Investigation on the Applicability of the Effervescent Atomizer in Spray Drying of Foods: Influence of Liquid Viscosity on Nozzle Internal Two‐Phase Flow and Spray Characteristics

Abstract

AbstractThe influence of viscosity of a food‐based model liquid on the flow patterns inside an effervescent atomizer as well as on the spray was investigated. Viscosity ranged from 0.001 to 0.308 Pa·s. The flow pattern inside the atomizer changes from annular to an unfavorable slug flow for liquids with increased viscosity with increasing liquid volume flow rate. We used the time averaged Sauter mean diameter (SMD) as well as the fluctuation κt of the time‐discrete drop size around its mean to characterize the spray. For an annular flow, small values of SMD and κt are observed regardless of viscosity; but as the flow pattern transforms to slug flow, a considerable increase of SMD and κt is observed. The results indicate that the application of the effervescent atomizing principle to the tasks of food spray drying requires a specific flow pattern inside the atomizer.Practical ApplicationThe effervescent atomizer, originally invented in the field of combustion science, is reported to be capable of atomizing liquids with elevated viscosity into small drops at low gas consumption. These attributes make the atomizing principle also interesting for other techniques such as the spray drying of foods. If an implementation is possible, the atomization technique offers the potential of drying feeds with high viscosity at low gas consumption. This, in turn, opens two new possibilities in spray drying of foods: first, to save drying energy via a higher concentrated feed and, second, to prevent heat‐sensitive ingredients from damage because a lower feed temperature prior to atomization could be chosen compared with conventional atomizers. Unfortunately, an unsteady spray is reported for certain operation conditions. In this case, an application is likely to be limited.