水平与微倾斜管内气液两相流长气泡形状实验和模型研究

针对水平管和倾斜管内气液两相段塞流的长气泡形状进行了实验和理论研究,实验中长气泡形状通过在管道中注入单气泡的方式获得,并利用双平行探针技术获得了2种不同管道内径条件下的长气泡形状数据.建立了可预测长气泡形状的一维理论模型,并将模型预测结果与实验结果进行了比较.结果表明:气泡形状取决于液体流速、气泡长度和管道倾角;所建立的理论模型对长气泡形状的预测结果与实验结果吻合良好.     

微重力蜡烛火焰特征数值模拟

建立了微重力蜡烛火焰的数学模型。计算与分析表明，火焰的形状由空气动力学特征决定，火焰的温度取决于化学反应动力学特征和火焰的热损失。在静止微重力环境中，自然对流的消失使火焰为半球形。辐射热损失对蜡烛火焰温度（颜色）特征的形成有重要贡献，在静止微重力环境下，化学反应放热速率受氧气扩散速率控制，辐射热损失的冷却使火焰温度低于正常重力温度值。但当环境气体的流动速度加大时，辐射热损失的影响逐渐减小，蜡烛火焰的温度逐渐接近正常重力蜡烛火焰的温度。当氧浓度较小时，火焰峰值温度小于烟黑形成的阈值温度（1300k）；当氧浓度较大时，火焰温度大于黑烟形成的阈值温度。     

黏性液体中锐孔处气泡的形成

考察一定流量气体,通过锐孔在静止黏性液体中连续溢出气泡的过程。应用动力学平衡半经验关系式,综合考虑气泡受力,分析气泡形成过程,给出合理假设,预测气泡直径。分析表面张力、气体流速、锐孔直径及液相物性对气泡脱离尺寸的影响,找到影响气泡脱离尺寸的主要因素。计算预报值与实验结果符合良好。     

具有线性温度分布的射流失稳研究

基于线性稳定性理论,针对具有线性温度分布的液体射流分裂过程,建立了射流扰动控制方程,给出了扰动方程在气/液分界面上应满足的边界条件,推导出了描述存在温度扰动的圆柱形液体射流自由表面三维扰动发展的色散关系;模型中同时考虑了空化气泡、射流周围气体的旋转以及射流和周围气体的可压缩性;对建立的数学模型及相应的求解方法进行了验证.在此基础上,分析了非轴对称扰动下具有线性温度分布的射流表面扰动波数和扰动增长率的演化,讨论了存在温度扰动时,空化气泡、气体旋转以及射流和气体可压缩性对射流稳定性作用的变化.结果表明:温度扰动的存在不仅会对液体射流稳定性产生较大影响,使得最大扰动增长率明显增大,扰动波波数范围显著拓宽,而且还会对空化气泡、气体旋转以及射流和气体可压缩性对射流稳定性的作用产生一定的影响.     

气泡雾化喷嘴颗粒平均直径经验公式的拟合

通过对有关气泡雾化喷嘴实验数据的系统归纳，分析了影响气泡雾化喷嘴雾化特性的主要因素，如气液质量流量比、液体质量流量、出口直径、相对速度、液体表面张力和粘性系数、气体密度等。利用因次分析方法得到了气泡雾化现象的相似准则关系，并利用最小二乘法对颗粒平均直径dm经验公式进行了拟合，拟合结果与实验数据符合良好。     

气泡雾化喷嘴在不同液体物性下的喷雾特性研究

利用PS-Ⅱ激光衍射粒度仪测量分析了气泡雾化喷嘴在雾化不同动力粘度，不同表面张力的液体时的特性，发现液体的粘性对于气泡雾化效果影响程度不大，随着动力粘度的增加，平均直径稍有增大，当动力粘度很高时由于泡状流更容易形成，所以平均直径有所减小，而液体表面张力的变化对于雾化质量的影响显。     

先进的CFD方法在高效率汽轮机设计中的应用

本文记录了先进的计算流体动力学（简称CFD）技术在高效率汽轮机设计中的应用，计算方法是通过强词经典的型线设计和一般的汽轮机设计方面，如整个通道的应力分析及几何特性的相互关系来描述的。该方法用于典型的汽轮机设计案例，即汽轮机多级全三维流场、叶片汽封和排汽缸的计算。CFD对设计过程的支持体现在：对复杂的流动特性提供更深入的物理认识，并为进一步研究和优化提供目标。通过比较计算结果和试验结果，评定了目前技术水平下CFD的预测能力。计算结果和试验结果取得很好的一致。还对由结构化网格和非结构化网格计算所得结果进行了相互比较，不仅证明了两者极好的一致性，而且示范了采用非结构网格的CFD软件模化复杂几何形状的特殊能力。总之，发现了CFD方法具备预测现代汽轮机组中发生的复杂三维粘性流动的能力，从而在整体上获得对流体动力机械更好的理解。性能进行预测，并对流场的总体动力特性有更好的了解。因此，先进的CFD技术是西门子发电集团设计高效率汽轮机的一个基本工具。     

大长宽比矩形微通道内的气泡生长与相变传热分析

研究了液体工质FC-72在大长宽比矩形截面微通道内流动沸腾过程中的单个气泡生长情况。选取的微通道水力直径为571、762和1 454μm,通道截面的长宽比分别为20、20和10。实验中运用透明加热技术,在对微通道表面加热的同时实现了通道透明可视化。观测获取了完整气泡生长周期内的三个生长阶段,探讨了气泡形状变化的主导因素。此外,气泡生长过程中几何形状的演变与通道截面长宽比密切相关。讨论了气泡当量半径、气泡长宽比等随热流密度、面积质量流量以及微通道尺寸和形状等的变化趋势。此外,还探讨了基于气泡体积增长得到的蒸发热流密度及其影响因素,对气泡生长过程中的热量传递进行了初步的分析。研究表明,蒸发热流密度随着气泡的生长逐渐升高,当气泡开始快速指数增长后蒸发热流密度高于微通道壁面的热流密度。另外,蒸发热流密度随着面积质量流量的增加而有所降低。     

进气温度与湿度对微型PSA制氧机产品气浓度影响的实验研究

通过实验的方法研究了进气温度和湿度对微型变压吸附吸附制氧机性能的影响，实验结果表明：在我们实验范围内，当原料气的温度或温度上升时，制氧机产品气浓度逐渐下降，且当原料气温度大于一定值时，其下降幅度迅速增加。     

磁场作用下单个气泡在磁性液体中的行为

采用可视化的方法对磁场作用下注有磁性液体的矩形窄通道中气泡的上升运动进行了试验研究,定性分析了磁场对气泡上升速度、轨迹及形状的影响。试验工质采用体积分数6.33%的水基Fe3O4磁性液体,同时对比了水中气泡的上升运动。矩形窄通道的宽度分别为1.32和2.04 mm,磁场为对称横向非均匀磁场,气泡由伸入通道底部的毛细管产生。试验结果表明:气泡在正梯度磁场区域做减速运动,在负梯度磁场区域做加速运动;施加垂直于气泡运动方向的横向磁场有助于增强气泡运动的稳定性,且气泡沿着磁场方向被拉长。     

Synchronous observation of rising soluble bubble through quiescent solution

An experimental method using computer image processing technology (CIPT) was proposed to observe and investigate the velocity, deformation, heat and mass transfer, etc. of a rising soluble gas (CO₂) bubble through a quiescent hot water. A model was set up to describe the behavior of the bubble in a visual experimental system in which a high-speed camera rose instantaneously with the movement of the bubble. A series of trajectory videos about the bubble were recorded by a computer linked to the camera. The trajectory, volume changes and rate of mass transfer of the bubble were obtained by the CIPT. It is found that the single bubble follows a rolling trajectory at the initial stage when there is mass transfer. With the volume decreasing, the disturbed behavior of the bubble becomes tempered. When the rising velocity of the bubble reaches the maximum, the velocity is nearly at a constant. The experimental and analysis results show that this method is useful for the research on the mass transfer and the movement of rising bubbles in liquid.     

Mixed Thermocapillary and Forced Convection Heat Transfer Around a Hemispherical Bubble in a Miniature Channel—A 3D Numerical Study

It has been established that for certain conditions, such as microgravity boiling, thermocapillary Marangoni flow has associated with it a significant enhancement of heat transfer. Typically, this phenomenon was investigated for the idealized case of an isolated and stationary bubble resting atop a heated solid that is immersed in a semi-infinite quiescent fluid or within a two-dimensional cavity. This article presents a three-dimensional numerical study that investigates the influence of thermal Marangoni convection on the fluid dynamics and heat transfer around a bubble during laminar flow of water in a minichannel. This mixed thermocapillary and forced convection problem is investigated for channel liquid inlet velocity of 0.01 m/s to 0.03 m/s and Marangoni numbers in the range of 10 to 300 under microgravity conditions. Three-dimensional effects become particularly important on the side and rear regions of the bubble. The thermocapillary forces accelerate the flow along almost the entire bubble interface. The hot core fluid from the heated bottom wall region is forced inward and propelled upward into the thermocapillary jet above the bubble. It can be quantified that the influence of thermocapillary flow on heat transfer enhancement shows an average increase by 40% at the downstream of the bubble and by 60% at the front and rear regions. This heat transfer enhancement depends mainly on the temperature differential as the driving potential for thermocapillary flow and bulk liquid velocity.     

水平管内油气水三相泡状流-弹状流转换的研究

结合压差波动法识别流型，对水平管内油-气-水三相泡状流-弹状流转换特性进行了理论和实验研究，建立了泡状流向弹状流转变的界线方程，结果表明，泡状流向弹状流转变的主要因素不仅包括气相折算速度和液相折算速度，而且含油率与管径也起重要作用，计算结果与实验结果基本相吻合。     

Bubble generation in quiescent and co-flowing liquids

A numerical simulation has been accomplished to analyze the problem of dynamic bubble formation from a submerged orifice in an immiscible Newtonian liquid under the condition of constant gas inflow. We have considered two cases for the surrounding liquid, namely the liquid in a quiescent condition and the liquid as a co-flowing stream with the gas. The full cycle, from formation to detachment of the bubbles and the corresponding bubble dynamics, was simulated numerically by using a coupled level-set and volume-of-fluid (CLSVOF) method. The role of the liquid to gas mean velocity ratio, the Bond number and the Weber number in the bubble formation process was studied and the order of magnitude of forces involved in bubble dynamics are presented. Our simulation results show that the minimum radius of the neck decreases with a power law behavior and the power law exponent in a co-flowing liquid is less than 1/2 as predicted by the Rayleigh–Plesset theory for quiescent inviscid liquids. Single periodic and double periodic bubbling (with pairing and coalescence) regimes are observed in the present investigation. It is identified that a moderate co-flowing liquid may inhibit the bubble coalescence. The volume of the bubble and the bubble formation time decrease with increasing liquid to gas mean velocity ratios. For small Bond numbers, significant differences pertaining to bubble dynamics are observed between the co-flowing liquid and the quiescent liquid. Furthermore, the generation and breakup of the Worthington jet after bubble pinch-off and formation of tiny drops inside the detached bubbles are observed.     

Transient temperature of liquid on micro metal layer heated by pulsed laser

INTRODUCTIONIntraditiontheresearchofboilingphenomenonfocusonlowtemperaturerisingrate(representedasr),10a相似文献   

A laser imaging-LDV coupling measurement of single bubble forming and rising in shear-thinning fluid

The shape evolution of bubble formed in carboxymethylcellulose （CMC） aqueous solution was real-time ob- served using laser image technique. The flow fields of liquid around growing and rising bubble were measured by laser Doppler velocimetry （LDV）, and the liquid mean velocity and its contour curves were obtained. The results show that bubble grows as spherical shape because of the dominant role of surface tension in the early period, and then is stretched gradually as a teardrop shape due to the common effect of buoyancy and shear-thinning of fluid. The axial mean velocity of liquid phase takes on Gaussian distribution with the symmetrical axis passing through orifice center. However, the radial mean velocity increases first and then decreases with the increase of the dis- tance from measured point to the symmetrical axis above. Further, the axial component along symmetrical axis decreases initially and increases with the rise of height, as well as its corresponding contour map diverging gradually. The radial component, yet, decreases steadily with the rise of height, and the maximum value deviates towards the two sides until disappear, as it contour shape of butterfly＇s ＂front wing＂.     

Unsteady heat conduction involving phase changes for an irregular bubble/particle entrapped in a solid during freezing – An extension of the heat-balance integral method

Temperature distributions in the molten layer and solid with distinct properties around a bubble or particle entrapped in the solid during unidirectional solidification are determined by applying a heat-balance integral approximation method. The present model can be used to simulate growth, entrapment or departure of a bubble or particle inclusion in solids encountered in manufacturing and materials processing, MEMS, contact melting processes, drilling, etc. In this work, the proposed heat-balance equations are derived by integrating unsteady elliptic heat diffusion equations and introducing the Stefan boundary condition. Due to the time-dependent irregular shapes of phases, coefficients of assumed quadratic temperature profiles are considered to be functions of longitudinal coordinate and time. Temperature coefficients in distinct regions therefore are determined by solving equations governing temperature coefficients derived from heat-balance equations, imposing boundary conditions, and introducing a fictitious boundary condition. The computed temperature fields show agreement with predictions from the finite-difference method. Since the number of independent variables is reduced by one, this work provides an effective method to solve unsteady elliptic diffusion problems experiencing solid–liquid phase changes in irregular shapes.     

Influence of inert admixtures on the rate of mass transfer during bubble collapse in an alternating electric field

In this study, we consider mass transfer under the influence of an alternating electric field in a system comprising liquid dielectric medium and stationary dielectric gas bubble composed of a solvable and inert gases. Resistance to mass transfer in both phases is taken into account. The applied electric field causes Taylor circulation around the bubble. Bubble deformation under the influence of the electric field is neglected. The bulk of a bubble beyond the diffusion boundary layer is completely mixed, and the concentration of an absorbate is homogeneous and time-dependent in the bulk. The thermodynamic parameters of a system are assumed constant. The moving boundary problem is solved in the approximations of a thin concentration boundary layers in the gaseous and liquid phases and infinite dilution of an absorbate in the absorbent. The partial parabolic differential equations of mass conservation for gaseous and liquid phases with time-dependent velocity components and time-dependent boundary conditions are solved by combining generalized similarity transformation method with Duhamel's theorem, and the solution is obtained in the form of Volterra's integral equation of the second kind for all the frequencies of the applied electric field. The asymptotic behavior of the obtained solutions is discussed. Numerical calculations are performed for different values of distribution coefficient.     

Numerical study on thermodynamic growth of single hydrogen bubble in an infinite space

In the liquid hydrogen storage and delivery, cavitation and boiling bubbles are prone to occur, which reduces the safety and economy of the liquid hydrogen delivery. For the bubble in liquid hydrogen, its growth process is different from that of room temperature media owing to the thermodynamic properties. In this paper, a single bubble growth model in liquid hydrogen is developed considering temperature distribution inside the bubble. The growth of single bubble in liquid hydrogen is described and predicted by solving Rayleigh-Plesset equation, thermal diffusion equation, thermal equilibrium equation, and heat conduction equation in semi-infinite space simultaneously. The growth trend of bubble radius, radius growth rate, vapor pressure, thermal boundary layer thickness and temperature difference between boundary and center are investigated by the model. The influence of superheat and ambient pressure on the growth of single bubble in liquid hydrogen is investigated by analysis of variance (ANOVA) and range analysis method. The mechanism of the single bubble transform from dynamic growth to thermal growth is clarified by comparing the critical time of the above physical indicators.     

CFD simulations of hydrodynamic characteristics in a gas–liquid vertical upward slug flow

Computational fluid dynamics (CFD) simulations are conducted using the volume-of-fluid (VOF) method to investigate the hydrodynamic characteristics of slug flow and the mechanism of slug flow induced CO₂ corrosion. The hydrodynamic characteristics are significantly affected by the viscous, interfacial, and inertial forces. In inertia dominated flows, the velocity of fully developed falling liquid film is increased with increased Taylor bubble rising velocity. The developing falling liquid film is formed at about the length of 0.5 diameter from the Taylor bubble nose, the fully developed falling liquid film is reached at about the length of 1.5–2.1 diameter from the Taylor bubble nose. The average mass transfer coefficient in the falling liquid film is always higher than that in the Taylor bubble wake zone. The iron ion near wall mass transfer coefficient is higher than that of hydrogen ion. The wall shear stress is increased with increased Taylor bubble rising velocity in fully developed falling liquid film zone, and the wall shear stress has a large fluctuation due to the chaotic and turbulent vortexes in Taylor bubble wake zone. The formation and the damage mechanism of the corrosion product scale are proposed for the gas–liquid two-phase vertical upward slug flow induced CO₂ corrosion. It is found that the wall shear stress of upward gas–liquid slug flow is alternate with high frequency, which is the key factor resulting in the corrosion product scale fatigue cracking. The CFD simulation results are in satisfactory agreement with previous experimental data and models available in literature.