1. Sutherland, J.J., Sojka, P.E., and Plesniak, M.W., "Entrainment by Ligament-Controlled Effervescent Atomizer-Produced Sprays," International Journal of Multiphase Flow, Vol. 23, No. 5, pp. 865-884, 1997.

2. Sutherland, J.J., Sojka, P.E., and Plesniak, M.W., "Ligament-Controlled Effervescent Atomization," Atomization and Sprays, Vol. 7, No. 4, pp. 383-406, 1997.

3. Panchagnula, M.V., Sojka, P.E., and Santangelo, P.J., "On the Three-dimensional Instability of a Swirling Annular Inviscid Liquid Sheet Subject to Unequal Gas Velocities," Physics of Fluids, Vol. 8, No. 12, pp. 3300-3312, 1996.

4. Luong, J.T.K. and Sojka, P.E., "Unsteadiness in Effervescent Sprays," Atomization and Sprays (accepted).

5. Sovani, S.D., Sivathanu, Y.R., and Sojka, P.E., "Predictions of Drop Size Distributions From First Principles: The Influence of Fluctuations in Relative Velocity and Liquid Physical Properties," Atomization and Sprays (accepted).

6. Schmidt, U.T. and Sojka, P.E., "Air-Assist Pressure-Swirl Atomization," Atomization and Sprays (accepted).

7. Lund, M.T., Jian, C.Q., Sojka, P.E., Gore* J.P., and Panchagnula. M.V., "The Influence of Atomizing Gas Molecular Weight on Low Mass Flow Rate Effervescent Atomization," ASME Journal of Fluids Engineering (December 1998).

Current coatings related research interests are focused in four areas: development of analytical tools to predict drop size distributions, development of design models to predict atomizer performance, the influence of coating physical properties on spray drop size, and improvements in transfer efficiency.

Drop size distributions play a key role in both finishing quality and process emissions level. On the one hand, a substantial number of large drops will lead to runs and, hence, unacceptable finish quality. On the other hand, a substantial number of small drops will lead to unacceptable levels of overspray and, consequently, increased solvent and particulate emissions because of poor transfer efficiency. The number of large and small drops are related to the drop size distribution, with wide drop size distributions being undesirable.

We are the only group in the US developing analytical tools to predict drop size distributions, including their widths. Our overall goal is to explain how nozzle operating conditions (coating feed rate and the quantity of atomizing and/or shaping air), nozzle internal geometry (the shape, roughness, and size of atomizer internal passages), and coating physical properties (viscoelasticity, surface tension, and density) control the width of the drop size distribution. Recent work indicates fluctuations in coating composition that lead to variations in the surface tension, density and Newtonian shear viscosity have little impact on the width of the drop size distribution. An increase in velocity fluctuations, i.e. higher turbulence, can have a substantial impact on drop size distribution width. Composition fluctuation induced variations in coating viscoelasticity may also play a key role.

An accurate prediction of how atomizer performance changes as coatings shift to low VOC versions can only be obtained if engineers have design models for performance prediction. Our group has developed such models for over five years, focusing early efforts on effervescent atomizers and, more recently, developing models for pressure-swirl and electrostatic units. Our overall goal is to predict how variations in nozzle geometry, operating conditions, and coating physical properties are inter-related, and how all three control spray mean drop size. Such information enhances our understanding of how atomizer performance relates to finish quality and spray emissions.

A variety of fluid physical properties influence atomizer performance. They include density and surface tension, plus various types of "viscosity." Our early work shows surface tension and density play minor roles, as does the "conventional", or Newtonian, shear viscosity. That same work indicated that visco-elasticity is dominant. We are currently continuing our investigation of how viscoelasticity influences spray drop size. Our overall goal is to provide guidance to coatings formulators so as to optimize spray performance.

Finally, transfer efficiency improvement will reduce both VOC solvent and particulate emissions. These reductions occur because an increase in transfer efficiency results in a higher fraction of the coating exiting the dispenser ultimately being deposited on the target. Since less coating is used less VOC solvent is released. Since overspray is reduced, post-process particulate removal is lessened.

Because transfer efficiency is related to both coating particle size and local turbulence levels, it can be increased by controlling either quantity. Work in our laboratory is aimed at modifying the flowfield produced by the atomizer, which in turn controls turbulence levels near the target surface and the probability of drop deposition.

Purdue
HomePage

General
Information

Engineering
HomePage

Computing
Network

Topic
HomePage