Estimation of a Boiling Curve of a Miniaturization Boiling Phenomenon and its Critical Heat Flux

本文研究了两种沸腾现象：微小气泡发射沸腾和微型化沸腾中液固接触的增强。在前者中，在受热表面上产生的气相不是覆盖表面，而是以许多微小的蒸汽泡的形式出现，喷射到过冷的液体中，在过冷池中沸腾。然而，在后一种情况下，当液体体积撞击加热表面时，会产生许多微小的液滴分散到大气中，这被称为液滴沸腾。液固接触的增强是通过微小气泡的喷射和微小液滴的分散引起的扰动来实现的，这些扰动分别由空隙探针和压电电位方法测量。比较了气泡喷射和液滴扩散的周期。在微型化沸腾情况下，采用点焊热电偶对受热面温度随时间的变化进行了监测，计算了微型化过程中受热面温度和热流密度的随时间平均，并与微泡发射沸腾过程的稳态池沸腾曲线进行了比较。采用图像处理方法对微型化沸腾过程中的瞬态行为进行了图形化描述，并以此图确定了液滴的分散强度。为了阐明微型化的机理，本文对金属液与水的反应进行了实验研究。熔融锡落在石英透镜上方的水膜上，因此可以使用石英透镜后面的全息干涉测量法捕获锡的行为。特别是，在熔融金属和水膜之间的界面上存在的微小蒸汽泡以及它破裂的过程被实时可视化。结果表明，两种微型化沸腾现象发生在相同的阈值温度下，均在180 ~ 210℃范围内，微型化发生的机理相同。本报告由六个部分组成。少

This paper concerns with augmentation of liquid-solid contact in two boiling phenomena : minute bubble emission boiling and miniaturization boiling. In the former, vapor phase generated on a heating surface, instead of covering the surface, appear in many minute-size vapor bubbles ejecting into subcooled liquid, in a subcooled pool boiling. In the latter, however, a liquid volume, upon its impingement upon a heating surface, produces numerous minute-size droplets dispersing into the atmosphere, referred to as liquid droplet boiling. Enhancements in liquid-solid contact are achieved through disturbances due to the ejection of minute bubbles and dispersion of minute droplets which are measured by means of the void probe and piezoelectric potential methods, respectively. The periods of bubble ejection and droplet dispersion are compared. In the miniaturization boiling case, the timewise variation of heating surface temperature is monitored using thermocouples that are spot-welded undernea … More th the heating surface, from which the timewise average surface temperature and heat flux during miniaturization process are evaluated and compared with steady-state pool boiling curve of the minute bubble emission boiling process. Transient behavior during miniaturization boiling is graphically illustrated by means of image processing method and the dispersion strength of liquid droplets is determined from this figure. To help clarify the mechanism of the miniaturization, experiments were conducted in the present study on the reaction of molten metal and water. Molten tin was dropped on a water membrane above a quartz lens, so the behavior could be captured using the holographic interferometry from behind the quartz lens. In particular, the existence of the minute vapor bubble at the interface between the molten metal and the water membrane and the process by which it breaks was visualized in real time.It is concluded from a comparison based on these measured results that the two miniaturized boiling phenomena occur at the same threshold temperature, in the range of about 180 to 210ﾟC with miniaturization taking place under the same mechanism. This report is consists of six parts. Less