Chaos in parametric resonance flow at water-mercury interface

In the electrochemical system with liquid-liquid interface, intense local convections by the resonance with potential pulses take place. Therefore, with laser beam scattering, temporal movement of the water-mercury interface was observed. As a result, the scattering efficiency showed non-linear oscillation.

Such non-linear response could be controlled by potential pulse height. As the potential height was increased, new scattering peaks in the oscillation emerged, which was expected of a kind of bifurcation phenomenon. From these results, phase portrait, Poincarè section, correlation dimension of the strange attractor and the largest Lyapunov exponent of the trajectories were obtained. Consequently, it was concluded that all the parameters indicate chaotic behavior of the resonance flow.     

Numerical simulation of the dynamic flow behavior in a bubble column: A study of closures for turbulence and interface forces

Numerical simulations of the bubbly flow in two square cross-sectioned bubble columns were conducted with the commercial CFD package CFX-4.4. The effect of the model constant used in the sub-grid scale (SGS) model, C_S, as well as the interfacial closures for the drag, lift and virtual mass forces were investigated. Furthermore, the performance of three models [Pfleger, D., Becker, S., 2001. Modeling and simulation of the dynamic flow behavior in a bubble column. Chemical Engineering Science, 56, 1737-1747; Sato, Y., Sekoguchi, K.,1975. Liquid velocity distribution in two-phase bubble flow. International Journal of Multiphase Flow 2, 79-95; Troshko, A.A., Hassan, Y.A., 2001. A two-equation turbulence model of turbulent bubbly flows. International Journal of Multiphase Flow 27, 1965-2000] to account for the bubble-induced turbulence in the k-ε model was assessed. All simulation results were compared with experimental data for the mean and fluctuating liquid and gas velocities. It is shown that the simulation results with C_S=0.08 and 0.10 agree well with the measurements. When C_S is increased, the effective viscosity increases and subsequently the bubble plume becomes less dynamic. All three bubble-induced turbulence models could produce good solutions for the time-averaged velocity. The models of Troshko and Hassan and Pfleger and Becker reproduce the dynamics of the bubbly flow in a more accurate way than the model of Sato and Sekoguchi. Based on the comparison of the results obtained for two columns with different aspect ratio (H/D=3 and H/D=6), it was found that the model of Pfleger and Becker performs better than the model of Troshko and Hassan, while the model of Sato and Sekoguchi performs the worst. It was observed that the interfacial closure model proposed by Tomiyama [2004. Drag, lift and virtual mass forces acting on a single bubble. Third International Symposium on Two-Phase Flow Modeling and Experimentation, Pisa, Italy, 22-24 September] performs better for the taller column. With the drag coefficient proposed by Tomiyama, the predicted slip velocity agrees well with the experimental data in both columns. The virtual mass force has a small influence on the investigated bubbly flow characteristics. However, the lift force strongly influences the bubble plume dynamics and consequently determines the shape of the vertical velocity profile. In a taller column, the lift coefficient following from the model of Tomiyama produces the best results.     

Numerical study of the flow structure in a hydrodynamic filter

Numeric studies of flow structures in a hydrodynamic filter have been presented. An analogy of flows that appear in a filter and the basic structure of flows in a hydrocyclone was drawn. The velocity and current line profiles in the operating domain of a filter were defined. Optimal correlations of regime parameters that provide a steady flow in the operating domain of a hydrodynamic filter have been found.     

Numerical study of a permeable capsule under Stokes flows by the immersed interface method

A two-dimensional model to simulate the mass transfer of a permeable, deformable, and adhesive capsule flowing in a binary solution of a vessel is proposed using the immersed interface method (IIM). The fluid flow is governed by the full Navier–Stokes equations and the solute distribution is governed by the advection–diffusion equation. Mass transport across the capsule membrane is computed using the Kedem–Katchalsky equations while the adhesion between the capsule and the walls is introduced via a potential function. The model is first validated for the simple shear flow away from the substrate walls and then for capsule adhesion and deformation next to a substrate wall. It is next used to study solute transfer between the capsule and the vessel walls with and without a flow field. In the absence of a flow field, the results show that the transient of the solute transfer between the capsule and the vessel walls depends on the membrane diffusive permeability. In the presence of a Stokes flow field, behavior of the solute transfer seems to be fairly similar to that found for the stationary capsule for the same physical parameters. Moreover, the results suggest that the total solute transfer between the capsule and the vessel walls is enhanced when the capsule moves near to one wall. The increased adhesion strength between the capsule and walls would further increase the total solute transfer to the vessel walls although quite marginal.     

方形微通道内流动凝结时气液相界面演进过程的数值模拟

基于VOF模型,模拟了R32在水力直径为50 μm的方形微通道内流动凝结时的气液两相流型演进过程,模拟涉及的流型包括环状流、喷射流、泡状流和收缩泡状流。模拟结果显示,由于沿通道周向气液界面存在曲率差异,凝结液内部存在表面张力导致的横向压力梯度,驱使凝结液流向通道壁面拐角处,减薄通道壁面中部液膜厚度。基于势能最小原理,解释了表面张力与界面黏性力主导的喷射流形成机理。小质量流率时,喷射流诱发环状流上游气液界面波动,界面波动在界面黏性力的作用下逐渐生长。这与大质量流率时,流向下游并逐渐生长的界面波动导致流型转换的机理不同。     

Mass transfer in a medium with a rapidly renewed interface

Specific features of the mass transfer in a medium with a rapidly renewed interface are theoretically analyzed. It is shown that, in the case of intense renewal of the interface, if the adsorption of gas molecules on the liquid surface is taken into account, an additional number of molecules of the substance being dissolved are transferred to the bulk of the liquid by convective transfer of surface adsorption layers. If this process is taken into account, there is an additional mass flux into the liquid and, consequently, the mass-transfer rate is higher. In particular, this allows one to increase the concentration of the substance being dissolved above the thermodynamically equilibrium value in the absence of chemical reaction. Types of mass-transfer apparatuses in which the considered mode can be realized are discussed.     

垂直管气液两相环状流界面扰动波频率特性

气液两相环状流的相界面存在扰动波,波动频率是描述环状流界面扰动波特性的关键参数,对环状流的传质传热研究有重要参考价值。利用近红外光的吸收特性,设计了液膜检测装置,采用垂直对射光路设计,并通过置入式导光管屏蔽一侧液膜和气芯夹带液滴,实现了对环状流局部液膜的非接触式检测。在此基础上对界面扰动波进行了频域分析,运用功率谱密度估计,对50 mm管径竖直上升管环状流界面扰动波波动频率进行了定量研究,得到0.1～0.8 MPa不同压强条件下,共70个流动条件的环状流界面扰动波频率值。利用实验结果对现有模型进行验证分析,在此基础上利用Strouhal数描述液相流动条件的影响,利用Froude数描述气相流动条件的影响,建立了预测环状流界面扰动波波动频率的St-Fr模型,经实验数据验证预测的平均绝对误差（MAE）为11.42%。     

Numerical study of nonisothermal polymer extrusion flow with a differential viscoelastic model

A numerical study of nonisothermal viscoelastic flow is conducted to investigate the complex flow characteristics of polymer melts in the extrusion process. A general thermodynamic model for the energy conversion related to viscoelastic fluid flow is introduced. The mathematical model for three‐dimensional nonisothermal viscoelastic flow of the polymer melts obeying a differential constitutive equation (Phan‐Thien and Tanner model) is established. A decoupled algorithm based on the penalty finite element method is performed on the calculation. The discrete elastic‐viscous split stress (DEVSS) algorithm, incorporating the streamline‐upwind Petrov‐Galerkin (SUPG) scheme is employed to improve the computation stability. Essential flow characteristics of polymer melts in the extrusion die for hollow square plastic profile is investigated based on the proposed numerical scheme with ignoring the outer thermal resource. The energy partitioning, which quantified the conversion of mechanical energy into thermal energy, is discussed. The effects of volume flow rate and die contraction angle upon the flow patterns are further investigated. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

旋流干燥器流场模拟研究

旋流干燥器(SMTD)作为一种新型的干燥装置,其结构简单、干燥效率高、处理量大,成为气固二相流干燥研究的新方向.文中用流体力学软件Fluent对旋流干燥器内部的流场进行了数值模拟研究,采用雷诺应力模型(RSM)模拟气相流动,模拟结果表明:旋流干燥器各干燥事内气流主要做旋转运动,穿过旋流板时,主要做返混运动;切向速度分布...     

轴向流固定床内流场的数值模拟与实验验证

The computational fluid dynamics model with porosity and drag coefficient was used to describe fluid flow in an axial flow fixed bed according to the characteristics of fluid flow in the fixed-bed of the reactor. The commercial computational fluid dynamics (CFD) code CFX was used to simulate the flow field in the axial flow fixed bed. The simulation predictions are in good agreement with experimental results of a large cold model. The influence of gas distributor on the flow field in the axial flow fixed bed was studied. A suitable gas distributor was used to attain less than 0.06 kPa radial pressure difference and less than 5.2% radial velocity difference in fixed bed.     

Numerical simulation of steady flow past a liquid sphere immersed in simple shear flow at low and moderate Re

This work presents a numerical investigation on steady internal, external and surface flows of a liquid sphere im-mersed in a simple shear flow at low and intermediate Reynolds numbers. The control vol...     

数值模拟中低Reynolds数下简单剪切流流过单液滴的稳态流场(英文)

This work presents a numerical investigation on steady internal, external and surface flows of a liquid sphere im-mersed in a simple shear flow at low and intermediate Reynolds numbers. The control volume formulation is adopted to solve the governing equations of two-phase flow in a 3-D spherical coordinate system. Numerical re-sults show that the streamlines for Re=0 are closed Jeffery orbits on the surface of the liquid sphere, and also closed curves outside and inside the liquid sphere. However, the streamlines have intricate and non-closed struc-tures for Re≠0. The flow structure is dependent on the values of Reynolds number and interior-to-exterior vis-cosity ratio.     

An experimental study of air entrainment at a solid/liquid/gas interface

Some data from an experimental study of air entrainment into a fluid bath by a continuous moving plane tape is presented. The separate effects of surface tension and viscosity are described and the various modes of air entrainment are given in the context of fluid properties. The velocity of air entrainment is found to be a function of surface tension and viscosity for viscosities less than 4.65 poise. For viscosities greater than this value, the air entrainment velocity tended to a constant value of 9.5 cm sec^?1 independent of surface tension. Relationships of the form: We = k Re^a and We = c (Bo + 1)Re^d, are suggested by analogy to describe air entrainment data without and with buoyancy effects. Data from studies on four tapes and nine fluids gave a very high correlation when plotted in the above form. The data is in substantial agreement with that from similar studies, and shows that the condition Ca = We/Re = constant is not a global criteria for air entrainment by a plunging surface. The experimental data shows that air entrainment velocity may be estimated from the relationship V_AF = 67.679 (μ√(g/ρσ))^?0.672 for the normally plunging plane tapes studied.     

Numerical study and acceleration of LBM-RANS simulation of turbulent flow

The coupled models of LBM(Lattice Boltzmann Method) and RANS(Reynolds-Averaged Navier–Stokes) are more practical for the transient simulation of mixing processes at large spatial and temporal scales such as crude oil mixing in large-diameter storage tanks. To keep the efficiency of parallel computation of LBM, the RANS model should also be explicitly solved; whereas to keep the numerical stability the implicit method should be better for RANS model. This article explores the numerical stability of explicit methods in 2D cases on one hand, and on the other hand how to accelerate the computation of the coupled model of LBM and an implicitly solved RANS model in 3D cases. To ensure the numerical stability and meanwhile avoid the use of empirical artificial limitations on turbulent quantities in 2D cases, we investigated the impacts of collision models in LBM(LBGK, MRT)and the numerical schemes for convection terms(WENO, TVD) and production terms(FDM, NEQM) in an explicitly solved standard k–ε model. The combination of MRT and TVD or MRT and NEQM can be screened out for the 2D simulation of backward-facing step flow even at Re = 10~7. This scheme combination, however, may still not guarantee the numerical stability in 3D cases and hence much finer grids are required, which is not suitable for the simulation of industrial-scale processes. Then we proposed a new method to accelerate the coupled model of LBM with RANS(implicitly solved). When implemented on multiple GPUs, this new method can achieve 13.5-fold acceleration relative to the original coupled model and 40-fold acceleration compared to the traditional CFD simulation based on Finite Volume(FV) method accelerated by multiple CPUs. This study provides the basis for the transient flow simulation of larger spatial and temporal scales in industrial applications with LBM–RANS methods.     

Numerical simulation of periodic bubble formation at a submerged orifice with constant gas flow rate

Extensive numerical simulations were carried out to study the problem of bubble formation at submerged orifices under constant inflow conditions. A combined volume-of-fluid and level-set method was applied to simulate the formation process, the detachment and the bubble rise above the orifice in axisymmetric coordinates. On the one hand, the operating conditions of the formation process such as orifice flow rate, orifice radius and wettability of the orifice plate were investigated for the working fluids of air and water at 20 °C. On the other hand, the influence of the variation of fluid properties (liquid density and viscosity, surface tension) was examined individually. In this frame, the present work focused on low and medium flow rate conditions, at which the formation takes place in a periodic manner, in contrast to aperiodic or double periodic modes. The results of the computations provide information on the influence of various conditions on the bubble shapes, the bubble volume and the transition from a single to a double periodic formation process. The numerical results were extensively validated with experimental data available in the literature.     

Numerical simulation of multi-layer flow for polymer melts—A study of the effect of viscoelasticity on interface shape of polymers within dies

A two-dimensional simulation was developed for multi-layer confluent viscoelastic flow in dies, using a finite element method. The simulated interface shape was compared with the experimental results of previous researchers, and the simulated results were confirmed. Two-layer and three-layer flows of two or three kinds of viscoelastic fluids were simulated. Fluids with different non-Newtonian viscosities and the first normal stress differences were used. The layer thicknesses in dies are mainly determined by the shear viscosity and less by the elasticity of the fluid. The normal stress difference between the fluids forming an interface may be related to interfacial instability, and normal stresses near the interface were examined. The normal stress difference between both fluids was affected by the first normal stress difference and elongational viscosity.     

Properties of lipid bilayers at a water-water interface

This paper is essentially a review of the work on black hydrocarbon films in aqueous media which has been carried out by the author and his colleagues during the last few years. The theory of the formation and stability of the films is discussed in terms of the structure and physical properties of the constituent molecules. Particular consideration is given to the adsorption of the stabilizing molecule and the metastable equilibrium of the resultant thin film. The various systems which have been examined experimentally are described. The interrelation of the film capacitances, thicknesses, and compositions is discussed in the light of the theoretical expectations. The films are permeable to water although the measurement of their permeability is complicated by the difficulty of stirring the boundary layers of the aqueous solutions. There is a discussion of the progress in this problem and the interpretation of the permeability measurements in terms of the structure and composition of the films. Finally some conditions under which films become strongly conducting are described.     

Numerical study on gas and liquid slugs for Taylor flow in a T-junction microchannel

The rapid development of microfabrication techniques creates new opportunities for applications of microchannel reactor technology in chemical reaction engineering. The extremely large surface-to-volume ratio and the short transport path in microchannels enhance heat and mass transfer dramatically, and hence provide many potential opportunities in chemical process development and intensification. Multiphase reactions involving gas/liquid reactants with a solid as a catalyst are ubiquitous in chemical and pharmaceutical industries. The hydrodynamics of the flow affects the reactor performance significantly; therefore it plays a prominent role in reactor design. For gas/liquid two-phase flow in a microchannel, the Taylor slug flow regime is the most commonly encountered flow pattern. The present study deals with the numerical simulation of the Taylor flow in a microchannel, particularly on gas and liquid slugs. A T-junction empty microchannel with varying cross-sectional width (0.25, 0.5, 0.75, 1, 2 and 3 mm) served as the model micro-reactor, and a finite volume based commercial computational fluid dynamics (CFD) package, FLUENT, was adopted for the numerical simulation. The gas and liquid slug lengths at various operating and fluid conditions were obtained and found to be in good agreement with the literature data. Several correlations in the T-junction microchannel were developed based on the simulation results. The slug flows for other geometries and inlet conditions were also studied.