Fundamental Research for the Development of Compact Cooling Systems Corresponding to Ultra High Heat Generation Density by Optimization of Boiling and Evaporation Conditions

为了获得高性能冷却系统中沸腾传热的基本知识和一般知识，用不同的方法进行了一些实验。利用88个薄膜温度传感器和微加热器组成的多阵列透明受热面，研究了沸点传热机理，研究了局部传热系数与附着蒸汽泡下液体微层行为的关系。通过反馈电路控制局部表面温度恒定，实现了传热表面简单理想的边界条件。局部热流密度的变化特征为微层蒸发引起的换热增强和干斑扩展引起的变差，这与观测到的合并气泡下的液-气行为相对应。为了证实自润湿效应会增加临界热流密度，采用醇水溶液进行了池沸腾换热实验。换热特性和临界热流密度与乙醇浓度有关。醇水溶液的临界热流密度高于纯水。此外，还制备了二元混合物的热性能和相平衡数据，用于数据还原。窄通道流动沸腾是高性能冷却系统中最有前途的应用形式之一。设计了一种狭长的主通道和不受热的辅助通道的冷却系统结构，通过辅助通道的供液使临界热流密度值提高了两倍以上。

In order to obtain the fundamental and general knowledge of boiling heat transfer in the high-performance cooling systems, a few experiments with different approaches were conducted.Transparent heating surface with multiple arrays of 88 thin film temperature sensors and micro-heaters was developed for the clarification of boiling heat transfer mechanisms, where the relation between local heat transfer coefficients and behaviors of liquid microlayer underneath attached vapor bubbles was investigated. Local surface temperature was controlled to keep constant by the feedback circuits, and a simple and ideal boundary condition on the heat transfer surface was realized. The local heat flux change characterized by the heat transfer enhancement due to the microlayer evaporation and the deterioration by the extending dry patches was detected corresponding to the observed liquid-vapor behaviors underneath a coalesced bubble.Experiments on pool boiling heat transfer were conducted by using the alcohol-aqueous solutions in order to confirm the increase in the critical heat flux due to the self-wetting effect. The heat transfer characteristics and critical heat flux were dependent on the alcohol concentration. The critical heat flux of alcohol-aqueous was observed higher than that of pure water. In addition, the thermal properties of binary mixtures and the phase equilibrium data were prepared for the data reduction.Flow boiling in a narrow channel is one of the most promising application forms for the actual high-performance cooling system. A devised structure of cooling system, which had a narrow main channel and an unheated auxiliary channel, was developed and the critical heat flux value was increased by more than twice by the liquid supply from an auxiliary channel.