Microphysical Measurements of Fog Formed in a Turbulent Jet

An investigation of fog formation in the flow field of a turbulent jet was conducted in order to determine the processes responsible for the microscopic and macroscopic behavior of the fog. Profiles of number density, mean droplet diameter, and size distribution were measured by using a Phase Doppler Particle Analyzer, for two different conditions of the jet effluent saturated at 62° C and 85° C. The data allow the behavior of the jet to be characterized by the competing mechanisms of heterogeneous nucleation on entrained nuclei, growth of droplets, and turbulent diffusion. At the higher jet temperature, the competing mechanisms result in bimodal size distributions. This behavior was shown by a simple model in which condensation occurs simultaneously with entrainment and mixing. Microscopic measurements were also taken for vapor-air jets in which a water aerosol was added to the jet effluent. A comparison of this seeded condition with the latter condition shows that seeding moves the condensation towards local thermodynamic equilibrium.