An experimental analysis of droplet charging in a wind tunnel

Abstract

The aim of this paper is to introduce an experimental analysis of droplet charging that occurs due to liquid film atomization on two different surfaces. The atomization of the droplets from the liquid film at high speed is still not satisfactory understood. The phenomena can be found in steam turbines, wind turbines, aeroplanes and other technical applications. The liquid film atomization is associated with the electrostatic charge of the formed droplets. The paper describes the experiment when the coated and non-coated surfaces were tested for an estimation of the droplet size distribution function and the droplet charge. A new wind tunnel was developed for the study of liquid film atomization in similar conditions in steam turbines. The coarse droplets are formed in the steam turbine from the liquid films on the blades and inner casings. The coarse droplets formed on the non-moving blades don´t exactly follow the bulk flow and they collide with the moving blades. These collisions cause erosion and corrosion processes which have an unfavourable effect on the reliability and the efficiency of steam turbines. The tunnel is equipped with the standard instrumentation for the measurement of the flow properties and for the analysis of the size distribution function of the droplets. Two measurements methods were used to attain the size of the droplets, along with their photogrammetry and light scattering. The first tested surface is polished stainless steel and the second is the electrical isolating and hydrophobic coating. The results from the measurement suggest the possibility of the better understanding the erosion processes in steam turbines.