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首页> 外文期刊>International Journal of Heat and Mass Transfer >Spatiotemporally resolved heat transfer measurements for flow boiling in microchannels
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Spatiotemporally resolved heat transfer measurements for flow boiling in microchannels

机译：时空解析传热测量，用于微通道中的流沸腾

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摘要

Spatiotemporally resolved wall heat transfer measurements can provide valuable insight into the fundamental mechanisms affecting flow boiling in microchannels. Operating at the microscale, necessitates resolving changes in local and instantaneous heat transfer characteristics on the order of 100 μm and 1 kHz, respectively. Straightforward interpretation of transient temperature measurements is often challenging due to the conjugate conduction effects in the substrate, which can dampen the measured and inferred heat transfer quantities. These damping effects are described using a slip coefficient (S), which represents the fraction of the change in the local heat transfer that is registered by a sensor (negligible thermal mass) located on a given substrate. Using S, arguments are presented that the conduction patterns in the substrate are predominantly 1-D (i.e. into the substrate) at suitable spatiotemporal-scales. Building on these fundamental considerations, a numerical procedure is adopted to allow a time varying estimate of the local convective heat flux and heat transfer coefficient from transient temperature measurements. Examples of this framework are showcased with experimental results and discussions for interactions observed during flow boiling of HFE 7000 in a single microchannel (hydraulic diameter = 370 μm). At the relatively low mass flux of 200 kg/m~2 s reported in this work, liquid evaporation was found to dictate the local heat transfer trends. High rates of heat transfer were observed to accompany the growth of bubbles and evaporation of the liquid film under vapor slugs. Local dryout was routinely observed in the bubbly and slug flow regime and found to initially enhance heat transfer (i.e. at the creation and subsequent propagation of the three-phase contact line) and present near-zero heat transfer rates in the dried-out domain.
机译：时空解析的壁传热测量可以提供有价值的洞察力，以了解影响微通道中沸腾的基本机理。在微尺度下运行，必须解决局部和瞬时传热特性分别为100μm和1 kHz量级的变化。由于基材中的共轭传导效应，对瞬态温度测量的直接解释通常是具有挑战性的，这可能会抑制所测得的热量和推断出的传热量。使用滑移系数（S）描述这些阻尼效果，滑移系数（S）表示局部传热变化的分数，该变化由位于给定基板上的传感器（可忽略的热质量）记录。使用S，提出了在合适的时空尺度下衬底中的导电图案主要是1-D（即到衬底中）的论点。在这些基本考虑的基础上，采用了一种数值程序，可以根据瞬态温度测量值对当地对流热通量和传热系数进行时变估计。通过实验结果展示了该框架的示例，并讨论了在单个微通道（液压直径= 370μm）中HFE 7000的流煮过程中观察到的相互作用。在这项工作中报道的相对较低的质量通量为200 kg / m〜2 s时，发现液体蒸发决定了局部传热的趋势。观察到高的热传递率伴随着气泡的增长以及在蒸汽团块下液膜的蒸发。在气泡和团状流态中常规观察到局部变干，发现其最初增强了传热（即在三相接触线的产生和随后的传播时），并且在变干区域中呈现接近零的传热速率。

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