Study of drag reduction by gas injection for power-law fluid flow in horizontal stratified and slug flow regimes

In this work, the drag reduction by gas injection for power-law fluid flow in stratified and slug flow regimes has been studied. Experimentswere conducted to measure the pressure gradient within air/CMC solutions in a horizontal Plexiglas pipe that had a diameter of 50mm and a length of 30 m. The drag reduction ratio in stratified flow regime was predicted using the two-fluid model. The results showed that the drag reduction should occur over the large range of the liquid holdup when the flow behaviour index remained at the low value. Furthermore, for turbulent gas-laminar liquid stratified flow, the drag reduction by gas injection for Newtonian fluid was more effective than that for shear-shinning fluid, when the dimensionless liquid height remained in the area of high value. The pressure gradient model for a gas/Newtonian liquid slug flow was extended to liquids possessing the Ostwald–de Waele power law model. The proposed model was validated against 340 experimental data point over a wide range of operating conditions, fluid characteristics and pipe diameters. The dimensionless pressure drop predicted was well inside the 20% deviation region for most of the experimental data. These results substantiated the general validity of the model presented for gas/non-Newtonian two-phase slug flows.

Studies on two-phase co-current air/non-Newtonian shear-thinning fluid flows in inclined smooth pipes

In this work. co-current flow characteristics of air/non-Newtonian liquid systems in inclined smooth pipes are studied experimentally and theoretically using transparent tubes of 20, 40 and 60 turn in diameter. Each tube includes two 10 m lone pipe branches connected by a U-bend that is capable of being inclined to any angle, from a completely horizontal to a fully vertical position. The flow rate of each phase is varied over a wide range. The studied flow phenomena are bubbly, plug flow, slug flow, churn flow and annular flow. These are observed and recorded by a high flow. stratified flow. -speed camera over a wide range of operating conditions. The effects of the liquid phase properties, the inclination angle and the pipe diameter on two-phase flow characteristics are systematically studied. The Heywood-Charles model for horizontal flow was modified to accommodate stratified flow in inclined pipes, taking into account the average void fraction and pressure drop of the mixture flow of a gas/non-Newtonian liquid. The pressure drop gradient model of Taitel and Barnea for a gas/Newtonian liquid slug flow was extended to include liquids possessing shear-thinning flow behaviour in inclined pipes. The comparison of the predicted values with the experimental data shows that the models presented here provide a reasonable estimate of the average void fraction and the corresponding pressure drop for the mixture flow of a gas/ non-Newtonian liquid. (C) 2007 Elsevier Ltd. All rights reserved.

Transition of oscillatory floating half zone convection from Earth's gravity to microgravity

Oscillatory features of floating half zone convection were experimentally studied by using the drop shaft facility of Japan Microgravity Center which supported microgravity period of 10 s. Coordinated measurements including free surface deformation and oscillation, temperature and flow pattern in both 1-g and micro-g environment were obtained. The oscillatory frequency and amplitude in micro-g condition were lower and larger than the ones in l-g condition, respectively. The results gave, at first time, the oscillatory features such as free surface wave in micro-g, coordinated measurements of more than two physical quantities in the micro-g, and transition of thermocapillary oscillatory convection from I-g to micro-g.

Formation, microstructure and development of the localized shear deformation in low-carbon steels

An investigation has been made into the effect of microstructural parameters on the propensity for forming shear localization produced during high speed torsional testing by split Hopkinson bar with different average rates of 610, 650 and 1500 s(-1) in low carbon steels. These steels received the quenched, quenched and tempered as well as normalized treatments that provide wide microstructural parameters and mechanical properties. The results indicate that the occurrence of the shear localization is susceptible to the strength of the steels. In other words, the tendency of the quenched steel to form a shear band is higher than that of the other two steels. It is also found that there is a critical strain at which the shear localization occurs in the steels. The critical strain value is strongly dependent on the strength of the steels. Before arriving at this point, the material undergoes a slow work-hardening. After this point, the material suffers work-softening, corresponding to a process during which the deformation is gradually localized and eventually becomes spatially correlated to form a macroscopic shear band. Examinations by SEM reveal that the shear localization within the band involves a series of sequential crystallographic and non-crystallographic events including the change in crystal orientation, misorientation, generation and even perhaps damage in microstructures such as the initiation, growth and coalescence of the microcracks. It is expected that the sharp drop in the load-carrying capacity is associated with the growth and coalescence of the microcracks rather than the occurrence of the shear localization, but the shear localization is seen to accelerate the growth and coalescence of the microcracks. The thin foil observations by TEM reveal that the density of dislocations in the band is extremely high and the tangled arrangement and cell structure of dislocations tends to align along the shear direction. The multiplication and interaction of dislocations seems to be responsible for work-hardening of the steels. The avalanche of the dislocation cells corresponds to the sharp drop in shear stress at which the deformed specimen is broken. Double shear bands and kink bands are also observed in the present study. The principal band develops first and its width is narrower than that of the secondary band.

Parameter-estimation of a spherical top inductively-coupled plasma source with global-model

Using spatially averaged global model, we succeed in obtaining some plasma parameters for a low pressure inductively coupled plasma source of our laboratory. As far as the global balance is concerned, the models can give reasonable results of the parameters, such as the global electron temperature and the ion impacting energy, etc. It is found that the ion flow is hardly affected by the neutral gas pressure. Finally, the magnetic effects are calculated by means of the method. The magnetic field can play an important role to increase plasma density and ion current.

Behavior of ar plasma formed in a high-density plasma source - an ecr reactor

In order to develop the ultra-large scale integration(ULSI), low pressure and high density plasma apparatus are required for etching and deposit of thin films. To understand critical parameters such as the pressure, temperature, electrostatic potential and energy distribution of ions impacting on the wafer, it is necessary to understand how these parameters are influenced by the power input and neutral gas pressure. In the present work, a 2-D hybrid electron fluid-particle ion model has been developed to simulate one of the high density plasma sources-an Electron Cyclotron Resonance (ECR) plasma system with various pressures and power inputs in a non-uniform magnetic field. By means of numerical simulation, the energy distributions of argon ion impacting on the wafer are obtained and the plasma density, electron temperature and plasma electrostatic potential are plotted in 3-D. It is concluded that the plasma density depends mainly on both the power input and neutral gas pressure. However, the plasma potential and electron temperature can hardly be affected by the power input, they seem to be primarily dependent on the neutral gas pressure. The comparison shows that the simulation results are qualitatively in good agreement with the experiment measurements.

Electric characteristics of pseudo-spark during breakdown phase

An analysis of the time-dependent resistive voltage and power deposition during the breakdown phase of pseudo-spark is presented. The voltage and current were measured by specially designed low-inductance capacitive voltage divider and current measuring resistor. The measured waveforms of voltage and current are digitized and processed by a computer program to remove the inductive component, so as to obtain resistive voltage and power deposition. The influence of pressure, cathode geometry and charging voltage of storage capacitors on the electrical properties in the breakdown phase are investigated. The results suggest that the breakdown phase of pseudo-spark consists of three stages. The first stage is mainly hollow cathode discharge. In the second stage, field-enhanced thermionic emission takes place, resulting in a fast voltage drop and sharp rise of discharge current. The third stage of discharge depends simply on the parameters of the discharge circuit.

Crack tip behavior and crack-propagation in ductile materials

Dilatational plastic equations, which can include the effects of ductile damage, are derived based on the equivalency in expressions for dissipated plastic work. Void damage developed internally at the large-strain stage is represented by an effective continuum being strain-softened and plastically dilated. Accumulation of this local damage leads to progressive failure in materials. With regard to this microstructural background, the constitutive parameters included for characterizing material behaviour have the sense of internal variables. They are not able to be determined explicitly by macroscopic testing but rather through computer simulation of experimental curves and data. Application of this constitutive model to mode-I cracking examples demonstrates that a huge strain concentration accompanied by a substantial drop of stress does occur near the crack tip. Eventually, crack propagation is simulated by using finite elements in computations. Two numerical examples show good accordance with experimental data. The whole procedure of study serves as a justification of the constitutive formulation proposed in the text.

DMFC内部气液两相流动与电性能的短时落塔实验研究

利用国家微重力实验室落塔提供的短时微重力实验环境，对常重力和微重力条件下直接甲醇燃料电池（DMFC）内部的气液两相流动形态和相应电性能等的影响进行了实验研究，发现在微重力条件下，DMFC阳极流道内CO_2气泡速度很小，气泡尺寸随着时间的推移而不断长大，甚至堵塞流道；流道堵塞现象随电流增大而急剧强化．电性能曲线显示，在浓差极化区存在显著的重力效应，电性能的恶化随浓差极化程度的加强而增大．

The Weekend-Dividend Effect in the Spanish Market

Revised: 2006-05

环与杆高速碰撞动态响应的分析和预测

采用量纲分析的方法，讨论了环与杆高速碰撞时影响杆被击断的主要因素，分别给出了相对临界速度、临界方位角及环的临界厚度与主要物理参数的函数关系，并通过计算机仿真确定这种函数关系。

水射流辅助破岩机理研究(2)——水滴撞击

利用MSC.Dytran中的具有强度的多材料欧拉网格模拟水滴和有限长连续射流对靶板(岩石)的高速冲击作用,研究了靶板破坏深度、破坏宽度与水滴初压力、速度、入射方向、板厚以及连续射流的密度等的关系及其物理意义.用应力波理论来解释靶板的层裂现象,试图多角度分析射流破岩机理.

钨球打钢靶数值仿真研究

通过对钨球垂直撞击钢靶的数值仿真，获得了模拟钨球撞击钢板的整个物理图象，并给出了多种人们所关心的侵彻过程和物理场的演化数据，仿真结果与试验数据有较好的一致性。

液滴热毛细迁移问题的研究进展

液滴或气泡的迁移现象无论是在流体力学的基础研究中,还是在材料加工,化学工程等实际应用中都是一个很重要的课题.在微重力环境中,如果液滴或气泡所在的母液中外加一个温度场,则液滴或气泡就会由于表面张力分布的不均匀而发生迁移运动.这种运动被称为Marangoni迁移或热毛细迁移运动.综述了液滴或气泡的热毛细迁移问题历史研究中理论分析,数值模拟以及实验方面的主要结果,阐述了该问题的研究发展过程.目前液滴迁移问题的研究,理论分析解还只限于线性及弱非线性的定常问题,数值模拟工作已经得到了在热对流作用较小时液滴的非定常迁移过程,对于热对流影响很大的情况(Marangoni数大于100)则尚未得到与实验中观测到的相一致的理论结果.在总结前人研究的基础上,给出了热对流作用较大时液滴热毛细迁移非定常问题的最新的数值模拟结果,并对该问题在此情况下产生的新变化给予了分析.最后,分析了当前研究中所存在的问题并进一步展望液滴热毛细迁移问题未来的发展方向.

应用PIVT技术测量单液滴热毛细迁移时的速度场和温度场

在地面实验中,使用粒子图像测速测温(Particle Image Velocimetry and Thermometry, PIVT)技术测量了单滴热毛细迁移时液滴周围同时刻的速度场和温度场.选用密度相近的豆油和硅油作为实验系统的母液和液滴.实验结果表明单滴周围的温度场扰动不同于线性理论预测的随到液滴距离的平方成反比,而是距离一次方成反比,这是由于重力引起的浮力效应造成的,地面实验中重力作用不能忽略.