Experimental Study on a Water Droplet Impacting on the Heated Glycerol Surface

Abstract: The phenomena of droplet impact on the heated liquid surface are difficult to unify due to complexity of the interaction, but this process has significance for the study such as direct fuel injection in internal-combustion engines or pool fire suppression. A series of experiments on a water droplet impacting on the heated glycerol surface are carried under various surface temperatures (111.4°C ≤ T_gly ≤ 270.6°C) and impact Weber number (50.5 ≤ We ≤ 297.9). Four regimes, including penetration, crater–jet, vapor explosion and crater–jet–vapor explosion, are discussed in detail. With increase in the T_gly and We, the phenomena transform easier from penetration to crater–jet. The jet formation is affected by the interaction of vapor explosion (T_gly ≥ 222.3°C) and this process is mainly caused by two factors: the vapor explosion appears at the liquid-liquid interface and the vapor explosion time is equal to 4.8–15.8 ms. Increase in T_gly and We prolongs the crater evolution process and leads to growth of the maximum dimensionless crater depth (h_max). The contribution index shows that h_max is significantly increased by the vapor explosion and continued to increase for the higher We. Furthermore, the secondary breakup of droplets is observed at T_gly ≥ 222.3°C and this phenomenon mainly includes the processes of puffing, sputtering, vaporization and deformation.