气泡曳力系数模型分区研究

由曳力系数表征的曳力模型作为重要的相间力模型之一，被广泛应用于Euler-Euler方法和Euler-Lagrange方法下的连续相和离散相动量方程中。由于现有气泡曳力系数模型形式各异且适用范围有限，因此需要对已有模型进行充分地评价。考虑到已有曳力系数模型的适用范围和气泡变形的影响，参考各曳力系数模型采用的相关参数，建议基于Reynolds数Re和Weber数We分区选择最佳模型。将分区曳力系数模型、已有曳力模型与实验数据对比，发现分区曳力系数模型总体预测结果更符合实验测量值。将分区曳力系数模型应用至数值模拟中，可以更精确地追踪不同尺寸气泡的位置，使数值模拟结果更接近真实的物理情况。     

Determination of interfacial area in a tapered bubble column

BACKGROUND: Investigations of hold up (ε_g) and interfacial area (a) in cylindrical bubble columns have been reported extensively but reported similar investigations in tapered bubble columns are sparse in the existing literature. Thus the current article reports the experimental determination of ε_g and a using a tapered bubble column. RESULTS: The present system generated ε_g (0.556 to 0.641) in a CO₂? NaOH system 20% higher than in an air–water system (0.466 to 0.534) and values were higher than in existing systems. Also, the values of ε_g in the air–water system were higher than reported for a column with shorter tapered angle. Values of ε_g fitted very well with the well‐known Akita and Yoshida correlation. The observed values of a (235 and 700 m² m^?3) were higher than values obtained (2 to 600 m² m^?3) in existing systems. The energy dissipation was 203 to 335 W m^?3, which was lower than that (100 to 1200 W/m³) in existing systems. A correlation developed to predict the pressure drop in terms of Euler number was statistically highly significant. CONCLUSION: The present research a chieved higher values of hold up and interfacial area, and lower values of energy dissipation per unit volume of dispersion compared with existing systems. Findings of the present study coupled with previous studies indicate that the tapered bubble column developed could find potential application not only in air pollution control but also in gas‐liquid mass transfer operations. Copyright © 2011 Society of Chemical Industry     

Numerical modeling of Kelvin–Helmholtz instability using smoothed particle hydrodynamics

This paper presents a Smoothed Particle Hydrodynamics (SPH) solution for the Kelvin–Helmholtz Instability (KHI) problem of an incompressible two‐phase immiscible fluid in a stratified inviscid shear flow with interfacial tension. The time‐dependent evolution of the two‐fluid interface over a wide range of Richardson number (Ri) and for three different density ratios is numerically investigated. The simulation results are compared with analytical solutions in the linear regime. Having captured the physics behind KHI, the effects of gravity and surface tension on a two‐dimensional shear layer are examined independently and together. It is shown that the growth rate of the KHI is mainly controlled by the value of the Ri number, not by the nature of the stabilizing forces. It was observed that the SPH method requires a Richardson number lower than unity (i.e. Ri?0.8) for the onset of KHI, and that the artificial viscosity plays a significant role in obtaining physically correct simulation results that are in agreement with analytical solutions. The numerical algorithm presented in this work can easily handle two‐phase fluid flow with various density ratios. Copyright © 2011 John Wiley & Sons, Ltd.     

Bubble behavior and heat transfer during pool boiling of binary mixtures

Heat transfer coefficients were measured during pool boiling of binary mixtures on a heated wire hung horizontally and bubble behavior was simultaneously captured with a high‐speed video camera. The experiment was carried out at a pressure of 0.4 and 0.7 MPa for the whole range of mass fractions in a binary mixture of R22/R11. We clarified the change in bubble behavior and heat transfer by measuring the bubble departure diameter, frequency and growth rate on the basis of the video images. Furthermore, we discussed the relationship between the bubble behavior and the boiling heat transfer coefficient in the binary mixtures. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 449–459, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20087     

吸气旋流式离心浮选机研制

吸气旋流式离心浮选机充分利用离心力场及重力场的作用，对细粒煤泥进行分选，是 高效的新型浮选机，具有占地面积小、效率高、效果好、维修量小、结构简单、造价低等特点，适用于 各类选矿厂。     

Meshfree particle simulation of micro channel flows with surface tension

This paper presents a study of micro channel flows using a meshfree particle approach. The approach is based on smoothed particle hydrodynamics (SPH) and its variant, adaptive smoothed particle hydrodynamics (ASPH). The incompressible flow in the micro channels is modeled as an artificially compressible flow. The surface tension is incorporated into the equations of motion. The classic Poiseuille flow and a practical micro channel flow problem of flip-chip underfill encapsulation process are investigated. It is found that the adaptive kernel can well match the computational geometry with long channels and can greatly save computational time. The simulation results are in close agreement with the analytical solutions.     

Rayleigh–Taylor-Like Instability in Near-Critical Pure Fluids

The hydrodynamic stability of a thermodiffusive interface in a near-supercritical fluid is studied. The Navier-Stokes equations written for a van der Waals gas above its critical point are solved by means of a finite volume numerical method. The growth rate of the fluctuations shows that there exists a cutoff wave number beyond which the short wavelengths are stabilized by diffusion. The good agreement between the obtained values and recent theories for miscible fluids confirms that a near-critical fluid subjected to a thermal gradient may develop a gravitational instability for which the density gradient is driven by thermal diffusion and large compressibility.     

水中气泡溃灭的理论与数值研究

从理论和数值两个方面研究了单个气泡在自由流场中的溃灭.采用Rayleigh方程推导出一个新的球形气泡演变的解析解.基于流体体积法( VOF),在考虑表面张力、粘度和可压缩性效应的情况下,对单个纯气体泡的运动进行了三维模拟.在第一次溃灭阶段,气泡体积演变的数值结果与解析解保持一致. 数值结果表明气泡体积到达最小值后开始回弹,气泡的形状、速度场和压力场在回弹点附近发生剧烈变化.     

Modeling effects of gas bubbles on the mechanical behaviors of Ag/Bi-2212 round wires using a double cantilever beam bridge model

Due to the larger current-carrying property, Bi₂Sr₂CaCu₂O_x (Bi2212) superconductors have a great potential application in high field magnet. Bi2212 superconducting material can be fabricated as an isotropic round wire. However, there is 30% void space in the wire, such as gas bubbles. The void space has a larger influence on the property of the wire. In this paper, we will study the effect of gas bubble on the fracture behavior. Based on the double cantilever beam model and critical state theory, the mechanical behavior of Bi2212 wire is studied for decreasing field. Two different damage mechanisms are discussed using the strain energy release rate and strain of bridge. The results show that the large gas bubble can increase the strain of bridge. The central filaments with gas bubble are easier to be damaged than the edge filaments with gas bubble.