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。     

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%。     

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。     

MM-4聚变装置中等离子体电位分布实验

本文描述了用静电探针测量探针悬浮电位的方法,给出MM-4中电位分布的实验结果。结果表明轴向电位分布不对称,径向分布对称;在等离子体中沿轴向和径向存在双离子位阱;最深位阱深度随注入电流和磁场增加而加深;最深位阱的位置随注入能量的增加渐渐向系统中心移动。此结果不同于其它国家同类装置的结果,文中对这些结果做了详细分析和讨论,对产生的机制和结果的重要意义进行了探讨。本文还给出了五种不同方法同时标定等离子体电位的初步结果。     

低空核爆炸火球可压缩上升阶段的数值研究

利用数值计算的方法研究了核爆炸火球及其周围流场在可压缩上升阶段的演变过程。计算结果表明,火球在上升过程中压力和密度的分布发生变化,火球上部的压力增大而下部压力减小;初始时刻位于火球中部的低密度区域向上部移动,同时火球上部和两侧的密度梯度增大,而下部的密度梯度减小,密度云图的计算结果与实验的阴影图吻合得较好。     

竖直圆管内低压过冷沸腾相分布特性实验研究

实验采用双探头光学探针对内径24 mm竖直圆管内低压过冷沸腾局部空泡份额、界面面积浓度及汽泡尺寸等局部相界面参数径向分布特性进行了研究。实验结果表明：竖直圆管内过冷沸腾相分布形态呈现轴对称特性,随着热流密度的增大,相分布形态出现近壁峰值并逐渐向中间峰值分布形态的发展,较高热流密度工况下出现轴心峰值分布;随着质量流速的增加,局部空泡份额减小,并出现中间峰值向近壁峰值分布形态的转变;随着压力的增大,局部相界面参数减小。     

倾斜和摇摆状态下矩形通道内泡状流局部参数特性研究

在倾斜和摇摆条件下,对矩形通道(40mm×3mm)内泡状流的局部参数分布特性进行了研究。竖直条件下,"核峰"和"壁峰"分布形式在实验中都有出现;在液相折算速度较小和气相折算速度较大的工况下,局部参数呈现"核峰"分布。倾斜条件下,通道上方的峰值随倾斜程度的增加而变大,而通道下方的峰值随倾斜程度的增大而减弱,直至消失。摇摆条件下,当摇摆角度与倾斜角度相同且逐渐增加时,局部参数的分布主要体现在通道上方峰值的增加,但不改变出现峰值的位置,相应地,通道下方的峰值略有减少。不同摇摆工况下,摇摆振幅越大,摇摆运动的程度越剧烈,其对相同倾斜角度的峰值的影响也越大。     

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。     

竖直窄矩形通道内弹状流中液膜特性研究

气液两相弹状流广泛存在于工程领域,弹状流中液膜特性对弹状流模型的建立具有重要意义。为此利用高速摄像系统,对竖直窄矩形通道(3.25 mm×40 mm)内弹状流中液膜进行了可视化研究。实验中发现窄矩形通道中气弹左右两侧窄边液膜厚度不等且存在波动,但其对两侧液膜速度影响较小,两侧液膜速度相等。液膜脱离厚度主要受两相流速及气弹长度影响。液膜脱离速度随液相折算速度增加而增大;在低液相流速时,随气相折算速度增加而减小;当液相流速≥1.204 m/s时,液膜不下落,液膜脱离速度随气相速度变化较小,主要受液相流速影响。     

竖直矩形窄缝通道内单个空气泡尾流特性的实验研究

采用粒子图像测速仪(PIV)测量流场的速度分布,对空气泡在矩形窄缝通道内上升的尾流特性进行了研究,分析入口平均流速和气泡直径对空气泡最终上升速度、尾流结构以及尾流场速度分布的影响。实验结果表明:气泡的最终上升速度随气泡直径的增加先减小后增加,随入口平均流速的增加而增加;尾流结构特性随着气泡直径的增加而改变,且扰动从流道中心向流道壁面转移;入口平均流速的增加导致气泡的尾流结构简化,尾流场扰动变小;在距离气泡尾部小于1.0 W(W为流道宽度,mm)的范围内,流场扰动明显,在大于1.0 W的范围,扰动减弱。     

基于竖直圆管空气-水两相流实验的相间曳力模型研究

研究两相流相间阻力特性对系统程序关键本构模型封闭具有重要意义。本文基于竖直圆管开展了空气-水两相流实验,采用四探头电导探针对空泡份额、气泡弦长和界面面积浓度等气泡参数的径向分布进行了测量。结果表明空泡份额和气泡弦长呈现“核峰型”分布,而界面面积浓度并没有表现出随流速的单调关系。进一步开发了泡状流和弹状流的相间曳力模型,考虑了液相表观流速与管径对气泡尺寸分布的影响,建立了临界韦伯数与不同液相流速的关系。计算得到的空泡份额和界面面积浓度与实验数据整体符合较好,验证了模型的可靠性,为两相流相间阻力特性研究提供参考意义。     

Void distribution and bubble motion in bubbly flows in a 4×4 rod bundle. Part I: Experiments

Lack of local void fraction data in a rod bundle makes it difficult to validate a numerical method for predicting gas–liquid two-phase flow in the bundle. Distributions of local void fraction and bubble velocity in each subchannel in a 4×4 rod bundle were, therefore, measured using a double-sensor conductivity probe. Liquid velocity in the subchannel was also measured using laser Doppler velocimetry (LDV) to obtain relative velocity between bubbles and the liquid phase. The size and pitch of rods were 10 and 12.5 mm, respectively. Air and water at atmospheric pressure and room temperature were used for the gas and liquid phases, respectively. The volume fluxes of gas and liquid phases ranged from 0.06 to 0.15 m/s and from 0.9 to 1.5 m/s, respectively. Experimental results showed that the distributions of void fraction in inner and side subchannels depend not only on lift force acting on bubbles but also on geometrical constraints on bubble dynamics, i.e. the effects of rod walls on bubble shape and rise velocity. The relative velocity between bubbles and the liquid phase in the subchannel forms a non-uniform distribution over the cross-section, and the relative velocity becomes smaller as bubbles approach the wall due to the wall effects.     

Measurement and modeling of average void fraction, bubble size and interfacial area

The local void fraction, bubble size and interfacial area concentration for co-current air-water bubbly flow through a horizontal pipe of 50.3 mm internal diameter were investigated experimentally using the double-sensor resistivity probe method. The local and area-averaged void fractions and interfacial area concentrations were analyzed as a function of liquid and gas flow rates. These parameters were found to increase systematically with decreasing liquid flow and increasing gas flow. However, variations with the liquid flow were not as significant as with the gas flow. A consistent variation of the gas phase drift velocity and distribution parameter with the liquid flow rate was observed. It was demonstrated that presentation of the average void fraction in terms of flowing volumetric concentration was more appropriate for horizontal bubbly flow. Several bubble break-up mechanisms were discussed. It was concluded that average pressure fluctuations generated by the turbulent liquid fluctuations acting across a bubble diameter are the only mechanism which causes distortion of a bubble. Based on this force and the competing surface tension force, a theoretical model was developed for mean bubble size and interfacial area concentration. The theoretically predicted mean bubble size and interfacial area concentration were found to agree reasonably well with those measured by the double-sensor resistivity method.     

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。     

Experimental study of vapor local characteristics in upward low pressure boiling tube

Radial distribution of vapor local parameters, including local void fraction, interfacial velocity, bubble size, bubble frequency and interfacial area concentration, are investigated through the measurement in an upward boiling tube using dual-sensor optical probe. In addition, a new local parameter -"local bubble number concentration" is developed on the basis of bubble frequency. The analysis shows that this parameter can reflect bubble number density in space, and has clear physical meaning.     

Upward air–water bubbly flow characteristics in a vertical square duct

In nuclear engineering fields, gas–liquid bubbly flows exist in channels with various shape and size cross-sections. Although many experiments have been carried out especially in circular pipes, those in a noncircular duct are very limited. To contribute to the development of gas–liquid bubbly flow model for a noncircular duct, detail measurements for the air–water bubbly flow in a square duct (side length: 0.136 m) were carried out by an X-type hot-film anemometry and a multi-sensor optical probe. Local flow parameters of the void fraction, bubble diameter, bubble frequency, axial liquid velocity and turbulent kinetic energy were measured in 11 two-phase flow conditions. These flow conditions covered bubbly flow with the area-averaged void fraction ranging from 0.069 to 0.172. A pronounced corner peak of the void fraction was observed in a quarter square area of a measuring cross-section. Due to a high bubble concentration in the corner, the maximum values of both axial liquid velocity and turbulent kinetic energy intensity were located in the corner region. It was pointed out that an effect of the corner on accumulating bubble in the corner region changed the distributions of axial liquid velocity and turbulent kinetic energy intensity significantly.     

Distribution of void fraction for gas-liquid slug flow in an inclined pipe

In order to investigate the effect of inclination angle on the spatial distribution of phases,experiments on gas-liquid two-phase slug flow in an inclined pipe were carried out by using the optical probe and an EKTAPRO 1000 high speed motion analyzer.It has been demonstrated that the inclination angle and the mixture velocity are important parameters to influence the distribution of void fraction for upward slug flow in the inclined pipe.At high mixture velocity,the gas phase profile is axial symmetry in the cross-section of the pipe.This is similar to that for vertical slug flow.In contrast.most of the gas phase is located near the upper pipe wall at low mixture velocity.By measuring the axial variation of void fraction along the liquid slug.it can be concluded that there is a high void fraction wake region with length of 3-4D in the front of liquid slug.In the fully developed zone of liquid slug.the peak value of the void fraction is near the upper wall.