CONTEXT
The use of computational fluid dynamics (CFD) has contributed greatly to the recent development and design of products in a range of industries, from aerospace and automotive to power and petrochemical. Over the past 50 years, CFD has emerged from being a research interest to become a very important tool for scientific and engineering advancement. Because CFD is such a general tool, this capability has found applications in a host of industries.

PROBLEM
However, for gas-particle flows, CFD has not been as productive. For lightly loaded systems in which the flow is so dilute that the interactions of the particles and the particles’ volume can be ignored, fairly successful computational methods have evolved by extending single-phase methods. These methods track the trajectories of individual particles as they interact with the carrier fluid. This approach is computationally very costly and difficult to extend to the class of gas-particle flows in which the particles do interact (through brief collisions or sliding contact) and when the volume they occupy is a significant fraction of the total volume.

For this latter type of flow, alternative approaches have been developed that describe the particles as a granular fluid (continuum), which is infused (interpenetrated), by the carrier fluid. This description is like that used to describe flow in a porous medium, except the porous medium is not fixed but can flow as well. A coupled set of equations is used to describe the flow of both phases. This approach, originally derived to describe bubbly flow (mainly for analysis of nuclear reactor safety issues), has been extended to analyze heavily loaded gas particles flows.

However, for many years, the computational issues were too difficult to allow full solution of the complex set of equations for practical systems—until the development of the MFIX (Multi-phase Flow with Interphase eXchanges) code.

RESEARCH OBJECTIVE
MFIX is a general-purpose computer code, developed at the U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL), for describing the multi-phase hydrodynamics, heat transfer, and chemical reactions that occur in heavily loaded fluid-solid or gas-particle systems. MFIX calculations give detailed transient information on the three-dimensional distribution of pressure, velocity, temperature, and species mass fractions.

The truly unique feature of MFIX is that it is being developed as an "open-source" code. It is distributed through the webpage (www.mfix.org) which includes extensive documentation. Many developers at different sites can now contribute to its improvement. All of these modifications are managed using "version control" software, so that each change is documented. New versions are tested against a suite of control cases. Thus, the code is now used as a "test-stand" for testing and developing multi-phase flow constitutive equations in support of a wide range of applications.