Hydrodynamics and boiling phenomena of water droplets impinging on hot solid

Abstract

a b s t r a c tThe collision of single water droplets with a hot Inconel 625 alloy surface was investigated by a two-directional flash photography technique using two digital still cameras and three flash units. The experiments were conducted under the following conditions: the pre-impact diameters of the droplets ranged from 0.53 to 0.60 mm, the impact velocities ranged from 1.7 m/s to 4.1 m/s, and the solid surface temperatures ranged from 170°C to 500°C. When a droplet impacted onto the solid at a temperature of 170°C, weak boiling was observed at the liquid/solid interface. At temperatures of 200 or 300°C, numerous vapor bubbles were formed. Numerous secondary droplets then jetted upward from the deforming droplet due to the blowout of the vapor bubbles into the atmosphere. No secondary droplets were observed for a surface temperature of 500°C at the low-impact Weber numbers ($30) associated with the impact inertia of the droplets. Experiments using 2.5-mm-diameter droplets were also conducted. The dimensionless collision behaviors of large and small droplets were compared under the same Weber number conditions. At temperatures of less than or equal to 300°C, the blowout of vapor bubbles occurred at early stages for a large droplet. At a surface temperature of 500°C, the two dimensionless deformation behaviors of the droplets were very similar to each other.

Studium kształtu kropli wody w warunkach Leidenfrosta

“…Przeprowadzone badania własne wyraźnie zaprzeczają takiemu stwierdzeniu, co również potwierdzają inne prace badawcze, w których zamieszczono mapy odwzorowujące życie kropli np. [8].…”

The effect of pressure and frequency on the dynamic behavior and evaporation time of successive water droplets impacting onto hot surface

“…This research focused on the observation during droplet levitation and has classified that phenomena into four types. Furthermore, the phenomena of hydrodynamics and boiling phenomena of water droplet have been studied by Fujimoto et al [5]. It covers various condition (impact velocities, droplet diameters, and temperatures) and used high speed camera to observe the behavior of droplet and the presence of secondary droplet.…”

Heat Transfer and Observation of Droplet-Surface Interactions During Air-Mist Cooling at CSP Secondary System Temperatures

“…[20][21][22][23][24][25][26][27][28][29][30][31] In the pioneering work of Wachters and Westerling, [20] which involved individual drops (d~2.3 mm) falling over a surface at 643 K (370°C) with velocities between~0.5 and 2.75 m/s, it was found that the impact outcome depended on the normal impinging Weber number…”

“…The authors described that film boiling occurred at 573 K (300°C) and that wetting, i.e., contact of the drop with the surface, in this regime was affected by T w , v, surface roughness, and liquid properties. [21] Fujimoto et al [22] stated that the critical We z for detachment of secondary droplets from a rebounding drop was~30, and the investigators worked with drops of 580 lm in diameter. The authors indicated that in the film boiling regime, with surface temperatures between 673 K and 773 K (400°C and 500°C), small (~600 lm) and large (~2500 lm) drops displayed very similar deformation behavior for similar We z ; the We z values used were~30 and~65.…”