Unraveling the mechanisms of nucleate boiling enhancement with electric fields using high-resolution optical diagnostics

We investigated the effect of an electric field on the boiling of a dielectric fluid, FC-72, in saturated pool boiling condition at atmospheric pressure using high-resolution optical diagnostics. A technique to detect the phase, liquid or vapor, in contact with the boiling surface enabled the quantification of key boiling parameters such as dry area fraction, contact line density, bubble footprint size, and surface dry and wet times. We found a signature of the boiling crisis in the bubble footprint area distributions. The nucleate boiling regime ends when the distribution of bubble footprint areas follows a scale-free power law, which may emerge due to an instability in the bubble interaction process. At a fixed heat flux, the electric field reduces the footprint area and growth time of discrete bubbles, decreasing bubble interaction probability and delaying the boiling crisis. Consequently, the electric field increases the heat flux at which scale-free distributions emerge and boiling crises occur. A mechanistic reconstruction of the boiling heat transfer curve suggests that heat transfer occurs primarily through contact line evaporation and quenching, and that the role of the electric field is secondary. In summary, electric fields seem to delay the boiling crisis not by improving heat transfer mechanisms but rather by delaying an instability in the bubble interaction process.