Standard Methods for Evaluating Electrostatic Spray Charge and Deposition of Conductive Liquids Used for Surface Disinfection

This work presents methods to quantify droplet charge and deposition of diverse types of electrostatic spray systems when used with highly conductive liquids such as disinfectants. Three types of spray-charge measurement methods are described where current drawn from the droplet cloud was measured by: ionizing probe; direct impingement of spray onto a conductive plate; and spray directed into an isolated tunnel comprised of a series of conductive impaction screens. The latter method was refined for long-duration spray current measurements necessary for evaluating spray charging consistency with highly conductive liquids, including disinfectants. Additionally, a spray-deposition evaluation method is described which utilizes an ungrounded target array sprayed with an inert, insoluble fluorescent tracer incorporated into the water-based disinfectant or a concentration of salt water that matches the conductivity of disinfectant. Using the fluorometric method, the mass transfer onto target coupons placed on each of the four sides of square wood posts was quantified to evaluate the ability of an electrostatic sprayer to deposit droplets onto the sides and backsides of target surfaces. Several commercial models of electrostatic sprayers based upon fundamentally different principles of atomization and droplet charging (e.g., air-atomizing induction-charging and hydraulic-atomizing conduction-charging) were evaluated for spray charge, spray deposition, and performance consistency using the described methods with liquids of high electrical conductivity. Air-atomizing induction-charging (AAIC) electrostatic spray systems exhibiting charge-to-mass levels above 1 mC/kg achieved significant spray deposition improvements to target surfaces out of the direct line-of-sight compared to uncharged spray and spray devices exhibiting low droplet charge.