Abstract:

In order to solve the problem of rapid volume expansion caused by phase change in the heat transfer process of two-phase flow in microchannels, which triggers the problems of uneven flow rate, pressure drop fluctuation, and local overheating, the flow boiling two-phase pressure drop in countercurrent microchannels with different phase-separated vents densities (PSP00, PSP04, PSP06, PSP10) with and without electric field was investigated. The integrated heat transfer performance of countercurrent microchannels with and without phase-separated structures under the action of different voltages (0, 200V, 400V and 600V) was investigated by introducing the performance evaluation criteria (PEC). The results showed that the greater the density of the vents of the phase-separated structure, the lower the flow resistance and pressure drop in the channel, and the reduction of the two-phase pressure drop was more pronounced with the increase of the heat flow density. The applied electric field increased the pressure drop of two phases in the channel, but the increase of the pressure drop of two phases in the channel was reduced after synergizing with the phase-separated structure, and the pressure drop of two phases in the channel was reduced after applying 600V voltage. Applying 600V to the PSP10 channel with the phase-separated structure reduced the two-phase voltage drop by 14.2% compared to the PSP00 channel without the phase-separated structure. Both the electric field and the phase-separation structure could reduce the length-to-diameter ratio of the confined bubbles in the microfine channel, and the greater the phase-separation pore density and voltage, the smaller the length-to-diameter ratio of the confined bubbles. The electric field alone, the phase separation structure alone, and the combined effect of the electric field and the phase separation structure were all conducive to the improvement of the integrated heat transfer performance PECof the microfabricated channels. Among them, the combined effect of electric field and phase-separated structure was the best, and the larger the density of permeable pores and voltage of phase-separated structure, the larger the PEC. The maximum PEC of the simultaneous action of electric field and phase separation structure (PSP10-600V) was 1.30, which was 13.0% higher than the maximum PEC of the action of electric field alone (PSP00-600V), and 7.4% higher than the maximum PEC of the action of phase separation structure alone (PSP10).

Key words: countercurrent microchannel, modified PVDF membrane, needle electrode, pressure drop, performance evaluation criteria, bubble

摘要：

为解决微通道两相流传热过程中相变导致体积急剧膨胀，引发的流速不均、压降波动、局部过热等问题，本文对有无电场作用下不同相分离透气孔密度的逆流微细通道（PSP00型、PSP04型、PSP06型、PSP10型）内流动沸腾两相压降进行了研究，引入性能评估指标（PEC）对不同电压（0、200V、400V、600V）作用下有无相分离结构的逆流微通道的综合传热性能进行了研究，并利用高速摄影仪对通道进行了可视化研究，引入了受限气泡长径比变化率来分析通道内受限气泡的生长行为。研究结果发现，相分离结构透气孔密度越大，通道内流动阻力和压降越小，随着热流密度的增大，两相压降减小程度更加明显；施加电场会使通道内两相压降增大，但与相分离结构协同作用后的通道内两相压降相比，增加幅度减小，施加600V电压的有相分离结构的PSP10型通道较无相分离结构PSP00型通道两相压降降低了14.2%；电场和相分离结构均可使微细通道内受限气泡长径比减小，且相分离孔密度和电压越大，受限气泡长径比越小；单独电场、单独相分离结构以及电场与相分离结构复合作用均有利于提高微细通道的综合换热性能PEC，其中电场与相分离结构复合作用效果最好，且相分离结构透气孔密度和电压越大，PEC越大，电场和相分离结构（PSP10-600V）同时作用时的最大PEC为1.30，比单独电场（PSP00-600V）作用时的最大PEC提高了13.0%，比单独相分离结构（PSP10型）作用时的最大PEC提高了7.4%。

关键词: 逆流微通道, 改性PVDF膜, 针状电极, 压降, 性能评估指标, 气泡