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

点击翻译按钮获取中文摘要

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.