液氮液滴撞击过热壁面是低温风洞液氮喷雾冷却过程中的基本现象，液滴与壁面的撞击特性直接影响液氮喷雾雾场的发展和气流的降温特性。为探究液氮液滴撞击壁面的动力学特性，设计并搭建了可视化实验平台，实现了粒径可控的液氮液滴生成，总结出液氮液滴撞击过热壁面的多种动力学形态及临界判据，探究了不同沸腾模式下韦伯数（We）对最大铺展系数的影响规律。在液氮液滴生成过程中，表面张力与重力相互对抗，出现了聚集、颈缩和断裂3个阶段；随着壁面温度的升高，液氮液滴撞击壁面后依次发生接触沸腾、雾化沸腾和膜态沸腾3种沸腾模式，所对应的两个临界温度值均不受We影响；随着We的增大，液滴的冲击动能增大，液滴的最大铺展系数逐渐增大，并且存在一个液滴开始发生飞溅的临界We，该临界值不受壁面温度的影响；壁面温度对液滴最大铺展系数的影响规律与Leidenfrost点密切相关，当壁温低于Leidenfrost点时，随着壁面温度的升高，沸腾气泡增多，液滴铺展受到的阻力增大，从而导致液滴的最大铺展系数下降；当壁面温度高于Leidenfrost点时，液滴撞击壁面后在壁面附近瞬间形成一层连续性气膜，液滴在气膜上铺展，其最大铺展系数几乎不受壁面温度影响。本研究有助于深入理解低温风洞中液氮液滴的微观动力学特性，可为液氮喷雾冷却系统的优化运行提供理论依据。

The impact of liquid nitrogen droplets on superheated wall is a fundamental phenomenon in liquid nitrogen spray cooling of cryogenic wind tunnels. The impact characteristics of droplets affect the advancement of liquid nitrogen spray field and the cooling performance of gas flow. In this study， a visualization experimental platform was designed and established to explore the wall-impact of a single liquid nitrogen droplet with controllable size and impact velocity. Various dynamic behaviors and transition criteria of liquid nitrogen droplets impacting superheated wall were obtained. In different boiling modes， the effect of Weber number （We） on the maximum spreading coefficient of liquid nitrogen droplets impacting wall was investigated. During the generation of liquid nitrogen droplets， surface tension worked against gravity， resulting in three stages of accumulation， necking， and breakup. As the wall temperature increased， the droplets successively exhibited contact boiling， atomization boiling and film boiling upon impact. The two corresponding critical temperatures were not affected by the We. The droplet spreading process involved the conversion of impact kinetic energy to surface energy. With an increase in We， droplets transitioned from non-splashing to splashing during the spreading process， and the corresponding critical We was not affected by the wall temperature. Furthermore， the spreading characteristics of droplets were associated with the Leidenfrost temperature. Below the Leidenfrost temperature， droplets spread on the wall， and an increase in the wall temperature led to intensified boiling bubbles， causing the maximum spreading coefficient to decrease. Above the Leidenfrost temperature， droplets spread on a vapor film， and the maximum spreading coefficient was independent of the wall temperature. This study deepened the understanding of the dynamic characteristics of liquid nitrogen droplets impacting superheated surfaces， and provided a theoretical basis for improving the spray cooling performance of liquid nitrogen in cryogenic wind tunnels.