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

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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