Numerical Study on the Dynamics of a Liquid Nitrogen Droplet Impacting on a Liquid Nitrogen Film

Liquid nitrogen spray cooling is crucial in cryogenic wind tunnels, while the understanding of its basic phenomenon, liquid nitrogen droplet impact, remains elusive. In this study, a numerical model of a liquid nitrogen droplet impacting on a liquid nitrogen film is established, and the impact mechanisms and influencing factors are analyzed. The dynamic behavior of the liquid nitrogen droplets reveals that as the dimensionless liquid film thickness varies from 0.1 to 0.8, the droplet impact behavior changes from deposition, and crown formation to splash with the Weber number increasing from 0 to 1000. The variation of the dimensionless crown diameter with the dimensionless time solely negatively correlated with liquid film thickness. The maximum dimensionless crown height increases approximately linearly with the Weber number. The splash characteristics indicate that the lower surface tension and viscosity of liquid nitrogen make the droplet easier to exhibit splash as compared with water droplets. As the dimensionless liquid film thickness increases from 0.1 to 0.4, the critical Weber number enabling splash to occur increases from 170 to 375, indicating that a thick liquid film suppresses the splash.