Fundamental Study of the Enhancement of Flash Evaporation in a Steam Accumulator by Means of the Injection of Artificial Bubble Nuclei

作为开发高效水蒸气蓄热器的一种尝试，实验研究了电解产生的气泡核注入对容器内突然压降下温水闪蒸的影响。结果表明，人工成核增强了池水的闪蒸，从而提高了蒸发后期的闪蒸效率，特别是在液体温度较低、液位较高和过热区较小的情况下。从过热区的无量纲深度和电解气体的质量速度出发，推导出了当蒸汽质量速度下降到任意给定值时的实际蒸发效率的半经验公式。由于过热液体中气泡的生长是闪蒸过程，数值分析了初始气泡半径对均匀过热液体中气泡生长速度的影响。结果表明，当初始气泡半径大于临界半径的两倍时，界面张力对气泡生长速率的影响可以忽略不计。从理论解出发，推导出了预测均匀过热纯液体中气泡生长速率的无量纲方程。

As an attempt to develop an efficient steam accumulator, an experimental investigation has been made of the effect injection of bubble nuclei generated by electrolysis on the flash evaporation of warm water exposed to a sudden pressure drop in a container.From the results, it is realizad that artificial nucleation enhances the flash evaporation of pool water thereby increasing the flash evaporation efficiency in the late evaporaion period, especially for the cases of lower liquid temperature, higher liquid level and smaller superheat regions. Semi-empirical equations are deduced for predicting the practical evaporation efficiency when the mass velocity of vapor declined to any given values, from the dimensionless depth of the superheated zone ane the mass velocity of electrolytic gases.Because bubble growth in a superheated liquid domains the flash evaporation process, a numerical analysis has been carried out to examine the effect of the initial bubble radius on the bubble growth rate in an uniformly superheated liquid. The results show that the effect of interfacial surface tension on the bubble growth rate can be neglected when the initial bubble radius is greater than two times of the critical radius. A dimensionless equation for predicting the bubble growth rate in uniformly superheated pure liquids is deduced from the theoretical solutions.