Isolated bubbles growing and detaching within an electric field in microgravity

The experimental outcomes of single bubbles nucleated and growth from a heated surface immersed in an electric field in high-quality microgravity level are presented. Data were obtained between September 2019 and January 2021 from the European experiment known as Reference mUltiscale Boiling Investigation (also multiscale boiling project), in which single bubbles of FC-72 were nucleated on a heated surface, on-board the International Space Station. In the experiments reported here, which are only a part of the complete dataset, an electrostatic field is imposed in the boiling region by means of a washer-shaped electrode, centred above the nucleation site. The experimental apparatus is designed to initiate a single bubble from an artificial nucleation site machined in the surface. Such bubbles are heavily distorted by the electric stresses; in particular, contact angles and contact line length increase with electric field intensity. While in the absence of electric field no detachment occurs, when the electric field is applied the bubbles are continuously and regularly sucked towards the electrode as they are attracted to regions of weaker electric field; a detailed analysis of the electric forces is provided as well. The significant contribution of electro-convection is highlighted by the bubbles growth rate. These experimental observations contribute to the insight of the basics of boiling and the effects of an electric field on the ebullition cycle and show promising opportunities for practical application of electric fields in space.