ACTIVE HEAT TRANSFER ENHANCEMENT BY UTILIZING ELECTRIC FIELDS
Active heat transfer enhancement techniques utilizing electric fields have been the subject of active research in recent years. These studies have used various kinds of fluids, including CFC alternatives. In this review, the effects of electric fields on heat transfer enhancement have been fundamentally and systematically explained from the viewpoint of electrohydrodynamics (EHD) that treats the interactions among electric fields, flow fields, and temperature fields. These interactions have been divided into three categories, namely, gas phase EHD interactions, liquid phase EHD interactions, and interfacial EHD interactions. In this review, the mechanism behind Corona wind generated by Corona discharge has been chosen as a typical gas phase EHD phenomenon, and its enhancement effects on convective heat transfer have been explained. An EHD liquid jet ejected through a ring electrode in the opposite direction of a plate electrode with a velocity on the order of 1 m/s was chosen as the representative liquid phase EHD phenomenon. The convective heat transfer from the plate electrode was enhanced by a factor of 100 due to the forced convection and the turbulence of the EHD jet. The active local EHD generation of turbulence was explained fundamentally. The EHD effects on condensation and boiling were chosen as the representative interfacial EHD phenomena and these mechanisms were explained both theoretically and experimentally. In addition, the EHD defrosting phenomena was explained. Heat transfer can be enhanced over a factor of 5 by electrohydrodynamically removing the condensate from the condensation surface and by using EHD pseudo-dropwise condensation. Furthermore, nucleate boiling heat transfer was increased by a factor of 50 over that given using the same system without electric fields. This increase was due to the EHD effects on the active movement and deformation of the boiling bubbles. In conclusion, the characteristics of active heat transfer enhancement techniques utilizing electric fields and the future potential of electric field effects on thermal engineering problems were described to show that the practical application of these EHD active heat transfer enhancement techniques would be effective for heat transfer control, microscale heat transfer techniques, and energy conservation and global environmental protection problems.
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