权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

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

在过冷沸腾中，在一定的过冷度和液体流速条件下，过渡沸腾区的热通量并不随着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，并伴随着异常响亮的声音。因此，我们把这种现象称为微泡发射沸腾，简称MEB。 MEB中远超过CHF的高热通量应被认为是该区域聚结气泡剧烈生长和破裂行为的结果，它将过冷液体强烈引入到受热表面。本研究通过条件采样方法，利用设置在表面中心上方适当位置的热电偶分别测量气泡生长和破裂过程中的液体温度分布，作为气泡运动的检测证据。在气泡破裂期间，高温仅出现在表面的中心部分。这个高温区域表明气相存在的可能性很高，表明气泡向表面中心收缩和破裂。在这里，我们试图用双电极空洞探针来获取气泡收缩阶段接近崩溃瞬间的液汽界面移动速度的信息，这里将其称为崩溃速度。与核态沸腾相比，MEB 中的速度非常高。在MEB中，塌陷速度随着热通量的增加而增加，在热通量为20 MW/sq.m时高达20 m/s。气泡运动可以通过电极空隙探针直接监测。空隙信号波动的频率表示液体供给到表面的机会的频率。因此，虚空信号波动功率谱的峰值频率应该是传热的指标，而热通量必然是频率的函数。获得了不同液体过冷度和速度条件下峰值频率与热通量之间的关系。尽管数据显示出广泛的分散性，但在较低的液体过冷度中可以看出较高的峰值频率的趋势。针对 CHF 的多余热通量对其进行了重新排列，以获得相关函数。较少的