AN INVESTIGATION OF ELECTROSTATIC CHARGE EFFECTS WITH A COVID-19 DISINFECTANT SPRAY TO COVER A VERTICAL CYLINDER

Abstract

Surface disinfecting has become a necessity in the global effort to control the COVID-19 pandemic, and the application of disinfectant liquid to completely and uniformly cover target objects is a common goal. Spraying of these materials offers a clearly beneficial solution where the liquid is atomized into droplets that are distributed on the target surface. However, while surfaces in the direct line-of-sight may receive adequate coverage, hidden surfaces on the sides and back of an object may be shielded and receive limited or no coating. Electrostatically charged sprays have received added attention and use because, in concept, a charged droplet may be more likely to not only land on a surface through direct impingement, but also be drawn further toward hidden surfaces due to attractive charge forces. Therefore, electrostatically charged sprayers provide a uniquely beneficial method to distribute disinfectant materials, although the actual effects have received limited scientific analysis. In the present study, a commercially available electrostatic sprayer has been investigated with electrostatic spray charge off and on in order to evaluate the resulting coating completeness, uniformity, and efficiency. Detailed measurements of the spray characteristics, such as drop size, velocity, and concentration, both upstream and downstream of the target object, offer explanations for differences in the resulting coverage. While this investigation is not comprehensive, it serves to offer insight into the potential benefits of electrostatically charged disinfecting sprays as well as explanations into how those improvements are achieved. Using the present sprayer, disinfectant material, and target object, coverage was improved by 40% using charged droplets, primarily due to increased coverage on the downstream (back) side of the target cylinder, which saw zero coverage without charged droplets. Through detailed analysis, this improvement is attributed to alterations in the velocity field of the droplets just downstream of the cylinder where the charged droplets are more susceptible to following the recirculating turbulence of the entrained air flow.