Particle nucleation and growth in a free turbulent jet

Liquid dibutyl phthalate (DBP) particles were generated by homogeneous nucleation as a heated gas stream laden with DBP vapour exited a nozzle and mixed with room temperature particle–free air. The nozzle diameters were 0.235 and 0.375 cm, the nozzle temperature was 413K, and DBP vapour concentrations were 100–500 ppm. Conditions were chosen to make the jet turbulent (Reynolds number 4000–7000) and to keep nucleation rates low so that the particle growth could be studied in the absence of coagulation and in the early stages of the transition to coagulation.Aerosol size distributions and number concentrations were measured at different positions and jet velocities. For low values of DBP vapour mole fraction, the size distributions were unimodal and the aerosol concentration followed jet dilution profiles, indicating that the particle formation was confined to the initial region of the jet. The final aerosol concentrations were correlated by simple scaling laws. For higher vapour mole fractions, nucleation continued to occur downstream from the shear layer, resulting in bimodal size distributions. Data for nozzles of different diameters indicate that the overall particle formation rate can be decreased by splitting a large nozzle flow into multiple smaller streams.