Experimental study of multi-bubble hydraulic efficiency of spark-generated bubbles

We investigated the hydraulic efficiency of spark-generated bubbles under conditions of different discharge polarities and different electrode numbers. A positive polarity discharge can generate a larger spark-induced bubble than a negative polarity discharge generated using the same electrical and electrode parameters. The hydraulic efficiency of both the positive and negative polarity discharges decreases with the increasing number of electrodes. Increasing the number of electrodes leads to faster energy injection times and higher average powers. We found that the hydraulic efficiency increases when energy injection time increases but that it decreases when the average power increases. When the energy injection time is longer than 100 µs and the average power is less than 100 kW, hydraulic efficiencies of more than 15% and 10% were realized for the positive and negative polarity discharges, respectively. These results indicate that longer energy injection times will be helpful in gaining higher hydraulic efficiency for these bubbles.