Controllable Segregation of Granular Particles for Powering Undersea Vehicles

Summary: Powering unmanned undersea vehicles (UUVs) in an energy-dense manner is critical to the Naval Research Enterprise?s Strateg,ic Hedge priority and National Defense Strategy. Currently, aluminum-water reactors producing hydrogen are a promising method for po,wering undersea vehicles, yet they cannot produce hydrogen controllably and efficiently. These issues arise because water cannot rea,ch unreacted aluminum steadily since the aluminum particles and reaction products are stationary. Here, we propose to use oscillatin,g gas flow to induce motion in the granular aluminum particles, controllably segregating unreacted particles from reaction products,to produce hydrogen steadily and efficiently. Energy losses to gas flow are negligible. We aim to make fundamental advances to multi,phase and granular flow physics and apply these insights to construct and test efficient prototypes of aluminum-water reactors.Techn,(i) water is injected to produce hydrogen, and liquid injected can form liquid bridges which impact particle dynamics; (ii) reaction,k water from reaching unreacted aluminum, preventing hydrogen production.Research has shown that gas flow and vibration can induce s,egregation in particles based on size and density, and the PI has recently demonstrated that the oscillating gas flow can lead to mo,re controllable, segregation behavior as well as the formation of scalable flow structures in the particles. Current understanding o,f how liquid injection and particle erosion affect segregation is lacking. Thus, our research plan seeks to answer the following fun,damental questions related to granular segregation which address the issues facing aluminum-water reactors: (A) How do particles of,different sizes and densities segregate or mix when subject oscillating fluidizing gas flow, and how can this be described mechanist,ically and non-dimensionally? (B) How do particle agglomeration, liquid injection and erosion affect mixing and segregation of parti,cles of different sizes and densities subject to oscillating gas flow? (C) How does controlled segregation of particles in aluminum-,water reactors affect the rate, duration and control of hydrogen production as compared to prior reactor designs? These questions wi,ll be addressed using (a) optical imaging, (b) magnetic resonance imaging and (c) detailed, 3D computational modeling. Optical imagi,ng in pseudo-2D systems will enable characterization of segregation behavior across a wide variety of conditions for binary mixtures, of particles and liquid injection to create regime maps for behavior. MRI will enable characterization of how segregation behavior,and rates change in a fully 3D system. Computational modeling will shed light on the mechanisms leading to segregation with the abil,ity to monitor the balance of forces inducing motion on the different types of particles. Advances to modeling will be developed to,account for liquid injection and erosion, and advances to MRI will be developed to image segregation rapidly in 3D. DoD Impact: The,proposed work will directly advance the development of the next generation of aluminum-reactors for powering undersea vehicles with,an energy density potentially 10x higher than the batteries currently used in UUVs. Current aluminum-water reactors only operate at,22% efficiency for hydrogen production due to reacted products blocking water from reaching aluminum. The use of oscillating gas flo,w to separate reactant products from fresh aluminum has the potential to bring efficiency towards 100% while lengthening mission tim,e for UUVs. Aluminum-water rea, Release