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首页> 外文期刊>International Journal of Heat and Mass Transfer >Heat transfer and critical phenomena during evaporation and boiling in a thin horizontal liquid layer at low pressures
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Heat transfer and critical phenomena during evaporation and boiling in a thin horizontal liquid layer at low pressures

机译：在低压下在水平液体薄层中蒸发和沸腾期间的传热和临界现象

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摘要

The results of an experimental study of heat transfer and high-speed video recording of evaporation and boiling processes in horizontal liquid films of n-dodecane are presented for the wide ranges of layer height and pressure. Evaporation regimes at low reduced pressures were characterized by formation of dry spots and structures with the shape of "funnels" (depressions with a hemispherical bottom on the layer surface) and "craters" in the layers. In contrast to dry spots, the surface of "craters" is covered with a residual layer of liquid. The paper presents regime maps indicating the regions of dry spots, "funnels", "craters", and nucleate boiling observed for each layer height depending on the reduced pressure and heat flux density. It is shown that in the region of low reduced pressures, the Kutateiadze formula describes change in hydrodynamics in the layers, whose height is equal to the Laplace constant or higher, by the regime where only "craters" remain in the layer. In the region of reduced pressures less than 7.4 • 10~(-5) (133 Pa) the critical heat fluxes (CHF) decrease with decreasing pressure. In the range of reduced pressures from 7.4 10~(-5) (133 Pa) to 5.5 1(T~(-3) (10~4 Pa), the CHF depends weakly on the pressure. With an increase in the layer height, CHFs increase sharply, and when achieving a constant value, are described by the Yagov dependence obtained for pool boiling of liquids. For the reduced pressure above 5.5 • 10~(-3) (10~4 Pa), in the layers with a height exceeding the Laplace constant, the CHF is the same as that calculated by the Kutateiadze and Yagov formulas for nucleate boiling crisis. The slope of the curve of heat flux dependence on the temperature head depends on the layer height at both evaporation and nucleate boiling.
机译：给出了在正十二烷水平液膜中的传热以及蒸发和沸腾过程的高速视频记录的实验研究结果，该研究结果显示了层高和压力范围很广。低减压下的蒸发方式的特征在于形成干燥点和结构，这些干燥点和结构具有“漏斗”形状（在层表面上具有半球形底部的凹陷）和层中的“凹陷”。与干斑相反，“火山口”的表面覆盖有残留的液体层。本文介绍了根据减压和热通量密度表示的各层高度上观察到的干燥点，“漏斗”，“火山口”和核沸腾区域的状态图。结果表明，在低压较低的区域中，Kutateiadze公式描述了层中流体动力学的变化，该层的高度等于Laplace常数或更高，这是因为层中仅存在“火山口”。在低于7.4•10〜（-5）（133 Pa）的减压区域中，临界热通量（CHF）随着压力的降低而降低。在从7.4 10〜（-5）（133 Pa）到5.5 1（T〜（-3）（10〜4 Pa）的减压范围内，CHF对压力的依赖性很小，随着层高的增加，CHF急剧增加，当达到恒定值时，由Yagov依赖关系描述为液体池沸腾；对于5.5•10〜（-3）（10〜4 Pa）以上的减压，在具有高度超过拉普拉斯常数时，CHF与通过Kutateiadze和Yagov公式计算出的核沸腾危机的CHF相同，热通量的曲线斜率取决于温度头，同时取决于蒸发和成核沸腾时的层高。

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