Melany L. Hunt Professor of Mechanical Engineering; Vice Provost
Office: 121 Thomas |
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Liquid-Solid Flows Liquid-saturated flows of particulate materials are ubiquitous in industrial and geophysical environments, including debris flows, slurries, mining and milling operations, and sediment transport. Unlike collision-dominated dry granular flows or sediment-laden liquid flows, this area of multi-phase flow research combines the mechanics of particle-to-particle interactions with the inertial effects of both phases and the effect of a viscous fluid. Rheological MeasurementsWe have designed a new particle-liquid rheometer to measure the shear and normal forces for Earth-based and low-gravity environments. These experiments provide a unique opportunity for exploring the transition from transport in a pure Newtonian fluid to transport occurring during a dense flow of particles. By carrying out the experiments in reduced gravity we can use fluids and particles of differing densities without encountering problems associated with sedimentation or flotation. The experimental database resulting from our measurements will show the dependence of the stresses on the Stokes and Reynolds number, concentration, and other experimental parameters (such as the stiffness of the particles, gap size relative to particle diameter, and density ratio). These results will also allow us to develop constitutive models for these flows. |
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To model flows of a liquid-plus-solid it is necessary to understand the role of particle collisions. We have done extensive measurements of normal and oblique particle-wall collisions. These results demonstrated that below a critical Stokes number, St <10, all of the particle’s kinetic energy is lost during the compression of the lubrication film with no rebound of the particle. Above a second Stokes number, St >2000, the particle rebounds with negligible effect of the lubrication layer. In an oblique collision, the lubrication layer can significantly reduce the effective wall friction provided that the particle and wall are suitably smooth. For rough surface, the frictional effects are equivalent to that found in dry flows. Related experiments involve binary-particle collisions in a liquid, which differs from the particle-wall collisions because the target particle may move prior to the impact. Measurements are also being undertaken on surface deformation and erosion during impact in a viscous fluid. Both normal and oblique collisions will be examined for different Stokes numbers and material properties. |
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| Booming Sand Dunes In approximately 30 known locations around the world with large sand dunes, an avalanching of sand is accompanied by a loud droning or booming sound, which is not a noise composed of many frequencies but instead contains a dominant audible frequency and several higher harmonics. The sound can be heard after a naturally occurring slumping event or triggered by forcing sand down the leeward face of a large dune. In the later case, the dune will continue to boom and vibrate even after the sand has visibly stopped moving. Field measurements show that the frequency ranges from 75 to 110 Hz depending on the desert location and time of the year. Our measurements suggest that the physical features (such as a moisture barrier) of the sand dune plus the characteristics of the shearing on the surface may contribute to a wave-guide phenomena that results in a resonate behavior at a characteristic frequency.
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Granular Flows -- Vibration, mixing, hoppersA primary area of recent work involves flows of particulates or granular materials. These flow occur in industry (for example: dry chemicals, pharmaceutical powders, plastic pellets, toner), agriculture (grains, food products), and natural environments (sand and debris flows). Dry flows of these materials are governed by the particle collisions, and the interstitial fluid has negligible effect on the momentum transport. These flows are often modeled analytically by exploiting ideas from dense-gas kinetic theory, and through discrete particle simulations. In addition, discrete element simulations are used to compute dry flows by modeling the inelasticity and friction of the particles, and computing the motion by integrating Newton's equation. We have been interested in mixing of granular materials--involving both identical particles (self-diffusion) and particles of differing density or composition (gradient diffusion). This work involves experiments, analysis and simulation. External vibrations are often used in transporting, handling, mixing granular materials. In addition, vibration is used to induce flow in hoppers. We have examined the effect of vertical vibrations on containers of granular material, and have observed complex wave patterns at different accelerations and frequencies. In addition, we have studied the effect of purely vertical or purely horizontal vibration on the discharge from a planar hopper.
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Heat Transfer in Particle Laden FlowsParticulate flows may also be accompanied by heat transfer processes. Although the interstitial fluid does not affect the momentum transport in dry flows, heat transfer through the fluid phase is a critical mechanism in heating, cooling, drying, or energy dissipation during mixing of granular materials. Previous efforts have involved dense granular flow past a heated plate. Results from the experiments and analysis indicate the critical role that the medium density adjacent to the wall plays in determining the overall heat transfer. Additional work has also focused on calculating the local energy dissipation rate in sheared flows. In many industries, the material may be temperature sensitive (food products, toner), and an understanding of the heat dissipation may be critical to the process. |
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Selected Recent Publications  B. Muite, M.L. Hunt & G.G. Joseph, The Effects of a Counter-Current Interstitial Flow on a Discharging Hourglass, Physics of Fluids, 16, 3415-3425 (2004).
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Courses
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Curent Graduate Students
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Former Graduate Students
Thesis: Interaction Law for a Collision Between Two Solid Particles in a Viscous Liquid
Gustavo Joseph (2003)
Thesis: Couette Flows of Granular Materials: Mixing, Rheology, and Energy Dissipation
Thesis: Buoyant Flows in Vertical Channels Relating to Smoke Movement in High-Rise Building Fires
Thesis: Collisional Mechanics in Solid-Liquid Flows
Thesis: Vibration of Granular Materials
Venkata Natarajan (1997)Head of IT for Bundled Business Services, ING United States Financial Services Thesis: Material and Thermal Transport in Vertical Granular Flows
Thesis: An Investigation of Velocity and Temperature Fields in Taylor-Couette Flows
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| Interesting Sites on the WWW
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