Lab-scale electrostatic droplet collection from a fog plume with droplet evaporation

Abstract

The electrostatic droplet collection shows a great potential in harvesting water from fog. However, how and to what extent the droplet evaporation affects the droplet collection efficiency is unclear, which is a key problem to promote the industrial application of the electrostatic fog collection technology. A lab-scale electrostatic fog plume collector was proposed and a numerical model was developed to take the droplet evaporation into account. Experimental and numerical results demonstrated that the fluid transport process in the electrostatic device can be numerically predicted with reasonable accuracy. The ionic wind generated by the corona discharge inhibits the droplet dispersion, which aids the droplet collection. The water vapor mass fraction difference between the fog plume and the ambient air was proposed as the indicator of the droplet evaporation degree. It was found that the droplet collection efficiency decreases with the increasing water vapor mass fraction difference in an exponential law. Furthermore, the droplet collection efficiency loss caused by the droplet evaporation enhances with the decreasing droplet mass concentration in the plume and a loss of 85% occurs when the droplet mass concentration is 6 g/m3. The droplet collection efficiency decreases with the increasing fog plume velocity and a droplet collection efficiency loss of 28%∼43% exists when the plume velocity ranges from 1.3 to 5 m/s.