Using microgravity to disentangle particle transport at the surface of an externally vibrated fluid*

Particle transport in a fluid is a rich phenomenon that involves a wide range of parameters. Characterization of such flows are crucial for understanding clustering and dispersion of microplastics or algae blooms in oceans and lakes. At the surface of a fluid, particle movement is driven by capillary immersion forces and capillary flotation forces. These interactions are entangled by the presence of gravity and are influenced by various characteristics such as particle size, surface tension, wettability, particle density, fluid wave length, and wave amplitude. The work presented here focuses on the influence of wave and particle characteristics on particle transport in microgravity conditions. Microgravity experiments aim to disentangle the dynamics of particle transport at the surface, isolating immersion forces on the particles. An open cylindrical container is placed on a wave driver, providing external harmonic forcing, and microparticles are placed at the surface of the fluid. Particle tracking is achieved through camera imaging from above for different wave frequencies and wave amplitudes. Experimental results presented are from drop tower experiments at Portland State University and compared to 1g control tests. Future work on the subject will be sent to the International Space Station for extended zero-gravity experimentation time.