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On the Occurrence, Stability and Heat Transfer Enhancement of Microbubble Emission Boiling

微气泡发射沸腾的发生、稳定性及强化传热研究

基本信息

批准号：
13650206
负责人：
KUMAGAI Satoshi
金额：
$ 2.24万
依托单位：
SHINSHU UNIVERSITY (2003)Tohoku University (2001-2002)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650206/
关键词：
Boiling Heat Transfer Microbubble Emission Phenomena Liquid Subcooling Bubble Motion Conditional Sampling Bubble Collapsing Velocity Power Spectrum Surface Erosion 伝熱沸騰気泡微細化気泡崩壊周期固液接触ボイド信号局所温度分布気泡崩壊

项目摘要

In subcooled boiling under certain conditions of subcooling and velocity of the liquid, the heat flux does not decrease with increasing of the surface temperature in transition boiling regime, but increases steeply. In this phenomenon a lot of minute bubbles are emitted from the surface accompanied by extraordinary loud sound. Therefore, we call this phenomenon microbubble emission boiling, abbreviated as MEB. The high heat flux in MEB far exceeding CHF should be considered a result of violent growing and collapsing behavior of coalescent bubbles in that region, which strongly introduces subcooled liquid to the heated surface.In this study, the liquid temperature profiles were measured at the process of growing and collapsing of bubbles separately with conditional sampling method, by using a thermocouple set at a suitable position above the center of the surface as a detecting prove of bubble motion. In the period of bubble collapse, the high temperature appeared only on the central pa … More rt of the surface. This high temperature region indicates the position of high provability for vapor phase to have existed, suggesting that the bubbles shrink and collapse toward the center on the surface. Here, we tried to get an information about the moving velocity of liquid-vapor interface in the bubble shrinking stage near the moment of collapse, which was named as the collapsing velocity, here, with a twin electrode void probe. The velocity was very high in MEB comparing with that of nucleate boiling. In MEB, the collapsing velocity increased with increasing of the heat flux, to be as much as 20 m/s at 20 MW/sq.m in the heat flux.The bubble motion can be monitored directly by an electrode void probe. The frequency of the fluctuation of the void signal indicates the frequency of the chance of liquid supply onto the surface. Therefore, the peak frequency of the power spectrum of the void signal fluctuation should be an index of heat transfer, and heat flux must be a function of the frequency. The relation between the peak frequency and heat flux was obtained for various condition of liquid subcooling and velocity. Though the data showed a wide scattering, a trend of higher peak frequency is distinguished in lower liquid subcooling. It was rearranged for excess heat flux from CHF, to get a correlation function. Less

在一定过冷和液体速度条件下的过冷沸腾中，过渡沸腾状态下的热流密度不随表面温度的升高而降低，而是急剧增加。在这种现象中，许多微小的气泡从表面喷出，伴随着巨大的声音。因此，我们称这种现象为微泡发射沸腾，简称为MEB。MEB中远超CHF的高热流密度应考虑为该区域内聚结气泡的剧烈生长和坍缩行为，将过冷液体强烈引入受热表面的结果。在本研究中，采用条件采样法分别测量了气泡生长和崩溃过程中的液体温度分布，并将热电偶设置在表面中心上方的合适位置，作为气泡运动的检测证明。在气泡破裂期间，高温只出现在中心区域，而在更多的区域。这个高温区域表明了气相存在的高可证明性的位置，表明气泡在表面上向中心收缩和坍缩。在这里，我们试图用双电极空洞探针获得气泡收缩阶段靠近坍缩时刻的液-气界面移动速度的信息，并将其命名为坍缩速度。与有核沸腾相比，MEB沸腾的速度非常高。在MEB中，坍塌速度随热流密度的增大而增大，在20 MW/sq时，坍塌速度可达20 m/s。M在热流中。气泡运动可以通过电极空隙探头直接监测。空洞信号波动的频率表示液体供应到表面的机会频率。因此，真空信号波动功率谱的峰值频率应该是传热的一个指标，而热流密度必须是频率的函数。得到了不同液体过冷和速度条件下的峰值频率与热流密度的关系。虽然数据显示出广泛的散射，但在较低的液体过冷度下，峰值频率有较高的趋势。对CHF的余热通量进行重新排序，得到相关函数。少