Multiphase flow refers to fluid flow consisting of two or more separated phases such as gas, liquid, and solid phases. The predictive capability of multiphase flow modeling helps with research and development of many engineering applications including fluidized bed reactors, oil pipelines, gas-turbine combustor, and pollution dispersion study, etc.
In disperse (gas-solid or liquid-solid) flow, two types of models are prevalent: Discrete Element Models (DEM), and Two-Fluid Models (TFM). The Discrete Element Models utilize Lagrange’s equations to trace the actual particles in Lagragian framework; while apply mass, momentum, energy equations to describe the gas-phase in Eulerian framework. In Two-Fluid Models, the particle phase is treated as a second gas (or liquid) phase, in which both phases are solved in the same Eulerian framework using mass, momentum, energy conservation.
In reacting multiphase flow modeling, the governing equations mentioned above further include chemical reactions governed by species balance equations. Based on the mass, energy conservation and pre-defined chemical reactions’ kinetics, the species balance equations solve for void fraction, density of each phase, as well as mass fractions of all species within each phase.
ACT has designed several innovative fluidized bed reactors using state-of-the-art CFD tools developed for multi-phase reactive flows. We also develop custom codes aimed at simulation of unique CFD/multiphysics phenomena based on requirements of our commercial and government customers. Shown here is an example of two-phase reactive flow simulation performed for a fluidized bed reactor designed at ACT, alongside its experimental cold flow validation studies. These simulations were undertaken using MFiX code (an open-source multiphase-flow code developed by DOE/NETL’s Multiphase Flow Science group). The approach takes into account all fluid flow aspects alongside relevant chemical reactions involved in the gasification process, such as partial and total combustion, gasification, methanation, and water-gas shift.
Such simulation studies are used to analyze new design as well as optimize operating conditions of fluidized bed reactor.