Co-rotating twin-screw extruders: Detailed analysis of conveying elements based on smoothed particle hydrodynamics. Part 1: Hydrodynamics

Abstract

We applied SPH to study the flow in a co-rotating twin-screw extruder. A new model which accounts for the flow in unresolved clearances was presented. We showed detailed results for pressure drop, flow rate and power consumption. We achieved excellent agreement with CFD data for the completely filled state. Detailed results for the partially filled state are included. a b s t r a c tDue to the complex geometry of the rotating screws and, typically, free surface flows in partially filled screw sections, first principles simulations of the flow in co-rotating intermeshing twin-screw extruders using the well-established, mesh-based CFD (computational fluid dynamics) approaches are highly challenging. These issues can be resolved via the smoothed particle hydrodynamics (SPH) method thanks to its meshless nature and the inherent capability to simulate free surface flows. In our previous work, we developed a novel method for modeling the boundary conditions with complex wall geometries, under which SPH could be efficiently applied to complex surfaces of typical screw geometries of extruders. In this work, we employed SPH and our boundary method to study the flow in a conveying element in detail. To address unresolved clearances, we developed a new model that is coupled to SPH and can correctly account for the flow through unresolved clearances. A validation of our approach using CFD data from the literature for a completely filled conveying element indicated excellent agreement. Consequently, we studied the flow in a partially filled conveying element and obtained results for the flow rate, the power input and the axial force with variable filling ratio. A detailed analysis of the corresponding mixing phenomena is presented in Part 2. Our results show that the proposed method is a comprehensive approach to study the flow in different types of screw elements in detail, providing an excellent basis for further development of simplified models of entire extrusion processes.

Distributive mixing in a corotating twin screw channel using Lagrangian particle calculations

“…[32] Eitzlmayr et al [33][34][35][36] proposed a new approach to adapt to complex boundary conditions by introducing the polynomial fit method. The smooth particle hydrodynamics (SPH) method, which is mesh-free, was successfully developed to simulate partially filled conditions in corotating twin extruders using boundary particles and ghost particles to model the boundary conditions.…”

The Future of Pharmaceutical Manufacturing Sciences

“…With this grid‐free method complex free‐surface flows can be captured. A recent example is the simulation of the complex flow in a co‐rotating twin‐screw hot‐melt extruder for pharmaceutical applications (a snapshot is shown in Fig. ).…”

An Overview of Pharmaceutical Manufacturing for Solid Dosage Forms

“…A novel approach based on advanced fluid dynamical simulations via Smoothed Particle Hydrodynamics (SPH) is presented in refs. [147,148]. Figure 16 shows a snapshot of an SPH simulation of a typical screw elements used in co-rotating twin-screw extruders, involving completely filled and partially filled regions.…”