Visualization and Collection of Overspray from Airless Spray Painting

Spray painting generates serious airborne pollution through “overspray”, the fraction (typically 50% or more) of the paint which fails to reach its target. This paper examines the phenomenology of “airless” spray painting by flow visualization, and shows how the knowledge thus gained can be used to capture the overspray efficiently near its source. Results show that the airless spray painting process combines the fluid-dynamic phenomena of wavy-sheet breakup, spray entrainment, spray impingement, inertial droplet impaction, and the turbulent wall jet. In view of this, the paper considers how the overspray-containing wall jet might be induced to separate, roll up, and be drawn away in a particular direction where it can be filtered to remove the overspray particles. The design of an aerodynamically-correct overspray collector results from these considerations.