Unstable flow of amorphous polymers through capillaries I. Velocity profiles of polymer having discontinuous flow curve

Ciné film was employed for recording the movement of tracer particles, thus directly determining the velocity profile in the capillary flow of model materials of polybutadiene over a range of shear stresses relating to (1.) flow conditions in which there is no distortion of the regular stream of melt emerging from a capillary, (2.) severe surface fracture, (3.) elastic turbulence, (4.) oscillatory flow of melts with discontinuous flow curves. No qualitative difference was found between the velocity profiles in conditions (1) and (2); surface fracture is not related to laminar flow disturbances and originates at the capillary exit. Surface fracture must be distinguished from elastic turbulence. The streamline velocities undergo both local and time variations within the capillary under conditions of developed elastic turbulence; the wall velocity is non-zero. A periodic pulsation of velocities occurs in the flow curve discontinuity region; it takes place throughout the capillary and is caused by stick-slipping of polymer on the capillary wall. The frequency of velocity pulsations coincides with the frequency of extrudate variations.     

变径毛细管流量关联式开发

变径毛细管是一种用于家用热泵的低成本节流装置,其非对称结构可以实现正反两个流向的流量不同,从而可以满足热泵系统制冷和制热所需的流量。为了实现变径毛细管工程设计,开发了变径毛细管流量的关联式。通过构建变径毛细管等效管径和等效管长计算公式并代入等径毛细管关联式,得到了变径毛细管流量的关联式的公式形式;通过数值计算模型产生用于拟合关联式系数的数据源。开发的变径毛细管流量关联式可计算变径毛细管正向和反向的制冷剂流量以及传统的等径毛细管的流量。开发关联式能很好地预测变径毛细管在不同工况下制冷剂流量的变化趋势,预测93%实验数据点的精度在10%以内。     

Hydrodynamics of slug flow inside capillaries

Understanding the motion of long gas bubbles (gas slugs) inside capillaries is a challenging problem that is relevant in many processes of chemical and biological interests. It has been proved by many workers that such long gas bubbles can be used successfully in enhancing mass and heat transfer in many chemical and biological processes. In order to quantify and understand this enhancement a light was shed on the hydrodynamics of such a flow pattern. The volume of fluid method implemented in the commercial CFD package, Fluent, is used for this numerical study. Velocity and bubble profile were obtained as functions of capillary number. Computed values of the bubble velocity and diameter were in excellent agreement with published experimental measurements. The detailed velocity field around the bubble was also computed and compared favourably with those experimental results reported in literature.     

Hydrodynamics of Taylor flow in noncircular capillaries

In this work, volume of fluid (VOF) technique, one computational fluid dynamics (CFD) method, was used to investigate the upward Taylor flow in vertical square and equi-triangular capillaries. For saving computation time, the simulations were carried out in a moving frame of reference attached to Taylor bubbles. The main flow parameters, involving bubble size and shape, liquid film thickness, velocity field and two-phase relative velocity, were studied as functions of capillary number. The numerical simulations were in good agreement with previous reports and showed that the flow in the sides and corners of polygonal capillaries were different. A comparative study was also conducted on Taylor flow in square and equi-triangular capillaries and their circular counterparts, where the influence of capillary geometry on the characteristics of Taylor flow was illustrated clearly.     

Acoustic initiation of powder flow in capillaries

Second generation solid freeforming devices will have the capability to render both shape and the spatial arrangement of composition directly from a computer file. In order to build three-dimensional functional gradients in selective laser sintering it is necessary to have a computer-controlled mixing and dispensing system. We report such a system based on the horizontal acoustic vibration of vertical capillary tubes that provides both switching and flow rate control. An orchestra of such tubes can be constructed to deposit a multi-component system onto a building platform. Our concern is the initiation of flow. It requires an “attack” waveform to break the domes that provide flow arrest and release the potential energy of powder above the dome. The intensity of attack also influences the mass that flows out before a new dome forms, i.e., the response time of the valve. Neither the extension to vibration caused by ringing nor the wave amplitude account for the over-run of the valve. Much better correlation is obtained with acceleration and with calculated kinetic energy of horizontally vibrating particles.     

卷径变化中的速度控制

介绍了一种自动卷径测厚系统，包括电气配置，激光传感器设定，变频器设定，以及模数模块、数模模块的设定。给出了一部分程序梯形图及控制接线图。     

Compressible flow in permeable capillaries under deformation

An improved pressure loss model for viscous compressible flow through a long, permeable, polymeric capillary, a relevant problem in capillary gas permeator design, has been developed and confirmed experimentally. Experimental verification was obtained by measuring pressure losses over a silicone rubber capillary at various flow rates and applied inlet pressures using carbon dioxide, helium, oxygen and nitrogen. In particular, a first-order approximation to the axial pressure gradient for compressible flow in a permeable capillary has been formulated. Radial and axial displacement of the capillary have also been incorporated into the model for small deformations.     

Gas separation by diffusion through silicone rubber capillaries

A study of pressure drop and separation of binary gas mixtures was conducted for gaseous diffusion cells, which consist of a bundle of silicone rubber capillary tubing. The Poiseuille equation, coupled together with the permeation equation, was used to describe the flow behavior of pure gases through the tubes. A successful correlation of pressure loss data for pure gases enabled us to model the flow of binary mixtures. Agreements were quite good between theoretical and experimental pressure losses for both pure gases and mixtures.Cascades of two and three stages were constructed out of several diffusion cells and separation experiments were carried out on these cascades. A comparison of theoretical and experimental cascade data is presented.     

On the slip phenomenon of polymeric solutions through capillaries

The slip phenomenon through capillaries has been analyzed experimentally using solutions of polyacrylamide and xanthan gum. These polymeric solutions present macromolecules with different conformations in flow. Attention was given to the influence of molecular conformation of those polymeric solutions upon the slip velocity. Considerable variations on the slip velocity were observed when the ionic strength of the xanthan solution was increased and also when the material of the capillaries was changed. Measured magnitudes were much larger in the xanthan solutions than those observed in the polyacrylamide solution.     

Multicomponent isothermal diffusion and forced flow of gases in capillaries

Isothermal transport is described of a multicomponent gas mixture in a capillary. The governing equation (eqn 24) derived in the paper accounts for sim and pressure. The equation applies to the transition region between the Knudsen diffusion and the region of continuum and provides also for the slip on equations for the H₂C₂H₂, H₂C₂H₂C₂H₄ and H₂N₂NH₃ mixtures indicates give rise to a pressure gradient representing the driving force for additional transport. Notions of a critical component and diffusion-stoichiometric     

Simulation of the slug flow of a gas-liquid system in capillaries

A mathematical model for the gas-liquid slug flow in a capillary is developed. The velocity profiles in the bubble, film, and interbubble liquid are calculated. The calculated results are in good agreement with the experimental data of other researchers. The experimentally found bifurcational behavior of the slip velocity of bubbles relative to the two-phase mixture reported in the literature is described and supported by the theory. The reasons for which the bubble can stop in a small-diameter dead-end capillary are discussed.     

Flow of viscoelastic polymer systems through round capillaries. Kinematic analysis

The effect of elasticity on the kinematic and deformation characteristics of flow of a viscoelastic polymer system through a capillary was examined. It was shown that the difference in elasticity over the radius of the capillary that arises during flow through the capillary is the cause of radial inhomogeneity in the fibre obtained to a great degree. Flow of an exponential fluid was examined. It was shown that there is no exponential fluid as such in nature, but it is the result of approximate solution of the equation of state for a viscoelastic polymer system. The value of this approximation was determined. __________ Translated from Khimicheskie Volokna, No. 3, pp. 26–30, May–June, 2006.     

变速、变螺距、变直径螺旋给料机的开发与设计

1.引言 螺旋输送机以其结构简单、工作可靠、造价比较低廉,对环境污染小等特点,被广泛地应用于粮食、建材、化工等行业。但螺旋输送机在连续输送时仅能保证物料的输送量和给料速度,当需要间断给料或给料精度要求比较高,特别是向称量设备给料时,螺旋输送机就不能满足要求。为此,我们在螺旋输送机的基础上开发设计了螺旋给料机。 螺旋给料机可以说是螺旋输送机的变型,通过螺旋给料机转速的变化和在同一台螺旋给料机上采用变化的螺旋螺距和直径,使螺旋给料机不仅能保证所要求的输送量和给料速度,而且还能使物料给料量实现较高的计量精…     

Polymer degradation in porous media flow

The hydrodynamic degradation of high molecular weight poly(acrylamide-co-Na acrylate) in 1M NaCl in porous media flow was studied as a function of polymer concentration in the dilute and semidilute concentration ranges. Porous media rheometry was used to monitor molecular weight changes due to chain scission. At equivalent superficial velocities of flow through a glass bead pack, polymers at dilute concentrations showed greater loss of molecular weight than polymers at semidilute concentrations.     

An experimental study of slip flow in capillaries and semihyperbolically converging dies

Slip velocity is measured in straight‐walled capillary dies and semihyperbolically converging dies (SHCDs) in three industrial polymer melts, with and without the presence of a viscosity reducing stearic acid (SA) additive. Data taken in shear flow through capillary dies indicated a substantial increase in the slip velocity caused by the addition of the SA. Data taken in the SHCDs showed much less of an increase in the slip velocity of the polymer/additive system relevant to the neat polymer. One possible explanation of this observation is that the magnitude of the slip velocity is directly related to the degree of orientation within the flowing polymeric material. POLYM. ENG. SCI., 47:159–167, 2007. © 2007 Society of Plastics Engineers