The 3-D optimization of an axial mixer propeller through high fidelity simulations

Abstract

Homogeneous mixing is an important process quality indicator in biogas fermenters for introducing fresh organic feed material to certain bacteria groups such as methanogenic bacteria for anaerobic digestion. Energy consumption for mixing processes is one of the highest operational costs in biogas plants. Thus, it is crucial to carefully consider the energy expenditure per generated thrust (the first performance metric of an axial mixer) for a biogas mixer, since biogas plants are considered as a net carbon zero energy plant. There are several different types of mixers. Axial mixers both high speed and low speed together with paddle mixers are most common among various types of mixers used in fermenter tanks. In this study it is planned to improve conventional axial biogas mixer efficiency using computer aided engineering tools for design and optimization. This goal will be achieved by using a parametric design strategy for blade geometry together with the open source CFD analysis suite OpenFOAM for measuring performance metrics (i.e. power, torque, and thrust). The most efficient design will be chosen from a set of design candidates residing inside a reasonably large parametric state space, via maximizing the thrust to power ratio.