Experimental and theoretical investigation of CO2 and air bubble rising velocity through kerosene and distilled water in bubble column

This paper concerns with developing of parameters which influence terminal velocities of air and CO₂ bubbles in distilled water and kerosene pools. The objective of this study is to validate and correct the formulas that were developed by previous investigators for prediction of terminal velocities. The investigation revealed that the terminal velocity of a single rigid spherical bubble in Newtonian fluids can be developed by balancing of mechanical forces acting on the bubble. However, for large bubbles, because of deforming of the bubble which is a result of interfacial tension, the effect of surface tension should be considered in the terminal velocity prediction formula. By using PSO algorithm and plotting experimental data of terminal velocity against the size of gas bubbles, the suitable equation for each of systems was chosen. Results showed that Jamialahmadi model is more practical for terminal velocity prediction. Jamialahmadi model requires a modification to be utilized for air-kerosene, CO₂-kerosene, air- distilled water and CO₂-distilled water systems. The developed PSO algorithm model is accurate for prediction of experimental data with an average R² value of 0.9722.     

Hydrodynamic instability of premixed flame propagating in narrow planar channel in the presence of gas flow

The paper analyses the hydrodynamic instability of a flame propagating in the space between two parallel plates in the presence of gas flow. The linear analysis was performed in the framework of a two-dimensional model that describes the averaged gas flow in the space between the plates and the perturbations development of two-dimensional combustion wave. The model includes the parametric dependences of the flame front propagation velocity on its local curvature and on the combustible gas velocity averaged along the height of the channel. It is assumed that the viscous gas flow changes the surface area of the flame front and thereby affects the propagation velocity of the two-dimensional combustion wave. In the absence of the influence of the channel walls on the gas flow, the model transforms into the Darrieus–Landau model of flame hydrodynamic instability. The dependences of the instability growth rate on the wave vector of disturbances, the velocity of the unperturbed gas flow, the viscous friction coefficients and other parameters of the problem are obtained. It is shown that the viscous gas flow in the channel can lead, in some cases, to a significant increase in instability compared with a flame propagating in free space. In particular, the instability increment depends on the direction of the gas flow with respect direction of the flame propagation. In the case when the gas flow moves in the opposite direction to the direction of the flame propagation, the pulsating instability can appear.     

EAST装置上W波段多道极向相关反射仪的研制

在EAST装置上安装了X模极化W波段多道相关反射仪，用于测量等离子体芯部密度涨落。该诊断利用低损耗(<3dB)多工器将4个不同频率(79.2GHz，85.2GHz，91.8GHz和96GHz)的微波耦合在一起，通过同一个天线发射。反射波由两个极向分离(~5cm)的天线接收，通过下变频技术实现外差测量。通过对两个极向天线接收的信号进行相关分析，获得芯部湍流垂直速度。对2018年低约束模式(L模)放电进行分析发现，在电子回旋共振加热(ECRH)等离子体中，芯部湍流垂直速度在电子逆磁漂移方向。而在注入同向中性束(co-NBI)后，芯部湍流垂直速度变为离子逆磁漂移方向。     

利用电磁法研究HMX与TATB混合钝感炸药的冲击起爆特性

为研究含有少量奥克托金(HMX)且以三氨基三硝基苯(TATB)为基的高能钝感炸药PBX-3的冲击起爆反应增长规律,采用火炮驱动蓝宝石飞片的方法和铝基组合式电磁粒子速度计技术进行了一维平面冲击实验。通过实验测量撞击表面及内部不同深度处的冲击波后粒子速度,得到PBX-3炸药的Hugoniot关系。根据冲击波示踪器所测数据绘制了炸药到爆轰的时间-距离(x-t)图,获得了反映炸药冲击起爆性能的Pop关系。将入射压力为12.964 GPa时达到爆轰的6条速度曲线修整成相同零点,通过读取6条曲线的分离点即反应区末端的C-J点,计算出化学反应区时间和宽度。     

Statistics of polymer capture by a nanopore: A Brownian dynamics simulation study

We investigate the statistics of polymer capture by a nanopore using Brownian dynamics simulations. It is found that when the velocity flux is greater than a critical velocity flux, the capture picture is a random selection process, otherwise it tends to a statistical process governed by energetic considerations. In addition, the chain ends capture probability decreases as the chain length increases and satisfies a power-law scaling of P0(N)~N-0.8.     

Exploring mathematical connections of pre-university students through tasks involving rates of change

This paper reports the results of a research exploring the mathematical connections of pre-university students while they solving tasks which involving rates of change. We assume mathematical connections as a cognitive process through which a person finds real relationships between two or more ideas, concepts, definitions, theorems, procedures, representations or meanings or with other disciplines or the real-world. Four tasks were proposed to the 33 pre-university students that participated in this research; the central concept of the first task is the slope, the last three tasks contain concepts like velocity, speed and acceleration. Task-based interviews were conducted to collect data and later analysed with thematic analysis. Results showed most of the students made mathematical connections of the procedural type, the mathematical connections of the common features type are made in smaller quantities and the mathematical connection of the generalization type is scarcely made. Furthermore, students considered slope as a concept disconnected from velocity, speed and acceleration.     

Hydrodynamic and Thermodynamic Nonequilibrium Effects around Shock Waves: Based on a Discrete Boltzmann Method

A shock wave that is characterized by sharp physical gradients always draws the medium out of equilibrium. In this work, both hydrodynamic and thermodynamic nonequilibrium effects around the shock wave are investigated using a discrete Boltzmann model. Via Chapman–Enskog analysis, the local equilibrium and nonequilibrium velocity distribution functions in one-, two-, and three-dimensional velocity space are recovered across the shock wave. Besides, the absolute and relative deviation degrees are defined in order to describe the departure of the fluid system from the equilibrium state. The local and global nonequilibrium effects, nonorganized energy, and nonorganized energy flux are also investigated. Moreover, the impacts of the relaxation frequency, Mach number, thermal conductivity, viscosity, and the specific heat ratio on the nonequilibrium behaviours around shock waves are studied. This work is helpful for a deeper understanding of the fine structures of shock wave and nonequilibrium statistical mechanics.     

小孔流速实验中的排水时间和流量系数的研究

本文以水作为理想流体,考虑到水头损失和孔口缩流效应,对小孔流速实验涉及的容器排水问题进行了系统的理论和实验研究.从理论上推导得出了圆柱形容器排水时间的解析解,分析了排水时间和自由液面速度、流量系数之间的规律,提出了排水时间的等效性.实验上,加工了底部开有不同小孔的大型圆柱形容器,测量了容器排水时间随液面高度的变化关系,借助实验结果计算了流量系数值,验证了容器排水时间的等效性关系,实验结果与理论计算符合较好.     

Recent advances of ultrasonic testing of cement based materials at early ages

To summarize some of the most important findings in the field of ultrasonic (US) testing of early age hydration and formation of structure of different cement based materials (CBMs), a review of literature with focus on US P-wave transmission and S-wave reflection methods is presented in this paper. The review shows a great ability of both US techniques to observe setting phenomena and to determine different milestones during the early age formation of CBM’s microstructure. Clear physical basis, high accuracy, and non-destructive nature of the method indicate that US methods could become standardized in the near future.     

Mean flow properties for equatorially trapped internal water wave–current interactions

The aim of this paper is to provide an analysis of the mean flow velocities, and the related mass transport induced by equatorially trapped internal water waves with a constant underlying current.