Augmentation of Laminar Forced Convective Heat Transfer of an Oil Flow in an Enhanced Tube by EHD Effect

Abstract

Listen

Translate article

Heat transfer enhancement using an applied electric field has fascinating application perspective since it can realize a good enhancement effect at the expense of only a little cost of energy. Many fundamental studies have been carried out in this field and the emphasis of the study has been gradually turning to application study. The electrohydrodynamic ~EHD! enhancement of the forced convective heat transfer refers to the coupling of an electric field with the fluid field in a dielectric fluid medium: The net effect is production of electrically induced secondary motions that destabilize the thermal boundary layer near the heat transfer surface. The effect of electrohydrodynamics on the phase-change heat transfer has been under investigation for the past two decades. On the other hand, the studies of the convective heat transfer enhancement by the EHD effect are relatively little. The experimental results reported by Franke and Hogue @1# and Hasegawa et al. @2# denoted that the strong electric field could disrupt the laminar thermal boundary layer of air or refrigerants in-tube and shift the flow conformation from the laminar flow to the turbulent flow. Compared with air and refrigerants, oil is a so viscous fluid that it keeps still the laminar flow when the external electric field is applied although the secondary flow may be aroused. It is quite meaningful to reinforce the forced convective heat transfer of oil in-tube, since it has a low heat transfer coefficient, but a widely practical perspective. In general, it is difficult to enhance the laminar forced convective heat transfer of oil in-tube. Common enhancement techniques use mainly various surface-worked tubes such as the two-dimensional or three-dimensional extended surfaces tubes ~see, for example, @3#! and the helical groove tubes ~see, for example, @4#!, the smooth tube inserted swirl-flow de-