Effects of flow constriction on foamed viscous shear-thinning fluids downstream of a continuous multi rotor-stator foaming device

Foam flow through processing equipment can seriously affect the structure of the foam and its quality attributes. In the design of a foam formulation and its flow system, it is therefore important to consider the possible implications on the end-of-pipe structure of the foam to ensure preservation of product quality. We study the flow through a straight pipe with and without the presence of a narrow orifice plate and, hence, the dynamic stability of wet food relevant foams of fine texture and high static stability generated from complex formulations of viscous shear-thinning fluids in a continuous multi rotor-stator device. The effects of fluid formulation, gas-liquid ratio, rotor speed and constriction aperture size are investigated. Constricted foam flow can cause important transformations in the foam due to significant bubble coalescence and loss of air volume resulting in much coarser and much less stable foam. Increased surfactant content, liquid viscosity and rotor speed reduce bubble coalescence and help preserve foam structure.