开式通道内液氮喷雾的降温特性

Cooling Performance of Liquid Nitrogen Spray in an Open Tunnel

为了研究液氮喷雾参数对环境模拟空间温度分布的影响,首先搭建了由液氮喷雾系统和低温测试系统构成的开式通道液氮喷雾冷却实验系统,利用CFD软件针对开式空气回路系统中实验段建立了三维液氮喷雾数值模型,采用欧拉-拉格朗日方法进行液氮喷雾模拟研究,最后进行了实验验证,分析了喷雾质量流量、粒径、喷嘴数量和气流速度对液氮喷雾蒸发和空间温度分布的影响。研究结果表明:随着液氮喷雾液滴直径的减小,液氮与环境气流的换热面积增加,换热效率提高,降温效果改善;当液氮喷雾质量流量增加时,单位时间内喷入空间的液氮量越多,蒸发率越大,冷却效果越好,空间及出口截面的温降越大,但降温速率的增加趋缓;随着喷嘴数量的增加,液氮蒸发量和蒸发率增加,降温效果改善,出口截面温降增加,但出口截面温度分布均匀性会受到喷嘴布置位置的影响;当喷嘴数量增加到一定程度时,液氮的蒸发和降温几乎不受影响;随气流速度增大,液氮的蒸发量和蒸发率逐渐减小,出口截面的平均温度较高。为了增强液氮的蒸发量并强化空间的降温效果,可增加液氮喷雾流量、减小喷雾粒径和气流速度,以及适当增加喷嘴数量,同时需考虑多喷嘴的布置位置。

A liquid nitrogen spray system is built in an open tunnel to study the influence of design parameters on cooling performance of an environmental imitation system.The experimental system is comprised of a liquid nitrogen spray system and a cryogenic measuring system.A 3D numerical model of the open tunnel with the liquid nitrogen spray cooling is established and validated by employing a Lagrangian-Eulerian approach.The effects of the mass flow rate,the droplet diameter,the nozzle number and the air velocity on the evaporation of liquid nitrogen and the temperature distribution are analyzed.Results show that the contact area between the droplets and air increases under a smaller droplet size,and the heat transfer efficiency and the cooling performance are improved.When the mass flow rate of liquid nitrogen spray increases,the more the liquid nitrogen that is sprayed into the tunnel per unit time,the greater the evaporation rate,the better the cooling performance,the greater the temperature drop of space and outlet section,but the slower the cooling rate.When the nozzle number increases,the evaporation intensity and the evaporation rate are enhanced,the cooling performance is improved and the temperature drop at the outlet is increased,but the temperature uniformity at the outlet section is affected by the positions of the nozzles.When the number of nozzles increases to a certain extent,the evaporation and the temperature drop of liquid nitrogen are almost unaffected.A higher air velocity reduces the evaporation of liquid nitrogen and increases the average temperature of the outlet.It is concluded that increasing the mass flow rate and the number of the spray nozzles and reducing the droplet size and the air velocity can strengthen the evaporation and enhance the cooling performance.Meanwhile,the arrangement of multiple nozzles should be considered.