Abstract The cooling rate of metallic objects quenched in liquid nitrogen can be enhanced by coating its surface with a material that has a low thermal effusivity. An early transition from film to nucleate boiling regime caused due to the formation of cold spots at the liquid-coating interface is reported as the reason for this enhanced cooling rate. However, untill now, optimization of the coating thickness to minimize the overall cooling time has only been an empirical proposition. Inspired by experimental data a phenomenological model is proposed. Using this model, an approximate insulation coating thickness that will approach the fastest cool down of an insulated metal quenched in liquid nitrogen can be predicted. This model is verified with experimental data of several copper cylinders coated with different thickness of epoxy quenched in saturated as well as subcooled liquid nitrogen. The optimum coating thickness reduces significantly with the degree of liquid sub-cooling.

中文翻译：

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在饱和和过冷液氮中冷却绝缘金属

摘要 在液氮中淬火的金属物体的冷却速度可以通过在其表面涂上一层具有低热扩散率的材料来提高。据报道，由于在液体涂层界面处形成冷点而导致从薄膜到核沸腾状态的早期转变是这种冷却速率提高的原因。然而，到目前为止，优化涂层厚度以最小化整体冷却时间只是一个经验建议。受实验数据的启发，提出了一种现象学模型。使用该模型，可以预测近似绝缘涂层厚度，该厚度将接近在液氮中淬火的绝缘金属的最快冷却速度。该模型通过在饱和液氮和过冷液氮中淬火的不同厚度环氧树脂涂层的几个铜圆柱体的实验数据进行了验证。最佳涂层厚度随液体过冷程度显着降低。