High Performance Cooling with Boiling Heat Transfer in Confined or Low Level Water Space

本研究包括两个主要课题。本文对多孔绝热干扰板限制沸腾空间的情况下，圆形铜表面的池沸腾进行了实验研究。传热表面和干涉板之间的空间在周边处被密封，以模拟大的传热表面。实验中得到了多条沸腾曲线，观察到了干涉板上孔的分布规律。在小于1K的小表面温度下，在狭窄的空间中获得了高的热通量。发现了与现有沸腾传热相媲美的高传热性能的干涉板 ...更多信息 r高性能表面。在水中，具有两种类型的孔的干涉板给出了最佳性能，即，其次，在低水位下，不仅在核态沸腾的低热流密度区，而且在最大热流密度区，都有沸腾传热强化作用。前者的增强来自于水汽穹窿下薄水膜的剧烈蒸发。后者是由于在这种低液位液体中，表面上没有形成蒸汽团，从而导致从圆周方向连续稳定地供水，并考察了影响传热表面供水传热性能应考虑的几个因素。沸腾器的尺寸和表面的润湿性对传热的影响很小。但换热面积的大小对传热有决定性的影响，特别是在高热流密度区域。小表面在低水位时释放的最大热通量远高于在足够深的水中释放的最大热通量，如直径为8mm的表面在1.0mm水位时释放的最大热通量是池沸腾最大热通量的1.47倍。直径为26mm的表面在低水位时最大热流密度仅略有增加，而圆锥表面在顶角从180 °变化到160 °时，最大热流密度也略有增加。在160 ° C的锥形管中，即使在0mm水位（锥顶测量）下也能保持稳定的核态沸腾，这对于实际应用来说是非常舒适的。与平面相比，顶角为160 °和170 °的锥形表面的最大热流密度有所增加，但差异不大。少

This research consists of two main subjects. The one is on the boiling heat transfer enhancement by means of confining the boiling space, and the other is on the boiling heat transfer to low leveled water.An experiment on pool boiling on a circular copper surface in water was performed for a case in which the boiling space was restricted by an adiabatic interference plate with many holes. The space between the heat transfer surface and the interference plate was hermetically sealed at the perimeter to simulate a large surface of heat transfer. Therefore, the vapor and liquid were exchanged through the holes in the interference plate.Many boiling curves were obtained, and appearances were observed for many distributing patterns of holes on the interference plates. High heat fluxes were obtained in the narrow space at a small surface superheat of less than 1K. The interference plate of high heat transfer performance was found which was comparable with other available boiling heat transfe … More r surfaces of high performance. In water, the best performance was given by the interference plate with two types of holes, i.e., 4mm and 1mm in diameter, if it was set 0.12mm above the surface.Next, boiling heat transfer enhancement were confirmed for low level of water not only in low heat flux region of nucleate boiling, but also at maximum heat flux. The former enhancement came from violent evaporation of thin water film under vapor domes. The latter arose from not forming vapor lumps over the surface in such low leveled liquid, which resulted in steady and successive supply of water from circumference.Several factors which should be considered to affect on heat transfer performance through supply of water to heat transfer surface was examined. The size of boiling vessel and the wetability of the surface had only little influence on heat transfer. But the size of heat transfer surface decisively affected on heat transfer, especially in high heat flux region. A small surface could release much higher maximum heat flux in low level of water than in sufficiently deep water, e.g. 8mm diameter surface showed 1.47 times of pool boiling maximum heat flux at the level of 1.0mm. The surface of 26mm diameter showed only a little increase of maximum heat flux in low leveled water.Conical surfaces were also examined changing the apex angle from 180ﾟ to 160ﾟ. Steady nucleate boiling was maintained even at 0mm of water level (measured at the top of the cone) with 160ﾟ cone, which is very comfortable character for practical use. Conical surface of 160ﾟ and 170ﾟ in apex angle showed increased maximum heat flux comparing with a flat surface, though the difference was not so large. Less