The effect of thermally-insulating layer, particularly oxide layer as found in metallurgical applications, on the water spray-cooling process was discussed. Such layers have been found to increase the quenching temperature at which the sprayed liquid begins to contact the hot surface, greatly increasing the cooling rate. The conventional, thermal-resistance based model can predict the shift of the quenching point qualitatively, albeit significant deviations remain due to the lack of fundamental understanding of the onset of liquid–solid contact. In the present paper, we conducted two sets of experiments in an attempt to shed light on the quench mechanism and the effect of oxide layer. First, we compared temperature histories during spray cooling of a stainless-steel plate with various oxide layers. The quench temperatures varied depending both on the composition and the thickness of the oxide layer. Additionally, quench was observed at temperatures as high as 350 °C, exceeding the thermodynamic wetting limit. Then, we moved on to single droplet impingement experiments to investigate the change of droplet behavior with respect to the surface temperature in detail. High-speed imaging allowed us to identify the transition of droplet impact behavior i.e. deposition and bouncing, which also occurred at different wall temperatures depending on the composition of oxide layer. Subsequently, we calculated the contact surface temperature assuming the transient heat conduction for a contact between two semi-finite bodies. As a consequence, the onset of droplet behavior transition was always found at the contact surface temperature of ca. 250 °C regardless of the composition and thickness of the oxide layer. The difference between the contact surface temperature and the wall temperature increased as the thermal effusivity of the oxide layer decreased, which was a direct cause of the inconsistent “apparent” quenching temperature.

讨论了隔热层，特别是冶金应用中发现的氧化物层，对喷水冷却过程的影响。已经发现这样的层增加了喷射液体开始接触热表面的淬火温度，大大提高了冷却速率。传统的基于热阻的模型可以定性地预测淬火点的变化，尽管由于对液-固接触的开始缺乏基本的了解仍然存在明显的偏差。在本文中，我们进行了两组实验，试图阐明淬火机理和氧化层的作用。首先，我们比较了具有各种氧化物层的不锈钢板喷雾冷却过程中的温度历史。淬火温度根据氧化物层的组成和厚度而变化。此外，在高达350°C的温度下观察到淬火，超过了热力学润湿极限。然后，我们继续进行单滴撞击实验，以详细研究液滴行为相对于表面温度的变化。高速成像使我们能够识别液滴冲击行为的转变，即沉积和反弹，这也发生在不同的壁温下，具体取决于氧化物层的成分。随后，我们假设两个半有限实体之间的接触具有瞬态热传导，计算出接触表面温度。结果，总是在约200℃的接触表面温度下发现液滴行为转变的开始。250°C，与氧化层的组成和厚度无关。接触表面温度和壁温之间的差异随着氧化物层热效率的降低而增加，这是“表观”淬火温度不一致的直接原因。