Evaporation Kinetics Of Droplets Research Articles

Kinetics of droplet evaporation

This paper presents research on evaporation of droplets containing dissolved or dispersed solids. Experiments on evaporation kinetics of droplets of water, colloidal silica, sodium sulphate and skimmed milk were performed. The experimental procedure was similar to that proposed by Charlesworth and Marshall (1960, A.I.Ch.E.J.6, 9–23). Individual droplets were suspended in a controlled air stream and their weight and temperature were measured as evaporation progressed. Video recording of the size and appearance of the droplets was made with magnification close to 100. The temperature was followed by a micro-thermocouple, while the mass was measured by using the deflection of a calibrated glass filament balance. Experimental data were compared with a computer simulation based on a model of heat and mass transfer, both within the droplet and from the droplet surface to surrounding air. Analytical and numerical solution of the set of equations was tested. A good agreement between experimental results and the numerical predictions for a variety of evaporation regimes is reported. Diffusion coefficients for three tested materials are determined. The model includes all stages of evaporation: initial heating and evaporation, quasi-equilibrium evaporation, crust formation and growth, boiling, and porous particle drying. Stage transition criteria are defined.

Measurement of droplet interfacial phenomena by light‐scattering techniques

AbstractTwo light‐scattering techniques have been applied to study the kinetics of droplet evaporation and attendant interfacial phenomena. The first technique, which is particularly useful for noisy data, utilizes the fast Fourier transform of phase function data (intensity vs. scattering angle) to obtain the size by comparing the phase function with Lorenz‐Mie theory. The second method applies optical resonance measurements to obtain very precise measurements of size and/or refractive index as functions of time. The techniques have been used to measure the slow evaporation of multicomponent and single‐component organic microdroplets, rapid evaporation of water droplets, and rapid evaporation of droplets of aqueous solutions and surfactant solutions. The experiments were performed in an electrodynamic balance, which was used to suspend single microdroplets in a polarized laser beam. Rapid evaporation rate data yield information on the surface temperature, and data for surfactant solution evaporation show that insoluble monolayer formation at the microdroplet surface reduces the evaporation rate by a factor of 200. In addition, it is shown that droplet explosion due to surface charge effects can occur well below the Rayleigh limit of charge.