Numerical analysis of mixing in block‐head mixing screws

Abstract

The research reported here used 3D non‐Newtonian flow simulations to investigate the pumping and mixing capability of block‐head mixers. Block‐head mixers are distributive mixing screws that are widely used to homogenize the polymer melt and eliminate thermal gradients. The polymer‐processing industry employs a variety of block‐head mixers, with little consensus on design and distribution of screw flights and mixing blocks. This analysis addresses this issue based on a computational design study in which the influence of three geometrical parameters was examined: (1) the number of flights at a mixing block, (2) the number of blocks along the screw, and (3) the stagger angle between the blocks. To examine the flow behavior of the mixing screws, the pressure consumption and energy dissipation is evaluated. Distributive mixing is analyzed using residence time distribution functions, kinematic stretching parameters, and the scale of segregation. Dispersive mixing is assessed by means of the mixing index and the shear stress. The results of this design study increase the understanding of block‐head mixers and contribute to the design and optimization of such geometries. The findings can further be applied to mixing screws of similar geometry, including pin‐type and knob mixers. POLYM. ENG. SCI., 59:E88–E104, 2019. © 2018 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers.

A Method for the Validation of Simulated Mixing Characteristics of Two Dynamic Mixers in Single-Screw Extrusion

“…For 80 kg/h, the numbers are ~48 Watt per Kelvin and ~0.25 Watt per Kelvin. Heat conduction in the screw also was neglected by [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 34 , 35 , 36 ].…”

“…More recently, Marschik et al have undertaken a comparable analysis of different block-head mixing screws using the finite element method [ 25 ]. Pressure drop, shear heating as well as distributive and dispersive mixing are studied for different geometries, but no validation takes place.…”

“…Validation of simulation experiments on dynamic mixing elements is relatively rare. Of the 15 simulation-driven research works cited as [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], only three [ 27 , 28 , 39 ] validate their findings. When validation is done, it frequently takes the form of only comparing the simulated and real pressure drop across the entire mixer, e.g., in [ 24 , 27 ].…”

Comparative computational analysis of dispersive mixing in extension‐dominated mixers for single‐screw extruders

“…The rheological model parameters were taken from Marschik et al [38] The material is a high-density polyethylene (melt flow rate = 0.25 g/min measured at 190 C/5 kg). The parameter values for the rheological model in Equation 4 ANSYS R19.1 Polyflow software, which is based on the finite-element method, was used to solve the governing flow equations.…”

“…[ 35 ] Numerical analysis has also been performed to investigate dispersive mixing in Maddock mixers. [ 36,37 ] Marschik et al [ 38 ] numerically analyzed dispersive and distributive mixing in block‐head mixing screws. The goal of this manuscript is to utilize the MST approach in finite‐elemental modeling to compare the CRD and EME mixing sections for their dispersive mixing capabilities in SSE and rank them relatively for their overall process and dispersive mixing performance.…”