Extent and mechanism of coalescence in rotor-stator mixer food-emulsion emulsification

• Coalescence and fragmentation rates for a 25 L rotor-stator mixer was measured.
• Coalescence rate scaling suggests a turbulent viscous collision driven process.
• Fragmentation scaling is in agreement with a turbulent viscous mechanism.
• Coalescence decreases the rate of drop size reduction by 9–17 percent.

Food-emulsions often have high volume fractions of dispersed phase and are thus expected to show coalescence during emulsification, however, food-emulsion coalescence is difficult to measure in homogenizer equipment. This study experimentally estimates the rates of fragmentation and coalescence in a high viscosity and high volume fraction model emulsion subjected to pilot-scale rotor-stator mixing in order to quantify the relative effect of coalescence and discuss the mechanism of coalescence during batch processing of high-fat emulsion foods. Rate constants of both processes are estimated using a previously suggested method relying on parameter fitting from the dynamic evolution of the total number of emulsion drops (Hounslow and Ni, 2004). The results show substantial coalescence taking place. Scaling of rates with respect to rotor tip speed suggests coalescence and fragmentation controlled by a turbulent viscous mechanism.