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

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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