Comparison of Three Rotor Designs for Rubber Mixing Using Computational Fluid Dynamics
In recent years, there has been an increasing demand for efficient mixers with high-quality mixing capabilities in the rubber product industry, with the focus of producing fuel-efficient tires. Depending on the functional characteristics of the tire and thus the compounding ingredients, different types of mixers can be used for the rubber mixing process. Hence, the choice of an appropriate mixer is critical in achieving the proper distribution and dispersion of fillers in rubber and a consistent product quality, as well as the attainment of high productivity. With the availability of high-performance computing resources and high-fidelity computational fluid dynamics tools over the last two decades, understanding the flow phenomena associated with complex rotor geometries such as the two- and four-wing rotors has become feasible. The objective of this article is to compare and investigate the flow and mixing dynamics of rubber compounds in partially filled mixing chambers stirred with three types of rotors: the two-wing, four-wing A, and four-wing B rotors. As part of this effort, all the 3D simulations are carried out with a 75% fill factor and a rotor speed of 20 rpm using a computational fluid dynamics (CFD) code. Mass flow patterns, velocity vectors, particle trajectories, and other mixing statistics, such as cluster distribution index and length of stretch, are presented here. All the results showed consistently that the four-wing A rotor was superior in terms of dispersive and distributive mixing characteristics compared with the other rotors. The results also helped to understand the mixing process and material movement, thereby generating information that could potentially improve productivity and efficiency in the tire manufacturing process.ABSTRACT
Geometry of the three rotors.
Average velocity of rubber in fully filled chamber and 75% chamber with time.
Polyhedral mesh on the rotors.
Mesh on the cross-sections.
Velocity profile along x-axis at the mid–cross-section of the left half rotor for 600 K, 1.3 M, and 2 M cells.
Comparison of pressure profile obtained from Freakley and Patel's experiment at 50 rpm at the speed ratio of 1:1.125 [ 32 ] and simulation at 20 rpm even speed.
Cross-sectional planes along the (a) axial and (b) and (c) transverse directions for analysis of flow rates (using (a) and (b)) and velocity vectors (using (c)) at time t = 0.
Instantaneous velocity vectors colored by velocity magnitude for two-wing (left), four-wing A (middle), and four-wing B (right) for cross-sections at 25%, 50%, and 75% (from top to bottom) of the rotor length at 1.2 revolutions; cross-sections shown in Fig. 7c.
Instantaneous velocity vectors colored by velocity magnitude for two-wing (left), four-wing A (middle), and four-wing B (right) for cross-sections at 25%, 50%, and 75% (from top to bottom) of the rotor length at 1.67 revolutions; cross-sections shown in Fig. 7c.
Instantaneous velocity vectors of two-wing (left), four-wing A (middle), and four-wing B (right) rotor at 1.2 (top) and 1.67 revolutions (bottom), for the cross-section through both rotors along their axis.
Joint probability density of the mixing index and shear rate calculated over a period of one rotor revolution after 17 revolutions for the (a) two-wing (b) four-wing A, and (c) four-wing B rotors.
Particle distribution for two-wing (left), four-wing A (middle), and four-wing B (right) at the initial condition, and after 1, 10, and 17 revolutions (from top to bottom).
Probability distribution of particles (a) at the initial time, and after 17 revolutions for (b) two-wing, (c) four-wing A, and (d) four-wing B rotors (solid lines); also shown are the corresponding ideal distributions of particles for the three different rotors in (b), (c), and (d) (lines with symbols).
Evolution of the cluster distribution index with time.
Evolution of the mean length of stretch with time.
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