微纳电子技术

为提升微通道相变换热器综合性能，包括同时实现降低沸腾起始过热度、提高传热系数和抑制沸腾传热不稳定性，提出了一种具有锯齿形肋壁的硅基微电子机械系统(MEMS)微通道结构，并对常规并联微通道与锯齿肋壁微通道开展了对比实验研究。结果表明，锯齿肋壁的齿根处提供了众多有效核化穴，实现了2℃低过热度下的沸腾启动，较常规并联微通道的沸腾起始过热度降低了18℃。由于大量锯齿形核化穴的存在，提高了通道内的气泡核化密度，使得锯齿肋壁微通道中心线处的平均换热系数较常规并联微通道最大提高了约85.5%。同时，较多的气化核心使得过热液层的能量从多个气液相变界面进行潜热释放，气泡生长膨胀速度减缓，抑制了沸腾传热不稳定性。锯齿肋壁的变截面结构对通道内液体产生毛细吸附效应，使得通道内倾向于形成环状流高效薄液膜对流蒸发传热模式，这也是锯齿肋壁强化传热的主要机制之一。

A silicon-based micro-electromechanical system(MEMS)microchannel structure with saw-toothed sidewalls was proposed to enhance the comprehensive performances of microchannel phase change heat exchangers, including achieving lower boiling initiation points, higher heat transfer coefficients, and stable boiling heat transfer simultaneously. Comparative experimental studies were conducted between conventional parallel microchannels and sawtoothed sidewall microchannels. The results show that the sawtoothed sidewalls provides numerous effective nucleation sites at the tooth root, enabling boiling initiation at a low superheat of 2 ℃ which is an 18 ℃ reduction in boiling initiation superheat compared to conventional parallel microchannels. The presence of numerous zigzag-shaped nucleation sites increases the bubble nucleation density inside the channel, resulting in an about 85.5% increase in average heat transfer coefficient at the center line compared to conventional parallel microchannels. Moreover, the presence of more vaporization cores allows the energy in the superheated liquid layer to be released as latent heat from multiple gas-liquid phase interfaces, slowing down the bubble growth rate and suppressing boiling heat transfer instability. The variable cross-sectional structure of the sawtoothed sidewalls induces capillary adsorption effects in the channel, promoting the formation of an efficient thin liquid film convective evaporation heat transfer mode. This is one of the main mechanisms for enhancing heat transfer with the sawtoothed sidewalls.