At-Line Characterization of droplet size distributions using a simple, voltage-based sensor for continuous production of dense oil in water emulsions

There is a growing need for real-time characterization of droplet size distribution (DSD) for the continuously produced emulsions. In this study, we developed an at-line DSD characterization method using a turbidity-based soft sensor and demonstrated its application for continuously generated oil in water emulsions using a vortex-based hydrodynamic cavitation device. The concept of using an off-line turbidity meter and an ANN-based soft sensor for estimating DSD was recently demonstrated in our previous study. In this study, we further developed this concept for real-time characterization of DSD using an inexpensive, at-line turbidity meter providing an output in terms of voltage. Combined with the previously developed ANN-based soft sensor, the at-line voltage measurements were shown to be useful for the estimation of DSD and characteristic diameters. The emulsions of rapeseed oil (RO) in water with oil volume fractions of 0.15, 0.30, and 0.45 were produced in a continuous mode. Vortex-based cavitation device was used in a loop configuration with a key operating parameter being the ratio of the circulating flow rate through the loop (Q) and the net flow rate of emulsion (qnet). The influence of the Q/qnet ratio and volume fraction of oil on DSD, Sauter mean diameter (d32), other characteristic diameters, and droplet breakage efficiency (η) was investigated. The at-line turbidity measurements and ANN-based soft sensor were able to estimate the Sauter mean diameter within ±10% for oil volume fraction up to 0.45 and Q/qnet ratio up to 100. The developed methodology and results will be very useful for realizing decentralized and continuous emulsion production with at-line DSD measurements.