Growth Rate Measurements for Single Suspended Droplets Using the Optical Resonance Method

An experimental technique described with which the growth rate of a single solution droplet by water vapor condensation can be repeatedly measured with high precision. The technique involves the use of an electrodynamic cell to suspend a NaCl solution droplet in water vapor and a CO2 laser to momentarily perturb the droplet-vapor equilibrium. The droplet size change during condensational growth is monitored with a tunable dye laser for a particular optical resonance due to Mie scattering. A consideration of the coupled heat and mass transfer processes during droplet growth indicates that the best agreement between theory and the experimental results is obtained with a condensation coefficient close to unity.