Flow of power law liquids through particle assemblages at intermediate reynolds numbers

The complete equations of motion and continuity have been solved numerically using the finite element method for the flow of power law liquids through assemblages of rigid spherical particles. The inter-particle interactions have been simulated using the free surface cell model. Extensive results on drag coefficients have been obtained under a wide range of physical and operating conditions (0.9999 ≥ 0.3), 1 ≥ n ≥ 0.4 and 20 ≥ Re ≥ 1. The observed dependence of drag coefficient on voidage and non-Newtonian flow behaviour index have been explained qualitatively with the aid of order of magnitude considerations. Finally, the theoretical predictions have been validated using suitable experimental data available in the literature.     

非圆小通道内非牛顿流体-氮气二相流型研究

采用可视化手段研究了水力直径为2.886 mm和0.866 mm的等边三角形截面微小通道内非牛顿流体气液二相垂直上升流动,表观气速0.1—100 m/s,表观液速0.01—6 m/s。根据观察和测量结果,得到三角形通道内的羧甲基纤维素钠(CMC)溶液-氮气的典型流型图像和流型转变界限。通过与常规通道的空气-水二相流型图对比,发现液体的黏性、表面张力以及截面形状和水力直径等因素对流型的转变具有显著的影响。     

圆管内含颗粒幂律流体的密相两相湍流

阐述了幂律流体控制方程的特点,研究了幂律流体的稠度系数和流动指数的变化对两相流动的影响.随着流动指数的增加,幂律流体在圆管中心附近的主流速度减小,同时颗粒相速度在圆管中心附近增大,而在管壁附近减小.随着稠度系数的增加,幂律流体和颗粒相的主流速度分布出现了与流动指数带来的影响相似的趋势.对带颗粒的幂律流体的两相流流动与液固两相流流动做了比较,幂律流体两相流的流体速度在管道中心附近的大部分区域比液固两相流的流体速度流动的速度大,而颗粒相的速度分布比较平坦.     

非牛顿流体非等温充模过程的Level Set方法模拟(英文)

A non-isothermal injection molding process for a non-Newtonian viscous pseudoplastic fluid is simulated. A conservative interface capturing technique and the flow field solving method are coupled to perform a dynamic simulation. The validity of the numerical method is verified by a benchmark problem. The melt interface evolution versus time is captured and the physical quantities such as temperature, velocity and pressure at each time step are obtained with corresponding analysis. A “frozen skin” layer with the thickness increasing versus time during the injection process is found. The fact that the “frozen skin” layer can be reduced by increasing the injection velocity is numerically verified. The fountain flow phenomenon near the melt interface is also captured. Moreover, comparisons with the non-isothermal Newtonian case show that the curvatures of the interface arcs and the pressure con-tours near the horizontal mid-line of the cavity for the non-Newtonian pseudoplastic case is larger than that for the Newtonian case. The velocity profiles are different at different positions for the non-Newtonian pseudoplastic case, while in the case of Newtonian flow the velocity profiles are parabolic and almost the same at different positions.     

Pressure losses in orifices for the flow of gas-non-newtonian liquids

An investigation has been carried out to evaluate the two-phase pressure drop for gas-non-Newtonian liquid flow across orifices. The method of dimensional analysis was used to correlate the experimental data. The correlation developed predicts the two-phase frictional pressure drop across the orifices with acceptable statistical accuracy.     

Holdup for two-phase flow of gas-non-newtonian liquid mixtures in horizontal and vertical pipes

The paper deals with the experimental investigations carried out to evaluate holdup for gas-non-Newtonian (pseudoplastic) liquid mixtures in vertical and horizontal flow in pipes. Correlations developed predict holdup in slug flow regime with acceptable statistical accuracy.     

基于颗粒动力学理论的搅拌器中固液流动的数值模拟

在欧拉双流体模型基础上引入颗粒动力学理论(KTGF),对带挡板圆盘涡桨式搅拌器内的固液两相流动进行数值模拟。结果表明,搅拌器底部颗粒温度分布与固相浓度分布趋势吻合,转速低于600 r/min时,槽底会形成明显的颗粒沉积,转速从600 r/min增至1500 r/min,堆积区向轴中心收缩,基于颗粒动力学理论可以合理解释挡板及叶轮转速对固相浓度分布的影响。随叶轮转速增大,搅拌器内固液两相湍流运动加剧,颗粒温度、湍动能及轴向速度增加,颗粒分布更均匀,但达到完全悬浮状态后颗粒温度趋于稳定。搅拌器底部和挡板处颗粒堆积导致了局部颗粒浓度增加及颗粒平均自由行程减少,颗粒温度反而降低;同时挡板布置使搅拌器内形成了双循环回路,加强了流体的湍流程度,增强了湍动能,但导致颗粒在挡板处积聚,不利于固相在挡板处均匀分布。     

垂直管中零净液流量气液两相流的持液率研究

Zero net-liquid flow (ZNLF) is a special case of upward gas-liquid two-phase flow. It is a phenomenon observed as a gas-liquid mixture flows in a conduit but the net liquid flow rate is zero. Investigation on the liquid holdup of ZNLF is conducted in a vertical ten-meter tube with diameter of 76 mm, both for Newtonian and nonNewtonian fluids. The gas phase is air. The Newtonian fluid is water and the non-Newtonian fluids are water-based guar gel solutions. The correlations developed for predicting liquid holdup on the basis of Lockhart-Martinelli parameter are not suitable to ZNLF. A constitutive correlation for the liquid holdup of vertical ZNLF was put forward by using the mass balance. It is found that the liquid holdup in ZNLF is dependent on both the gas flow rate and the flow distribution coefficient.     

Flow pattern of the phases and liquid saturation in gas-liquid concurrent downflow through packed beds

Flow pattern was visually observed for non-foaming and foaming Newtonian and non-Newtonian liquids under concurrent downflow with air in packed beds using different configurations of column geometry and packins. Flow maps delineating the different flow regions were presented based on the present study as well as that of earlier investigations. The total and dynamic liquid saturation were experimentally measured and correlations were presented in terms of (i) the Lockhart-Martinelli parameter, χ, and (ii) the flow variables.     

A numerical study of the accelerating motion of a dense rigid sphere in non-newtonian power law fluids

The equations of motion of an accelerating sphere falling through non-Newtonian fluids with power law index n in the range 0.2 ≤ n ≤ 1.8 were integrated numerically using the assumption that the drag on the sphere was a function of both power law index and terminal Reynolds number, Re_t For 10^?2 ≤ Re_t ≤ 10³ both dimensionless time and distance travelled by the sphere under transient conditions showed a much stronger dependence on the flow behaviour index, n, for shear-thinning than for shear-thickening fluids. The form of this dependence is investigated here. Furthermore, results in four typical shear-thinning fluids suggested a strong correlation between the distance and time travelled by the sphere under transient conditions and the value of the fluid consistency index. The analysis reported herein is, however, restricted to dense spheres falling in less dense fluids, when additional effects arising from the Basset forces can be neelected.     

Friction factor for gas-non-newtonian liquid flow in horizontal bends

Experimental investigations have been carried out to evaluate the two-phase pressure drop data across different types of horizontal bends for gas-non-Newtonian liquid flow. The non-Newtonian liquids used were different concentrations of the sodium salt of carboxymethyl cellulose (SCMC) which behaved like pseudoplastic fluids. Correlations have been developed to predict the gas-non-Newtonian liquid two-phase friction factor as a function of various physical and dynamic parameters of the system. Statistical analysis of the correlations suggests that the correlations are of acceptable accuracy.     

偏心组合桨搅拌槽内层流混合过程的数值模拟

目前,处理高黏流体和对剪切敏感介质的层流搅拌槽的报道并不多见。本文建立了描述双层组合桨搅拌槽内高黏非牛顿流体层流流动、混合过程的数学模型,利用Laminar模型、多重参考系法（MRF）和示踪剂浓度法对其流场特性、示踪剂扩散过程进行数值模拟,分析搅拌槽内轴向速度曲线、示踪剂浓度响应曲线和混合时间。结果表明：中心搅拌中间面将介质阻隔在各自的半层内运动,偏心搅拌介质作全局运动,轴向混合能力突出;转轴中心搅拌依靠上下半层浓度差的增大向下扩散,转轴偏心搅拌通过不对称结构扩散示踪剂,叶轮相对转轴偏心搅拌则利用叶片的不对称分布;距离加料点较近和较远的监测点浓度响应曲线因振荡和调整,混合时间较长,处于中间面的监测点拥有最短的混合时间。     

基于JFO空化和幂律模型的螺旋槽液膜密封流体动压特性

密封端面间润滑流体的非牛顿特性对密封的性能有重要影响。基于满足质量守恒的JFO空化边界条件及描述流体非牛顿特性的幂律模型,建立了考虑流体非牛顿特性的螺旋槽液膜密封数学模型。采用有限差分法对控制方程进行离散,通过SOR迭代方法对离散方程进行求解,得到了密封端面液膜压力分布。探讨了润滑流体的非牛顿特性对螺旋槽液膜密封的液膜承载能力、泄漏量、摩擦扭矩等性能参数及液膜中空化发生情况的影响规律。结果表明：随着幂律指数的增大,液膜承载能力先增大后减小,泄漏量和空化率增大,摩擦扭矩减小;幂律指数为0.96时,相对于牛顿流体,液膜承载能力提升约4.6%,密封端面空化率下降约98.6%,泄漏量下降约5.8%,摩擦扭矩增加约0.3%;随着操作参数的改变,不同幂律指数下的流体动压性能参数变化规律具有相似性;润滑流体的合理选择对液膜密封性能改善有重要意义。     

多管陶瓷过滤器内耦合效应数值模拟

The Reynolds stress transport model and the Eulerian two-fluid model provided by the FLUENT code were applied to evaluate the gas-particle two-phase flow in the ceramic filter vessel. The ceramic filter vessel contains six candle filters, which are arranged in the form of equilateral hexagon. The variation of the areal density of the filter cake during the filtration and the back-pulse process were analyzed. The coupling effect between filters, gas and solid, filtration and pulse cleaning process were investigated, respectively. The numerical results show a good approach to predict the particle distribution in the vessel and the particle deposition on the filter element. This study provides the base for the intensive study on the analysis of the gas-particle flow in the filter vessel.     

Flow simulation of herschel-bulkley fluids through extrusion dies

The flow of viscoplastic materials through extrusion dies has been studied numerically using the finite element method. Rheological data for viscoplastic doughs have been fitted by the Herschel-Bulkley model, which incorporates a yield stress into the power-law model. Non-isothermal simulations show the extent and shape of yielded/unyielded regions and the development of temperature field assuming different modes of heat transfer at the boundaries. The results reveal that viscous dissipation causes appreciable temperature rises in the extrudate in agreement with measured values at the extruded material surface. The extrudate swell results show a maximum for a certain range of apparent shear rates also observed experimentally. However, the inelastic simulations based on the Herschel-Bulkley model always under-predict the experimental swelling values. A heuristic approach is also used to determine the level of elasticity required to produce the experimental values.     

Liquid wall friction in two-phase turbulent gas laminar liquid stratified pipe flow

The main result of the present work is an analytic expression for the mean liquid wall shear stress in two-phase turbulent gas/laminar liquid stratified pipe flow. The Navier-Stokes equations are solved assuming a flat fluid-fluid interface subject to a constant interfacial shear — approximating the interfacial drag exerted by the gas. The effect of a pipe inclination is accounted for, thereby retaining the interesting two-phase phenomenon of backflow in upwardly inclined pipes. The corresponding expression for the wall shear stress distribution is obtained by formal differentiation. Its limiting behaviour in the triple points, where the fluid-fluid interface meets the pipe wall, is determined by residue calculus. The expression for the mean wall shear stress is given by integration. It is found to be a linear combination of two terms. The first term accounts for the free surface liquid flow in the absence of the gas. The corresponding approximate hydraulic diameter model is found to be in surprisingly good agreement with this term. The second term represents the shear flow associated with the interfacial drag exerted by the gas (not accounted for by the hydraulic diameter approximation). The shear flow increases the flow rate near the interface on behalf of the flow rate near the pipe wall, thus reducing the wall shear stress below the free surface flow value. Expedient evaluation of the expression for the mean wall shear stress, suitable for use in a 1-D multiphase pipe flow simulator, is facilitated by replacing certain one-parameter integrals with highly accurate rational approximations.     

随机粗糙表面上剪切变稀流体液滴的沉积过程模拟

采用计算流体力学相场方法模拟了单个剪切变稀非牛顿流体液滴在随机粗糙表面的沉积过程,并分析揭示了随机粗糙表面形貌对液滴运动状态及平衡状态的影响。结果表明,在指定的相同操作条件下,即使在光滑表面,剪切变稀流体液滴比牛顿流体液滴铺展更大且回缩至平衡所需时间更少,不存在二次铺展;剪切变稀流体液滴最大铺展直径随均方根粗糙度Rr与Wenzel粗糙度Wr的增加而略有增加。Wr相同时,随着Rr增大,液滴最终铺展系数减小,高度系数增大,平衡接触面积及接触角有所减小。在Rr相同情况下,随着Wr增大,液滴达到平衡所需时间缩短,平衡接触面积线性增大。     

空气钻井环空气固两相流动规律数值模拟

基于FLUENT软件中Euler模型,采用有限容积法建立了空气钻井环空气固两相流三维计算模型,分析了压力分布规律、流体分布规律、浓度分布规律。研究表明,从井底到井口压力逐渐降低;速度在钻铤内逐渐增大,在交界面处迅速降低,而后在钻杆内呈现增大趋势,岩屑速度在整体环空内逐渐降低;在交界面处形成漩涡,对岩屑进行了不同程度的清洗;同时空气浓度达到最大值、岩屑浓度为最小值;随着入口空气的逐渐增加,空气速度、岩屑速度变化率逐渐增大,而交界面处高空气浓度、低岩屑浓度区域逐渐增大,能较大程度的清洗岩屑。