Abstract This study investigates the interfacial behavior and heat transfer mechanisms associated with flow boiling of R-134a in a micro-channel test module. The test module features 100 of 1 × 1 mm2 square micro-channels. Large length of micro-channels used (609.6 mm) is especially important to capturing broad axial variations of both flow and heat transfer behavior. The fluid is supplied to the test module in subcooled state to enable assessment of both the subcooled boiling and saturated boiling regions. The study employs a combination of temperature measurements along the test module and high-speed video to explore crucial details of the flow, including dominant flow regimes, flow instabilities, and downstream dryout effects. It is shown that, unlike macro-channel flows, where flow regimes can be clearly demarcated, flow regimes in micro-channels are associated with transient fluctuations that are induced by flow instabilities. The dominant flow behavior and associated dryout effects are characterized with the aid of a new transient flow regime map and a dryout map, respectively. Two sub-regions of the subcooled boiling region, partially developed boiling (PDB) and fully developed boiling (FDB), are examined relative to dominant interfacial and heat transfer mechanisms, and a previous correlation is identified for accurate prediction of the heat transfer coefficient for both PDB and FDB. The saturated boiling region is shown to consist of three separate sub-regions: nucleate boiling dominated for qualities below 0.3, combined nucleate and convective boiling for qualities between 0.3 and 0.5, and convective boiling dominated for qualities above 0.5. Above 0.5, dryout effects begin to take effect, causing a gradual decline in the heat transfer coefficient followed downstream by a more severe decline. A previous correlation is identified for prediction of the heat transfer coefficient in the saturated boiling region.

中文翻译：

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大长径比微通道散热器的过冷和饱和沸腾传热机制、不稳定性和瞬态流态图的研究

摘要 本研究在微通道测试模块中研究了与 R-134a 流动沸腾相关的界面行为和传热机制。测试模块具有 100 个 1 × 1 mm2 方形微通道。使用大长度的微通道（609.6 毫米）对于捕捉流动和传热行为的广泛轴向变化尤其重要。流体以过冷状态提供给测试模块，以评估过冷沸腾和饱和沸腾区域。该研究结合测试模块的温度测量和高速视频来探索流动的关键细节，包括主要流动状态、流动不稳定性和下游干涸效应。结果表明，与大通道流动不同，大通道流动可以清楚地划分流动状态，微通道中的流动状态与流动不稳定性引起的瞬时波动有关。主要流动行为和相关的干燥效应分别借助新的瞬态流态图和干燥图进行表征。过冷沸腾区域的两个子区域，部分发展沸腾 (PDB) 和完全发展沸腾 (FDB)，相对于主要的界面和传热机制进行了检查，并确定了先前的相关性以准确预测传热系数PDB 和 FDB。饱和沸腾区域显示为由三个独立的子区域组成：质量低于 0.3 的核沸腾占主导地位，质量在 0.3 和 0.5 之间的核沸腾和对流沸腾相结合，以及质量高于 0.5 的对流沸腾占主导地位。0.5 以上，干涸效应开始生效，导致传热系数逐渐下降，随后更严重的下降。确定了先前的相关性以预测饱和沸腾区域中的传热系数。