黏弹性对液体初次雾化特性的影响

以糖浆溶液和糖浆聚合物溶液为液相介质、空气为气相介质,采用同轴双通道气流式雾化喷嘴研究黏弹性对液体初次雾化特性的影响,根据高速摄像拍摄的图片对雾化模式进行研究,并重点探讨了液柱表面的不稳定特性。研究结果表明,两种液相介质的初次雾化可分为非轴对称振荡模式、膜破裂模式和拉丝破裂模式,糖浆聚合物溶液各个破裂模式的边界Weber数大于同等黏度的糖浆溶液。液体表面的不稳定波长与气速及液体自身的黏弹性密切相关,在考虑边界层影响的不稳定波长理论模型的基础上引入弹性参数Wi,并通过数据拟合得到新的不稳定波长关系式。     

Numerical flow simulation of viscoplastic fluids in annuli

This paper describes numerical solutions for the laminar flow of non-Newtonian fluids in vertical annuli using the Herschel-Bulkley model to describe the rheological behaviour of such materials. Numerical solutions have been obtained when there is both axial and tangential flows in either a concentric or eccentric annulus. The tangential flow arises from the rotation of the inner cylinder of the annulus and the axial flow from a constant axial pressure gradient. The flow is analysed by solving the momentum and continuity equation numerically using the finite element method. The dimensionless velocity, deformation and stress profiles with other quantities such as the apparent viscosity and pressure distribution have been calculated for various eccentricities, radius ratios, fluid properties and flow parameters; the results give insights into the flow behaviour in the annuli. It is shown that the inclusion of rotational effects, for a fixed pressure gradient, is likely to increase the axial volumetric flowrate over non-rotating situations in concentric geometries. New results reveal that, in eccentric annuli, the situation is reversed and the flowrate gradually decreases as the rotation rate is increased.     

非牛顿特性对偏心圆筒内流体混沌混合的影响

Effect of fluid elasticity and shear-thinning viscosity on the chaotic mixing between two alternately rotating cylinders has been studied. The h-p finite element method is used to obtain high accurate solutions of the steady flow. The unsteady, periodic flow is simulated using the piecewise-steady approximation. Characteristics of the chaotic mixing axe analyzed by examining the asymptotic coverage of a passive tracer and the lineal stretching ofthe fluid elements in the annulus. For the viscoelastic fluids modeled by the upper-convected Maxwell constitutive equation (UCM), our computation predicts little effect of the fluid elasticity on the mixing patterns. On the other hand, the shear-thinning viscosity, modeled by the Carreau equation, has a large impact on the advection of a passive tracer and the distribution of lineal stretching. We find that the zones of the lowest stretching match remarkably well with the regular zones in the tracer-coverage plotting. Our study reveals the vital importance of reducing the discretization errors of the velocity field in the numerical simulation of chaotic flows.     

非电解质水溶液黏度的关联

许多化工过程的设计需要估算含水体系的黏度,但目前的黏度关联方法用于含水体系时误差较大.今以作者所在课题组近期提出的非水液体混合物黏度关联方程为基础,通过引入形状因子,得出了一个非电解质水溶液的黏度方程.该方程可用于二元非电解质水溶液黏度的关联,且能利用二元黏度得到的关联参数推算三元非电解质水溶液的黏度.该方程对54个二元非电解质水溶液体系黏度(总计2876个黏度数据点)关联的总平均相对偏差为4.60%;对7个三元非电解质水溶液体系黏度(总计352个黏度数据点)推算的总平均相对偏差为3.75%.结果表明,该方程具有较高的关联精度和推算精度.     

A simplified couette flow solution of non-newtonian power-law fluids in eccentric annuli

Flow of non-Newtonian fluids in both the concentric and eccentric annuli is of great importance in extruders for molten plastics and wellbore fluid circulation for the removal of drilling cuttings. The steady laminar couette flow of non-Newtonian power-law fluids in eccentric annulus is employed in this study to analyze the problems of surge or swab pressures encountered when running or pulling tubular goods (pipes) in a liquid filled borehole. This is similar to the annular space created by two long co-axial cylinders with the inner cylinder in motion at a steady velocity, and a stationary outer cylinder. The solutions of the equations of motion are presented in both dimensionless form and as a family of curves for different pipe/borehole eccentricity ratios and power-law fluid index values for a more general application. The expected error in surge computation for concentric annulus as a result of eccentricity is evaluated.     

FREE CONVECTION MASS TRANSFER IN VERTICAL ANNULI

Natural convection mass transfer at the inner surface of the outer cylinder of annuli was investigated using an electrochemical technique involving the deposition of copper from acidified copper sulphate solution. Variables studied were: annulus height, annular gap width and physical properties of the solution. Mass transfer data for annuli of large gap width (L/d ≤ 3.225) were correlated by the equation:

For annuli of small gap width the data were correlated by the equation:     

FREE CONVECTION MASS TRANSFER IN VERTICAL ANNULI

Natural convection mass transfer at the inner surface of the outer cylinder of annuli was investigated using an electrochemical technique involving the deposition of copper from acidified copper sulphate solution. Variables studied were: annulus height, annular gap width and physical properties of the solution. Mass transfer data for annuli of large gap width (L/d ≤ 3.225) were correlated by the equation:

For annuli of small gap width the data were correlated by the equation:     

The capillary break-up of a binary liquid column inside a tube

The break-up of a stationary viscous liquid cylinder surrounded by an immiscible viscous liquid contained in a circular tube by capillary forces at the fluid interface is considered. It was found that the maximum growth-rate parameter f* depends upon η'/η, the ratio of the viscosity of the inner liquid to that of the outer liquid and a/S, the ratio of the radius of the inner liquid cylinder to that of the tube. Both f* and corresponding wavelength parameter (2πa/λ)* have been calculated theoretically; measured values of both parameters are in good agreement with the theory.     

Semianalytical solution for power‐law polymer solution flow in a converging annular spinneret

A semianalytical solution for a power‐law fluid flowing through a conical annulus was derived to estimate the velocity profile in the axial direction, the shear rate and the elongation rate within a spinneret during the spinning of hollow fiber membranes. The angle coefficient was introduced as a new parameter to account for the effect of radial flow and to modify the governing equation, which initially neglected the effect of radial flow. The results estimated from this semianalytical solution agreed more closely with computational fluid dynamics simulation results than those obtained from the approximate analytical solution in our previous study. By accurately predicting the velocity profile in the axial direction and the shear and elongation rates in a conical annulus, the solution derived in this study is expected to provide a reliable criterion for spinneret design to achieve a specified membrane morphology with a desired performance. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3489–3499, 2015     

Velocity Field Structure and Flocculation Efficiency in Taylor-Couette Flow

Velocity field data were acquired for Taylor-Couette flow in the annulus gap between a rotating inner cylinder and a fixed concentric outer cylinder by using particle image velocimetry. The flocculation efficiencies were also obtained in the same Taylor-Couette flow under the conditions corresponding to the velocity field measurement. The flocculation efficiencies reached the maximum values due to the closed vortices, their contraction and expansion with time in wavy vortex flow. But out of the wavy vortex flow range, the comparatively low flocculation efficiencies were obtained due to the no-closed vortices which connected with each other.     

洗涤冷却室垂直环隙空间内液相流动结构的研究

在与工业气化炉几何相似的洗涤冷却冷态模拟装置内,借助双头电导探针和皮托管-差压变送器,测量了环隙空间的气含率及内轴向和切向的液相速度分布,对洗涤冷却室内的液相流动结构进行研究。结果表明：下降管出口及破泡板下方轴向液速呈现近下降管外壁向下流动,液池内壁向上流动的结构,液相转折点分别为 r/R=0.7和r/R=0.6;破泡器的存在使轴向液速呈抛物线分布;切向速度相比轴向速度较小,在-0.15~0.1 m/s范围内波动;不同表观气速下的液相速度分布具有相似性,随着表观气速的增加,液相速度增大;通过对h=523 mm处液相速度分布的归一化处理,得到U_z/U_c模型关联式;经检验,环隙中心速度随塔径和表观气速的变化可近似用Nottenkaemper关联式描述。     

Effects of viscosity and relaxation time on the hydrodynamics of gas–liquid systems

Effects of liquid properties on the hydrodynamics of gas–liquid systems were investigated in lab-scale bubble column (BC) and internal loop airlift (ILA). Alginate solutions, a glycerol solution and a Boger fluid were adopted to separately address the effects of viscosity and of surface tension for Newtonian fluids, and the effects of relaxation time for non-Newtonian fluid characterized by approximately constant viscosity (low shear thinning). Hydrodynamic regimes were characterized in terms of overall gas holdup, gas–liquid mass transfer coefficient, drift-flux and liquid circulation velocity. The superficial gas velocities at the transition between hydrodynamic regimes (homogenous regime–vortical-spiral regime–heterogeneous regime) as a function the liquid viscosity was characterized by a maximum. The same behavior was observed for the maximum stable gas holdup and gas–liquid mass transfer coefficient in BC. Viscosity enhances homogeneous regime stability for μ<4.25 mPa s, in BC, and μ<7.68 mPa s, in ILA. For non-Newtonian fluids the transition velocity increases with liquid elasticity. The stabilization mechanism related to the relaxation time of Boger fluids has been discussed.     

粘弹性流体在偏心环空中非定常流动的流量数值计算

利用有限体积法（FVM）对双极坐标系下变系数二阶流体在内管做轴向往复运动的偏心环空中非定常流的控制方程进行了离散,其中时间积分方案采用全隐式,再利用交替方向隐式方法（ADIP）对离散方程组进行了数值求解;通过对视为变系数二阶流体的不同质量分数的聚丙烯酰胺（HPAM）水溶液在内管做轴向往复运动的偏心环空中的非定常流动实验,在相同条件下,在利用该方法数值求解上述控制方程后得到速度场的基础上,结合流量公式,将数值计算得到的流量与实测流量进行了比较,并将比较的吻合程度与其它方法得到的吻合程度进行了对比。结果表明：本文所给数值计算方法是正确的;利用本文方法数值计算得到的流量与实测流量的吻合程度比另外两种方法更好,且数值计算步骤较为简便、计算速度较快。     

Helical flow of curing highly viscous liquids

For profile extrusion of rubber, a shear head is frequently placed at the outlet of the extruder. In the shear head, the rubber compound is heated to its cure temperature by means of internal friction between two coaxially rotating cylinders (annulus). The aim of this examination is to find suitable operating parameters for all rubber compounds. The highest possible temperatures and an even cure profile are the characteristics of suitable operations. The degree of cure should be as close as possible to the maximum cure permitted. For examination of the processes in the annulus, a coupled system of differential equations is set up and solved numerically. The cure profiles established along the annulus are of special interest. The effects of the geometry, the rotational speed of the inner cylinder, the volumetric flow, the operating temperatures, and the viscosity as a function of the shear rate and the temperature are examined. The results of the calculations show that the viscosity, which increases with increasing cure, has a strong effect on the velocity and dissipation profiles. The results of the experimental investigations on a shear head coincide well with theoretical prediction.     

Experimental study on effect of elasticity on drag reduction and turbulent fluctuations in laminar-turbulent transition region in pipe flow of dilute polymer solutions

By utilizing the fact that physical properties exclusive of elasticity of dilute polyacrylamide solutions do not change with elapsed time after preparation, the effect of elasticity on drag reduction and turbulent fluctuations in pipe flow was investigated experimentally. The oscillations of axial velocity and velocity gradient and the drag reduction in the laminar-turbulent transition region are affected significantly by the value of elasticity. The laminar-turbulent transition region moves to a higher Reynolds number as the value of elasticity increases.     

Influence of molecular weight distribution on the elasticity and processing properties of polypropylene melts

In a study of the flow behavior of polymer melts a semi-empirical viscometric equation has been used which contains an elasticity parameter relating the shear dependence of the viscosity to the normal-stress effect. The way in which both these effects are influenced by the molecular weight distribution of the polymers investigated is shown, and the influence of melt elasticity on polymer processing behavior is discussed. From previously published viscosity data the elasticity parameter has been determined for a number of polypropylene grades, and the possibility of classifying these grades according to a characteristic time constant is indicated.     

The viscosity of dimethyl silicone oil and the concentration of absorbed air

We studied the viscosity behavior of 500 cSt dimethyl silicone oil with considerable concentration of absorbed air. For this purpose, a Couette rheometer with a transparent rotating outer cylinder and a fixed inner cylinder was established, in which the ambient pressure is controlled by a piston–cylinder apparatus. Careful torque calibration and equilibrium examination for the air–silicone–oil mixture were carried out. In the range of ambient pressure from 1 to 5 atm, corresponding to the air molar fraction from 11 to 35%, it was found that viscosity of the silicone oil decreases monotonically as the air concentration increases. The viscosity variation can be explained by the Eyring's model in which the free energy of activation is modified to account for the nonideality of the air–silicone–oil mixture. The excess free energy used to fit the viscosity variation is approximately equal to that used in the Krichevsky–Ilinskaya equation, which accounts for the nonideal solubility of the air–silicone–oil solution. The activation energy in the Arrhenius equation for viscosity–temperature relationship is identified as the activation enthalpy. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

基于段塞流捕捉的高黏油气两相流模型的建立与验证

随着传统油田的快速消耗,高黏稠油的开发逐渐引起了重视。有关高黏油的气液两相流研究主要集中在国外,国内的相关研究目前还较少。本文针对高黏油气混输管路,建立了一种捕捉段塞流的形成和发展过程,并进行两相流水力计算和液塞长度统计的组合模型。通过气液相间滑移速度和液相连续性方程的求解得到管路中不同时刻和位置的持液率,以持液率的变化反映段塞的形成和发展。建立气液动量守恒方程关联持液率和压力,得到管路中各位置的压力变化。闭合关系式中,通过液塞平移速度、壁面及气液相界面的剪切力关系式加入黏度的影响,最终建立适用于高黏油气两相流的段塞捕捉模型。使用不同来源的数据验证模型计算压降和液塞长度的准确性,数据分别来源于国外研究者的实验数据和大庆油田的现场数据。结果表明,模型具有较高的计算精度,大部分压降误差在±15%以内,大部分液塞长度误差在±20%以内。     

强制液体外循环气升式内环流反应器的流体力学特性

在有机玻璃制成的主体反应器(φ0.286 m×3.0 m)内,采用空气-水的气液两相体系考察了不同表观气速下带有中心下料管和环管式气体分布器的环流反应器内局部气含率和内环气泡上升速度的流体力学特性。结果表明：气含率均随表观气速的增大而增大;从外环流入内环的气泡数量比较少;在相同条件下外环的气含率远远低于内环的气含率;新型气体分布器的采用和液体外循环的引入可以增大床层气含率并使其分布趋于均匀,从而增大了内环中气液两相的接触面积和湍动强度,使传递过程得到强化。在此基础上采用商业软件ANSYS CFX10.0对该反应器进行了数值模拟研究,模拟结果与实验数据基本吻合,说明了基于实验验证的Euler-Euler法可以用于该反应器开发和放大研究。     

Gas-liquid dispersions in structured packing with high-viscosity liquids

Gas holdup in bubble columns containing structured packing was determined for varying liquid phase viscosity and different construction materials of the packing. Three columns, containing packing made from smooth nickel plate, perforated nickel plate and plastic sheets, respectively, were tested. The gas holdup in a column with no internals was also measured for comparison purposes. The effect of viscosity on gas holdup was studied by using water, aqueous glycerol and aqueous CMC solutions as the liquid phase; some of the solutions showed non-Newtonian behavior.The experimental results of gas void fraction were correlated in terms of superficial gas velocity and liquid viscosity through a simple homographic expression. The geometric characteristics of the structured packings were found to influence gas holdup, thus yielding slightly different equations for each structured packing. This effect is discussed in detail. Nevertheless, for engineering purposes a single equation representing all the data is also proposed, which permits the prediction of gas holdup in structured packing with sufficient accuracy.