Experimental and numerical study on evaporation characteristics of Leidenfrost droplets in a meso-scale tube

To comprehensively elucidate collision dynamics, evaporation, and combustion in spray droplet combustion, this study examines direct evaporation of a droplet in gas flow and its evaporation upon collision with a high-temperature wall. An experimental system with a suspended droplet and a Leidenfrost droplet was established, and corresponding theoretical models were developed. The VOF model first simulated droplet spreading upon wall impact. Subsequently, Leidenfrost droplet evaporation was analyzed. By integrating the suspended-droplet evaporation model, the evaporation characteristics of the system were numerically investigated at fuel flow rates of 95–170 μL/min and wall temperatures of 600–1000 K. The system operates in two distinct modes. At a wall temperature of 600 K and fuel flow rate <126 μL/min, the suspended droplet&apos;s descent period exceeds the Leidenfrost droplet&apos;s wall lifetime. Here, at most one Leidenfrost droplet exists on the wall, and the system oscillates between fuel-lean and fuel-rich states. Increasing the flow rate reduces the oscillation period below the Leidenfrost droplet lifetime, triggering the second mode. In this mode, the Leidenfrost droplet persists on the wall, and the system remains fuel-rich. Two outcomes occur: independent evaporation or droplet coalescence. Independent evaporation increases fuel vapor available for combustion in a single cycle, whereas coalescence reduces evaporation efficiency and impairs combustion performance.