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1.
The poor solutions of numerical simulations at a contraction has often been attributed to the numerical scheme used. However, the solution of a numerical simulation is also highly dependent on the constitutive equation. A study of various constitutive equations on the simulation of the 4:1 contraction flow is made in this paper, and their effects on the results analyzed. The constitutive models considered include the Upper Convected Maxwell model, the Oldroyd-B model, the White-Metzner model, the Phan-Thien-Tanner model and the Giesekus-Leonov model. It was found that although the Phan-Thien-Tanner model gave the best results, the solution at higher shear rates were still not satisfactory. 相似文献
2.
The ultimate properties of a molded article arc directly related In the microstructure of the article and are consequently influenced by the thermomechanical history experienced by the melt during processing. The mold filling behavior of thermopalastic polymer melts has been analyzed quantitatively by means of a computer simulation. The mathematical model is based on the equations of continuity, motion, and energy, along with appropriate constitutive relations and relevant initial and boundary conditions. The governing system of equations is solved numerically by means of a Marker-and-Cell computational scheme. One to the significant implications for microstructure development, the fountain effect at the advancing free surface is explicitly taken into consideration in the simulation. The model yields data on filling time and melt front position as well as velocity, temperature, pressure, and shear stress distributions within the mold cavity. The rearrangement of the velocity and temperature profiles in the vicinity of the melt front are considered in detail. Experimental studies have also been undertaken in order to verify the predictions of the computer Simulation. 相似文献
3.
In recent years, the development of CAE (Computer Aided Engineering) in polymer processing has been remarkable, and it is expected to be more realistic in viscoelastic numerical simulation, particularly in three-dimensional complex geometry. Because of the problems of computational memory capacity, CPU time, and the numerical convergence of viscoelastic flow simulation, three-dimensional viscoelastic simulation applicable to industrial flow behaviors has not yet been attempted. In this paper, we developed the numerical simulation of three-dimensional viscoelastic flow within dies using a decoupled method, streamwise integration, and penalty function methods to decrease memory, and the TME (“Transformation of Equation of Motion to the Elliptic Equation,” S. Tanoue, T. Kajiwara, and K. Funatsu, The Eleventh Annual Meeting, the Polymer Processing Society Seoul, Korea, Extended Abstracts p.439) method, which raises the stability of convergence. We confirmed the reliability of this simulation technique to compare simulation results with experimental data of the stress field at a downstream wall shear rate of 5.41s?1 within a 60° angle tapered contraction die. We compared the predictions of a viscoelastic model (Phan-Thien and Tanner model) with a pure viscosity model (Carreau model) at a downstream wall shear rate of 120s?1 and discovered a remarkable effect of viscoelasticity in the shear stress and first normal stress difference in particular in the tapered region. 相似文献
4.
Fountain flow for isothermal viscoelastic fluids is simulated by a numerical method based on a combination of a finite element method and a finite volume method. For the treatment of moving free surfaces, a fringe element generation method is used. Circulating flow and elongation in the transverse direction at the melt front are simulated well. Numerical results also suggest that circulation in fountain flow and viscoelastic retardation may give rise to symmetric V-shaped patterns of birefringence between the center-plane and wall. Such information on molecular orientation in fountain flow is important for physical properties of thick molded products. 相似文献
5.
B. Šiška 《Chemical engineering science》2006,61(24):8089-8094
Fluidization of spherical and non-spherical particle beds with shear thinning viscoelastic polymer solutions was investigated experimentally in the transition flow region. It was observed that the influence of elasticity on the anomalous expansion course weakens with the increasing value of Reynolds number. After exceeding a critical value of Reynolds number, which depends on the measure of liquid elasticity, the effect of elasticity vanishes and the expansion curves have the same linear shape as for fluidization with Newtonian (or purely viscous non-Newtonian) fluids. Semi-empirical equations based on the Carreau viscosity model were proposed for predicting the critical value of Reynolds number and the bed expansion in the region of diminishing elasticity effects. 相似文献
6.
A numerical simulation of entry flow in a slit die has been undertaken for a fluid that is Newtonian in shear but exhibits normal stresses (Boger fluid). Experimentally measured normal stress and viscosity data are included in a simple rheological model. Flow patterns reveal the existence of vortices in the reservoir corners. Vortex size and intensity increase rapidly with elasticity level. 相似文献
7.
应用毛细管流变仪测量了在接近实际挤出工艺条件下低密度聚乙烯熔体的流变性质,应用流动可视化技术,观测了试样熔体流经突然收缩的轴对称口模时的入口收敛流型,发现,在口模入口前区的两侧存在明显的环流区,环流区长度随着挤出速率和流道收缩比的增加而增大,而随着温度的升高而减小,采用环流区长度的公式估算了实验条件下试样的环流区长度值,结果表明,预测值与实测值之间有较好的一致性。 相似文献
8.
Viscoelasticity is a characteristic of many complex fluids like polymer melts, petroleum, blood, etc. The investigation of viscoelastic flow mechanism has practical significance in both scientific and engineering field. Owing to strongly nonlinear, numerical method becomes a practical way to solve viscoelastic flow problem. In the study, the mathematical model of three-dimensional flow of viscoelastic fluids is established. The planar contraction flow as a benchmark problem for the numerical investigation of viscoelastic flow is solved by using the penalty finite element method with a decoupled algorithm. The multi-mode finitely extensible nonlinear elastic dumbbell with a Peterlin closure approximation (FENE-P) constitutive model is used to describe the viscoelastic rheological properties. The discrete elastic viscous split stress formulation in cooperating with the inconsistent streamline upwind scheme is employed to improve the computation stability. The numerical methods proposed in the study can be well used to predict complex flow patterns of viscoelastic fluids. 相似文献
9.
Theoretical solutions for unsteady flow of a three constant Oldroyd fluid and a second order fluid under several different flow conditions of practical interest are obtained. The response of these fluids to suddenly applied external force is investigated in each case. Without using the stick-slip boundary condition at the wall, it is possible to show that pressure oscillation occurs with both fluids under a certain case. 相似文献
10.
Detailed study was carried out in order to investigate flow phenomena occurring at the junction of two incoming stratified flow layers with junction angles. Various combinations of fluids with Newtonian and non‐Newtonian rheological characteristics were tested in a relatively high‐speed stratification where the inertia of flow cannot be neglected. The flow characteristics at the junctions were classified into six main flow modes, which were arranged in mode maps by use of generalized Reynolds numbers and viscous ratios. From the resultant mode maps it was found that a mutual relation of inertial and viscous effects is essential for the determination of flow modes in the stratified flows. 相似文献
11.
Transient flow behavior of an incompressible quasi-linear viscoelastic fluid under suddenly applied constant pressure as well as under a periodic pressure gradient was investigated using a three-parameter relaxation function. In the light of these solutions, the roll of viscoelastic relaxation in the overshooting of volumetric flow rate and the effect of viscoelastic parameters on the mean square velocity profile are discussed. 相似文献
12.
Tube entrance-region flow is examined by measuring the thrust of jets of liquid emerging from capillary tubes of different lengths. The liquids used are water, toluene, n-pentanol and two aqueous polyacrylamide solutions possessing viscoelastic properties. The jet thrust behavior of each liquid is compared with the behavior calculated on the assumption that the liquid is Newtonian in character. Several facts emerge (a) the water behavior is near-Newtonian. (b) for other liquids, the entry region is much more extensive than that predicted by Newtonian theory. (c) there is a striking peak in the jet thrust for intermediate values of L/D. (d) the steady state thrust levels are generally lower than those predicted by Newtonian theory. (e) for n-pentanol and the more dilute polymer solution, these reduced thrust levels are consistent with previously published normal stress data. Possible reasons for the presence of a peak in jet thrust are discussed; this may well depend on shear elasticity possessed by the liquids. If so, the controversial suggestion that simple organic liquids possess shear elasticity is supported. It is shown that, in some cases, L/D ratios in excess of 350 are required for the establishment of steady laminar flow in the tubes. 相似文献
13.
14.
The abnormally high resistance of viscoelastic fluids to sudden deformations and to stretching may be expected to cause the structure of turbulent velocity fields in these systems to differ appreciably from those of Newtonian fluids. An analysis based on these considerations is presented and supported using friction factor data for three concentrations of a water soluble polymer. Pressure losses predicted by use of this correlation are within 15% or less of the experimental values, but as all dimensionless groups which influence the results were not varied independently, the correlation developed may not be universally applicable to all fluids. Suggestions for further and more more specific analyses are made. 相似文献
15.
G. Astarita 《Chemical engineering science》1974,29(5):1273-1278
Dimensional analysis of viscoelastic flow phenomena is analyzed in general terms, and it is shown that the method can only be used for “rheologically homologous” fluids (defined rigorously in the paper). Few generally useful results can be obtained from dimensional analysis when the condition of homologousness is met by making experiments with the same fluid for which predictive equations are sought. Other ways of meeting the condition are discussed, and some results of a general nature are obtained. 相似文献
16.
The viscous flow in the filling stage of injection molding can be described in terms of an one-dimensional fully developed main flow and a complex two-dimensional flow near the advancing front, which is often termed the fountain flow. The transport characteristics in the front region of the mold flow are of increasing importance in injection process of composite materials such as resin injection molding (RIM). By using of finite element method, the simulation of non-isothermal viscous flow between two isothermal parallel plates with the generalized newtonian fluid is presented in detail. The un-folding of the fluid particles towards the mold wall directly affects transport characteristics such as the distribution of temperature, the orientation and the concentration of molecule near the front in filling stage. 相似文献
17.
The deformation of nylon drops in polyethylene, with and without an interfacial agent, in an extensional flow has been studied. The presence of an interfacial agent reduces the size of the dispersed phase, and the deformation of the drop is reduced. An analysis is given, which accurately predicts the deformation for all values of the capillary number considered. The predicted and observed shapes are, however, only in agreement at low values of capillary number. Possible causes for this discrepancy are discussed. © 1996 John Wiley & Sons, Inc. 相似文献
18.
Florian Habla Holger Marschall Olaf Hinrichsen Laura Dietsche Hrvoje Jasak Jovani L. Favero 《Chemical engineering science》2011,(22):5487
In this work a new solver is developed for the OpenFOAM® CFD toolbox, which handles viscoelastic two-phase flows. A derivative of the volume-of-fluid (VoF) methodology is used to describe the interface. Established constitutive equations derived from kinetic theory, such as Oldroyd-B, Giesekus, FENE-P and FENE-CR, from network theory of concentrated solutions and melts, such as linear and exponential Phan-Thien–Tanner (PTT), and from reptation theory, such as Pom–Pom and XPP models, as well as multi-mode formulations are implemented in OpenFOAM. Validation of the numerical technique is performed by comparing detailed simulation predictions to data from several experimental studies, numerical studies and analytical models found in the literature. Two well-known viscoelastic free-surface effects, namely the Weissenberg and the Die Swell effect, are simulated. Furthermore, transient and steady-state droplet flow in shear and elongational flows is examined. 相似文献
19.
Fusheng Pan 《Chemical engineering science》2008,63(4):1072-1080
Detailed atomistic structures of blend (class I) and chemical tethered (class II) poly vinyl alcohol (PVA)-silica hybrid membranes were constructed to investigate the diffusion behavior of small molecules at the interfacial region. Stronger interaction between PVA and silica, as well as more appropriate interfacial morphology which was evaluated by interchain distance, chain mobility and free volume were found in class II hybrid membranes due to the presence of covalent bonds. The effects of interfacial morphology on diffusion behavior of small molecules including benzene and cyclohexane were tentatively explored, and found that diffusion coefficients were closely related to fraction of free volume (FFV). Subsequently, the diffusion selectivity was calculated by the ratio of FFV probed by benzene and cyclohexane molecules. Hopefully, this study will offer some important qualitative insight into the transport phenomena within organic-inorganic hybrid membranes. 相似文献
20.
Using Laplace transformation technique, semi-analytical solutions are obtained for three basic viscoelastic fluid flow problems under the effect of the Jeffreys model. These semi-analytical solutions are not available in the literature. The present work investigates the effect of two types of driving forces on the flow behavior. These two types are the velocity-type and shear-type driving forces. The effect of the relaxation and retardation times on the flow behavior for these two types of driving forces may be viewed well using the obtained semi-analytical solutions. The three fundamental problems are transient Couette flow, transient wind-driven flow over finite domains and the transient Poiseuille flow in parallel-plates channels. It is shown that as the dimensionless relaxation time (λ1) increases, the flow response to the imposed driving force becomes slower. This implies that the flow needs more time to feel the presence of the driving force and hence needs more time to attain steady-state behavior. On the other hand, the effect of the dimensionless retardation time (λ2) depends on the type of the driving force imposed on the system. For a velocity-type driving force, the flow response becomes faster as the dimensionless retardation time (λ2) increases and for a shear-type driving force the flow response becomes slower as the dimensionless retardation time (λ2) increases. 相似文献