Experimental Study On The Heat Transfer Characteristics In Capillary Microgrooves Heat Sink Under An Electric Field

The heat flux in capillary microgrooves heat sink even gets close to in the order of109W/m2because of the combined heat transfer of evaporating heat transfer in the extended thin film region and nucleate boiling heat transfer in the intrinsic meniscus region at a high heat load. It can be used to realize heat exchange of low thermal resistance and small temperature difference with high heat transfer coefficient and heat flux. It is capable of meeting the severe cooling need of power electronic devices and systems.A visualization experimental investigation has been conducted on subcooled boiling phenomenon and bubble dynamic behaviors in open vertical capillary microgrooves working in the electric field. The experimental results show that bubble doesn’t fall apart in quite a long time in an electric field and hence the bubble life time has been extended greatly. The gas-liquid interface and bubble in the microgrooves are continuously oscillating throughout the entire experiment due to the liquid-extraction phenomena caused by the EHD-induced surface instability and inertia of the gas-liquid interface. While the liquid subcooled degree is very small, only the patterns of isolated bubble growth in a single microgroove and bubble coalescence along the same microgroove have been found, the patterns of isolated bubble growth across neighboring microgroove and bubble coalescence across neighboring microgroove didn’t appear.The bubble growth has been quantitatively analyzed with an established bubble volume model put forward under the circumstance without an electric field, the calculation results show that electric field intensity, the distance between the needle electrode and microgrooves, the size of the microgrooves and the heat load have important influences on the bubble dynamic behaviors. The bubble life time becomes larger with the increasing electric field intensity and the distance between the needle electrode and microgrooves. The bubble size and life time in the microgrooves with groove width of0.25mm and groove depth0.5mm are larger than that in the microgrooves with groove width of0.3mm and groove depth0.4mm, besides neighboring bubbles coalescence and interaction along the same microgroove, bubble and gas-liquid interface constant vibration in the microgrooves with groove width of0.25mm and groove depth0.5mm, therefore, the microgrooves with groove width of0.25mm and groove depth0.5mm have a better heat transfer ability.The characteristics of heat transfer are considered as well, it has been found that there exists a threshold voltage, only when the voltage is greater than the threshold voltage, the electric field affects the heat transfer dramatically. The experimental threshold voltage is smaller than the theoretical prediction. The distance between the needle electrode and microgrooves, the size of the microgrooves and the heat flux density have significant influences on the threshold voltage and the characteristics of heat transfer, and the effect of the distance is particularly remarkable. The power consumption of the electric field is also researched owning to the corona wind occurs in the experiment, it turns out that the absolute temperature drop△T increased sharply with the power consumption at the beginning, then it varied slightly, the maximum of△T turns up at the time of break-down.