Flow field effects on nucleation in a reacting mixing layer

Chemical nucleation was studied numerically in a stagnation point mixing layer in which reactants in two counterflowing streams form a condensable monomer. The response of the subsequent nucleation kinetics to the velocity gradient in the flow is described in terms of a Damkohler number. Two limiting cases were established: (1) if the Damkohler number for monomer production is small, then the nucleation of particles can be strongly affected by the flow field in a manner which is equivalent to the effect of supersaturation in a uniform vapour; (2) if the Damkohler numbers for cluster growth are small, the concentrations of clusters do not achieve equilibrium levels. This can result in the suppression of particle formation over a critical range of Damkohler numbers. It is found that the behavior of the nucleation kinetics is analogous to the transient phase of nucleation in a uniform vapor.