低温氦气引射液氮时液滴群在引射器扩散腔中的流动与传热特性

Heat transfer and flow of droplets in ejector diffusion chamber for liquid nitrogen ejection by low-temperature gas helium

为了优化低温氦气引射液氮过程中固体颗粒的生成效果,对氮液滴群与氦气在引射器扩散腔内的传热与流动过程建立数学模型,分析了液氮凝固的阶段性变化特征及传热机制,重点研究了液滴初始直径、气体初始状态和液气流量比对氮浆生成效果的影响。结果表明:不同粒径液滴的凝固过程存在显著差异,粒径小的液滴更容易凝固,但在固体调温阶段会反向传热;随着液滴直径的增大,完全凝固位移呈现指数增长;传质的贡献随气体温度的升高而增大,在大液滴的冻结阶段起主导作用。降低气体初始速度和温度有利于提高出口凝固率,在30 K的气体初始温度下改变液气流量比时凝固率均高于99%;但固体生成速率和换热效率主要随液气流量比的增大而增大。

To optimize the formation of solid particles during liquid nitrogen injection by lowtemperature gas helium,mathematical models for the heat transfer and flow of nitrogen droplets and gas helium in the ejector diffusion chamber were built to analyze their characteristics and also the heat transfer mechanism of liquid nitrogen solidification.The influence of initial droplet diameter,initial gas condition and liquid-gas flow ratio on the slush nitrogen formation was emphatically studied.The results show that the solidification processes of droplet with various diameters are significantly different.Smaller droplets are easier to solidify,but heat transfer reverses in the stage of solid temperature regulation.With the increase of droplet diameter,the complete solidification displacement increases exponentially.The heat transfer caused by mass transfer is enhanced with the increase of gas temperature and plays a leading role in the freezing stage of large droplets.Reducing the initial gas velocity and temperature is conducive to increasing the solidification rate at the outlet.The solidification rate is higher than 99% when the liquid-gas flow ratio is changed at the initial gas temperature of 30 K.However,the solid formation rate and heat transfer efficiency increase mainly with the increase of liquid-gas flow ratio.