Single-phase flow

In single-phase laminar flow we can obtain very accurate solutions and in turbulent flow we can in most cases obtain satisfactory flow simulations. The main problem is usually simulation of the mixing of reactants for fast reactions in laminar or turbulent flow. When the reaction rate is fast compared with mixing, there will be strong concentration gradients that cannot be resolved in the grid, and a model for mixing coupled with a chemical reaction must be introduced. Combustion in the gas phase and ion–ion reactions in the liquid phase belong to this category.