This Small Business Innovation Research Phase I research project will develop numerical methods and corresponding computational tools for modeling the fluid-particle flows in gas fluidization of multi-sized particles. This work involves the combination of Computational Fluid Dynamics (CFD) to describe the continuum flow of the fluid and the Discrete Element Method (DEM) to describe the discrete flow of the solid particles. The aims of this project are: 1) to develop and validate at the particle level computer models that can satisfactorily describe fluid-particle flows under different conditions; 2) to quantify fluid-particle and particle-particle interactions and their effects on the fluid-particle flow via detailed micro-dynamic analysis; 3) to apply the fundamental findings to support the continuum modeling through typical case studies; and 4) to produce high-performance, state-of-the-art software packages capable of simulating the dynamics of the fluid-particle systems. Such simulations will be extremely computationally intensive and it is therefore imperative to use the presently most advanced computational technique, i.e. parallel computation. The parallel computing algorithm with options of Serial, PVM or MPI to accommodate any types of machines will be implemented in the fluid-particle solver to exploit the unlimited power of parallel computers. The potential outcomes of this project will be to provide a CFD model that can reliably simulate the fluid-particle systems that occur often in chemical, pharmaceutical and mineral industries, and to obtain a comprehensive understanding of the fundamentals of fluid-particle flows that can lead to improvement of the fluidization technology