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首页> 外文期刊>International Journal of Heat and Mass Transfer >Investigation of subcooled and saturated boiling heat transfer mechanisms, instabilities, and transient flow regime maps for large length-to-diameter ratio micro-channel heat sinks
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Investigation of subcooled and saturated boiling heat transfer mechanisms, instabilities, and transient flow regime maps for large length-to-diameter ratio micro-channel heat sinks

机译：研究大长径比微通道散热器的过冷和饱和沸腾传热机理，不稳定性和瞬态流态图

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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 x 1 mm(2) square microchannels. 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. (C) 2018 Elsevier Ltd. All rights reserved.
机译：这项研究调查了与微通道测试模块中R-134a的流动沸腾相关的界面行为和传热机理。该测试模块具有100个1 x 1 mm（2）方形微通道。使用大长度的微通道（609.6 mm）对于捕获流动和传热行为的广泛轴向变化特别重要。流体以过冷状态供应到测试模块，以便能够评估过冷沸腾和饱和沸腾区域。这项研究结合了沿着测试模块进行的温度测量和高速视频，以探索流动的关键细节，包括主要的流动形式，流动不稳定性和下游变干效应。结果表明，与宏通道流不同，在流通道中可以清楚地划分出流态，而微通道中的流态则与由流动不稳定性引起的瞬态波动有关。分别借助于新的瞬态流动状态图和干燥图来表征主要的流动行为和相关的干燥效果。相对于主要的界面和传热机制，研究了过冷沸腾区域的两个子区域，即部分发达的沸腾（PDB）和完全发达的沸腾（FDB），并确定了先前的相关性，以准确预测PDB和FDB。示出的饱和沸腾区域由三个单独的子区域组成：对于质量低于0.3的原子核沸腾占主导地位，对于质量介于0.3和0.5之间的核和对流沸腾组合，对于质量高于0.5占主导地位的对流沸腾。高于0.5时，变干效应开始生效，导致传热系数逐渐下降，而下游则更为严重。确定先前的相关性以预测饱和沸腾区域中的传热系数。 （C）2018 Elsevier Ltd.保留所有权利。

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