矩形通道内泡状流-弹状流转换边界判定方法

两相流系统中,流型会直接影响系统的摩擦阻力和传热等特性,而流型的转变过程会受到通道的形状和尺寸的影响。常温常压下,以空气和水为介质,对八种不同尺寸矩形通道中竖直向上泡状流向弹状流转变过程进行了研究。结果表明,矩形通道间隙大于2 mm时,随着通道水力直径的增大,泡状流向弹状流转换边界左移。在窄通道范围内,可采用Ishii(1977)提出的基于漂移流模型的判定准则计算流型转换边界;在常规矩形通道中,转换准则中的临界空泡份额与气泡初始尺寸有关,选用赵建福提出的方法计算临界空泡份额,转换边界预测结果与实验结果符合程度较好;在利用漂移流方法计算截面含气率时,对于窄矩形通道,分布系数可以用Ishii(1977)提出的方法计算,而对于常规矩形通道,分布系数为1.2。     

基于区域分解的CTF全堆子通道热工计算研究

分别用CTF和反应堆蒙卡程序RMC对BEAVRS基准题进行全堆精细建模，由RMC统计径向及轴向功率分布并作为CTF的功率输入。利用CTF的区域分解技术，进行BEAVRS全堆pin by pin子通道计算，采用193个核并行计算，耗时268 s，得到了精细的燃料棒中心及表面温度、冷却剂温度及密度、空泡份额、包壳温度等重要参数，验证了CTF进行全堆子通道计算的高效性及可靠性，为实现基于RMC和CTF的核热耦合计算奠定了重要基础。     

垂直上升管内空泡份额的数值计算

本文对垂直向上流动的均匀加热管内空泡份额的轴向分布拟定了计算数学模型,在一定参数范围内对制冷剂12实验管段进行了计算,计算结果与测得的实验值吻合良好,平均误差为5％.经与目前通用的几种经验计算公式比较,数值计算结果均处于各公式适用范围之内.因此本数学模型可以在较广的参数范围内替代经验公式.模型计算还证实空泡份额沿流道轴向是非线性分布.随参数不同、其非线性程度也不相同.     

单纤光纤探针测量空泡份额的实验研究

1前言气（汽）液两相流广泛应用于工业过程中。空泡份额是气（汽）液两相流的重要参数，它与流场、压力、热流密度和流型等密切相关。由于目前的理论计算模型还有较大的局限性，因此实验测量是研究气（汽）液两相流空泡份额的最主要的研究手段。经过近几十年的研究，各国学者开发出了许多有价值的空泡份额测量方法，其中包括平均空泡份额测量方法和局部空泡份额测量方法，这些测量方法本身各有各的局限性和一定的针对性。本文研究水平管束间汽液两相流流动和沸腾传热特性，流道中加热管柬的存在对流体流动产生强烈的影响，使管束间汽液两相…     

水平加热管束间汽液两相内循环特性的研究

本文针对卧式火管式蒸汽发生器的结构特点，对水平加热管束间的汽液两相内循环特性进行了实验研究。用单纤光导探针测定了加热管束间的空泡份额分布。同时开发了二维汽液两相低雷诺数湍流漂移数学模型和相应的数值计算方法。数值计算结果与实验测量值符合良好，证实本文开发的数值模拟方法是可靠的。     

振动工况下过冷流动沸腾界面参数实验研究

过冷流动沸腾中局部时均界面参数对发展两流体模型十分重要,而振动工况下过冷流动沸腾的界面参数变化很少有文献报道。本研究采用四探头电导探针分别对静止工况和低频水平振动工况下环管内过冷流动沸腾的时均空泡份额、界面面积浓度和汽泡平均直径进行了测量,并且研究了不同流动工况对局部参数在径向位置处分布的影响。实验发现,低频水平振动对局部时均参数的影响比较有限,局部时均空泡份额和界面面积浓度略有下降,汽泡直径分布出现轻微波动。     

核内核子–核子非弹散射截面(Ⅰ)

在与平均场、核内核子-核子弹性散射截面以及输运方程相统一的理论框架内推导了核内核子-核子非弹散射截面的解析表达式.其数值结果能很好地重现自由非弹截面的实验值,所计算的有效非弹截面与Dirac-Brueckner的计算结果相一致.     

D+DBr反应的态-态动力学研究

在0—2.0 eV的碰撞能范围内采用含时量子波包方法和二阶分裂算符传播子对初始量子态为(v_0=0,j_0=0)的D+DBr反应进行了态分辨理论水平上的动力学计算.计算了抽取反应通道D+DBr→Br+D_2和置换反应通道D'+DBr→D+D'Br的反应概率、积分截面、微分截面、产物的振动和转动分布以及速率常数等动力学性质,并与相应的理论和实验结果进行了比较.结果表明:计算的速率常数与实验结果十分符合.微分截面的结果表明:对于抽取反应,前向的剥离反应机制在反应过程中占据主导地位;对于置换反应,头碰头的反弹机制占据主导地位.     

喷注电荷截面方法

我们提出了一种新的计算方法(喷注电荷截面)。用这种方法进行微扰QCD计算,不但能像末态正反强子截面差dσ(AB→h⁺X)—dσ(AB→h^-+X)那样少受海夸克和胶子分布函数的影响,而且与任何部分子的碎裂函数无关。用这种方法还可以在不能识别夸克味道的实验条件下,间接测定各种夸克喷注的平均电荷。 关键词：     

直流辉光等离子体阴极鞘层电子的输运过程

采用蒙特卡罗方法对氦直流辉光放电平板电极等离子体阴极鞘层内电子的输运过程进行了研究。利用实验数据拟合得到的电子与中性粒子的碰撞截面,计算了电子的平均能量及能量分布的空间变化,同时研究了电子的其它参数分布.     

Void fraction prediction in two-phase flows independent of the liquid phase density changes

Gamma-ray densitometry is a frequently used non-invasive method to determine void fraction in two-phase gas liquid pipe flows. Performance of flow meters using gamma-ray attenuation depends strongly on the fluid properties. Variations of the fluid properties such as density in situations where temperature and pressure fluctuate would cause significant errors in determination of the void fraction in two-phase flows. A conventional solution overcoming such an obstacle is periodical recalibration which is a difficult task. This paper presents a method based on dual modality densitometry using Artificial Neural Network (ANN), which offers the advantage of measuring the void fraction independent of the liquid phase changes. An experimental setup was implemented to generate the required input data for training the network.ANNs were trained on the registered counts of the transmission and scattering detectors in different liquid phase densities and void fractions. Void fractions were predicted by ANNs with mean relative error of less than 0.45% in density variations range of 0.735 up to 0.98 gcm⁻³. Applying this method would improve the performance of two-phase flow meters and eliminates the necessity of periodical recalibration.     

水平管液塞区相分布特征研究

设计建造了研究段塞流中液塞卷吸气体的实验装置,采用双头电导探针测量了水平管内固定液塞区域的局部相分布。液塞区含气率的径向分布存在峰值,表明液塞区存在湍流剪切层。随着进入液塞距离增大,含气率峰值减小,峰值对应的径向位置升高。这说明湍流剪切层内的湍流程度减弱,剪切层厚度变大。提出了计算水平管液塞截面平均含气率的方法,发现随着进入液塞距离的增大,截面平均含气率首先迅速减小,然后逐渐趋于稳定。     

螺旋管内气-液两相流截面含气率试验研究和理论模型

１前言关于螺旋管内气－液两相截面含气率的预报是一个重要的课题。即使只考虑平均截面含气率,也有气液两相间的滑移、各相流速和气相沿流通截面的不均匀分布等影响因素。查阅有关文献［１,２］,对螺旋管内气－液两相截面含气率的研究还很不够。因此,本文重点从二方面进行了研究。首先借助快速关闭球阀法,得出三根不同螺旋管平均截面含气率的试验测定结果,考查了螺旋升角和螺旋直径对其产生的影响;其次,按不同流型,依据“分相动量模型”和“漂移流率模型”、得出计算螺旋管内主要流型平均截面含气率的经验关系式。本文研究对象：三…     

Bubble Velocity and Size Measurement with a Four‐Point Optical Fiber Probe

The possibility to measure the velocity and size of individual bubbles in a high‐void fraction bubbly flow is investigated by using a four‐point optical fiber probe. The air bubbles have an initial spherical equivalent diameter ranging from 4 to 10 mm and the void fraction is up to 0.3. Firstly, single bubble experiments show that intrusiveness effects, i.e. bubble deformations due to the probe, are negligible provided that the bubble approaches the probe at the axis of the central fiber. A selection criterion is utilized for multiple bubble experiments. A good compromise can be found between the required accuracy, the duration of the measurements and the number of validated bubbles required for reliable statistical averaging. In an air‐water high‐void fraction vertical bubbly pipe flow, the void fraction obtained with the instrument is found to be in good agreement with both local single‐fiber probe measurements, and with the volume average void fraction obtained from pressure gradient measurements. The area average volumetric gas flow rate, based on the bubble velocity and void fraction as measured with the four‐point probe, agree with the measured gas flow rate. Also, the liquid velocity is measured by means of a laser‐Doppler anemometer, to investigate the slip velocity. The results show that reliable and interesting measurements can be obtained by using a four‐point optical fiber probe in high void fraction flows.     

利用声衰减反演气泡群分布的方法研究

通过测量含气泡水的声衰减反演气泡群参数是获取水中气泡分布的重要方法,但是经典方法忽略了较高浓度气泡水中的强频散特性和气泡振动参数的改变,导致反演较高浓度气泡群分布时会产生巨大误差.为解决这个问题,本文基于等效媒质理论建立起了声衰减和相速度的联系,并考虑了含气泡水平均量对气泡阻尼系数和共振频率的影响.在此基础上,通过将反演气泡分布和修正相速度及气泡振动参数交替迭代的方法,有效地消除了高浓度气泡水中由频散和气泡振动特性改变引起的误差.与实验数据对比发现,气泡群孔隙率达到10^-5时,考虑含气泡水的频散特性会显著降低反演误差;而当气泡群孔隙率达到10^-3时,气泡阻尼系数和共振频率的修正会对反演结果变得重要.本文方法在反演孔隙率为10^-3-10^-2的高浓度气泡群时,仍有较好效果,这可为获取水下较高浓度气泡群分布提供方法借鉴.     

An Experimental Study of the Two-Phase Flow Adjacent to a Wire in Nucleate Boiling Under an Electric Field

An experimental study of the two-phase flow near a heated wire in nucleate pool boiling is presented. A nonuniform electric field of cylindrical geometry was imposed to the heater. The two-phase flow parameters were measured using specifically developed local phase-detection optical probes. The study includes experiments varying the vertical distance from the heater (z) and measurements of the void fraction and the impact rate in a plane perpendicular to the heater (y-z). The results show that the void fraction decreases with applied voltage and with z. The dependence of the void fraction and the impact rate with heat flux is complex, with a strong decrement in the impact rate and void fraction near the critical heat flux when voltage is applied. The maximum void fraction and impact rate move from the vertical centerline (z) to a position 3 heater radii away.     

垂直圆管内向上稀疏层流泡状流相分布的实验研究

采用三维照相法对垂直圆管内稀疏层流泡状流充分发展段的相分布进行了实验研究。得到了８个流动工况下均匀尺寸气泡形成的泡状流的空泡率分布以及６个流动工况下非均匀尺寸气泡形成的泡状流的总体和大、小气泡组各自的空泡率分布．实验结果表明当气泡组的平均直径小于约３．５ｍｍ时,其空泡率分布在管壁附近出现尖峰;当气泡组的平均直径大于约 ３．５ ｍｍ时,其空泡率分布的尖峰移向管中心;气泡尺寸对泡状流的相分布有重要影响．     

Asymmetry of the wall shear stress in a stimulated ascendant flow of a liquid with monodisperse bubbles

Results of an experimental investigation of the two-phase wall shear stress averaged over the tube perimeter and the pulsation of wall shear stress in a stimulated ascendant flow with monodisperse bubbles with an average diameter of 1.2 and 2.2 mm are presented. Regimes with various hydrodynamic parameters such as high shear stress on the wall, low and negative wall shear stress, a high level of shear stress pulsation on the wall, and possible decrease in this level of pulsation are found. An increase in the void gas fraction results in a monotonic increase of perturbation of the single-phase flow. The dependences of the ratio of two-phase and single-phase wall shear stresses for two average bubble diameters seem to be qualitatively similar. The analysis of data revealed a complex dependence of the shear stress pulsation on the bubble diameter. The averaged flow characteristics quantitatively change upon the decrease in the bubble diameter. A further decrease in the average bubble diameter at the same void gas fraction will probably increase the heat-and mass-transfer characteristics of the flow. This is an issue for the futures study.     

VOID FRACTION MEASUREMENT IN SUBCOOLED FORCED CONVECTIVE BOILING WITH REFRIGERANT 12

Abstract

This article presents investigations and results of void fraction and pressure drop of dichlordifluormethane (CCl₂ in forced convective, subcooled boiling. The data were taken at different heal fluxes in a 12- to 25-bar pressure range, the mass fluxes have been varied from 500 to 3000 kg/ m2 s with an inlet subcooling in the range from 10 to SO K. The experiments have been conducted in an annular test channel with a 0.016-m inner diameter and a 0.03-m outer diameter. The inner tube of the annulus was heated by direct current. The void fraction data were gauged with a γ -densitometer and a specially designed impedance void meter. The experimental results reveal that the void fraction is nearly constant from the onset of nucleation boiling to a subcooling of about δ T = 10 K. A method for predicting the void fraction based on the drift flux model will also be presented.     

Local characteristics of the upward bubbly flow in an annular channel

Results of experimental investigation of the bubbly gas-liquid flow in a vertical annular channel are presented. The average and pulsation shear stresses and distributions of local void fraction were measured by the electrochemical method on both channel walls. It is shown that with a rise of gas flow rate ratio the value of wall shear stress increases significantly, and this effect becomes higher at a decrease in superficial liquid velocity. A presence of the gas phase effects significantly shear stress on the inner wall. Relative intensity of shear stress pulsations increases similarly on both channel walls.