Pet food for cats and dogs is typically manufactured in full production chains. Initially, the raw mass is pumped into an extruder. Through an extrusion die, the mass is pressed out into separate strands. These strands are transported via a conveyor belt through a hot-air oven. After being cooked, the strands are automatically cut into individual pieces and packaged into cans and pouches.
The critical phase of the process is the extrusion. Despite the high static pressure within the extruder and the die, it must be guaranteed that the product is not damaged. Furthermore, the individual strands must exhibit exact consistency in quality and mass flow. Meeting these two requirements is particularly challenging because a wide spectrum of different products with entirely different densities and viscosities must be processed by a single machine. These product properties (density and viscosity) have a strong influence on the flow of the product through the extruder.
To obtain more information about the distribution of the raw mass flow rates during the design phase of a new machine, FlowMotion was commissioned to provide their fluid mechanics expertise. Since measurements inside the extruder are difficult to conduct, computational fluid dynamics (CFD) simulations were employed to investigate the internal flow processes for various extrusion concepts.
Due to the variety of products with highly diverse compositions, the material properties necessary for the simulation—such as density and viscosity—are normally unknown. Consequently, it was necessary to develop an ‘artificial fluid’ based on pressure and mass flow measurements that could represent the real products. By varying the density and viscosity of the ‘artificial fluid’, the operational range of the extruder could be determined. Additionally, the simulations provided new ideas for developing further improved production systems in the future.
