Gear pumps are frequently used for the transport of high‐viscosity fluids, for instance, for the extrusion of polymers. The flow rate of this extrusion process is regularly controlled by an external gear pump. In this work, the 2D flow of a viscous fluid through such an external gear pump is studied using the finite element method. Local mesh refinement based on the respective distance between moving boundaries is essential to capture the relatively narrow clearances in the pump. The gear pump works against the pressure driven flow, therefore its performance is strongly dependent on material and processing parameters. The flow of Newtonian and shear‐thinning fluids through the external gear pump is studied for a range of processing conditions. Pump curves are obtained that display the volumetric efficiency against the Hersey number, which is defined as viscosity times rotation speed divided by pressure difference over the pump. Analysis of the residence time of the fluid in the pump, shows that vortices are present in the inflow channel causing material to remain in the pump for longer times.

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An external gear pump is a relatively simple and inexpensive pump, that is used in a variety of production systems. Numerous works have studied the external gear pump using numerical simulations; however, typically low-viscosity fluids and turbulent flow conditions are considered. Previous work of the authors focused on predicting the output fluctuation and the volumetric efficiency of an external gear pump processing high-viscosity fluids using a 2D representation. For certain conditions, backflow through all clearances could occur, resulting in a drop in volumetric efficiency. This calls for a full 3D model. Furthermore, high residence time zones are observed in the inflow channel of the pump. The 3D shape of these zones is still unknown. The aim of this work is to investigate the effect of the axial clearances on the performance of the external gear pump. A 3D mesh is generated by extruding the 2D mesh in the third direction, resulting in prism elements. This reduces the required number of elements and therewith makes the simulations computationally feasible. Introducing the axial clearances results in a lower efficiency compared to the 2D simulations. With particle tracking, the high residence time zones in the inflow channel are visualized in the 3D simulations.