竖直圆形通道周向均匀和非均匀加热临界热流密度实验研究

以混合堆次临界包层为研究对象,开展对竖直圆形通道的均匀加热和非均匀加热条件下的临界热流密度实验。基于均匀加热实验获得实验关系式,并通过数据统计规律的分析和与现有关系式的比较,验证本实验关系式的准确性和可靠性。以该实验关系式作为基础,比较周向非均匀加热效应对临界热流密度的影响。结果表明:偏心管形式的周向非均匀加热的临界热流密度受质量流速的影响不大,在低含汽率下低于均匀加热的预测结果,在高含汽率下高于均匀加热的预测结果;二者比值随含汽率呈线性关系。     

摇摆运动下矩形窄通道内流动沸腾阻力特性

本工作对摇摆运动下水在矩形窄通道内流动沸腾阻力特性进行实验研究分析。一方面利用竖直静止实验数据对已有两相压降的计算方法进行评价,结果表明,应用于常规通道的关系式已不适用于窄通道中流动沸腾压降的计算,基于窄通道的Zhang-Mishima及Sun-Mishima关系式预测结果与实验值符合较好;另一方面得出了摇摆运动下流动沸腾阻力特性,摇摆运动使两相压降周期性波动,但摇摆角度和摇摆周期对压降的波动幅度、两相平均摩擦压降几乎无影响。     

随机填充球床通道内氦气流动特性实验研究

在聚变堆氦冷固态包层氚增殖区，球床通道内氦气流动压降特性对泵功率的设计具有重要意义。以氦冷固态包层氚增殖区为背景，研究了氦气流速、球床颗粒直径及球床通道长度对球床通道内氦气流动压降特性的影响。实验段采用20 mm×20 mm×500 mm的矩形通道，实验中氦气流速为0.1～0.6 m/s，球床颗粒直径为0.5、0.8、1.0、1.5、2.0 mm。实验结果表明，压降与氦气流速以及球床通道长度呈正相关，与球床颗粒直径呈负相关。对比Ergun关系式发现，在球床颗粒直径较小时，Ergun关系式预测值低于实验值，这主要是由于氦气可压缩性的影响。通过动量方程，理论推导出经可压缩性修正的Ergun关系式，结果发现修正后的Ergun关系式预测值与实验值符合良好。本研究为氦冷固态包层氚增殖区设计提供了数据支撑，为球床通道内流动特性的数值模拟提供了验证手段。     

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%。     

含内热源多孔介质通道内流动沸腾两相压降的预测

为预测含内热源多孔介质通道内流动沸腾的两相阻力压降,以Ergun方程为基础,定义了多孔介质通道的Chisholm参数Y和全液相折算因子Φ_l0。通过理论分析和实验数据测量,明确了出口质量含气率x_e、质量流速G和小球直径d等对参数Y和Φ_l0的影响,并提出1个Lockhart-Martinelli（L-M）类型的两相阻力压降关系式。与文献中的其他公式相比,本工作提出的公式对实验结果能做出更好的预测。     

矩形通道内气水两相流摩擦阻力计算模型

常压下以空气和去离子水为工质,对横截面为1.41 mm×40 mm和3 mm×40 mm的竖直矩形通道内两相流动阻力特性进行了实验研究。利用获得的764组实验数据,对11种典型两相流摩擦阻力计算模型进行评价。结果表明：Lee-Lee模型整体预测精度最高,但在分液相雷诺数较小（Re_l<600）和较大（Re_l>8 700）区域,与实验值符合较差;在分液相紊流区(Re_l≥2 000) Chisholm B模型适用性较好,对于两实验段预测值与实验值绝对平均误差分别为6.13%和6.43%,但在分液相层流区(Re_l<2 000)其预测值与实验值偏差较大。根据压降特性提出修正两相动力黏度,并针对分液相层流区提出修正计算关系式,其预测值与实验值符合较好。     

环形通道内液态金属钠沸腾两相流动特性实验研究

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。实验中质量流速G≤2 000kg·m-2·s-1,系统压力p≤0.1 MPa,热流密度q≤550kW·m-2。两相流动摩擦压降通过在相同质量流量的单相流动摩擦阻力系数的基础上引入两相摩擦倍增因子来考虑两相的影响。实验结果表明:环形通道内液态金属钠两相摩擦倍增因子随Martinelli参数的增大有减小趋势。综合本文实验数据、Lurie等的实验数据以及Kaiser等的棒束实验数据,拟合得到了计算液态金属钠沸腾两相流动摩擦倍增因子的关系式。计算了本文拟合得到的关系式与各组实验数据间的相对标准偏差(RSD),表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流动特性。     

窄矩形通道内两相流动压降特性研究

以空气和水为工质,在40mm×1.6mm的窄矩形通道中对竖直向上气-液两相流动压降特性进行了实验研究。对比了现有的两相流动阻力计算关系式,结果表明,传统的计算关系式均不适用于窄矩形通道内两相流动阻力的计算;而以窄矩形通道为基础的Lee-Lee关系式误差相对较小,但预测值与实验值相比整体偏小。为此结合实验数据,以分液相-分气相雷诺数之比Re_l/Re_g为依据将流动分为两个区域,分别对Chisholm关系式进行修正,修正关系式与实验数据的误差较小,能够很好地预测本次实验结果。     

圆形通道内饱和流动沸腾传热特性实验研究

采用圆形通道实验本体对饱和沸腾传热特性进行实验研究。实验本体加热长度1000 mm,通道尺寸为φ9.5 mm×1 mm。采用全液相雷诺数(Relo)和沸腾数(Bo)作为描述圆形通道内饱和沸腾传热特性的无量纲参数,在实验数据的基础上,拟合获得了圆形通道内饱和沸腾传热系数经验关系式,关系式对94.5%实验数据预测偏差在±20%以内。     

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。     

Experimental Study on Two-phase Flow Boiling Pressure Drop Characteristics in Narrow Rectangular Channel

The flow boiling pressure drop characteristics of a vertical rectangular channel (2 mm×60 mm×1 000 mm) were studied under transverse uniform and non uniform heating. The test section was double-sided heating with an effective heating area of 56 mm×700 mm. Three kinds of heating power distributions (uniform, polynomial and sinusoidal) were selected, and the working fluid was deionized water. A wide range of operating conditions was obtained by varying the inlet pressure and mass flux. The results show that the pressure drop gradient decreases with the increase of saturation pressure and increases with mass flux. The influence of vapor quality on two-phase pressure drop is related to mass flux, and the transverse power distribution has an important effect on the flow boiling pressure drop. Based on the experimental data of uniform heating, the existing two-phase pressure drop prediction model was evaluated. The homogeneous model using the equivalent viscosity assumption significantly underestimated the experimental values, and the data dispersion is relatively large. The Müller-Steinhagen and Heck and Li and Wu formulas are found to be the best with mean absolute errors of 11.8% and 12.3%, and most of predicted values are within ±20% error band. In this study, a new correlation based on the form of Müller-Steinhagen and Heck formula was proposed, and the Bond number Bo was introduced to consider the effect of surface tension. The prediction error of the new correlation for experimental data is within 8% error band.     

中低压条件下矩形窄缝通道两相流动传热试验研究

在中低压条件下,对矩形窄缝通道两相流动传热进行试验研究,分析两相流动传热的变化规律,拟合出饱和沸腾传热系数计算关系式,并采用简化的一维分析方法对两相压降进行分析计算。试验结果表明:在相同热平衡含汽率(x)情况下,两相流动压降随系统压力(p)的降低而增大,随系统流量的增大而增大的变化规律;p越低,两相流动压降随x的增加而增大越剧烈;流量越大,两相流动压降随x的增加而增大越剧烈。通过数据回归方法得到汽相湿周长比例因子F并拟合了计算关系式,其计算值与试验值符合得较好。矩形窄缝通道内饱和沸腾平均传热系数受p、质量流量及热流密度的影响较大。     

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。      

基于CFD方法的高温热管特性研究

高温热管运行特性的分析与预测,对热管设计和应用具有重要意义。为分析高温热管内两相流动传热特性,首先建立钠热管的计算流体力学（CFD）分析模型,并对模型计算值与钠热管稳态实验数据进行对比校核,模拟结果与实验测点温度的绝对误差小于40℃,相对误差在5%以内;其次,利用本文模型与方法对不同传热功率和倾角下的热管内部流场特性进行分析研究。研究表明,均匀加热条件下,蒸气腔内的速度在蒸发段接近线性变化,而在冷凝段,气体流速减小致使压强回升,同时,蒸气的流动压降和速度随加热功率增加呈下降趋势;在热管水平和倾角运行工况,热管内两相流动压降中液相压降均占主导;而气液间剪切效应中,气体流动速度为主导效应。本文模型可为热管堆等高温热管应用领域提供热管设计与分析方法。      

Two-phase flow and boiling heat transfer in two vertical narrow annuli

Experimental study associated with two-phase flow and heat transfer during flow boiling in two vertical narrow annuli has been conducted. The parameters examined were: mass flux from 38.8 to 163.1 kg/m² s; heat flux from 4.9 to 50.7 kW/m² for inside tube and from 4.2 to 78.8 kW/m² for outside tube; equilibrium mass quality from 0.02 to 0.88; system pressure from 1.5 to 6.0 MPa. It was found that the boiling heat transfer was strongly influenced by heat flux, while the effect of mass velocity and mass quality were not very significant. This suggested that the boiling heat transfer was mainly via nucleate boiling. The data were used to develop a new correlation for boiling heat transfer in the narrow annuli. In the two-phase flow study, the comparison with the correlation of Chisholm [Chisholm, D., 1967. A theoretical basis for the Lockhart–Martinelli correlation for two-phase flow. Int. J. Heat Mass Transfer 10, 1767–1778] and Mishima and Hibiki [Mishima, K., Hibiki, T., 1996. Some characteristics of air–water two-phase flow in small diameter vertical tubes. Int. J. Multiphase Flow 22, 703–712] indicated that the existing correlations could not predict the two-phase multiplier in the narrow annuli well. Based on the experimental data, a new correlation was developed.     

矩形窄通道内流动沸腾阻力实验与计算方法研究

基于换热器小型化的研究背景,对水在矩形窄通道内流动沸腾阻力特性进行了实验研究与分析,并利用实验结果对常规通道和窄通道的两相摩擦压降计算的6种方法进行了评价。结果表明,应用于常规通道的关系式已不适于窄通道中流动沸腾压降的计算,而基于窄通道的Zhang-Mishima及Sun-Mishima关系式预测结果与实验值符合较好。实验结果和理论分析表明,利用分相流方法得到的分液相摩擦因子计算式中Chisholm系数C与Martinelli参数X存在指数关系,且随着质量流速的变化也有所不同,据此给出了新的分液相摩擦因子的计算方法,新方法具有更高的计算精度。     

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。     

Boiling of Potassium in Vertical Tube under Transverse Magnetic Field

The experimental study was conducted to examine the applicability of boiling potassium two-phase flow to the blanket cooling of fusion power reactors. A high flux heater pin of 44mm heating length and 6.5mm O. D. with eight thermocouples of 0.5mm O. D. was inserted from the bottom of a vertical channel which was made of a 4m long, 14.9mm I.D. and 17.5mm O. D. stainless steel tube and placed in a D.C. magnet of 50cm long poles. The experimental conditions were the heat flux: 0~67W/cm², the magnetic field strength: 0~1.8T, the Ar cover gas pressure: 1.0bar, the potassium level above heater: 1.8m, and the temperature of upper unheated section: 400°C.

In the absence of magnetic field, boiling occurred intermittently, repeating the cycles between superheating with moderate temperature fluctuation and desuperheating with condensing shock pulses. When a weak magnetic field was applied, the temperature fluctuation was enhanced by natural convection, the incipient boiling superheat was reduced, and the boiling pattern became continuous. With increasing the magnetic field strength, the fluctuation was suppressed and the incipient boiling superheat increased but tended to level off around 1.5 T. Violent incipient boiling caused by a large superheat inherent in liquid metals was mitigated by magnetohydrodynamic interaction under a transverse magnetic field of 1.0T or larger, and subsequently followed by continuous saturation boiling with small fluctuation. No burn-out of the heater pin occurred in spite of symptom of dryout within the experimental range: q=67W/cm² and B=1.5T.