The effects of airflow velocity and particle size on dust accumulation for Titan dust simulants on transparent windows

The factors controlling the adhesion of dust particles are critical for the design of camera systems used on the Moon, Mars, asteroids, and now Titan. Previous experiments determined that the adhesion of Titan dust simulants to a camera window can be minimized by maximizing the electrical conductivity of the window surface and minimizing its surface energy. To test the effects of airflow velocity, sapphire windows with an indium tin oxide coating and fluorosilane treatment were exposed to aerosols of three Titan dust simulants: melamine, polymethyl methacrylate, and polystyrene. The airflow velocity ranged from 0.02 to 0.22 m/s. The results showed that dust adhesion was largest over a relatively narrow range of airflow velocities centered on 0.11 m/s. Little fouling occurred at 0.02 m/s. Primarily fine particles less than 100 mu m in diameter were lofted toward the window from 0.07 to 0.11 m/s. Above 0.16 m/s, the presence of large particles greater than 400 mu m appeared to prevent the adhesion of medium sized particles (100-200 mu m). Particles larger than 200 mu m were generally too heavy to adhere to the window at all velocities. The results are consistent with modeling to a first approximation of spheres on a flat surface if one considers that irregularly shaped particles have multiple point contacts with radii that are much smaller than that of the particle.