Experimental investigation of electrically enhanced boiling of FC 72 using high-resolution phase-detection diagnostics

Abstract

This work features the boiling of FC72 on a transparent sapphire substrate. Tests are performed using a thin ITO film (indium tin oxide) coated on the sapphire substrate as the heat source, a fast speed video camera to capture the boiling process using a technique to track the phase (liquid or vapor) in contact with the heating surface, an InfraRed video camera to capture the average temperature on the surface, and a metallic grid to impose an electric field perpendicular to the boiling surface. The maximum average electric field tested in this work is 3.3kV/mm, which led to a 18% increase of the critical heat flux. This study analyses in detail the phase distribution data showing that (1) there is no evidence of microlayer formation, and suggesting that (2) the triple contact line evaporation accounts for approximately 20% of the total heat flux, while (3) the quenching stage accounts for approximately 80%. Finally, phase distribution images are processed to characterize the size of vapor patches, showing that a boiling crisis occurs when the distribution of the vapor patches becomes scale-free, and corroborating the hypothesis that the boiling crisis can be modelled as a bubble interaction instability using a percolation model.