Development of Boiling Type Cooling System Using Electrohydrodynamics Effect

Abstract

This paper describes results from an experimental study of the effect of an electric field on nucleate boiling and the critical heat flux (CHF) in pool boiling at atmospheric pressure. A dielectric liquid of HFE7100 (3 M Co.) was used as working fluid. A heating surface was polished with the surface roughness (Ra) of 0.05 خ¼m. A microsized electrode, in which the slits were provided, was designed in order to generate non uniform high electric fields and to produce electrohydrodynamic (EHD) effects with the application of high voltages. The obtained results confirmed the enhancement of CHF since the EHD effects increased the CHF to 47 W/cm2 at the voltage of −1500 V, which was three times as much as CHF for the free convection boiling. From the observations of the behavior of bubbles over the electrode and of the boiling surface condition, the instability between the liquid and the vapor increased the heat flux, the heat transfer coefficient (HTC), and the CHF. The usual traveling wave on the bubble interface induced by the KelvinHelmholtz instability was modified by adding the EHD effects. The ratio of critical heat flux increase with and without the electric field was sufficiently predicted by the frequency ratio of liquid–vapor surface at the gap between the boiling surface and the electrode.