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

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.