The effect of extensional viscosity on the effervescent atomization of polyacrylamide solutions

The paper contains the results of experimental investigation of the rheological characteristics and atomization process of solutions of polymer. The solutions had the polyacrylamide (PAA) mass fraction in the range from 0.0025 to 0.001. The solutions of polymer have non-Newtonian characteristics. It has been shown that shear viscosity increases with polymer concentration in the solutions. Extensional viscosity increases with increasing extensional rates. The Trouton ratio for glycerol solution is about 5.4. The Trouton ratios observed for the polymer solutions increase with increasing shear (extensional) rate and polymer concentration in solution. This paper draws a link between the extensional viscosity and the effervescent atomization. The polymer addition to cause the solution viscosity to increase, thereby different disintegration of liquid could be obtained. During two-phase atomization process of polymer solutions the characteristic stages in spray development have been observed. The phenomenon of the formation of "beads on a string" for solutions with low concentrations of polymer has been observed. The thin filament between droplets and/or bubbles was observed for all polymer solutions studied. Analysis of photos on forming the droplets showed that droplets diameter increases with increasing of polymer concentration. In all two-phase systems studied the Sauter mean diameter decreases with increase of gas to liquid flow rates ratio value. Sauter mean diameter is dependent on gas and liquid flow rates and the liquid properties. It is particularly important in processes in which the value of the average droplet diameter plays a key role. High molecular polymers added to a solvent involve the changes in the rheological properties of liquid and the disintegration of liquid jets and/or sheets. The effect of extensional viscosity on the droplets formation has been shown. The data obtained in the present study have shown that the decreasing of the extensional viscosity of the solution will reduce the spray's Sauter mean diameter. The results may be used, for example, to verify numerical models or in comparison with similar atomization processes. (C) 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.