Microparticle detachment from surfaces exposed to turbulent air flow: Effects of flow and particle deposition characteristics

This work presents he results of experiments conducted to provide quantitative information on particle detachment from surfaces. The effects of certain, controllable factors on the detachment of 70 mum-diameter stainless-steel spheres from a glass surface exposed to accelerated air flow in a wind tunnel were studied. Changes in the free-stream velocity required to detach 50% of the particles, the threshold velocity for detachment, were measured for variations in the controlled factors. These factors were air relative humidity, residence time between particle deposition onto the substrate and flow application, mean flow acceleration, deposition density, final free-stream velocity, and final flow Reynolds number. Results reveal that deposition density was the most effective factor that enhanced detachment at all relative humidities. Residence time was found to be the most effective factor that suppressed detachment at high relative humidity. The threshold velocity increased with increasing relative humidity and was lower for turbulent flow versus laminar flow. Within the uncertainty limits, the mean flow acceleration in the transient period was found not to affect the threshold velocity in the range from 0.014 to 0.34 m/s(2). The final free-stream velocity also did not affect the threshold velocity, provided it was greater than the threshold. A set of experimental conditions that lead to a relatively small uncertainty is presented. (C) 2004 Elsevier Ltd. All rights reserved.