Heat and mass transfer of a convective-stratified flow in a trough type tundish

Fluid flow, heat and mass transfer of liquid steel in a trough type tundish were physically and mathematically simulated using a water model. Flow structures were determined through particle image velocimetry (PIV) techniques. Under isothermal conditions fluid flow approaches that of a plug pattern. Non-isothermal conditions provoked long recirculating flows along the vessel and makes the flow to departure form the plug pattern. Buoyancy forces increased fluid velocities close to the bath surface and enhanced convection mass transfer of a tracer injected in the flow and the flotation of solid particles. Measured fluid velocity fields maintained an acceptable good agreement with mathematical simulations under isothermal and non-isothermal conditions.     

A PIV study of hydrodynamics in gas-liquid high throughput experimentation (HTE) reactors with eccentric impeller configurations

High-throughput experimentation (HTE) is used for the screening of novel catalyst formulations via miniature agitated gas-liquid reactors with vessel volumes of an order of magnitude below the laboratory scale. An investigation of the macroscopic hydrodynamic performance of a miniaturised unbaffled stirred vessel of diameter 45 mm for an air-water system has been carried out at gassing rates of 0.25 and 0.5 vvm (dispersed flow regime) using particle image velocimetry (PIV). Measurements of bubble size and gas hold-up were also made. Eccentric agitation was employed as a means of breaking solid body rotation within the vessel, using a 6-blade, up-pumping pitched blade turbine. The gas phase was introduced via sintered glass panel spargers mounted in the vessel base. Two different configurations were used: firstly where the sparger located directly below the impeller, and secondly where the sparger was located opposite the impeller on the other side of the vessel. Measured distributions of turbulent kinetic energy (TKE) for both gassed configurations were similar and showed significant differences to the ungassed case. Estimates of the gas-liquid interfacial area were at least 2-3 times higher than those found in conventional, lab-scale baffled vessels; this was attributed to the creation of very small bubbles at the sparger ().     

重力式油水分离设备内流场的PIV技术测试

粒子图像测速（PIV）系统是由图像采集部分（包括工业摄像机、录像机、监视器等）与图像处理部分（包括计算机、监视器、打印机等）所组成。并采用PIV技术对重力式油水分离试验模型的主要构件（入口件、整流件、聚结件和集液件）中的几种典型结构进行了模拟试验筛选，并成功地获得了模型流场的两维速度图像，进而提出了一些流动特性良好的分离设备优化结构模型，由此建立了一些新型分离设备的结构优化模型，为今后深入研究重力式分离设备打下了良好的基础。     

Flow in the nose region and annular film around a Taylor bubble rising through vertical columns of stagnant and flowing Newtonian liquids

The flow in the nose region and in the annular film around individual Taylor bubbles rising through stagnant and co-current vertical columns of liquid were studied, employing particle image velocimetry (PIV) and pulsed shadowgraphy techniques (PST) at the same time. The combined techniques enabled simultaneous determination of the bubble shape and the velocity profiles in the liquid film. Experiments were performed with water and aqueous glycerol solutions in a wide range of viscosities , in an acrylic column of 32 mm ID.Values for the distance ahead of the nose in which the flow is disturbed by the presence of the bubble are presented for the conditions studied. The bubble shapes in the nose region are compared with Dumitrescu's shape for potential flow. The velocity profiles show that after the nose region the liquid begins to accelerate downwards, and at a certain distance from the bubble nose the velocity profile and the liquid film thickness stabilise. The liquid film acquires characteristics of a free-falling film. Values of the developing length and film thickness are reported for the experimental conditions studied. Average velocity profiles in the fully developed film are also presented. A critical Reynolds number of around 80 (based on the mean absolute velocity in the liquid film and on the film thickness) is reported for the transition from laminar to turbulent regime. Shear stress profiles (in the fully developed film) are also provided.The data reported are relevant for the validation of numerical codes in slug flow.     

Flow characteristic of the horizontal cylinder placed on the plane boundary

In this study, the flow characteristic of the circular cylinder laid on the free surface is studied quantitatively using the particle image velocimetry technique. The flow phenomena in the upstream and downstream regions of the horizontal cylinder and free surface junctions increase the instability of the vortical flow structure significantly. Since the scour and burial process of the pipelines laid on the seabed depends mostly on the hydrodynamic behavior of the flow, the present investigation concentrates on the characterization of the flow structures using the time-averaged and instantaneous flow data. Distributions of velocity vectors, patterns of streamlines, vorticity contours and corresponding Reynolds stress correlations characterize the flow structure in detail.     

Use of angle resolved PIV to estimate local specific energy dissipation rates for up- and down-pumping pitched blade agitators in a stirred tank

Up-pumping pitched blade turbines (and similar impellers) have recently been shown to be particularly effective for achieving a variety of mixing duties. Here, their turbulent flow characteristics are analysed by angle-resolved particle image velocimetry (PIV) for the first time and compared with their down-pumping equivalent, the usual time-averaged parameters also being determined for each. The work was conducted in 0.15 m diameter vessel (T) with a 45° impeller of diameter D (=0.45T) in water. The angle-resolved PIV enables a number of novel features to be identified. Firstly, the two pumping directions are shown to give very different vortex structures, even though the flow numbers, Fl, are the same (=0.79). In addition, the ‘spottiness’ of the normalized kinetic energy along a radius as the trailing vortex moved away from each impeller can be identified, which is not shown from time-averaged data. Often, the most important parameter for processing is the local normalized specific energy dissipation rate, and this is estimated using three methodologies: by measurement of the components of the stress tensor directly, ; by dimensional analysis, , with measured integral length scales (ILS); and by the Smagorinsky closure method, , to model unresolved scales (with a Smagorinsky constant used in the literature on stirred vessels). Again, only the angle-resolved results show the spottiness of and also higher values than the time-averaged. Differences in the values obtained by the three methods are discussed and compared with the existing literature. Most importantly, for the first time, the power input in the PIV-interrogated region is calculated from the three methods and compared to the input based on the impeller torque. Both DA and SGS methods are shown to overestimate the true power by a factor of 5 and 2, respectively, whilst the DE method provided a significant underestimate (1/5th) due to the limitation of the resolved length scales. The SGS method shows the greatest promise and by changing the value of the Smagorinsky constant in accordance with recent recommendations, good agreement is obtained. Nevertheless, it is concluded that there is still a need for improved methods for determining the important mixing parameter, .     

Investigation of the DBD Plasma Effect on Flat Plate Flow

Particle image velocimetry experiments and simulations were conducted in this study to clarify the influence of the DBD plasma actuator on the flow over a flat plate. The result shows that the actuator not only effectively leads to a local rise in near-wall velocity, but also efficiently causes a decrease in the displacement thickness of the boundary layer. Actuator-induced vorticity is generated to intensify the energy exchange between the main flow and the boundary layer, and dynamic energy is thus added directly to the low-energy fluid by the actuator. Although the increase in fluid velocity also brings a rise in dynamic energy loss, the energy added by the actuator can cover this to provide growth in the energy of the boundary layer. The plasma actuator presents a better performance when the free-stream velocity is lower.     

基于新给料方式的重介质旋流器流场的研究

针对目前重介质旋流器导向筒段湍流及转向突变较大的问题,设计出入口向底流端倾斜的新给料方式重介质旋流器。在PIV试验研究的基础上,在FLUENT中选用RSM模型对新给料方式重介质旋流器的流场进行了数值模拟。试验和模拟结果表明,在相同给料压力下,新给料方式旋流器相比传统给料方式旋流器,在相同横截面处切向速度增大,中心负压减小,这表明该给料方式可以有效降低旋流器内的能耗,有利于增大旋流器的离心系数,提高分选效率。     

应用PIV技术对气固喷射器流场的试验研究

建立了气固喷射器射流流场特性研究的试验装置,采用PIV(粒子成像测速)技术对气固喷射器内部射流流场进行了测量,分析了整个喷射器内部流场的流动特性。结果表明,先进的PIV流场测量技术应用于气固喷射器射流流场特性研究的可行性。     

Chaotic characteristics of pseudoplastic fluid induced by 6PBT impeller in a stirred vessel

Xanthan gum solutions with different mass concentrations were used to study the chaotic characteristics induced by the impeller of perturbed six-bent-blade turbine(6 PBT) in a stirred vessel. Based on the velocity time series obtained by the experiment of particle image velocimetry(PIV), with the software MATLAB(R2016a), the distributions of the largest Lyapunov exponent(LLE) and Kolmogorov entropy(K entropy) of the system, as two important parameters for characterizing the chaotic degree, were investigated respectively. Results showed that both of the LLE and K entropy increased with the increasing speed at the beginning. As the speed was up to 200 r·min-1, the two parameters reached the maximal values meanwhile, corresponding to 0.535 and 0.834, respectively, which indicated that the chaotic degree of the flow field was up to the highest level. When the speed was increased further, both of the LLE and K entropy decreased on the contrary, which meant that the chaotic degree was decreasing. It was also observed that the chaotic characteristics of flow field were hardly affected by the fluid rheology and the detecting positions. The research results will enhance the understanding of the chaotic mixing mechanism and provide a theoretical reference for optimizing impeller structure.