Liquid-Vapor Structure near Heating Surface at High Heat Flux in Subcooled Pool Boiling

过冷池沸腾高热通量受热面附近的液-汽结构

• 批准号: 13650204
• 负责人: SAKASHITA Hiroto
• 金额: $ 1.28万
• 依托单位: HOKKAIDO UNIVERSITY
• 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 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650204/
• 关键词: Subcooled boiling; Conductance probe; Capacitance probe; Critical heat flux; Liquid macrolayer; Primary bubble; Growing time; Waiting time; マクロ液膜厚さ; 静電容量法; 触針法; 気泡寿命; プール沸騰; 気液挙動; 測定

In subcooled pool boiling on heating surfaces with high thermal capacity, large coalesced bubbles are formed and detach repeatedly and rest thin liquid-rich layer (termed liquid macrolayer) on their bottom. Critical heat flux occurs when the liquid-rich layer dries out before detachment of the large coalesced bubbles. On the other hand, with low thermal capacity, numerous fine bubbles are formed and collapse in very short time even at high heat flux near critical heat flux, and coalescence of these fine bubbles triggers the critical heat flux. Therefore, clarifying both the structure of liquid macrolayer and the behavior of short-lived fine bubbles is important to resolve the mechanism of critical heat flux of subcooled pool boiling.The present sutdy developed two measurement methods ; a conductance probe method and a capacitance probe method. In the conductance probe method, the probe with about 5μm tip diameter was used to measure liquid-vapor structure with high accuracy. Measuremen … More ts were made for water boiling on an upward-facing surface in the range of subcooling 0K to 30K. It was found that the probe signals corresponding to the large coalesced bubbles disappear at the almost same height from the heating surface. This height was regarded as the liquid macrolayer. The measured macrolayer was considerably thicker than the extrapolation of the previously proposed correlations for saturated pool boiling to higher heat flux and this is most likely to be the cause that the CHF increases with the increase in subcooling.A capacitance probe method was developed to measure the behavior of fine vapor bubbles in subcooled boiling with high accuracy. The capacitance probe has high sensitivity enough to detect the bubble cycle from generation to collapse that terminates within 0.1msec. Or less. The growing time and the waiting time of primary bubbles were measured for water boiling on upward surfaces in the range of subcooling 0K to 70K. The growing time decreases rapidly with the increase in the subcooling over 10K. The waiting time show the tendency that initially increases and then decreases with increasing subcoolong, which is inconsisitent with the prediction of classical nucleation theories. Less

在高热容量的加热表面上沸腾的子冷池中，形成大的聚集气泡并反复脱离，并在其底部静止富含液体液（称为液体macrolayer）。当液体富含液体层在大型聚集起来之前梦dream以求时，就会发生关键的热通量。另一方面，即使在临界热通量附近的高热通量下，也会在很短的时间内形成许多细气泡，并在很短的时间内塌陷，并且这些细气泡的合并触发了关键的热量通量。因此，阐明液体大花层的结构和短寿命的细气泡的行为对于解决亚冷池沸腾的临界热通量的机制很重要。目前的饱和两种测量方法。电导探针方法和电容探针方法。在电导探针方法中，使用大约5μm尖端直径的探针以高精度测量液体蒸气结构。测量人员…在子冷0k至30k的范围内，在向上的表面上沸腾了更多的Ts。发现与加热表面几乎相同的高度上，对应于大型聚集的探针信号消失了。该高度被认为是液体大型层。测得的宏观层被认为比先前提出的饱和池沸腾到更高热通量的相关性的外推要厚，这最有可能是由于CHF随着亚冷的增加而增加的原因。A的电容探针方法是为了测量具有高精度沸腾沸腾的高精度泡泡的行为。电容探针具有高灵敏度，足以检测出从产生的气泡循环到终止0.1msec之内的气泡循环。或更少。测量了在0K至70K的范围内，测量了在向上表面沸腾的水的增长时间和等待时间。随着子冷却超过10K的增压，增长时间迅速减少。等待时间表明，最初增加并随后增加的趋势而增加，这与对经典核化理论的预测不一致。较少的