The boiling crisis of water under exponentially escalating heat inputs in subcooled flow boiling at atmospheric pressure
The boiling crisis of water under exponentially escalating heat inputs in subcooled flow boiling at atmospheric pressure
复制标题
大气压下过冷流沸腾中指数级递增热输入下水的沸腾危机
DOI：
10.1016/j.ijheatmasstransfer.2020.120137
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发表时间：
2020
影响因子：
5.2
通讯作者：
M. Bucci
中科院分区：
文献类型：
--
作者：
A. Kossolapov;F. Chavagnat;R. Nop;N. Dorville;B. Phillips;J. Buongiorno;M. Bucci
我们调查了沸腾危机的水指数上升的热输入下，使用一个专门设计的实验装置，具有高速红外热成像测量随时间变化的温度和热流密度分布的沸腾表面上，和高速视频诊断图像的气泡生长过程。在平板加热器上进行了大气压下水的流动沸腾实验。我们测试了不同的流速值（对应于0至35，000的雷诺数）、水过冷度（10至75° C）和功率上升速率（对应于1.5至500 ms的指数功率上升周期τ）。在长时间内，临界热通量（CHF）是独立的功率升级期间和沸腾过程似乎是物理上类似的稳态。随着周期的减小，CHF值趋于增加，遵循渐近1/τ趋势。决定这种趋势的机制取决于过冷。对于高过冷度，CHF随着周期的减小而单调增加，并且DNB通过充分发展的核沸腾过程发生。相比之下，对于低过冷度，CHF首先增加所观察到的高过冷度，然后减少，最后再次增加的周期减少。我们观察到，这种非单调过渡是由于沸腾危机机制的变化。具体而言，对于非常短的时间和低过冷度，沸腾危机发生在第一代气泡的生长过程中，这些气泡在核态沸腾开始后不久就不会从加热表面分离。在这种情况下，不能实现充分发展的沸腾。
We investigated the boiling crisis of water under exponentially escalating heat inputs using a specially-designed experimental apparatus featuring high-speed infrared thermography to measure the time-dependent temperature and heat flux distributions on the boiling surface, and high-speed video diagnostics to image the bubble growth process. We conducted flow boiling experiments with water at atmospheric pressure on a plate-type heater installed in a 3× 1 cm 2 cross section channel. We tested various values of flow velocity (corresponding to Reynolds numbers from 0 to 35,000), water subcooling (from 10 to 75° C) and rate of power rise (corresponding to exponential power escalation periods, τ, from 1.5 to 500 ms). At long periods critical heat flux (CHF) is independent of the power escalation period and the boiling processes appear to be physically similar to steady state. As the period decreases, the CHF values tend to increase following an asymptotic 1/τ trend. The mechanism that determines this trend depends on subcooling. For high subcooling, CHF monotonically increases as the period decreases, and the DNB occurs through a fully developed nucleate boiling process. By contrast, for low subcooling, CHF first increases as observed for high subcoolings, then decreases, and finally increases again as the period decreases. We observe that such non-monotonic transition is due to a change in the boiling crisis mechanism. Specifically, for very short periods and low subcooling, the boiling crisis happens during the growth of the very first generation of bubbles, which never detach from the heated surface, shortly after the onset of nucleate boiling. In such cases, fully-developed boiling is not achieved.