真空闪蒸喷雾冷却中非等温液滴闪蒸特性的研究

Influence of Characteristics of Non-Isothermal Flashing Droplet on Vacuum Flash-Spray Cooling

真空闪蒸喷雾冷却是利用液体工质在真空环境下相变吸热来冷却加热表面的新型冷却手段。具有散热能力强、所需工质少,与加热表面没有接触热阻等优点,在航天器电子元器件冷却方面具有广阔的应用前景。液滴闪蒸是真空闪蒸喷雾冷却闪蒸过程的重要组成部分,要研究整个真空闪蒸喷雾冷却系统的闪蒸过程就必须对液滴的闪蒸特性进行研究。本文考虑液滴闪蒸过程中液滴内部存在的温度梯度和对流的影响,采用扩散控制蒸发模型并结合导热方程,对液滴的热导率进行修正,建立了热导率修正模型计算直径为微米级液滴在毫秒量级时间内的真空闪蒸特性,并通过实验验证。研究结果表明,导热模型较等温模型能更准确地预测液滴温度的变化;液滴闪蒸导致液滴到达被冷却表面时,其温度下降明显,但体积几乎没有变化;并且,环境压力越低,液滴的初始半径越小,液滴速度越大,液滴闪蒸对液滴温度的影响越明显。

The impact of the characteristics of the non-isothermal flashing droplet（ on micron and millisecond scale）,including the internal temperature gradient and heat convection,on vacuum flash-spray cooling was physically modeled,theoretically analyzed on the basis of the heat conduction equation in radial direction and diffusion-controlled evaporation,numerically simulated and experimentally measured. The dependence of the droplet temperature on the flash-spray conditions,such as the pressure,velocity and initial diameter of droplets,was evaluated. The simulated results show that the newly-modified non-isothermal model predicts the droplet＇s temperature more accurately than the conventional isothermal model. The surface evaporation of the droplet sharply decreases its own temperature but little affects its volume. Besides,we found that a faster flash evaporation originates from a lower pressure,a smaller size and a higher initial velocity of the droplet. The simulated results agree fairly well with the measured data.