Effect of small-diameter coaxial reactors on ozone production using nanosecond pulsed power

In ozone production using streamer discharges by pulsed power, the concentration of ozone is not high although ozone is produced with high efficiency. To improve ozone concentration, we studied the effects of electrode separation in a coaxial reactor using nanosecond pulsed power. We found that ozone concentration and yield increase with decreasing inside diameter of the outer electrode in the reactor. This occurs because dense plasma forms in a small-diameter reactor that has a small electrode separation. As the repetition rate of applied pulses was increased, the ozone yield remained nearly constant, while the ozone concentration increased proportionally. However, in a reactor having a small diameter of 17 mm, the tendency for the concentration to saturate and reductions in the ozone concentration were found to depend on pulse repetition rate. In such a small-diameter reactor, spark discharges occurred owing to the reduced separation of electrodes; these discharges cause the temperature of electrodes and gases to increase. Consequently, ozone molecules thermally dissociated and ozone concentration decreased. The occurrence of spark discharges was affected by not only the small separation of electrodes but also other factors. Potential of a small-diameter coaxial reactor for ozone production were presented and a control of occurrence of spark discharges was paramount.