预测宽实验参数范围内的汽泡脱离频率。无量纲汽泡脱离频率与无量纲泡核沸腾热流密度相关。新的关系式与现有的低壁面过热度下的实验数据吻合良好。     

低压低流速条件下的过冷沸腾换热特性

为探究低压低流速条件下的过冷沸腾换热特性，开展本实验研究。通过分析实验中采集的热工参数和可视化图像，探究了沸腾滞后现象、沸腾失稳现象以及沸腾换热特性。实验发现沸腾起始点壁面过热度较高，而沸腾的发生大幅提高了换热系数，因此出现了显著的沸腾滞后现象。实验中较为光滑的加热面可达到较高的过热度，而低压下快速产生的气泡尺寸较大，在较低的热流密度下气液界面发生剧烈变化，使气泡破裂为多个小气泡并成为核化点。在过冷沸腾换热系数的预测中，Dittus-Boelter对流换热关系式不再适用，采用Hallman关系式和Gnielinski关系式计算对流换热系数，并引入壁面过热度对池式沸腾换热系数进行修正，可使过冷沸腾换热系数的预测精度大幅提高。     

竖直矩形流道中泡核沸腾起始点的研究

竖直矩形窄流道由于具有良好的换热效果和紧凑的结构而被广泛应用于工程领域。针对两个间隙分别为1.8 mm和2.8 mm的竖直矩形流道,以可视化的方法研究了过冷沸腾条件下进口温度、质量流速和流道高度对泡核沸腾起始点(Onset of Nucleate Boiling,ONB)的气泡成长和壁面过热度的影响。以去离子水作为工质,使用高速照相机拍摄气泡的成长过程并使用热电偶记录背板温度。发现两个流道中进口温度和质量流速对ONB点的气泡成长以及ONB点壁面过热度的影响一致;质量流速一定时,流道高度对ONB点的气泡成长无明显影响;流道高度对ONB点壁面过热度与面热流密度的关系无明显影响;ONB点壁面过热度与面热流密度的关系可以由文献中的经验关系式预测。     

窄缝通道内过冷沸腾区域汽泡脱离频率研究

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%。     

环形窄通道内过冷沸腾起始点的实验研究

在1.0-4．5MPa的压力范围内研究了1．2mm间隙环形窄缝通道内过冷沸腾起始点．分析了部分热工参量对沸腾起始点的影响。引入双面加热影响因子．对环形窄缝内过冷沸腾起始点的数据进行回归分析,得出了适用于环形窄缝过冷沸腾起始点的实验关系式     

环形窄缝双面加热通道内欠热沸腾传热实验研究

在压力0.84～6.09 MPa、质量流速41.9～300.2 kg/(m2·s)、热流密度2.61～114.41 kw/m2范围内,以去离子水为工质,对间隙为1.5 mm环形窄通道实验段竖直向上流动的欠热沸腾传热特性进行了实验研究,得出了适用环形窄缝通道的欠热沸腾传热经验关系式。     

矩形流道中的传热与压降特性研究

随着高性能电子芯片的发展以及电路和其它紧凑系统的小型化，迫切要求开发与之相适应的高热流密度下高效的传热技术。为此，在矩形通道内以FC－84为工质，进行了单相强制对流、过冷沸腾及饱和泡核沸腾实验。实验段由五个平行的水平通道组成。各通道参数如下：水力直径Dh=0.75mm，长径比（L／Dh)=409.8，通道两面的热流密度相等。实验中主要调节参数包括质量流量、入口过冷度和热流密度。实验中测量了沿流动方向不同位置处的液相温度和壁面温度。基于测量向出的温度、压降和整个试验段的热平衡，计算出单相强制对流和流动沸腾的传热系数。实验中同时测量了单相及两相工况下的实验段压降，并推出了一个计算过冷沸腾及饱和泡核沸腾压降的关系式。此外本文还提出了适用于对冷沸腾及饱和沸腾的两个新的传热关系式。     

Experimental research on the incipient boiling wall superheat of sodium

Incipient boiling wall superheat of sodium flowing in annulus was experimentally investigated. The annulus was 800 mm in length, 6 mm as inside diameter and 10 mm as outside diameter. The heat flux in the experiment was from 128 to 846 kW/m², with inlet subcooling from 63.1 to 287.8 °C, mass flow rate from 7.2 to 122.0 kg/h and system pressure from 0.85 to 28.79 kPa. The experimental results indicated that the incipient boiling wall superheat increased with the increasing heat flux and inlet subcooling. And lower liquid velocity and system pressure could result in a higher incipient boiling wall superheat. Furthermore, a semi-empirical correlation was obtained from the experimental results. It was also found that the predicting results agreed well with the experimental data.     

人工神经网络在预测流动沸腾曲线中的应用

选用20世纪60年代以来的实验数据，应用人工神经网络分析入口欠热度、质量流速、压力等主要参数对沸腾曲线的影响。在整个传热区内，热流密度随入口欠热度的增加而增大；在过渡沸腾和膜态沸腾区，热流密度随质量流速的增加而增加；压力起重要的作用，除膜态沸腾区外，增加压力能强化传热。除泡核沸腾外，稳态和瞬态的流动沸腾曲线的差异很小。     

Density Wave Instability of Sodium Boiling Two-phase Flow in a Vertical Annulus at Low Pressure

Experiments of density wave instability in a sodium boiling two-phase flow in an annulus were carried out with the parameters of heat flux from 80 to 976kW/m², inlet subcooling from 25.6 to 226.8°C, mass flow rate from 7.92 to 68.9 kg/h, and system pressure from 2,600 Pa to 0.06 MPa. It was found that the density wave instability occurred in the case of low exit quality, and the oscillation of flow rate was so large that the flow would be reversal. The lower inlet temperature, the higher system pressure and the larger mass flow rate could result in a more stable boiling two-phase flow. The oscillation period of the instability increased with the system pressure and the inlet subcooling, but it decreased with the mass flow rate. A correlation for the onset condition of the density wave instability was obtained from the experimental data.     

Applications of Artificial Neural Network for the Prediction of Flow Boiling Curves

An artificial neural network (ANN) was applied successfully to predict flow boiling curves. The databases used in the analysis are from the 1960's, including 1,305 data points which cover these parameter ranges: pressure P=100–1,000 kPa, mass flow rate G=40–500 kg/m²-s, inlet subcooling ΔT_sub =0–35°C, wall superheat ΔT_w = 10–300°C and heat flux Q=20–8,000kW/m². The proposed methodology allows us to achieve accurate results, thus it is suitable for the processing of the boiling curve data. The effects of the main parameters on flow boiling curves were analyzed using the ANN. The heat flux increases with increasing inlet subcooling for all heat transfer modes. Mass flow rate has no significant effects on nucleate boiling curves. The transition boiling and film boiling heat fluxes will increase with an increase in the mass flow rate. Pressure plays a predominant role and improves heat transfer in all boiling regions except the film boiling region. There are slight differences between the steady and the transient boiling curves in all boiling regions except the nucleate region. The transient boiling curve lies below the corresponding steady boiling curve.     

单棒通道流动振荡诱发沸腾临界可视化实验研究

为深入分析沸腾两相流动振荡诱发沸腾临界的影响特性,本文以去离子水为工质,横截面19 mm×19 mm、中心为外径9.5 mm的单棒通道为研究对象,通过在不同热工参数下开展沸腾两相流动特性可视化实验研究,结合汽泡行为和汽-液界面特性,分析流动振荡诱发沸腾临界的影响特性。研究结果表明,低压力、低质量流速和低入口过冷度下,极易出现流动振荡,并导致沸腾临界提前发生,此时的临界热流密度与稳定工况下相比明显偏低;随着壁面热流密度不断增加,流道中两相流型先后出现泡状流、弹状流、合并弹状流、搅混流、剧烈搅混流、不稳定环状流;当流动出现剧烈振荡时,流道存在回流;发生沸腾临界时流道压降波动最大,对应的流型为不稳定环状流。因此,单棒通道内流动振荡可能会导致沸腾临界提前发生。      

Experimental research on heat transfer to liquid sodium and its incipient boiling wall superheat in an annulus

Liquid sodium is mainly used as a cooling fluid in the liquid metal fast breeder reactor （LMFBR）, whose heat transfer, whether convective heat transfer or boiling heat transfer, is different from that of water. So it is important for both normal and accidental operations of LMFBR to perform experimental research on heat transfer to liquid sodium and its boiling heat transfer. This study deals with heat transfer with high temperature （300-700℃） and low Pe number （20-70） and heat transfer with low temperature （250-270℃） and high Pe number （125-860）, and its incipient boiling wall superheat in an annulus. Research on heat transfer involves theoretical research and experiments on heat transfer to liquid sodium. It also focuses on the theoretical analysis and experimental research on its incipient boiling wall superheat at positive pressure in an annulus. Semiempirical correlations were obtained and they were well coincident with the experimental data.     

竖直圆管内向上流动的干涸实验研究

在直径为8.2 mm的竖直向上均匀加热圆管上进行了干涸型临界热流密度实验研究，加热长度2.4 m，压力3.2～19.7 MPa，质量流速963～2 707 kg/（m²•s），进口欠热度34～213 ℃，出口含汽率0.11～0.78。研究发现：临界热流密度随进口欠热度、质量流速的增加而线性增加，随出口含汽率的增加而迅速减小。通过对临界气液两相参数的分析发现，本实验参数范围内，蒸汽速度是导致干涸的主要原因。当达到临界蒸汽速度时，近壁面液体消失触发临界。随压力的增加，表面张力逐渐减小，液膜更易被撕裂，因而临界蒸汽速度随压力的增加而减小。从高压实验数据出发得到临界蒸汽速度U_cr，参考Steen和Wallis推荐的夹带开始速度U₀，建立了预测临界蒸汽速度的模型：U_cr=25U₀+4。利用低压实验数据对预测模型进行了验证，符合较好。     

Experimental study of onset of subcooled annular flow boiling

An experimental study on the onset of nucleate boiling (ONB) is performed for water annular flow to provide a systematic database for low pressure and velocity conditions. A parametric study has been conducted to investigate the effect of pressure, inlet subcooling, heat and mass flux on flow boiling. The test section includes a Pyrex tube with 21 mm inner diameter and a stainless steel (SS-304) rod with outer diameter of 6 mm. Pressure, heat and mass flux are in the range of 1.73 < P < 3.82 bar, 40 < q < 450 kW/m² and 70 < G < 620 kg/m² s, respectively. The results illustrate that inception heat flux is extremely dependent on pressure, inlet subcooling temperature and mass flux; for example in pressure, velocity and inlet subcooling as 3.27 bar, 230 kg/m² s and 41.3 °C; consequently q_w,ONB is 177.3 kW/m². In other case with higher inlet temperature of 71.5 °C and with P, 3.13 bar and G, 232 kg/m² s the inception heat flux reached to 101.6 kW/m². The data of ONB heat flux are over estimated from the existing correlation, and maximum deviation of wall superheat (ΔT_w,ONB) from correlations is 30%. Experimental data of inception heat flux are within 22% of that predicted from the correlation.     

微细化沸腾传热实验研究

气泡微细化沸腾是沸腾到达某个临界热负荷后,加热面温度升高不大,与该临界热负荷相比,热流密度大幅提高的沸腾现象。本文在设计完成一可视化实验装置的基础上,通过高速摄影仪观察并结合采集的壁温数据,对常压下直径为10 mm铜加热面上的池式气泡微细化沸腾现象进行了研究,并讨论了液体过冷度对其的影响。实验发现,气泡微细化沸腾状态下,加热面上生成1层极其不稳定的气膜,气液交界面上不停地有大量微小气泡生成并以极高速度射入过冷液体中。随加热面热流密度的增大,气膜厚度波动周期缩短,气膜最大厚度减小,所生成微小气泡的直径也明显减小。实验中获得的最高热流密度达9 MW/m²。