Flow of a FENE Fluid in Packed Beds or Porous Media

An analysis describing viscoelastic flow of a FENE fluid in packed beds or porous media is presented based on the capillary hybrid model of the flow. A close similarity is revealed between the functional relationship of the reduced elongational viscosity to and that relating the reduced mean elongational viscosity λ_H ? to the Deborah number which is utilized in the flow expressions. The agreement obtained between the predicted and experimentally determined evaluations of the resistance factor, including the effects of variation of polymer concentration, molecular weight and solvent quality was found to be satisfactory. Onset Reynolds numbers for enhanced flow resistance are also predicted successfully.     

螺旋内翅片管内充分发展流体流动与传热的数值分析

采用常规模型对一种新型螺旋翅形裂解炉管内充分发展的流体流动与传热进行了数值分析。采用变量置换法把控制方程由原来的三维问题转化为计算平面内的二维问题,并采用ＳＩＭＰＬＥＣ方法计算考察了周向恒壁温、轴向恒热流的螺旋内翅片管内充分发展条件下的流体流动与传热问题,得到了与实验值相近的结果。进一步用所述的方法对相同横截面的直翅和螺旋翅片管内的流场和温度场进行了数值模拟研究,它揭示了螺旋翅片管相对于直翅管而言阻力增加而传热效率下降的机制。     

Numerical Analysis of Thermal Development of Laminar Flow in a Concentric Multilayer Annulus

The thermal behavior of laminar flow in a concentric multilayer annulus is investigated numerically for varying dimensionless inner radii and a defined number of fluid layers. Under a hydrodynamically developed flow assumption within the fluid layers, the development of temperature profiles and heat transfer along the annulus are analyzed for two different boundary conditions. The mean temperature distribution, local Nusselt number, and mean Nusselt number are discussed in detail with an emphasis on the effects of the inner radius and number of fluid layers. The obtained results indicate that the change in heat transfer coefficient in a layered annulus is more pronounced at a small inner radius or larger radius ratio. A further insertion of more than ten layers has insignificant influence on the convective heat transfer in a layered annulus.     

湍流气固两相流动状况的数值模拟

应用已建立的提升管反应器固两相流动反应模型,对工业催化裂化提升管反应器内在有传热及裂化反应时的湍流气固两相流动进行了数值模拟,得到了气固两相湍充动状况的详细信息,揭示了提升管内部有反应和传热时气固两相湍流流动的基本特征。模拟结果表明,在轴向,径向和圆周方向都存在着流动,湍能与率剂颗粒浓度的不均匀分布,进料段内的流动是整个反应器最复杂的部分。工业提升管反应器内这一复杂的气固两相湍流流动必将对传热和裂     

螺旋内槽管内的层流流动与传热的数值模拟

应用数值方法对一种螺旋内槽管管内的流体层流流动和传热进行了数值分析。采用数学变量置换把控制方程由原坐标系中的三维动量、能量及连续性方程转化为二维螺旋坐标系下的数值计算模型，并利用现有的二维数值模拟软件进行模拟计算。计算考察了恒壁温、轴向恒热流螺旋内层流充分发展流体的流动与传热随雷诺数的变化，并研究了螺距的影响。     

Study of Turbulent Flow in a Long Permeable Channel

Stationary liquid flow in a long (to L/d = 1440) permeable channel was studied for input Reynolds numbers from 28700 to 83000. The distributions of water pressure along the channel were obtained. Experimental data were compared with the numerical solution of equations derived from the energy equation.     

Flow Characteristics of Gas Permeation through a PVF Porous Tube

PVF (polyvinyl formal) porous materials have attractive properties, such as noise attenuation, good structural integrity, thermal and chemical stability, high permeability and large specific surface area, for many flow‐through applications. Several characteristics of the porous material will have an impact on the permeability, and gas flow and diffusion. However, the shape and the design of the device may also have significant impact on the gas flow. A porous media model and Darcy‐Forchheimer principle were used as the basic theoretical frame. The unified governing equations were used to describe the compressible flow in and out of a PVF porous tube. A robust NND numerical scheme was used to discretize the equations and the TDBC (time‐dependent boundary conditions) were used to treat the nonreflective boundaries. Numerical simulations of an interior and exterior flow field of a PVF porous tube were completed. The detailed flow characteristics of the inner and outer flow fields of the tube were obtained. The velocity distribution of the outside of the tube compare very well with the experimental data.     

埋地管道夏季泄漏土壤温度场及原油分布数值计算

基于分布式温度光纤传感技术检测管道泄漏机理,研究了埋地管道泄漏传热特点,并采用有限容积法建立了管道泄漏多孔介质流固耦合换热控制方程,针对夏季埋地热油管道不同位置泄漏前后大地温度场的变化及原油在土壤中的分布规律进行数值计算,得出了管道正上/下方穿孔泄露后土壤温度场及原油分布随时间的变化关系.研究表明:夏季泄漏初期管道周围土壤温度场变化剧烈,泄漏位置对土壤温度场分布影响较大,检测管道发生泄漏可以使用分布式温度传感技术.     

Numerical Simulation of Forced Convection in a Porous Circular Tube with Constant Wall Heat Flux: An Extended Graetz Problem with Viscous Dissipation

Thermal development of forced convection in a circular tube filled with a saturated porous medium, subjected to the constant wall heat flux with a step change including the effect of viscous dissipation and the longitudinal heat conduction, has been studied numerically. Numerical computations for various values of the governing independent parameters, the Peclet number, Pe, the Darcy number, Da, the Brinkman number, Br, and the thermal conductivity ratio, Γ, were performed to disclose the influence of these parameters on the thermal behavior of flow through the corresponding porous circular tube. Results show that the presence of the viscous dissipation significantly elevates the level of the wall temperature, especially in the downstream region where the wall heat flux is uniformly applied. The local Nusselt number exhibits a monotonically increasing characteristic with the increase in the value of Γ. Results also show that the effect of the thermal conductivity ratio, Γ, alters the rate of the wall temperature evolution along the flow direction as well as the transversal profile of the temperature. This implies that the heat transfer is strongly controlled by conduction, and this is significant when the value of the Peclet number, Pe, is small.     

Numerical Simulation of Fluid Flow and Heat Transfer in Thermoplates

A thermoplate is a heat transfer device consisting of two metallic sheets that are spot‐welded according to an appropriate pattern over the whole surface area whereas the edges – except for connecting tubes – are continuously seam‐welded. By applying a hydro‐form technique, a channel having a complex geometry is established between the sheets. Such heat transfer devices are encountered in several areas of cooling and heating techniques and process technology, e.g. as condensers or evaporators. The objective of the described investigations was to numerically obtain the optimal geometry of the thermoplate with respect to heat transfer of the inside fluid that passes through the channel as a single phase. The numerical experiments show that the heat transfer potential of the thermoplate having a staggered arrangement of welding spots is markedly higher than that of a common flat channel, particularly at larger Reynolds numbers. The variations of the geometrical parameters show the potential for the heat transfer improvement in comparison to a corresponding parallel plate channel.     

Numerical investigation on flow and heat transfer characteristics of corrugated tubes with non-uniform corrugation in turbulent flow

Based on finite volume method, the pressure drop and heat transfer characteristics of one smooth tube and ten different axisymmetric corrugated tubes, including two with uniform corrugation and eight with non-uniform corrugation, have been studied. A physical model of the corrugated tube was built, then the numerical simulation of the model was carried out and the numerical simulation results were compared with the empirical formula.The results show that: the friction factor decreases with the increase of Reynolds number ranging from 6000 to 57000, the value of which in the corrugated tubes with non-uniform corrugation(tube 03–10) are smaller than those with uniform corrugation(tube 01–02). The geometry parameters of tube(01) have advantages on the heat transfer enhancement in low Reynolds number flow region(from 6000 to 13000) and tube(07–08)have advantages on the heat transfer enhancement in high Reynolds number flow region(from 13000 to 57000). The vortex, existed in each area between two adjacent corrugations called second flow region, is the root of the enhancement on heat transfer in the corrugated tubes. The effectiveness factor decreases with the increasing of Reynolds number and the performances of the corrugated tubes with pitch of 12.5 mm have advantages than these of 10 mm under the same corrugation geometric parameter.     

薄膜蒸发器内流体流动特性的数值模拟

建立了薄膜蒸发器的计算模型,采用大型计算流体力学(CFD)分析软件CFX4.4模拟了薄膜蒸发器内水及粘性料液的流动过程,得到了各种速度分布. 结果表明,刮板转速、进料量对流体流动状态影响显著. 提高刮板转速,可明显促进液膜和圈形波内流体的物质交换. 在任一转速下,各料液均存在同一最佳进料量,此时其圈形波截面内平均速度达到最大值. 对纯物质水,最佳进料量对应的流动边界层厚度与膜厚之比最小. 粘性料液和水的轴向速度分布存在差异,且在液膜厚度内未形成明显的流动边界层.     

Laminar flow in channels with wall suction or injection: a new model to study multi-channel filtration systems

A one-dimensional model to determine the laminar flow of a fluid in a porous channel with wall suction or injection is proposed. The approach is based on the integration of the Navier-Stokes equations using the analytical solutions for the two-dimensional local velocity and pressure fields obtained from the asymptotic developments at low filtration Reynolds number proposed by Berman (J. Appl. Phys. 24 (1953) 1232) and Yuan and Finkelstein (Trans. ASME 74 (1956) 719). It is noticeable that the resulting one-dimensional model preserves the whole flow properties, in particular the inertial terms which can affect the wall suction conditions and the spatial distribution of the growing particle cake layer at the wall encountered in filtration processes. The model is validated in the case of a single porous channel of rectangular or circular cross-section with uniform or variable wall suction. Then the model is applied to a two-dimensional multi-channel system which consists of a great number of adjacent entrance and exit channels connected by a filter porous medium. It is shown that the effect of non-uniform boundary conditions and the influence of heterogeneous geometrical characteristics on the heterogeneity of the fluid flow structure can be studied using such a model.     

埋地天然气管道泄漏危险区域的数值模拟

针对埋地输气管道的特点,建立埋地输气管道持续泄漏模型,运用有限容积法,对比分析多孔介质对天然气埋地天然气管道泄漏气体扩散的影响,得出管道上层土壤作为多孔介质,对气体扩散有重要的影响,由于其土壤阻力和毛管压力作用,使气体在地下消耗大量湍能,气体在地下危险区域呈下窄上宽,而在地上由于气体湍能减小,加上大气压的作用,致使气体危险区域呈上窄下宽。结计算结果为埋地天然气管道合理设计管道区域,指导管道敷设和安全运行提供理论指导。     

三通管中不同流体介质冲蚀磨损的数值模拟

运用Fluent软件中的DPM模型对三通管中冲蚀磨损过程进行了数值模拟计算,从详细流场数据的分析中得到了流体对三通管冲蚀磨损较严重的部位,并对四种不同流体介质在三通管中的冲蚀磨损情况进行了对比研究,结果表明,流体的粘度/密度的平方根与流体对管道的冲蚀磨损速率成正比。     

Numerical Simulation of Gas‐Liquid Flow in a Stirred Tank with Swirl Modification

Although the standard k‐? model is most frequently used for turbulence modeling, it often leads to poor results for strongly swirling flows involved in stirred tanks and other processing devices. In this work, a swirling number, R_S, is introduced to modify the standard k‐? model. A Eulerian‐Eulerian model is employed to describe the gas‐liquid, two‐phase flow in a baffled stirred tank with a Rushton impeller. The momentum and the continuity equations are discretized using the finite difference method and solved by the SIMPLE algorithm. The inner‐outer iterative algorithm is used to account for the interaction between the rotating impeller and the static baffles. The predictions, both with and without R_S corrections, are compared with the literature data, which illustrates that the swirling modification could improve the numerical simulation of gas‐liquid turbulent flow in stirred tanks.     

弯管内部油水两项流的数值模拟

在油井出油管道以及石化生产中,油水两项流是非常常见的现象。为了减少能耗、便于制订防腐措施,利用GAMBIT软件建模以及FLUENT软件的可实现模型对弯管中油水两项流的压力场和速度场进行模拟。结果表明,管内入口直管压力呈逐阶减小趋势;弯管内壁出形成低压区且又内向外逐渐增大;而速度分布正好与压力分布规律相反,恰好与自由涡流理论的模型相符。且通过对油水两项所占体积分数分别为30%、50%、80%三种情况的模拟得出,由于水密度大于油的原因,随着油相体积分数的下降,管内整体压强减小,整体速度增大。     

Synergistic and interference effects in coaxial mixers: Numerical analysis of the power consumption

This paper is concerned with the design and application of coaxial mixers with the aid of analysis of interaction between each individual impeller.Two types of coaxial mixers pitched blade turbine (PBT)-helical ribbon (HR) and inner-outer HR operated in laminar regime were studied experimentally and numerically.The interaction implies synergistic and interference effects,which was revealed through the investigation of axial circulation rate,energy dissipation rate and power consumption.The influence factors including rotational speed ratio,rotating mode and impeller configuration were explored systematically.Quantitative analysis of power consumption involves three parameters:rate of variation in power consumption,interactive mode and ratio of power consumption.Analysis indicated that some important properties were embodied in the power curve.These properties are one-way and two-way interactions,critical speed ratio and dominant impeller.Finally,a new suggestion for power estimation was given.     

CFB用旋风分离器内气相流场的数值研究

采用RSM非稳态湍流模型对循环流化床锅炉用旋风分离器内气相流场进行了数值模拟。计算值与实验值比较吻合。数值计算的结果表明:排气管下口存在明显的短路流,排尘口附近存在明显的返混现象;排气管直径增加,分离空间切向速度值降低,上行流轴向速度减小。用CFD方法计算的旋风分离器内流场可为高效CFB锅炉用旋风分离器的设计提供参考依据。     

Experimental and Numerical Investigations on the Dynamic Fracture of a Cylindrical Shell with Grooves Subjected to Internal Explosive Loading

A detailed experimental investigation on the dynamic fracture of a cylindrical shell with internal and external grooves subjected to internal explosive loading was carried out. Distributions of fragment velocities and fragment masses were measured and analyzed for specimens with different depths of the external grooves and different explosive materials, with the internal grooves of a fixed rectangular shape. Based on the experimental results, corresponding numerical simulations using the commercial software LS‐DYNA were undertaken. By inspecting the fragments recovered from the experiments and the numerical results, the dynamic fracture of the casing led to fragments of approximately three shapes: a large cuboid fragment, a small cuboid fragment, and two irregular fragments formed by three classical fracture trajectories. The formation mechanism of fragment shapes was analyzed using the fracture trajectories. A good agreement has been obtained between the numerical and experimental results. Finally, a parametric study for the casing thickness, grid patterns of the grooves and explosive materials was carried out in order to investigate the effects of fracture. The results showed that grid patterns of grooves and explosive materials had significant effects on the fracture mechanism of the casing. The numerical technique was used to predict the dynamic fracture of casing with internal and external grooves under internal explosive loading and for structural design in order to achieve desirable fragments with controlled shapes.