Numerical Analysis of Rotational Speed Impact on Mixing Process in a Horizontal Twin-Shaft Paddle Batch Mixer with Non-Newtonian Fluid

Nowadays, the priority of food industry processes is based on mixing of the various flavour pastes with the air. Optimal mixing process in the results means the instantaneous preparation of the homogenous and easily spreadable paste while consuming the lowest power. For achieving the brand precise and repeatable flavour, of major importance are, beside the filling parameters, the mixing setup parameters. This work presents the influence of rotation velocity, as one of the setup data, on: the paste quality and the mixing index, obtained by the CFD. The paste was prepared of soy flour and water, and described by the experimentally determined rheological characteristics. Mixing vessel, of the twin-shaft paddle type, introduced mixing by the laminar shear-thinning. This mixing process was modelled through 3D fully transient numerical simulations employing the volume of fluid (VOF) multiphase model of the Eulerian-Eulerian approach. In two cases, the influence of the angular velocity to the mixing-index value can be neglected. At the mixing area two regions were marked off. First one and dominant, was the region of active mixing preoccupied with high shear flow, described with high mixing index. Opposite, in the passive mixing region, the flow was almost rotational, represented by low mixing indexes. The rotation velocity change made the significant influence to wall shear stress levels achieving the highest values at the tips of the paddles.