The Method And Principle Of Regulating The Ratio Of Extensional-Shear Flow Between Eccentric Cylinders

The melt flow in polymer processing is a mixture of shear flow and extensional flow. The strength and ratio of both flows exert significant influence on the micro structure(i.e. the orientation of macromolecule, the dispersion state) which affects the macro properties of the end products(i.e. size, shape, mechanical properties). Most of the traditional rheometry methods are based on simple shear flow and extensional flow, therefore, the rheological properties obtained can only reflect the rheological properties of the melt in simple shear or extensional flow. The development of extensional-shear controllable rheometer and the application of the equipment in the research of mixture flow would contribute to a new characterization method for the rheological behavior in mixture flow. This is of great scientific value to the investigation on the essence of rheology and is of practical significance to the development of polymer processing technique.Development of a precise and widely applicable rheometer is demanding and challenging which involves precise machinery, automation controlling and mathematical modeling. Given this, it is essential to investigate the main flow of this novel equipment which helps the designers to better understand the characteristics and behavior of the main flow field, and provide data support and reference to the design and development of extensional-shear controllable rheometry equipment. In this work the viscous and viscoelastic flows between eccentric cylinders are investigated in a numerical way, which includes the distribution of velocity, deformation rate, pressure and stress in the flow field. It is observed that in the sector near the minimum gap, there is prominent acceleration in the upstream and deceleration in the downstream of the minimum gap which indicates that the melt experiences prominent extensional flow in the sector; The stress field is sensitive to the elasticity while the elasticity makes no difference on velocity field and strain field which implies that feasibility of developing a strain rheometer based on flow between eccentric cylinders; the eccentricity between inner cylinder and outer cylinder would lead to pressure variation in the azimuthal direction while the elasticity of the fluid would lead to the pressure variation in the radial direction and vortex growth. We further investigate the effects of rotating speed, eccentricity and radium ratio on the flow between eccentric cylinders and the main findings are listed below:(1)The strengths of shear flow and extensional flow are adjustable by changing the rotating speed, eccentricity and radium ratio.(2)The ratio of extensional flow in the mixture flow could be increased when increasing the eccentricity; the ratio of shear flow in the mixture flow could be increased when increasing the radium ratio.(3)The formulation mechanism of vortex near the maximum gap is discussed and the effects of process parameter and geometrical parameters on the vortex. This helps to avoid the influence of vortex on measuring field and improves the precision of the objective equipment and the later rheological test.(4)When the radium ratio of extensional-shear controllable rheometer is no less than 0.7, the pressure distribution in the flow field is similar to that in planar contraction flow, therefore, the converging flow theory could be applied to analyze the rheological behaviors in the flow between eccentric cylinders.