Enhanced Heat Transfer in Biporous Wicks in the Thin Liquid Film Evaporation and Boiling Regimes
Enhanced Heat Transfer in Biporous Wicks in the Thin Liquid Film Evaporation and Boiling Regimes
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DOI：
10.1115/1.4006106
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发表时间：
2012-10-01
影响因子：
--
通讯作者：
Majumdar, Arun
中科院分区：
文献类型：
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作者：
Coso, Dusan;Srinivasan, Vinod;Majumdar, Arun
由微通道分隔的微尺度针翅组成的双多孔介质被研究作为蒸汽室热管蒸发芯的候选结构。这些结构是使用标准的光刻和蚀刻技术由硅制成的。分离微尺度针翅的孔用于产生高毛细吸力，而较大的微通道用于降低整体流动阻力。发现传热系数取决于三相接触线弯月面附近几微米量级的厚度的液膜的面积覆盖率。我们操纵的面积覆盖率和薄膜厚度通过改变表面积与体积比，通过使用微结构。实验是在芯体处于垂直方向的情况下，针对1 cm（2）的加热器面积进行的。结果呈现为具有大致相同的孔隙率，固定的微通道宽度W近似为30 μ m和W近似为60 μ m，和针翅直径范围从D = 3-29 μ m的结构。由于微观结构的表面积增加和蒸发的抑制，由于减少孔隙规模的竞争效应进行了探讨。在一些样品中，观察到从蒸发传热到核态沸腾的转变。虽然很难确定何时发生转变，但可以确定蒸发在核沸腾上占主导地位的状态，反之亦然。在119.6（+/-4.2）W/cm（2）的热通量下获得20.7（+/-2.4）W/cm（2）-K的传热系数，直到芯在蒸发主导的状态下变干。在核态沸腾为主的状态下，277.0（+/- 9.7）W/cm（2）的热通量可以通过具有面积为1 cm（2）的加热器的芯来耗散，而高达733.1（+/- 103.4）W/cm（2）的热通量可以通过具有旨在模拟局部热点的较小加热器的芯来耗散。[DOI 10.1115/1.4006106]
Biporous media consisting of microscale pin fins separated by microchannels are examined as candidate structures for the evaporator wick of a vapor chamber heat pipe. The structures are fabricated out of silicon using standard lithography and etching techniques. Pores which separate microscale pin fins are used to generate high capillary suction, while larger microchannels are used to reduce overall flow resistance. The heat transfer coefficient is found to depend on the area coverage of a liquid film with thickness on the order of a few microns near the meniscus of the triple phase contact line. We manipulate the area coverage and film thickness by varying the surface area-to-volume ratio through the use of microstructuring. Experiments are conducted for a heater area of 1 cm(2) with the wick in a vertical orientation. Results are presented for structures with approximately same porosities, fixed microchannel widths w approximate to 30 mu m and w approximate to 60 mu m, and pin fin diameters ranging from d = 3-29 mu m. The competing effects of increase in surface area due to microstructuring and the suppression of evaporation due to reduction in pore scale are explored. In some samples, a transition from evaporative heat transfer to nucleate boiling is observed. While it is difficult to identify when the transition occurs, one can identify regimes where evaporation dominates over nucleate boiling and vice versa. Heat transfer coefficients of 20.7 (+/- 2.4) W/cm(2)-K are attained at heat fluxes of 119.6 (+/- 4.2) W/cm(2) until the wick dries out in the evaporation dominated regime. In the nucleate boiling dominated regime, heat fluxes of 277.0 (+/- 9.7) W/cm(2) can be dissipated by wicks with heaters of area 1 cm(2), while heat fluxes up to 733.1 (+/- 103.4) W/cm(2) can be dissipated by wicks with smaller heaters intended to simulate local hot-spots. [DOI: 10.1115/1.4006106]