EHD Enhanced Heat Transfer with Needle-Arrayed Electrodes

Natural convection heat transfer enhanced by electrohydrodynamics (EHD) is experimentally investigated in this work. Four kinds of electrode arrangements on a plate fin heat sink are made and tested under a controlled environment. Previous and present test results show that the rate of heat transfer with EHD is greater than that under natural convection due to the corona wind generated by the electron avalanche mechanism. To identify the effect of EHD, the enhancement ratio, defined as the heat transfer coefficient with EHD (h_EHD) relative to that without EHD (h_NC), is proposed to examine the performance. Generally, the enhancement ratio increases with the supply voltage regardless of the electrode arrangement or with the electrode polarity. This ratio reaches a maximum of around 4.4 within the operating voltage of 0 ~ 18 kV. For a fixed voltage, the negative polarity has a better performance compared with the positive one no matter the electrode arrangement and the electrode distance. In addition, the threshold voltage for the negative polarity is also lower than that for the positive one. Both phenomena can be attributed to the greater emission current emitted from the electrode surface for the negative polarity. For a fixed electrode distance, there is an optimal electrode density under which the area impinged by the corona wind is insufficient, and beyond which the flow interference by adjacent electrodes is encountered.