连通微通道内过冷流动沸腾传热强化机理分析

Analysis of heat transfer enhancement mechanism on subcooled flow boiling in interconnected microchannels

连通微通道(平行主通道由支流通道连通)流动沸腾传热具有优越的换热性能,但其传热传质强化机理尚不够明确,限制了其实际应用。鉴于此,本文基于流体体积函数(VOF)方法,对连通微通道内过冷流动沸腾进行二维非稳态数值模拟,研究了流场扰动、脱落汽泡与壁面间的薄液膜分布对微通道当地传热系数的影响规律。结果表明,连通微通道存在两种强化换热机理:支流通道脱落汽泡可增强主通道流场扰动,进而促进了通道热边界层再发展;脱落汽泡与热壁面间可形成薄液膜,该薄液膜减小了换热热阻。同时研究了支流通道倾角(θ)对连通微通道强化换热的影响,结果发现,不同θ时,连通微通道整体平均传热系数提高10.51%~17.66%,单个主通道平均传热系数最高可提升27.94%,且θ=45°时连通微通道具有最佳换热特性。该研究有望为芯片高效冷却结构的设计提供指导。

The flow boiling of interconnected microchannels, in which main channels are connected by branch channels, has superior heat transfer characteristics. However, the mechanism of heat and mass transfer enhancement is not clear enough, which limits its practical application. Hence, based on the volume of fluid(VOF) method, a two-dimensional unsteady numerical simulation of subcooled flow boiling in the interconnected microchannels was carried out. The influences of local flow field disturbance and thin liquid film distribution between shedding bubbles and heating wall on the heat transfer characteristics of microchannels were discussed. It was found that the mechanisms of heat transfer enhancement contain two types. The first one is that the shedding bubbles of branch channel can enhance the flow field disturbance of main channel, thus promoting the redevelopment of thermal boundary layer of main channel. The second one is that thin liquid film can be formed between shedding bubbles and heating wall, which reduces the heat transfer resistance. The effect of dip angles(θ) of branch channel on the heat transfer characteristics of interconnected microchannels was further studied. It was found that the overall average heat transfer coefficient of interconnected microchannels was improved by 10.51% to17.66% compared to unconnected microchannels, and the average heat transfer coefficient of single main channel was improved by up to 27.94%. When θ=45°, the interconnected microchannels showed the best heat transfer characteristics. The research could provide guidance for the design of efficient chip cooling structures.