Convective heat transfer enhancement of a flat plate and LED using ionic wind

Abstract

An experimental investigation on the enhancement of convective heat transfer of a flat plate and LED using ionic wind is reported. The natural and forced convection heat transfers were considered. The ionic wind describes the generation of airflow between two electrodes held at a potential difference and is known to enhance heat transfer. An in-depth review of literatures is provided, where the enhancement of heat transfer is attributed to the generation of secondary flow and disruption of existing boundary layer. Two experimental setups have been constructed, for the natural convection heat transfer enhancement of a flat plate and for the forced convection heat transfer enhancement of LED. The bulk flow forced convection of the LED was generated by an axial fan. For the investigation with the flat plate, the parameters involved were the applied voltage to generate the ionic wind, the flat plate heat flux, the separation gap of electrodes and the number of emitter electrodes used. As the applied voltage increased, the enhancement increased. While as the flat plate heat flux increased, the enhancement of ionic wind decreased due to overwhelming effects of buoyancy. With separation gaps of g = 1.5 cm and g = 1.75 cm, the ionic wind produced similar enhancements, while the heat transfer enhancement was lower with a separation gap of g = 2 cm. Increasing the number of emitter electrodes did not increase the enhancement as the enhancement was linked to the corona current. The maximum heat transfer enhancement recorded was η = 1.41. For the enhancement of heat transfer of the LED, the parameters investigated were the bulk flow velocity represented by the Reynolds number and the orientation of electrodes relative to the LED. In the laminar flow regime investigated, the effect of the Reynolds number on the heat transfer enhancement was minimum. At a given low power consumption, the ionic wind enhanced setup produced a lower average heat transfer coefficient as compared to those produced by the setup cooled solely by the axial fan. This was due to the significant heat transfer produced by the axial fan at low power. However, as the total consumption of power increased, the heat transfer enhancement of the ionic wind increased beyond the reach of the setup with axial fan. The maximum heat transfer enhancement of the LED was η = 1.38. An analysis of the electrodes geometry was performed and showed that the enhancement of heat transfer was dependent on the orientation of the electrodes relative to the LED. An average Nusselt number correlation was formed.