Numerical Simulations of the Effects of Rotor Speed in Non-Isothermal Partially-Filled Rubber Mixing
Department of Mechanical Engineering, The University of Akron, Akron, OH 44325-3903
NUMERICAL SIMULATIONS OF THE EFFECTS OF ROTOR SPEED IN NON-ISOTHERMAL PARTIALLY-FILLED RUBBER MIXING
REFERENCE: Hari Poudyal1, Pashupati Dhakal, Suma R. Das and Abhilash J. Chandy2 “Numerical simulations of the effects of rotor speed in non-isothermal partially-filled rubber mixing,” submitted for presentation at the 190th Technical Meeting of the Rubber Division, ACS, Pittsburgh, PA.
Abstract: Mixing is one of the initial and critical steps for the industrial process of manufacturing tires. Mixing brings together different materials and results in a homogeneous final product, whose consistency and quality depends on various factors, such as properties of the filler materials, mixing duration, fill factor, rotor geometry, rotor speed, etc. Another important factor that must be taken into consideration is the effect of temperature, which in turn influences the viscosity and flow characteristics. High-fidelity numerical simulations can help one understand the effect of these different parameters on the mixing characteristics with relative ease, and can further optimize the manufacturing process for high throughput and better quality. While several previous studies in the literature have focused on fully filled and/or isothermal simulations, there have been none with a consideration of both partially filled and non-isothermal conditions. In this paper, three different rotor speeds (20 RPM, 40 RPM and 60 RPM) have been tested to analyze the mixing performance of two counter-rotating rotors in a partially filled (75%) internal mixer under non-isothermal conditions. The motion of the rotors in the computation is accomplished through a sliding mesh technique, and the Eulerian-based Volume of Fluid (VOF) method is employed to capture the interface between the rubber and air phase. The non-Newtonian Bird-Carreau model along with an Arrhenius formulation are used to define the shear- and temperature-dependent viscosity of rubber, and the 2D compressible Navier-Stokes equations are solved using a commercial computational fluid dynamics (CFD) software. The high viscosity of rubber leads to viscous heating, especially in the narrow clearance region that has a high shear, and this further affects the rubber viscosity and flow characteristics in a manner that is quite different compared to an isothermal mixing simulation. Material movement in the simulations at different speeds is analyzed via flow patterns and velocity vectors. In addition, particle tracking is employed to assess dispersive and distributive mixing characteristics. Specifically, statistics of maximum shear stress, mixing index, and particle pairwise distances in the form of length of stretch and cluster distribution index, are compared between the three speeds to better understand the effect of rotor speed on mixing efficiency.
Keywords: Mixing, rotor speed, VOF, compressible, non-Newtonian, viscous heating, dispersive mixing, distributive mixing
2 Corresponding Author