Heat transfer enhancement by needle-arrayed electrodes – An EHD integrated cooling system

Abstract

Natural convection heat transfer enhanced by electrohydrodynamics (EHD) is experimentally investigated in this work. Four kinds of needle-arrayed electrodes combined with a plate fin heat sink are made and tested under a controlled environment. Previous and present test results show that convection heat transfer is enhanced with the presence of EHD due to corona wind generation by the electron avalanche mechanism. To identify the effect of EHD, the enhancement ratio ( ξ), defined as the heat transfer coefficient with EHD ( h ec ) relative to that without EHD ( h nc ), is proposed to examine the performance. It is found that the negative corona has a lower threshold voltage and a better performance compared with the positive one. The enhancement ratio increases with electric power input and linearly with the 1/4 power of total corona current. Heat transfer enhancement is evident when a corona discharge above 1 μA is established. For moderate test condition, the enhancement ratio is around 3–5 with a preferable normalized electrode height of around 0.25–0.35 compared to the edge of the heat sink. For a given electrode height, there is an optimal electrode density below which the required area exposed to the corona wind is apparently insufficient, and beyond which the flow interference caused by adjacent electrodes offsets the effective performance. In particular, the enhancement ratio decreases with increasing the heat dissipation as a result of augmented buoyancy convection.