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首页> 外文期刊>International Journal of Heat and Mass Transfer >Homogeneous nucleation boiling during jet impingement quench of hot surfaces above thermodynamic limiting temperature
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Homogeneous nucleation boiling during jet impingement quench of hot surfaces above thermodynamic limiting temperature

机译：高于热力学极限温度的热表面的射流冲击淬火过程中的均相成核沸腾

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What happens in the early stages of jet impingement quenching, when the surface temperature remains well above the thermodynamic limiting temperature for stable solid-liquid contact, is not clearly understood yet. The footage of the boiling and flow phenomena of this period of quenching reveals that the jet impacts on the surface due to hydrodynamic force and immediately splashes away violently, because of explosive boiling or boiling explosion that leaves the surface dry again. It is speculated that, a repetition of wetting and drying of the surface continues until the surface is cooled enough down to allow stable solid-liquid contact. However, neither high speed visual observation nor temperature measurement can help us to find out any concrete and quantitative explanation of the above mentioned wetting and drying phenomena of the surface as it takes place within a very short time. In the present study, we focused on the event of explosive boiling due to homogeneous nucleation that occurs when a liquid jet comes in contact with a very hot surface during jet impingement quenching. Assuming the liquid jet as 1-D semi-infinite solid during its brief contact with the solid, the authors proposed a model based on the concept of 1 -D semi-infinite heat conduction and that of molecular theory of homogeneous nucleation boiling. In this model, a characteristic liquid cluster at the boundary is considered and the corresponding energy balance is obtained by accounting two parallel competing processes that take place inside the cluster, namely, transient external heat deposition and internal heat consumption due to bubble nucleation and associated growth. Results obtained are presented in terms of the liquid temperature escalation within the cluster, the limit of maximum attainable liquid temperature and the time necessary to reach the temperature limit at the boiling explosion. From the present model, the temperature at which homogeneous nucleate boiling takes place during quenching of carbon steel with water (20 ℃) at atmospheric pressure can be obtained to be higher than 335 ℃ which might be regarded as the lower limit of surface temperature for homogeneous nucleate boiling. This lower limit of surface temperature for homogeneous nucleate boiling depends on the ratio of thermo-physical properties of the solid and the liquid, namely, β = √(ρcλ)_s/(ρcλ)_l As the precontact temperatures of the hot surface increases above the lower limit, the interface temperature between the solid and the liquid increases and the time at which homogeneous nucleation boiling appears is greatly shortened.
机译：当表面温度仍远高于热力学极限温度以稳定固液接触时，在喷射冲击淬火的早期阶段会发生什么，目前尚不清楚。这段淬火期间的沸腾和流动现象的录像显示，由于爆炸性沸腾或沸腾爆炸而使表面再次干燥，射流由于流体动力而撞击表面并立即剧烈飞溅。据推测，表面的润湿和干燥的重复持续进行直到表面被充分冷却以允许稳定的固液接触。但是，高速目视观察和温度测量都无法帮助我们找到上述提到的表面润湿和干燥现象的任何具体和定量的解释，因为这是在很短的时间内发生的。在本研究中，我们重点研究了在射流冲击淬火过程中，当液体射流与非常热的表面接触时，由于均匀成核而导致的爆炸沸腾事件。假定液体射流在与固体短暂接触期间为一维半无限固体，则作者基于一维半无限热传导的概念和均相成核沸腾的分子理论提出了一个模型。在该模型中，考虑了边界处的特征液体团簇，并通过考虑团簇内部发生的两个并行竞争过程获得了相应的能量平衡，这两个过程是瞬时外部热量沉积以及由于气泡成核和相关生长而产生的内部热量消耗。根据群集中的液体温度升高，最大可达到液体温度的极限以及在沸腾爆炸时达到温度极限所需的时间来表示获得的结果。从目前的模型中，可以得出碳钢在大气压下用水（20℃）淬火时发生均相核沸腾的温度高于335℃，这可能被认为是均质表面温度的下限。核沸腾。均匀核沸腾的表面温度下限取决于固体和液体的热物理性质之比，即β=√（ρcλ）_s /（ρcλ）_l随着热表面的预接触温度增加到该下限使固体和液体之间的界面温度升高，并且大大缩短了均匀成核沸腾出现的时间。

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