As described in the previous section, the method of moments can be used as one option in the Particle Tracking feature to determine statistics of the particle-size distribution. The method of moment calculates total particle number density and volume fraction. Average properties of distribution such as average particle diameter can be estimated. Although the method of moments has advantages over other methods in terms of computational efficiency, one limitation it has is that only statistics of the size distribution are predicted, rather than the size distribution itself. This becomes an issue when trying to quantitatively compare predictions of the shape of the distribution against experimental data, especially when the size distribution form is complex. Such quantitative predictions can be important in understanding and formulating particle-gas kinetics mechanisms.

To address this issue, an alternative approach is available with the Particle Tracking module for a subset of the Ansys Chemkin models that can use the moment method. The sectional model approach provides more direct prediction of the size-distribution shape. It is available for the Chemkin Closed 0-D and Open 0-D reactors models (without plasma), Plug-flow, the Pre-mixed Burner-stabilized Stagnation Flame model, Premixed Burner-stabilized Flame, Premixed Laminar Flame Speed Calculator, and Opposed-flow Diffusion Flame model. For the sectional-model approach, the number density is computed as a function of different "bins" that are defined for different particle sizes. The disadvantage of this approach is that it requires relatively more computational resources, due to the need to add one equation per bin that would be considered. In this way, the more resolved the distribution is, the more computationally expensive the calculation.