Thermal Gradient Determination Inside Vaporizing Droplets by Combining Rainbow and Laser Induced Fluorescence Measurements

This paper describes the setting of two measuring techniques on a rectilinear monosized droplets stream allowing the validation of droplet vaporizing models for internal spatial temperature distribution. Indeed, the vaporizing rate depends strongly on droplet surface temperature and consequently on physical phenomena inside droplets. However, the measurement of temperature in small droplets whose diameter is about 100μm is not easy. To determine the thermal gradient, two experimental techniques have to be coupled: the first must be sensitive to the thermal gradient and the second to the mean temperature. The two chosen experimental techniques, the rainbow refractometry and the Laser Induced Fluorescence (LIF) in liquid phase, agree with these criteria. Some experiments have been done on ethyl alcohol and acetone droplet streams with different injection temperatures and in vaporizing or burning conditions. Then, the results have been compared to numerical predictions.