Influence of feed viscosity on the two-phase flow inside the exit orifice of an effervescent atomizer and on resulting spray characteristics

• We examine the flow pattern inside the exit orifice with an optical sensor.
• Small and spherical spray drops are formed during an annular flow in the exit orifice.
• Large and irregular spray drops result from a slug flow inside the exit orifice.
• For spray drying purposes a slug flow must be avoided at all costs.

The effervescent atomizer, originally developed for combustion applications, is reported to atomize viscous liquids into small drops at low working costs. This offers the possibility to enhance the energy efficiency of spray drying foodstuffs by the atomization of a higher concentrated feedstock. For a stable drying process a steady formation of small drops must be ensured which depends mainly on the two-phase flow inside the exit orifice. In this study, the influence of the viscosity of a food based liquid on the flow pattern inside the exit orifice was investigated by measuring the time-dependent gas phase distribution using an optical sensor. Further, the spray in the near nozzle region as well as the shape and the size of the spray drops was characterized by means of shadowgraphy. The results indicate an atomization into small and spherical drops when an annular flow is formed inside the exit orifice. In contrast, very large and deformed spray drops are present for a slug flow, which are critical for spray drying purposes.