Influence of discharge polarity on the dynamics of spark-induced bubble in saline water

Spark discharge in saline water has been confirmed to generate violently oscillated bubble, where the discharge only occurs at the electrode tips. In this Letter, it is found that the discharge polarity has obvious influence on the dynamics of such a bubble. The spark discharge with positive polarity can generate larger bubble than that induced by the negative discharge. The electrolytic effect is considered to play an important role during the spark discharge, e.g., the additional Cl-2 for positive discharge and H-2 for negative discharge are generated and trapped into the bubble. In addition, a more obvious increase in bubble size is observed in the bipolar discharge, in which the molecular number of Cl-2 and H-2 is the same. Finally, this phenomenon is numerically confirmed regardless of the chemical reactions.