液氮滴撞击壁面相变行为的数值研究  

Numerical study on phase change behavior of liquid nitrogen droplets impinging on solid surface

作　　者：赵可 佘阳梓[1] 蒋彦龙[1] 秦静 张振豪 Zhao Ke;She Yang-Zi;Jiang Yan-Long;Qin Jing;Zhang Zhen-Hao(Key Laboratory of Aircraft Environment Control and Life Support,Ministry of Industry and Information Technology,Nanjing University of Aeronautics and Astronautics,Nanjing 210000,China)

机构地区：[1]南京航空航天大学飞行器环境控制与生命保障工业和信息化部重点实验室

出　　处：《物理学报》2019年第24期195-209,共15页Acta Physica Sinica

基　　金：航天低温推进剂技术国家重点实验室基础研究基金(批准号:SKLTSCP1811);飞行器环境控制与生命保障工业和信息化部重点实验室(批准号:KLAECLS-E-201902);江苏高校优势学科建设工程项目资助的课题~~

摘　　要：采用Level Set-VOF方法建立单液氮滴撞击壁面的数值模型,探索壁面润湿性(30°-150°)、撞击速度(0.1和1.6 m/s)及壁面温度(300-500 K)对液滴撞壁演化过程中相变行为的影响,并理论推导了气膜生长数学模型.结果表明:增强壁面润湿性、提高撞击速度有利于液滴沿径向铺展,从而增大了换热面积并降低热阻,使换热性能得到显著提升;提高壁面温度增大了换热温差,热流密度随之上升;三相接触线处热阻较小导致边缘处热流密度高于中心处,不同润湿壁面上热流分布的差异性因初始速度的增大而缩小,呈现明显的速度效应;在膜沸腾区,传热过程主要集中在撞击初期,气膜是主要换热热阻;基于质量守恒和能量守恒建立气膜生长数值模型,模型预测结果与本文模拟结果和其他研究结果非常吻合.The distinct physical properties of liquid nitrogen make liquid nitrogen spray cooling a promising technique in aerospace engineering,the electronic industry,superconductor cooling,cryobiology,etc.In-depth study of the dynamics and thermodynamic behavior of liquid nitrogen droplets impinging on the wall surface is helpful to understand the heat transfer mechanism of spray cooling technology with liquid nitrogen.Therefore,the mathematical model of single-liquid nitrogen droplet impacted solid surface is developed by Level Set-VOF method.The effects of wall wettability(30°-150°),initial velocity(0.1,1.6 m/s)and wall temperature(300-500 K)on the phase change behavior during the evolution of droplets are investigated,and the mathematical model of film thickness is established.The results show that enhancing the wall wettability and increasing the impact speed facilitate the spreading of the droplets in the radial direction,thereby increasing the heat exchange area and reducing the thermal resistance.Ultimately,the heat exchange performance is significantly improved.Increasing the wall temperature results in an increase in the difference between temperatures of the solid surface and the liquid,thereby significantly increasing the wall heat flux density.The lower thermal resistance at the three-phase contact line results in a higher heat flux density at the edge than in the center;the difference among the heat flux distributions on different wetted walls decreases due to the increase of initial velocity,showing a significant velocity effect.In the film boiling region,the heat transfer process is mainly concentrated in the initial stage of impact,and the gas film is the main heat transfer resistance.Based on conservation of mass and energy,a numerical model of film thickness is developed in this paper.The model predictions are in good agreement with the simulation results of this paper and others.

关 键 词：Leidenfrost 液氮 液滴撞击 LEVEL Set模拟 

分 类 号：G63[文化科学—教育学]