On the Heat Transfer Mechanism and Stability of High Heat Flux Microbubble Emission Boiling

微泡喷射沸腾（MEB）是指在高过冷度条件下，从核态沸腾到膜态沸腾的过渡过程，在不显著增加壁面沸腾量的情况下，实现极高的热流密度。MEB具有不同于普通沸腾的独特方面，例如从传热表面发射的大量微气泡。该实验研究表明，这种现象包括两个区域，即，微泡发射波的暴风骤雨和风平浪静。这项研究还显示了传热表面的温度fulctuations和表面附近的液体中的压力波动分类MEB到上述制度。在任一制度的温度波动小于那些在临界热通量。与临界热流密度下的压力波动相比，风暴MEB中的压力波动较大，而平静MEB中的压力波动较小。液体过冷度和接近表面的流速为： ...更多信息 重要的方面，以产生这些制度。大量实验得出了MEB状态图，其中包括液体过冷度和流速。在一定条件下，两个区域之间的声压级呈现振荡特征，当存在MEB时，声压级的频率分布有两个峰值。从500 [Hz]开始出现的第一个峰值具有最高的声压级，并且在核态沸腾区难以发现。第二个峰值出现在8000 ~ 16000 [Hz]，该峰值不仅出现在MEB区，而且出现在核沸腾区，特别是在高过冷度下。这两个峰的强度取决于液体过冷度和热流密度。在MEB区域中的气泡向传热表面塌陷。气泡溃灭频率和声压级具有相似的频率分布。上述结果表明，气泡的溃灭是MEB传热机制的一个重要或控制因素。少

Microbubble Emission Boiling (MEB) is the regime that occurs in the transition process from nucleate to film boiling with high liquid subcooling condition, and realizes extremely high heat flux without a marked increase in the amount of wall superheat. MEB has unique aspects different from that of ordinary boiling, such as a profusion of microbubbles emitted from a heat transfer surface. This experimental investigation reveals that this phenomenon includes two regimes, i.e., the stormy and calm microbubble emission boilings. This study also shows temperature fulctuations of a heat transfer surface and pressure fluctuations in the liquid near the surface to classify MEB into the above regimes. The temperature fluctuations in either regime are smaller than those at the critical heat flux. The pressure fluctuations are larger in the stormy MEB,and smaller in the calm MEB as compared with those at the critical heat flux. The liquid subcooling and flow velocity approaching the surface are i … More mportant aspects by which to generate those regimes. A number of experiments lead to the map of MEB regimes that consists of liquid subcooling and flow velocity. An oscillatory character between the two regimes appears under several conditions.The frequency distribution of sound pressure level when MEB exists, has two peak levels. The first peak that appears from 500 [Hz] has the highest sound pressure level and is difficult to be found out in nucleate boiling region. The second peak appears from 8000 to 16000 [Hz] and this peak is not only in MEB region but also in nucleate boiling region, especially with high liquid subcooling. The intensity of the both peaks is depending on liquid subcooling and heat flux. Bubbles in MEB region collapse toward the heat transfer surface. Bubble collapse frequency and sound pressure level of MEB have similar frequency distributions. Consideration of the above results lease to a hypothesis that collapse of a bubble is an important or controlling factor of the heat transfer mechanism of MEB. Less