Effect of Atomizer Geometry and Rheological Properties on Effervescent Atomization of Aqueous Polyvinylpyrrolidone Solutions

The investigated effervescent atomizer is a special type of internal mixing pneumatic atomizer with a significantly reduced atomization gas consumption compared to conventional external mixing pneumatic atomizers. First the concentration influence of aqueous polyvinylpyrrolidone (PVP) solutions of concentrations from 15 to 45 % on the spray drop size distribution was investigated. As a significant increase in Sauter mean diameter and distribution width was only observed for concentrations above 40 % a change in breakup mechanism is assumed. This assumption is supported by the fact that also the improved model of Lund failed in the prediction of drop size at these concentrations. An essential challenge is the large width of the spray drop size distribution which is assumed to be connected to the spray pulsation. Therefore, the influence of nozzle orifice elongation and gas injection hole diameter reduction were investigated. Both depict no significant influence on Sauter mean diameter itself but reduced the standard deviation of Sauter mean diameter and the standard deviation of the distribution width enhancing thus the reproducibility of the spray characteristics. Also, reduction of the gas injection hole diameter reduced slightly the width of the distribution itself. The pulsation frequency of the spray was measured by high frequency laser diffraction spectroscopy. Nozzle orifice elongation and gas injection hole diameter reduction increased both the pulsation frequency as well as an increasing air-liquid mass ratio. The actual impact of the pulsation on the drop size distribution was not investigated in this work but will be future subject