Abstract:

The boiling heat transfer enhancement by porous materials is an important topic in the fields of energy and chemical industry. The subcooled flow boiling experiment was carried out with the deionized water as the working fluid. Two types of sintered structures were investigated: parallel porous microchannel and flat channel (only the bottom layer sintered). It was found that parallel porous microchannels presented higher HTC (heat transfer coefficient) and CHF (critical heat flux) than flat microchannels, which was attributed to the excellent capillary liquid supply performance of porous microchannels. The ratio of the bottom thickness to the particle size (δ/d) had a great effect on the boiling heat transfer performance of parallel porous microchannels. Too high δ/d would cause a deterioration in heat transfer performance. The mass flux exerted different influence on heat transfer performance over sintered samples with small or large particle size. Parallel microchannels showed greater pressure drops than flat microchannels. With the same bottom thickness, the average pressure drop increased almost linearly with sintered particle size. The visual observation showed that the flow patterns of the two channels were different at medium and high heat flux, and the main phase-change mechanism was thin film evaporation.

Key words: microscale, porous microchannel, flow boiling, vapor-liquid flow, evaporation

摘要：

多孔材料对沸腾换热的强化是能源化工领域的重要主题。本文针对两种不同的烧结结构——并联微通道和扁平通道（仅有烧结底层），以去离子水为工质，进行了过冷流动沸腾换热实验对比研究。研究发现：并联微通道的传热系数和临界热流密度远高于扁平通道，这和并联微通道优异的毛细供液性能相关。底厚粒径比对并联微通道的沸腾换热性能影响较大，过大的底厚粒径比会造成换热性能的下降。质量通量对小粒径样品的沸腾曲线和换热性能均影响较大，对大粒径（d=120μm）样品的沸腾曲线影响较小。烧结并联微通道的平均压降大于扁平通道。相同底厚下，平均压降随着微通道粒径的增大而增大。可视化观察表明：两种通道在中高热流密度流型不同，其主要相变机制均为薄液膜蒸发模式。

关键词: 微尺度, 多孔微通道, 流动沸腾, 汽液两相流, 蒸发