Considering multiple chemical species in a CFD analysis

Multiple species can be easily included in any CFD analysis. Reactions between the species can be modeled, and the creation or destruction of species can be tracked. The treatment of reactions can range from a simple two-step process through reaction mechanisms with hundreds of steps – with intermediate species – considered. Some areas where reactions must be included are:

• Combustion, including in-cylinder flows and power generation analysis
• Gasification
• Oxidation
• Decay of ozone within contact basins
• Performance analysis of catalytic converters

The ability to track hundreds of reaction steps makes CFD particularly useful for modeling combustion. Combustion is a complex process that does not lend itself to scale modeling. Scale models must be constructed using transparent materials so that the flow can be visualized. Because of the mechanical properties of most transparent materials, combustion cannot actually be included in the scale model, as the operating temperatures would destroy it. Additionally, for combustion that uses solid fuel, the size of the fuel particles must be scaled, leading to rates of drying, devolatilization, and char combustion that are different than would occur than in reality.

CFD can model such systems at a 1:1 scale at all levels, with the combustion completely included. Additionally, since turbulence is a controlling parameter in many combustion rates (due to the mixing it provides), performing the modeling at a 1:1 scale provides much better turbulence information. PMI has experience with natural gas, sour gas, and coal combustion as well as a suite of other reacting flow situations.