A numerical study of stir mixing of liquids with particle method

The process of stir mixing of two viscous liquids is simulated using the moving particle semi-implicit (MPS) method. A mixing rate is defined within the particle method to characterize the level of mixing, as the number, position, period, and rotating speed of the stirring stick(s) and liquid viscosity are changed. The motions of liquid particles are tracked to reveal the flow field and mixing mechanisms. The variation of the mixing rate shows that the mixing rate is higher when the sticks are rotating monotonically at high speed, and an optimum position of the stick can be identified. The mixing rate does not enhance significantly when three or more sticks are employed, and the liquid viscosity has minor influences on the mixing rate. These results give useful qualitative suggestions on controlling the mixing rate during chemical reactions.     

Scaling of the bubble/slug length of Taylor flow in a meandering microchannel

In order to reduce or avoid the fluctuations from interface breakup, a meandering microchannel with curved multi-bends (44 turns) is fabricated, and investigations of scaling bubble/slug length in Taylor flow in a rectangular meandering microchannel are systematically conducted. Based on considerable experimental data, quantitative analyses for the influences of two important characteristic times, liquid phase physical properties and aspect ratio are made on the prediction criteria for the bubble/slug length of Taylor flow in a meandering microchannel. A simple principle is suggested to predict the bubble formation period by using the information of Rayleigh time and capillary time for six gas-liquid systems with average deviation of 10.96%. Considering physical properties of the liquid phase and cross-section configuration of the rectangular mcirochannel, revised scaling laws for bubble length are established by introducing Ca, We, Re and W/h whether for the squeezing-driven or shearing-driven of bubble break. In addition, a simple principle in terms of Garstecki-type model and bubble formation period is set-up to predict slug lengths. A total of 107 sets of experimental data are correlated with the meandering microchannel and operating range:0.001 < Ca_TP < 0.05, 0.06 < We_TP < 9.0, 18 < Re_TP < 460 using the bubble/slug length prediction equation from current work. The average deviation between the correlated data and the experimental data for bubble length and slug length is about 9.42% and 9.95%, respectively.     

扶正器钻具组合在定向井施工中的应用

本文介绍了单扶钻具组合、双扶钻具组合的特点及用途,分析了影响井眼轨迹控制的因素,并结合现场应用,分析了扶正器钻具组合对定向井施工的影响。实钻结果表明调整单扶正器组合中扶正器的安放位置,可以获得理想的稳斜效果,既能保证井下安全,又能实现定向钻井的目的,是理想的钻具选择。     

井筒中起下钻过程的两相波动压力研究

为避免井下井喷、井漏、井塌等复杂情况和事故的发生,在钻井设计和施工时应考虑起下钻作业中产生的波动压力的影响。实际工况中,钻井流体多以气液两相流的形式出现,而以往的波动压力计算模型将钻井流体作为单相液流,存在一定的误差。本文以气液均相流为研究对象,通过理论推导,建立了井筒起下钻或下套管过程中,以气液两相形式存在的钻井液的粘滞性产生的波动压力预测模型,编制了气液两相波动压力预测软件,对不同工况下的起下钻波动压力进行了预测,绘制了不同情况下波动压力系数变化规律图,并与油田钻井实例进行对比,结果表明,该预测模型对钻井现场的起下钻速度控制有一定的指导作用。     

Characterisation of flow and heat transfer patterns in low aspect ratio packed beds by a 3D network-of-voids model

Using an illustrative sphere packing assembly, it is demonstrated that flow structure and wall heat transfer patterns in low aspect ratio fixed bed reactors are more realistically modelled by properly accounting for the discrete void fraction variations. A 3D network-of-voids (NoV) model has been devised to characterise and examine the discrete flow and heat transfer phenomena in a low aspect ratio packed bed with d_t/d_p = 1.93. The model as formulated is deliberately designed to be not too complicated so as not to place severe demands on computational resources. Hence, the model can potentially easily be applied to simulate the typically large sets of tubes (often comprising more than 10,000) in the case of industrial multi-tubular reactors, where every tube is different due to the random insertion of the packing particles. Because of its simplicity, the model offers an opportunity of coupling the individual catalyst pellet level transport with the complex interstitial flows at the reactor scale. Illustrative studies of this NoV model on a random packed bed of spheres predict large variations of discrete in-void angular velocities and consequently wall heat transfer coefficients within a single tube. The wide variations of wall heat transfer coefficients imply that the different angular sections of the tube will transfer heat at radically different rates resulting in potentially large temperature differences in different segments of the tube. This may possibly result in local temperature runaway and/or hot spot development leading to several potentially unanticipated consequences for safety and integrity of the tube and hence the reactor. The NoV model predictions of the overall pressure drop behaviour are shown to be consistent with the quantitative and qualitative features of correlations available in the literature.     

钻具旋转对岩屑运移的影响规律研究

本文通过岩屑运移的启动条件及悬浮条件分别建立考虑钻具旋转影响的岩屑颗粒翻滚、上升的临界启动速度模型,分析钻具旋转对岩屑临界启动速度的影响规律,通过计算发现：在150RPM下,宽间隙处最大影响率为38%,窄间隙处最大影响率为47%;最后根据岩屑临界启动速度模型,考虑钻具旋转作用对偏心环空不同间隙处岩屑启动与运移规律的影响,真实的描述了岩屑在环空中不同位置处的运动状态,提出了评价井眼清洗效果的新方法。     

Scale-up of fluidized-bed combustion - A review

Methods for scaling of fluidized-bed combustors are reviewed. It is found that a general scaling methodology, including simultaneously fluid-dynamic and combustion scaling, cannot be applied in practical scaling tests. Simplifications are needed. The approach followed here is to differentiate between fluid-dynamic scaling, combustion scaling, both related to the basic equations describing the phenomena, and boiler scaling that means scale-up from one boiler size to another, where established design elements can be utilized in the scaling procedure.     

Ideal micromixing performance in packed microchannels

In this work, the hydrodynamics and the micromixing characteristics in the packed and non-packed microchannels were studied experimentally at low Reynolds numbers (8–300). The mixing performances in microchannels were observed with high-speed CCD camera, and were evaluated in terms of a segregation index by the Villermaux/Dushman method. The fluid elements were drastically stretched, folded, and sheared with the effects of micro-particles in packed microchannels, resulting in extremely shorter diffusion distance and larger effective interfacial area, and much higher micromixing efficiency compared with those of non-packed microchannels. Under enough packing length and appropriate packing position of micro-particles, the ideal micromixing performance could be obtained in packed microchannels. Furthermore, the micromixing time in packed microchannels was determined based on the incorporation model, and its value was in the range of 0–0.1 ms.     

An analytical method for selecting the optimal nozzle external geometry for fluid dynamic gauging

Fluid dynamic gauging (FDG) was developed to measure, in situ and in real time, the thickness of a soft deposit layer immersed in a liquid without contacting the surface of the layer. An analysis based on the lubrication assumption for the flow patterns in the space between the nozzle and the surface being gauged yielded analytical expressions for the relationships between the main flow variables and system parameters. Nozzle shapes for particular pressure, pressure gradient and shear stress profiles could then be identified. The effect of flow rate, nozzle geometry and nozzle position on the pressure beneath the nozzle and shear stress on the gauged surface showed very good agreement with computational fluid dynamics (CFD) simulations. Case studies presented include nozzle shapes for uniform pressure and shear stress profiles, which are useful for measuring the strength of soft deposit layers.     

A two-scale model for discrete cell gravure roll coating

A two-dimensional model for predicting the fluid pickout and coated film thickness characteristics of a discrete cell direct gravure roll coater operating in reverse mode is derived. A novel multiscale approach is adopted for this purpose and the resulting equations solved numerically for inertia-less flow conditions. A system of stiff ordinary differential equations is found to be sufficient to capture the major gross flow features, while at the cell level the analysis is based on a finite element solution of the momentum and continuity equations. It represents the first such predictive model of its kind, with particular interest placed on the nature of both the pressure distribution and web-to-roll gap profile spanning the coating bead. The effect of key operating parameters, web-to-roll speed ratio, web-tension, wrap-angle, capillary number and cell-geometry, on the degree of fluid pickout from gravure cells and the coated film thickness is explored. Although an idealised model, the trends observed show qualitative agreement with existing experimental data collected on a small-scale gravure coating rig and point the way forward to the eventual formulation of a full three-dimensional predictive model of the process.