Application of the laser induced phosphorescence method to the analysis of temperature distribution in heated and evaporating droplets

Abstract

Results of detailed analysis of temperature fields in droplets of four widely used liquids (water, kerosene, Diesel and gasoline (petroleum oil) fuels) are presented. Single droplets suspended on a wire were heated in a flow of hot air. The initial droplet radii were in the range 1 to 2 mm, air temperature was in the range 20 ∘C to 500 ∘C, air flow velocity was 3-3.5 m/s. The droplet temperature was measured based on Laser Induced Phosphorescence (LIP). BAM:Eu (BaMgAl10O17:Eu2+) microparticles were introduced into the droplets for the emission of a temperature-sensitive phosphorescent signal. Optical sectioning inside the droplet was performed using a thin laser sheet, while two cameras detected the phosphorescence signal in two spectral bands. A ratiometric approach using the pixel-to-pixel ratio of the images recorded by the two cameras allowed us to determine the local temperature within the heated and evaporating droplet. The range of applicability and the advantages/shortcomings of the method are established alongside the sources of errors. The experimentally observed droplet surface temperatures are compared with the predictions of the customised version of ANSYS Fluent with the Effective Thermal Conductivity (ETC) model implemented into it via User Defined Functions (UDF). It is shown that ANSYS Fluent can correctly predict the trend of the time evolution of these temperatures.