Study of the mixing with chemical reaction in a cross flow impinging jet aerosol reactor

A reactor has been designed for the study of the nucleation and growth of an ammonium chloride aerosol starting from ammonia and hydrogen chloride in the gas phase at ambient conditions. The reactor configuration was derived from other aerosol reactors used for the production of ultrafine ceramic particles: two opposed jets containing one reactant discharging into a cross stream containing the second reactant. The fluid flow was in a transition state from laminar to fully turbulent. The reactor had essentially a two-dimensional configuration. Three types of measurements were performed to characterize the reactor: velocity, tracer concentration and aerosol particle size distribution (PSD) measurements. A mathematical model was developed to simulate the experimental reactor.;The measurements demonstrated that the flow could be divided into two important regions: the principal jet trajectory and the main recirculation downstream of the jet along the reactor wall. Most of the mixing between the two jets and the main flow occurred along the principal jet trajectory, the recirculation zone was well mixed in most cases. Higher jet velocities increased the extent of mixing in the reactor. The nucleation of aerosol particles occurred close to the reactor inlets. In the recirculation zone, larger particles were found and in a lower concentration compared to the aerosol along the principal jet trajectory. The numerical computations showed that neither a laminar nor a turbulent flow model were able to accurately reproduce the experimental fluid flow. A good agreement with measurements was nevertheless obtained for the modeling of the mixing of a tracer. For the nucleation and growth of the aerosol, a model based on the residence time distribution of the reactor gave a good agreement with experiments for certain values of the rate constant and surface free energy of formation. However, this model neglects key features of the reactor behavior because it assumes well mixed reactants at the entrance and that particles of different ages are not mixed together. Another model using spatial transport of the species failed to reproduce the experimental aerosol measurements. It nevertheless emphasized the role of the recirculation zone in the reduction of the nucleation by favoring condensation onto existing particles.