Electrohydrodynamically Coupled Minimum Film Boiling in Dielectric Liquids
The Zuber hypothesis for the minimum film boiling point as a hydrodynamic condition is modified to account for the effects of strong electrohydrodynamic coupling at the vapor-liquid interface surrounding a heated cylindrical wire when the interface is stressed by a strong nonuniform electric field. Different models for ac voltage highly insulating and ac/dc conducting fluid cases are proposed, based on charge relaxation effects. The models predict the effect of electrohydrodynamic coupling on dominant unstable wavelengths and heat flux values at the minimum film boiling condition. The ac voltage, highly insulating fluid model compares favorably with theory. The dc data do not deviate substantially from the ac data. Further, for both ac and dc voltages above some critical voltage, which depends on the heater wire radius, the appearance of the instability of the vapor film changes drastically, indicating an upper limit on the validity of the electrohydrodynamic model developed.