Numerical study on the Leidenfrost behavior of a droplet stream impinging on a heated wall.

A detailed understanding of drop-wall interactions at high-temperature and high-pressure conditions can help optimize fuel injection, engine operation, and material design. The existing formulas developed for simulating drop-wall interactions are either valid only for a small range of operating conditions or based on the single-drop impact scenarios neglecting the effect of the nonstationary liquid film on the wall. The Leidenfrost temperature is a critical parameter in determining the impact outcome and needs to be considered in characterizing the impact behavior at extreme conditions. In this study, the smoothed particle hydrodynamics method, a Lagrangian-based method, is used to study the impact of an n-heptane droplet stream on a heated wall near and above the Leidenfrost temperature. The impingement frequency and wall temperature are varied to understand the impact dynamics and outcomes. Visualizations of the impact outcomes are provided to explain the interaction between the succeeding drops and the liquid film created by the preceding drops. To further characterize the shift in the Leidenfrost behaviors and the corresponding impact outcomes caused by the change in ambient pressure, simulations are also conducted at the corresponding fluid states for ambient pressures of 5 and 20 bar. Results show that the increase in ambient pressure impedes splashing and the film is concentrated inwards near the impingement point.