Secondary atomization of electrostatically charged drops
Abstract
When a drop is subjected to a surrounding dispersed phase that is moving at an initial relative velocity, aerodynamic forces may cause it to deform and fragment. This is referred to as secondary atomization and has been studied for nearly 100 years. ^ In electrostatic atomization a charge is applied to the fluid to be atomized. The repulsive effects of the charged particles act against the restorative forces of surface tension, and the likelihood of breakup is expected to increase. Despite its many practical applications, no experimentalists have considered secondary atomization of charged drops. ^ This work begins with a thorough review of the secondary atomization of uncharged drops. Experimental methods, breakup morphology, breakup times, fragment size and velocity distributions, and modeling efforts are reviewed and discussed. Focus is placed on experimental and numerical results which clarify the physical processes that lead to breakup. From this, a consistent theory is presented which explains the observed behavior. It is concluded that viscous shear plays little role in the breakup of liquid drops in a gaseous environment. This is followed by a short discussion of the very limited data available for charged drops. ^ Following this a new theoretical consideration of the secondary atomization of charged drops is presented. The initial deformation phase is considered in which the drop shape is approximated as an oblate spheroid. Both highly conductive and non-conductive drops are modeled. Contrary to initial intuition, the results indicate that deformation due to aerodynamic forces is opposed by electrostatic stresses. Consequently, secondary atomization is not likely to be enhanced by the addition of charge to a drop. ^ Finally experimental results are presented which were obtained from a new experimental apparatus created for this investigation. The results indicate that charge has a minimal effect on the breakup morphology, initiation time, and total breakup time, confirming the theoretical predictions.^
Degree
Ph.D.
Advisors
Paul E. Sojka, Purdue University.
Subject Area
Engineering, Mechanical
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