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 nozz le and mixed with room temperature particle-free air. The nozzle diame ters were 0.235 and 0.375 cm, the nozzle temperature was 413 K, and DB P vapour concentrations were 100-500 ppm. Conditions were chosen to ma ke the jet turbulent (Reynolds number 4000-7000) and to keep nucleatio n rates low so that the particle growth could be studied in the absenc e of coagulation and in the early stages of the transition to coagulat ion. Aerosol size distributions and number concentrations were measure d at different positions and jet velocities. For low values of DBP vap our mole fraction, the size distributions were unimodal and the aeroso l concentration followed jet dilution profiles, indicating that the pa rticle formation was confined to the initial region of the jet. The fi nal aerosol concentrations were correlated by simple scaling laws. For higher vapour mole fractions, nucleation continued to occur downstrea m 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.