Abstract: Microchannel heat exchangers are widely developed in recent years. Heat transfer enhancement and pressure drop reduction are two important goals for designing microchannel heat exchangers. Pin-fin arrays formed porous walls are used as phase separator in flow condensation in microchannels to meet above two challenges. Pressure drop reduction and heat transfer enhancement achieved at the same time. An energy-dissipation based on pressure drop reduction theory was proposed. The reduced two-phase interface area in phase separation flow was the key point to pressure drop reduction. On the other hand, extra liquid was sucked into liquid passage, leaving high-temperature vapor directly contacting pin-fin walls, greatly enhancing condensation heat transfer by deducing film thickness. The diverging liquid channel cross section area ensured liquid being trapped in liquid passage without flooding, accommodating ever increasing liquid along flow direction and ensuring heat transfer enhancement along flow direction. The above phase-separation theory offers new visions for design of condensation heat exchanger in the future.

Key words: microchannels, two-phase flow, heat transfer, interface, dissipation model, pressure drop reduction

摘要： 微通道换热器应用广泛，强化传热和减阻是新型换热器设计的重要目标。为了同时实现这两相目标，本文提出了一种分相式多孔壁微通道冷凝器，利用微针肋阵列组成的多孔壁在冷凝传热过程中实现了汽液两相分离。采用实验研究方法对比了分相式多孔壁微通道与普通实心壁微通道的流动和传热特性，结果证明分相式微通道在冷凝传热中同时具备强化传热和减阻的作用。深入研究了通道内两相流动摩擦耗散原理并提出了相分离减阻理论，指出汽液两相流内部摩擦耗散的减小是分相流减阻的关键。另一方面，分相过程使针肋换热面侧壁直接与高温蒸汽接触，极大消减了蒸汽与换热壁面之间的传热液膜厚度。沿流动方向不断扩展的液通道截面与不断减缩的汽通道截面积适应了流动冷凝过程延工质流动方向"水渐多，汽渐少"的规律，保证沿程传热效果不会恶化。

关键词: 微通道, 两相流, 传热, 界面, 耗散模型, 减阻