Collision dynamics of two liquid nitrogen droplets under a low-temperature condition

Abstract

Collision of nitrogen droplets is a basic phenomenon in an array nitrogen spray cooling system, while the understanding on which is still lacking. We conduct a numerical simulation to investigate the collision dynamics of two nitrogen droplets in a low-temperature environment under various Weber numbers, Reynolds numbers and impact parameters, and simulation of collision of two water droplets is conducted for comparison. Incompressible Navier-Stokes equations are solved to simulate the colliding process, and Volume of Fluid (VOF) method and adaptive mesh refinement technique are used to capture gas-liquid interface. Three regimes of collision are found for nitrogen droplet collision, including coalescence, reflection separation and stretching separation. Upon collision, a lower surface tension and lower viscous dissipation consume less initial kinetic energy, which is conducive to the separation of droplets. Compared with water droplets, collision of nitrogen droplets easily enables breakage due to the lower surface tension and viscous dissipation. Separation of nitrogen droplets leads to the increase of secondary droplet number and enlarges heat transfer area of droplets and gas, which would enhance droplet vaporization and temperature descendence of the environment.