Pressure distribution at impeller blades of some radial flow impellers in saccharose and xanthan gum solutions: a CFD visualization approach

Food-mixing operations often require distribution of components, e.g. sweeteners and thickeners, in various liquids, e.g. syrups or pulps. Generation of homogeneous texture and composition depends strongly on drag distribution at the impeller blades. In view of the fact that the substantial part of impeller power draw is due to pressure drag, pressure distribution across blades is a measure for impeller performance in food-blending operations. The study objective has been to reveal the pressure distribution profiles in the vicinity of some typical blades employed in blending operations and fermentation. Three typical radial flow impellers, namely, the conventional flat-blade disc turbine, an impeller with half-pipe cylindrical blades and an impeller with half-pipe parabolic blades, are studied. In order to gain more information, a CFD visualization has been employed for the analysis. The CFD analysis included RANS modelling and an MRF solving method. As a result, the pressure field in three typical liquids - water, a 64% saccharose solution and a 0.5% hetero-polysaccharide (xanthan gum) solutions - has been elucidated. The effects of blade design and fluid physical properties are discussed and interpreted in terms of power draw for mixing operations.