Feasibility Study of an EWICON System using the Self Adjusting Multinozzle Electrospraying Technique
This thesis describes the research which have been conducted on the self adjusting multinozzle electrospraying technique, applied in an electrostatic wind energy converter (EWICON). An EWICON system directly converts wind energy to electrical energy by the displacement of charged droplets in the opposite direction of an electric field. Electrospraying referrers to a process where nozzles are formed by so called Taylor cones. These cones form the nozzles which spray an aerosol of charged droplets. The self adjusting technique offers advantages compared to other methods with respect to electrospraying properties and utilization of material. For practical implementation, the following components have been simulated and tested.
First the electrode configuration was optimized for electrospraying. This configuration exists of two cylindrical conductors at a distance of 42 mm and a diameter ratio of 1 to 8. This ratio appeared to be able to generate the desired electric field for stable electrospraying while minimizing the velocity in which the charged droplets are attracted back to the system. A wind shield was designed and applied to locally increase wind speed and provide stable Taylor cone formation.
Secondly the creation of charged droplets was examined with this setup. A mixture of 30% ethanol and 70% demineralized water appeared to be the most suitable spraying liquid. Experiments were conducted to observe the relation between the flow rate and applied potential and the number of Taylor cones with the coresponding current. From these experiments can be concluded that it is desirable to generate a large number of Taylor cones while maintaining an as low as possible flow rate and charging potential. Higher potential will result in unstable spraying and corona discharges. It was discovered that the number of cones could be significantly be increased by making use of the hysteresis effect.
Finally the charging system was placed on an insulated self-supplying platform to complete the EWICON system. Experiments have been conducted, using a wind generator, to assess the performance according to output power. Results were compared to a similar needle configuration (using needles as nozzles) investigated by D. Djairam. There has been a significant improvement according to previous charging experiments with the self adjusting multinozzle system. However, the system efficiency is low compared to the needle system, due to the inability of removing all charged droplets from the system by the wind. A comparable output power could be achieved, when all charged droplets would be removed and improvements are realized according to the output power per nozzle. In this stage of this research, the advantages of the self adjusting character of the systems are being outweighed by the sensitivity to variations in flow rate, wind speed and electric field distribution. Another important aspect is the humidity of the surrounding air which causes leakage currents and disturbing the electrospraying process. In general, it can be concluded that the self adjusting multinozzle system offers perspective for implementation in an EWICON system. However, further research should be conducted to improve electrical, as well as aerodynamic performance.