开式通道内液氮喷雾的降温特性

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.