水平管泡状流局部统计特性的实验研究

利用双头电导探针技术测量了水平管内空气－水两相流的局部统计特性。分析了两相流局部统计参数如局部空隙率、气泡频率、气泡速度、气泡尺寸、界面浓度等参数随气液两相流量的规律变化。研究发现水平管内相分布与垂直管内相比呈现出更为复杂的形态,水平管内局部空隙率、界面浓度在同一直径方向的分布呈现类似分布,在管内除沿水平管径,即９０°线外,沿其它直径的分布都是非对称的。界面浓度在管内最高可达６００ ｍ － １,反映靠近管子上壁的热质交换最强烈。     

竖直圆管内泡状流界面参数分布特性

采用双头光纤探针对内径为50 mm竖直圆管内空气-水两相泡状流界面参数径向分布特性进行了实验研究。气液两相表观速度变化范围分别为0.004～0.05 m/s和0.071～0.283 m/s。结果表明,竖直管内向上泡状流局部界面面积浓度（IAC）、空泡份额及气泡频率径向分布相类似,即气相流速较低时管道中间很大范围内以上3个局部界面参数几乎恒定,近壁区迅速下降到较低值;随气相流速的增加,局部界面参数在管道中心出现峰值。本实验中气泡聚合与破碎现象较少发生,索特平均直径沿径向近似均匀分布,且随气液两相流速变化很小。通过气泡横向受力解释了局部界面参数分布的影响机理。     

用热膜测速仪测量水平管内气液泡状流的液相速度和紊流结构

对热膜测速仪应用于气液两相泡状流中的测量方法进行了研究。提出了一套全新的相鉴别技术，用此方法对水平管内的气液两相泡状流的液相速度和紊流强度进行了测量。并对液相水质及温度对测量结果的影响进行了探讨。实验结果表明．在水平管泡状流中．靠管道下部液流速度和紊流强度分布与单相液流的分布差别不大；管道上部较多的气泡使两相液流速度明显低于单相液流速度，增强了紊流强度；使紊流强度分布在r／R=0．5附近有一峰值。     

螺旋直径对螺旋管泡状流截面分布特性的影响

研究了不同螺旋直径螺旋管中泡状流的相界面参数（空泡份额、相界面浓度、气泡尺寸等）的截面分布特性。通过图像法标定了电导探针的测试精度,并通过合理地处理双头电导探针,得到了螺旋管中泡状流的空泡份额、相界面浓度和气泡数量频率的定量分布云图。为进一步量化地描述相界面参数的分布特征,采用统计方法定义了截面平均参数、相界面离散系数和气泡平均聚集坐标来表征其特性。实验结果表明,随着管道旋转直径的增大,气泡截面平均空泡份额有所下降,分布范围缩小,平均聚集坐标向上方和外侧移动,气泡尺寸整体上有所下降。     

倾斜管内上升泡状流界面参数分布特性实验研究

采用双头光纤探针对倾斜圆管内空气-水两相泡状流界面参数分布特性进行了实验研究,包括局部空泡份额、气泡通过频率、界面面积浓度及气泡当量直径径向分布特性。实验段内径为50 mm,液相表观速度为0.144 m/s,气相表观速度为0~0.054 m/s。结果表明倾斜管内向上泡状流气泡明显向上壁面聚集。局部界面浓度、空泡份额及气泡通过频率径向分布相似。倾斜条件下局部界面参数分布下壁面附近峰值相对于竖直状态被削弱甚至消失,上壁面附近峰值被加强,中间区域从下壁面往上逐渐增大,且随倾斜角度的增加变化更加剧烈。气泡等价直径随径向位置、气相速度及倾斜角度的不同无明显变化,气泡聚合和破碎现象较少发生。通过气泡受力分析解释了倾斜对泡状流局部界面参数分布的影响机理。     

倾斜、摇摆对矩形通道内泡状流局部界面参数分布的影响

借助高速摄像机,对倾斜和摇摆条件下矩形通道(43 mm×3.25 mm×2000 mm)内泡状流局部界面参数的横向分布特性进行实验研究,包括局部气泡比例、空泡份额及界面面积浓度(IAC)。实验结果表明,竖直、倾斜及摇摆条件下,局部气泡比例、空泡份额及IAC三者的横向分布形状相类似。竖直静止及摇摆至竖直位置时,通道内中间较大范围内各局部参数变化缓慢,在xi/(w/2)=±0.5(xi为以通道宽边中心轴线为原点到窄边内壁面的距离,w为宽边尺寸)附近出现峰值;随着倾斜和摇摆角度的增大,下壁面附近峰值被削弱,上壁面附近峰值被加强。实验摇摆参数范围内,摇摆时局部参数的横向分布与实验段倾斜至相同角度时的分布十分相近;主要原因为在横向上摇摆引起附加惯性浮力远小于气泡受到的浮力。     

竖直圆管内泡状流空泡份额径向分布实验研究

常温常压下,采用光学探针测量方法,对圆管（内径50 mm）内空气 水两相竖直向上泡状流空泡份额的径向分布特性进行了实验研究。结果表明,竖直圆管内泡状流空泡份额的径向分布随气液两相表观流速不同而变化。液相流速较高时空泡份额分布呈“壁峰型”,即中心区域变化平缓,近壁区出现峰值后迅速降低;液相静止时,随气相流速增加,空泡份额增加速度沿径向向外逐渐减小,气相流速较大时分布呈“核峰型”,即空泡份额随径向位置向外呈减小趋势;液相流速较低时分布呈现出过渡型。探针测量面积加权平均空泡份额与通过重位压降得到的空泡份额的相对偏差小于10%。     

水平管内气-液两相泡状流壁面切应力预测模型

水平管泡状流时气泡主要集中在管道的上部,在管下部只有少量的气泡.由于气泡的非均匀分布,壁面切应力沿周向变化.本文以水平管内气-液两相泡状流壁面切应力均相预测模型为基函数,在实验测量结果的基础上,建立了考虑气泡非均匀分布的水平管内气-液两相泡状流壁面切应力预测模型,预测模型能够反映不同工况下的壁面切应力沿周向的变化趋势,与实验测量结果比较,误差范围小于10%.     

水平管内气-液两相泡状流的混沌特征

运用相空间重构法,对实验测得的局部空隙率信号时间序列进行处理,计算出水平管内气-液两相泡状流系统的局部空隙率信号的Kolmogorov熵和关联维数.计算结果表明,气-液两相泡状流系统具有非线性混沌现象;系统普遍存在2～3个分维;随着折算液速的增加,系统的混沌程度下降;Kolmogorov熵和关联维数沿径向的分布呈波动特征;在r/R＝0.6～0.85区域,系统的混沌程度较高.     

竖直下降两相流相界面结构输运特性

竖直下降两相流具有与竖直上升两相流不同的相界面结构特征及输运特性。本文对竖直下降管内的气水两相流进行了实验研究,运用微型四头电导探针对7.5、31.5及55.5倍管径横截面处的空泡份额、相界面浓度、气泡直径、气泡频率及气泡速度等相界面结构参数的局部分布进行了测量。分析获得了相界面结构参数的沿程变化规律,并研究了气相表观流速对相界面结构发展的影响及一维相界面结构输运特性。发现竖直下降泡状流的升力指向管中心,导致相界面结构参数基本呈中心峰值分布;气相表观流速的增大会提高空泡份额和相界面浓度分布的峰度;竖直下降两相流在距入口31.5倍管径处基本达到充分发展。     

Combinated Flow Pattern Map for Cocurrent and Countercurrent Air-Water Flows in Vertical Tube

Flow patterns for cocurrent and countercurrent air-water flows in vertical tubes (40 and 80mm I.D.) at volumetric flux densities of air and water in the ranges ?115–158 and ?100–102 cm/s were observed. A flow pattern map presenting the entire data of the observed flow patterns, i.e. bubbly, slug and annular flow for each mode of flow operation (upflow, countercurrent flow and downflow) were presented on the j_l vs. j_g plane. The flow pattern maps showed significant difference of flow pattern transition boundaries with upflow, countercurrent flow and downflow. Flow pattern transition curves were smoothly continuous with the change of the direction of water flow, on the other hand the change of flow direction of air showed complicated effect on flow pattern transition near zero j_g . Comparison of the present flow pattern data with the reported general flow pattern maps for upflow showed that the correlation of Taitel et al. for bubble-slug flow transition is applicable to both cocurrent and countercurrent air-water flows.     

管内向下气液两相流动界面参数分布特性

借助双探头光纤探针测量方法,对管内竖直向下空气-水两相流动的界面参数局部分布特性进行了实验研究。实验段采用内径50 mm、长度2 000 mm的圆管,气液两相表观速度范围分别为0.004～0.077 m/s和0.43～0.71 m/s。实验结果表明,不同于竖直向上两相流动中局部界面参数径向分布呈现的“壁峰”或“核峰”型分布,向下流动中局部界面参数径向分布呈“壁峰”或“宽峰”型分布;向下流动时空泡份额截面平均值均比向上流动时大119.6%～145.0%,界面面积浓度截面平均值比向上流动时大18.8%～82.5%;向下流动时界面参数分布表现出明显的均匀化趋势。     

Electrical Conductivity of Liquid Metal Two-Phase Mixture in Bubbly and Slug Flow Regime

A correlation function for reactor noise is determined through a conditional polarity-correlation technique in which the polarity of neutron-counting fluctuations is analyzed with the start condition that the counting rate reaches a preset level. This technique, evidently, is an example of flash-start technique, developed for the purpose of improving the efficacy of reactor noise analysis. In the present case, the conditional polarity-correlation function is described mathematically assuming that the counting fluctuations of the detector conform with a Gaussian distribution. The expression thus derived reveals that this function is approximately proportional to a cross-correlation function and is a differential type of polarity-correlation function.

In order to examine the validity of the obtained expression, an experiment was performed in a graphite-moderated reactor at slightly subcriticai state to measure the conditional polarity-correlation function. A novel contrivance was adopted in the experiment to eliminate the dead-time effect created during the busy time of the multi-channel time analyzer. The dependence on the preset level—i.e. flash-start condition—exhibited by the conditional polarity—correlation function showed good agreement with that expected from the mathematical expression. The prompt mode neutron decay constants were determined from the experimental data within statistical error of 3～4 %.     

Measurement of Acoustic Velocity and Attenuation in an Air-Water Two-Phase Medium

Actinides, mainly responsible for the long term risk of spent fuel, are the principal candidates to transmutation due to their large absorption cross sections.

Systems driven by particle accelerators have been investigated in the past to produce fissile material. Recently these systems have been reconsidered to destroy minor actinides (MA) and long-lived fission products (LLFP), reducing the need for the traditional final confinement of radioactive waste.

Two Monte Carlo calculation models have been developped to determine the criticality safety conditions and the burning capability of MAS and of Pu.

A Pu burner, whose core is poisoned with Th to compensate by producing ²³³U the burnup reactivity due to the even Pu isotopes, can operate at a low proton current using perhaps a cyclotron, incinerating 70% of the charged Pu; its burning capability would be the production of about 1.5 PWRs.

Liquid fuel accelerator driven systems can be used in the future (due to the accelerator dimensions) for MA burning using D₂0 as carrier in a homogeneous core; such a system can burn the production of more than 15PWRs.

In the future, also the problem of LLFP burning could be solved definitively using a system with D₂0 as carrier.     

Local measurement of bubbly flow in helically coiled tubes using double-sensor conductivity probe

ABSTRACT

The two-phase flow in helically coiled tubes (HCTs) is rather important in many industries, such as the heat exchange facility in nuclear power plant. In this work, a double-sensor conductivity probe was used to study the air/water bubbly flow in HCTs. The cross-sectional distribution profile of the interfacial parameters (void fraction, interfacial area concentration, bubble size, etc.) of air–water bubbly flow were systematically studied. Through carefully processing the raw data collected by the double-sensor conductivity probe, the distribution of the void fraction, interfacial area concentration, the bubbles number frequency over the cross-section are demonstrated, as well as the bubble velocities and sizes vertically in the dense region. Some statistical parameters of cross-sectional-averaged quantities, coefficients of variation, and bubble aggregation core coordinates are defined to quantitatively describe the distribution characteristics of interfacial parameters. The measured data are helpful for improving the understanding of two-phase flow characteristics in HCTs.     

Experimental Study of Counter-Current Two-Phase Flow in Horizontal Tube Connected to Inclined Riser

In order to determine the Counter-Current Flow Limitation (CCFL) in hot legs of PWRS, CCFL characteristics of air-water and saturated steam-water flow were experimentally investigated in a modeled flow path of a horizontal tube connected to an inclined riser. The ranges of dimensions of experimental tubes were as follows: diameter D 0.026–0.076 m, length of horizontal tube H 0.01–0.4 m, length of inclined riser I 0.038–0.6 m and inclination angle of inclined riser θ 40° or 45°.

Wallis-type correlation (J _g ^*1/2+mJ _i ^*1/2=C) was applicable to the data during a steady separated flow. An analysis based on envelope theory showed that the constant C should be a function of H/D and I. A function of C with those parameters was empirically determined by using data obtained in this study. The developed function correlated well with the results of Richter et al. (D = 0.203 m, H = 1.26 m, I = 0.5 m and θ = 45°). The constant m in the Wallis-type correlation was almost constant 0.75. The problems were discussed, which should be made clear to apply the correlation obtained in this study to an actual PWR hot leg.