Temperature and velocity fields of the gas-vapor flow near evaporating water droplets

Abstract

Experimental studies of unsteady temperature and velocity fields of the gas-vapor flow in the immediate vicinity of evaporating water droplets were performed in the interests of developing high-temperature (over 300°С) gas-vapor-droplet applications. The formation time of virtually homogeneous (temperature variations of under 2–3°С) temperature fields of evaporating water droplets was established using Particle Image Velocimetry, Laser Induced Phosphorescence, Planar Laser Induced Fluorescence. We observed highly inhomogeneous and unsteady temperature and velocity fields of the gas-vapor mixture and determined the lateral and transversal dimensions of the aerodynamic and thermal traces of evaporating water droplets. The degree of impact of several parameters on the latter was evaluated: initial temperature (20–500 °C) and velocity of the incoming flow (0.5–5 m/s), as well as the initial droplet size (1–2 mm). The role of evaporation and convective heat exchange between a droplet and gases in forming of thermal and aerodynamic trace was analyzed. The heat flow density was found to vary nonlinearly with time (in the immediate vicinity of an evaporating droplet), and the impact of droplet trace temperature and velocity on the heat flow density was evaluated. Both advantages and limitations of the used techniques are established in terms of reliable plotting of unsteady temperature and velocity fields of gas-vapor mixture in the trace of evaporating water droplets, considering the heating lag of the latter.