ID 377

Effect of pressure on droplet breakup during hot wall impact

 

Abstract:

Combustion systems must perform optimally over a range of operating conditions which result in large variation of the chamber wall temperature and ambient pressure. Although the outcome of fuel droplets impacting a wall is primarily driven by the wall temperature and the Leidenfrost effect (vapor layer formation), the shifting liquid-vapor saturation point with pressure may influence the droplet-wall heat transfer rate and transition from nucleation to film boiling. The role of ambient pressure on the droplet impact regimes and spreading rate during impact is explored for both low- and high-boiling point alkanes (n-heptane and n-dodecane). Experiments were conducted for ambient pressures of 1-20 bar and wall temperatures ranging from 30-300 °C. For these test conditions, droplets were generated in a nitrogen-filled static pressure vessel. Droplet impact with a stainless steel substrate took pace for Weber number of approximately 50. Droplet impact sequences were recorded using a high-speed CMOS camera and were processed to measure droplet spread and instantaneous velocity. The shifting saturation point with pressure is shown to influence the droplet impact regime for both fuels. The range of film boiling shifts to higher wall temperature as pressure (and corresponding saturation temperature) increases. Detailed investigation of the dependence of varying ambient pressure on droplet impact phenomena with heated walls will inform the importance of capturing the thermodynamic state of the liquid-vapor interface, and will provide validation data for modeling of single-droplet dynamics.