航空学报 > 2025, Vol. 46 Issue (7): 130970-130970   doi: 10.7527/S1000-6893.2024.30970

低温风洞中液氮液滴撞击壁面动力学特性

刘秀芳1,2(), 陈佳军1, 苗庆硕1, 钟富豪1, 李亚楠1, 郑勉1, 侯予1,2   

  1. 1.西安交通大学 能源与动力工程学院,西安 710049
    2.西安交通大学 深低温技术与装备教育部重点实验室,西安 710049
  • 收稿日期:2024-07-22 修回日期:2024-08-27 接受日期:2024-09-09 出版日期:2024-09-24 发布日期:2024-09-20
  • 通讯作者: 刘秀芳 E-mail:liuxiufang@mail.xjtu.edu.cn
  • 基金资助:
    国家自然科学基金(52076164);国家科技重大专项(J2019-Ⅲ-0010-0054)

Wall-impact dynamics of liquid nitrogen droplets in cryogenic wind tunnels

Xiufang LIU1,2(), Jiajun CHEN1, Qingshuo MIAO1, Fuhao ZHONG1, Yanan LI1, Mian ZHENG1, Yu HOU1,2   

  1. 1.School of Energy and Power Engineering,Xi’an Jiaotong University,Xi’an 710049,China
    2.Key Laboratory of Cryogenic Technology and Equipment,Ministry of Education,Xi’an Jiaotong University,Xi’an 710049,China
  • Received:2024-07-22 Revised:2024-08-27 Accepted:2024-09-09 Online:2024-09-24 Published:2024-09-20
  • Contact: Xiufang LIU E-mail:liuxiufang@mail.xjtu.edu.cn
  • Supported by:
    National Natural Science Foundation of China(52076164);National Science and Technology Major Project of China (J2019-Ⅲ-0010-0054)

摘要:

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。

关键词: 低温风洞, 液氮液滴, 过热壁面, 动力学形态, 铺展特性

Abstract:

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.

Key words: cryogenic wind tunnel, liquid nitrogen droplet, superheated wall, dynamic morphology, spreading characteristic

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