Thermal bubble dynamics in cryogenic liquids under non-uniform electric fields on superconducting power apparatus

Thermal bubbles in the liquid coolant of superconducting and cryogenic apparatus are considered to be one of the factors that reduce the electrical breakdown voltage of the apparatus. This paper describes an experimental study of the influence of a non-uniform electric field on bubble behaviour and motion in liquid nitrogen. The electric field effect is quantitatively investigated by performing experiments at various electric stresses using a rod-to-plane gap. Thermal bubble motion and bubble deformation processes were observed in these experiments. The experimental result shows bubbles move closer to the plane electrode from a higher field region to a lower one, irrespective of electric field direction in the presence of non-uniform electric fields. Furthermore, the bubble dynamic mechanism has been analysed and explained by considering the electric field distribution and the electric field force. Results show that the gradient force greatly affects the bubble dynamics.