Enhancement of Liguid-Solid Contact in Miniaturization Phenomena

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This research concerns with augmentation of liquid-solid contact in two boiling phenomena : minute bubble emission boiling and miniaturization boiling of droplets. 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 were measured by means of the void probe and piezoelectric potential methods, respectively. The periods of bubble ejection and droplet dispersion were compared. In the miniaturization boiling case, the timewise variation of heating surface temperature was monitored using thermocouples that were embedded underneath the heating surface, from which the time-wise average surface temperature and heat flux during miniaturization process were evaluated and compared with steady-state pool boiling curve of the minute bubble emission boiling process.In connection with the liquid-solid contact boiling, the liquid-liquid, direct-contact boiling was performed at steady state by placeing a molten ally of low melting point into a pool filled with water. The boiling curve was obtained in the range of the superheat from 20 to 200K.It was disclosed that the heat flux was under 1 MW/m^2, although a violent interaction was observed between the melt and the water.It is concluded from a comparison based on these measured results that the three 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.