DSMC Comparison between Two Different Models Evaluating the Occurrence of Chemical Reactions

Two different models, evaluating the occurrence of a chemical reaction in a collision between two molecules, have been compared in a Direct Simulation Monte Carlo (DSMC) process: the phenomenological model by Bird and the microscopic model by Fan and Shen. A “simple” DSMC code, simulating just the collision between two molecules, has been developed for this purpose. The runs have been made considering: i) three dissociation and two exchange reactions in air, ii) a range of temperature from 4.0103 to 1.9104 K, iii) a number of collisions up to 2.5105. The results showed that, practically for all reactions and independently from the number of collisions and temperature, the occurrence of reaction from the Fan-Shen model is higher than the one from the Bird model. This is due to the different handling of vibration. In fact, unlike the Bird model, the Fan-Shen model takes into account the physical relationship between vibrational excitation and dissociation/exchange reaction. In order to deepen this evaluation, the inclusion of these models in an advanced DSMC code, allowing the comparison of the results with experimental data, should be suitable.