Abstract The geyser boiling instability in a two-phase closed loop thermosyphon (TPCLT) is experimentally investigated through flow visualization and simultaneous measurement of pressure and temperature fluctuations. Wide ranges of filling ratios of R134a fluid from 90% to 53%, and heat flux from 20 W cm−2 to 220 W cm−2 are examined. The Power Spectrum Density (PSD) method is applied to analyze the periodicity of geyser boiling, and the parameter Standard Deviation (SD) is used to characterize the oscillating amplitude. The effects of heat flux and filling ratio on the geyser boiling occurrence and the oscillation characteristics are discussed in detail. The results show that, the flow regimes experience the consecutive variation of single-phase flow, bubbly flow, churn flow, bubbly flow, and single-phase flow within each geyser boiling cycle, leading to the fluctuation of flow and heat transfer characteristics. The geyser boiling is more liable to occur in the conditions of higher filling ratio and moderate heat flux. The initiating heat flux for the onset of geyser boiling decreases with the increase of filling ratio, but the range of heat flux for the geyser boiling occurrence is narrow under the high filling ratio conditions. The frequency of geyser boiling increases with the increase of heat flux for a certain filling ratio. With the increase of filling ratio, the oscillating frequency firstly decreases and then increases. The minimum oscillating frequency occurs at the combination of filling ratio of 76% and heat flux of 90 W cm−2 under the experimental conditions in this work. Both the fluctuation amplitude of pressure and temperature increase with the increase of heat flux, while decrease with the increase of filling ratio. Compared to R134a under the same filling ratio of 76%, the water has higher heat flux for geyser boiling occurrence, smaller oscillating amplitude of pressure, and lower oscillating frequency due to the difference in thermophysical properties.

中文翻译：

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高填充率两相闭环热虹吸中间歇泉沸腾的实验研究

摘要 通过流动可视化和压力和温度波动的同时测量，对两相闭环热虹吸管 (TPCLT) 中的间歇泉沸腾不稳定性进行了实验研究。研究了从 90% 到 53% 的 R134a 流体的广泛填充率和从 20 W cm-2 到 220 W cm-2 的热通量。应用功率谱密度(PSD)方法分析间歇泉沸腾的周期性，参数标准偏差(SD)用于表征振荡幅度。详细讨论了热通量和填充率对间歇泉沸腾发生和振荡特性的影响。结果表明，在每个间歇泉沸腾循环内，流态经历了单相流、气泡流、搅动流、气泡流和单相流的连续变化，导致流动和传热特性的波动。在较高的填充率和适中的热通量条件下更容易发生间歇泉沸腾。间歇泉沸腾发生的起始热通量随着填充率的增加而减小，但在高填充率条件下间歇泉沸腾发生的热通量范围较窄。对于一定的填充率，间歇泉沸腾的频率随着热通量的增加而增加。随着填充率的增加，振荡频率先减小后增大。在这项工作的实验条件下，最小振荡频率出现在 76% 的填充率和 90 W cm-2 的热通量的组合下。压力和温度的波动幅度都随着热通量的增加而增加，而随着填充率的增加而降低。与R134a相比，在76%的相同填充率下，由于热物理性质的差异，水具有更高的间歇泉沸腾发生热通量、更小的压力振荡幅度和更低的振荡频率。