Presidential Young Investigators Award: Convective Transport Complex Flows

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Heat and mass transfer in fluid-solid flows encompasses many engineering disciplines from handling and processing of granular material to chemical synthesis using packed and fluidized beds. Though petrochemical, process, and energy industries have extensively used these technologies, models governing the bulk fluid-solid transport rates are based largely on empirical data. To simplify the analysis the fluid-solid systems are often viewed as macroscopically homogeneous; however, on the microscopic or pore level, the medium consists of a random distribution of individual particles in a surrounding fluid. The pore-level transport depends on the bed structure, frequency of the particle collisions, heat, mass and momentum exchange between the particles and fluid, and interactions with bounding surfaces. Though exact descriptions incorporating these local or microscopic effects appear inextricable, the current efforts focus on understanding the local mechanisms with the intent of furthering development of the industrially-important macroscopic relations. The planned analytical and experimental research will investigate transport in the bulk and in the boundary regions of the particle flows. In the bulk region, the overall flow appears uniform, but locally the individual particles rotate and translate laterally. This local motion increases the cross-stream heat and mass diffusion and yields higher transport rates. Near a bounding surface, the particles are not uniformly distributed but contact the surface at distinct points causing a near-wall alignment of particles. The distribution depends on the surface conditions of the wall, the type of particle, and the flow rate and affects the velocity profile, molecular diffusivity and local particle convection. The work performed with this PYI grant will emphasize fluid-solid transport involving heat and mass transfer in contact-dominated granular flows. This field has many industrial applications in energy, process, and food industries, and also combines aspects of the simpler fixed-bed problems with the more complex moving- particle flows. These aspects of granular flows are poorly understood and yet they comprise the mechanisms that govern the heat, mass and momentum transport. Continued research in these areas will advance the modeling of granular material flows and may lead to other fluid-solid research areas such as fluidized beds and suspension flows.