Gas-solid flows are ubiquitous in both nature (landslides, avalanches, planetary rings, etc.) and industry (pharmaceuticals, food products, chemical and petroleum industries). High-velocity gas-solids flows that are found in a wide range of applications (circulating fluidized beds, pneumatic transport lines, sand flow modeling, erosion prevention, planetary rings, etc.), in particular, often develop instabilities that are referred to as ?clusters?, which are known to have a large impact on system performance. Accurate prediction of onset and evolution of the clusters is critical to the design, scale-up, and optimization of related systems. It is shown that inelastic inter-particle collisions and gas-solid drag can both independently lead to instabilities; in real systems, however, they always cooperate and their relative importance has not been examined. The objective of this research is twofold: (i) to elucidate the relative importance of the various origins of the instabilities in high-velocity, gas-solid flows, and (ii) to critically assess the ability of a new kinetic-theory (continuum) model to predict the quantitative nature of such instabilities. This research will begin with a simplistic, time-dependent cooling system where kinetic energy input is absent, and then move to more complex and practically relevant fluidization systems with and without solid boundaries to investigate time-independent statistics. Four different computational methods will be used. Lattice Boltzmann simulations that solve the detailed flow around particles will be used to provide first-principle-based data sets needed to assess the relative importance of collisions and gas phase effects as well as cluster formation and evolution. On the continuum level, linear stability analyses based on two-fluid kinetic theories will first be used to predict the stability boundary; Euler-Lagrangian method where only gas phase is treated as a continuum and particles are discrete, and Euler-Euler models where both gas and particle phases are treated as continua, will then be used to simulate the evolution of the clusters. These results will be compared to the lattice Boltzmann data for a critical assessment of the predicative ability of the various continuum models. This research will generate first-principle-based simulation data on cluster formation and evolution for high-velocity gas-solid flows, and these data will be used to establish an accurate theory able to predict both onset and evolution of the clustering instability on the continuum level.
The simultaneous flow of gas and solid particles occurs in windstorms, landslides, reactors used for energy production, and mixing units used by the pharmaceutical industry, to mention just a few. The complex physical interactions occurring in these systems make them difficult to predict from past experiments alone. In this project, mathematical models with no fitting parameters will be developed and used to predict flow phenomenon unique to these systems. The availability of such a modeling tool is expected to reduce to improved design of reactors in shorter turn-around times and at smaller costs than is currently possible. The model will be made available to researchers worldwide via an existing open-source code, and thus is expected to find future use in numerous sectors, including pharmaceuticals, chemical process industries, energy production, geology, and astrophysics.
