Computational fluid dynamics and scaling study on ultrasonic pulsation atomizer for waterborne paint

We conducted computational fluid dynamic simulations to improve the currently available inkjet technology. This study was motivated by the general problems related to lack of precision control over the quality of droplets emanated from the industrial atomizer sprayers and growing needs for higher quality droplets in the coating industry. We focused on an ultrasonic pulsation atomizer (UPA) capable of producing monodispersed droplets operating with waterborne (WB) paint as the working liquid. The volume-of-fluids multiphase model was applied to investigate the process of droplet generation under the effects of different factors on the quality of the droplets. Droplets were generated using various novel input waveforms induced on the working liquid in the atomizer incorporating a piezo sensor. Scaling analysis is used to relate the results of the numerical simulations to larger scale inkjet nozzles being used in industries. Our numerical study specifically examined effects of various parameters including inlet liquid and airflow rates, type of the waveform, frequency of pulsation, viscosity of the working liquid on the quality of the droplets, transfer efficiency, and optimum working conditions. As a result, the UPA design was found to be capable of producing monodisperse droplets operating under favorable conditions, even without implementing pulsation. Our new design showed excellent capabilities for using even higher viscosity fluids, viscosities in the rage of WB paint used in coating industries, and producing droplets of acceptable size. With this new design, if the conditions are met, we should be able to control the droplet size and frequency of their generation.