Investigation on temperature of evaporating droplets in linear stream using two-color laser-induced fluorescence

This article presents investigations on the temperature evolution of monodisperse, low evaporating, and interacting ethanol droplets in a linear stream. The droplets are injected over the ambient temperature, and the influence of injection parameters such as velocity. temperature, interdroplet spacing, and droplet size on the droplet's cooling process is analyzed. It is shown that the typical droplet cooling process is characterized by two well-separated phases. In the first, the temperature decreases strongly, since the effect of forced convection is enhanced by the transport of air and the fuel vapor concentration in the boundary layer is far from saturation conditions. The second phase exhibits a reduction of the temperature rate of change, in connection with the decrease of the forced convection effects and enhancement of the fuel vapor concentration in the boundary layer. The effect of the injection velocity on the droplet cooling process is low, as a significant effect of the interdroplet spacing is observed. The respective influences of the injection temperature and droplet size on the heat transfer are jointly studied. It is shown that for a given injection temperature, the total energy extracted from the droplet per unit surface is insensitive to the droplet size. In this article, the mean droplet temperature is measured by two-color laser-induced fluorescence.