Relationship between the Dispersed Droplet Diameter and the Mean Power Input for Emulsification in Three Different Types of Motionless Mixers

Abstract

Continuous emulsification of low-viscosity liquids was investigated with three different types of motionless mixers, i.e., needle jetting mixer (NJM), Kenics Static Mixer® (KSM) and Ramond Supermixer® (RSM). Kerosene and n-heptane were used as the continuous phase, in which nonionic surfactant (Span80) was dissolved, and deionized water as the dispersed phase. All emulsification runs were carried out at the constant temperature of 303 K. The dispersed droplet diameters in the W/O emulsion were measured by means of microphotography. The size distributions of water droplets in emulsions were normalized by the Sauter mean diameter (d32), and then they obeyed a log–normal distribution function with an upper-limit. The ratio of the maximum droplet diameter (dmax) to d32 was estimated to be 2.30 for NJM and KSM and 1.86 for RSM, respectively. The correlations of d32 with the mean power input per unit mass of the media (PM) were derived. The slopes of the correlation lines on the d32–PM correlation chart took the almost same value of –0.4. This value agreed with the one derived from an isotropic turbulence law in low-viscosity liquids. The line for RSM was located below those for NJM and KSM.