Flow process conditions to control the void fraction of food foams in static mixers

Previous studies have shown the feasibility of food foam production in a SMX10 static mixer. Nevertheless the void fraction, α, obtained was high (>0.85) compared to the target range in food industry (0.5-0.7). This work aims to reduce α by using a smaller hydraulic diameter of the static mixer (SMX+6) and higher liquid base viscosities. The hydrodynamic study exhibits slight differences in the pressure drop and process shear constants. The foams are processed with a liquid base of whey protein isolates (3%) and xanthan gum (0.35% or 0.6%). The boundaries between “slug flow” and “bubble flow” are determined for the two SMX and represented in a flow pattern map. Only the latter flow regime is suitable as α (0.73-0.96) can directly be controlled from the flow-rates. Working with a SMX+6 mm offers a substantial enlargement of the convenient velocity range that allows attaining lower void fractions compared to the SMX10.