ISS: Uncovering transient dynamics and equilibrium states of particle aggregates in fluids

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Pollen deposition, paleoecology, algae growth linked to water quality, plastic pollution, and storm transported sea salt in bodies of water are at first examples of particles in fluid-gas interfaces. After a certain time, when and if particles sediment, the dynamics change and the involved processes can become those of a fluid-saturated granular media. Of particular interest for this proposal are externally vibrated particle-laden fluids that are used to segregate different particle sizes and materials, or to fluidize the granular material and thus improve its flow characteristics such as particulate transport and enhanced heat transfer. This project aims at exploring and quantifying transient dynamics of particles in an interface and bulk fluid in the absence of gravity and leading to improved aggregation models. The proposed research represents an important step forward towards the understanding of aggregation of particles in a bulk fluid and gas/fluid interface where times scales are relatively large and the effects are relatively small on Earth. This can aid the improvement of models of these transport phenomena in the overall balance of particle transport processes constantly occurring on Earth. This project is structured such to have a broader impact on the participating students and the broader public.A systematic experimental exploration of aggregation dynamics of particles in an unforced and forced interface and bulk fluid will be pursued. New knowledge and understanding about how these forces affect particle agglomeration rates in the absence of gravity will be created. To elucidate aggregation at liquid-gas interfaces and in a bulk fluid free from gravitational effects, a set of experiments to be performed on the International Space Station is proposed. Drop tower experiments at Portland State University will be performed to narrow parameters relevant to the study to inform relatively long experiments on the International Space Station under zero gravity in collaboration with ZIN Technologies. This project has three main objectives: 1.) Experimentally disentangle the effects on particles of capillary immersion from capillary floating and study the long-term particle dynamics of fluid saturated granular media through a zero-g environment unforced and subjected to an external harmonic forcing; 2.) Quantify collective effects promoted by agglomeration/clustering, particle-fluid and/or particle-particle interactions in a forced and unforced zero-g environment; and 3.) Develop agglomeration models truly representing effects in the absence of gravity on inertial particles. Broader impact activities are coordinated as: 1.) STEM training at the graduate and undergraduate level by a.) Leveraging existing programs at Portland State University as well as b.) Providing experiences to interface with partner company ZIN Technologies and NASA astronauts; and 2.) Oregon Museum of Science and Industry science communication training program will provide an important opportunity for the graduate student and post-doctoral researcher to effectively communicate their science with the broader public.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.