Characterization of sprays generated by the expansion of emulsions with liquid carbon dioxide

Abstract

Expanding emulsions with liquid CO2 facilitates the creation of aerosols with an average droplet diameter in the low micrometer size range, which is challenging with conventional atomizers. The droplet formation process of the expansion of high-pressure emulsions was investigated using a plain-orifice atomizer and different swirl nozzles. The local droplet size and droplet velocities were measured and used to estimate the local Weber number and thus infer the droplet size reduction. Measurements of the local mass concentration in the aerosol showed that, for the swirl nozzle, the highest concentration was found outside of the central axis, indicating radial momentum generated by the swirl nozzle. Furthermore, it was shown that the type of expansion nozzle used has an influence on the resulting median droplet size in the aerosol. For a water mass load of 0.01, the median droplet diameter was reduced from 8 to 3 μm by increasing the swirl number from 0.01 to 0.1.