Effervescent atomization of viscous liquids

Abstract

The study of high viscosity liquid atomization is of interest especially in agricultural food processing and pharmaceutical industries, where the viscosity of the liquid increases with an increase in the dry matter content. Effervescent atomizer is one kind of twin-fluid atomizer used for effective atomization of high viscosity liquids. The present study focuses on correlating internal two-phase flow characteristics of an effervescent atomizer with the external spray characteristics. Spray structure images covering a distance of 80 mm downstream of the exit orifice, and images of the entire two-phase flow mixing region were captured by diffuse backlit imaging using a high-speed camera. The spray cone angle was estimated at different gas-to-liquid ratios (GLRs), when operated at a liquid injection pressure of 0.5±0.01 MPa. Spray unsteadiness was studied by estimating the variation in the moving average of the spray cone angle (taken over 50 images). The study shows that the internal two-phase flow governs the external spray characteristics in effervescent atomization. Annular flow regime formed at higher GLRs gives a stable spray while slug flow regimes formed at reduced GLRs leads to a larger variation in spray structure. Though the bubbly flow regime for higher viscosity liquid shows smaller variation in spray cone angle, the atomization was observed to be inferior with an intact liquid jet.