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 (BaMgAl 10 O 17 :Eu 2+ ) 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

Evaporation issues of acoustically levitated fuel droplets

“…The experiment required 1 h to maintain equilibrium in the mesosuspender's temperature [34] . Abhishek Saha [75] (2010) studied the intensity of Marangoni flow with the intensity of significant flow perturbations in acoustic flow, proposed a time scale for convection within droplets, and established surface tension gradients for inducing Marangoni convection via tunable laser heating of suspended droplets [13] , [106] . Zaitone [41] (2011) demonstrated the significance of acoustic stream on droplet evaporation by comparing acoustic field and single-component droplet evaporation in glass filaments and also further classified the evaporation of suspended droplets into three categories: (1) evaporation rates controlled by offsetting effects at very low blowing rates; (2) internal acoustic flow making evaporation rates higher than diffusion-controlled evaporation rates; and (3) external acoustic flow causing vapor enrichment around the droplet, resulting in lower evaporation rates.…”

Temperature measurements in a string of three closely spaced droplets before the start of puffing/micro-explosion: Experimental results and modelling

“…Pixels with unwanted fluorescence values were set to zero intensity in all the video frames (algorithmic masks), as in our previous papers [27,28] . The mean fluorescence intensity of water sub-droplets was determined in the selected recording area within 10 to 15 frames.…”

Two-photon fluorescence lifetime imaging applied to the mixing of two non-isothermal sprays: temperature and mixing fraction measurements

“…Raman scattering was exploited to characterize the chemical composition and, in some cases, also the temperature using both the surface area and the position of the peaks in the Raman spectrum (Carns et al 1990;Schweiger 1990;Müller et al 2000). A second group of measurement techniques relies on photoluminescence processes like fluorescence (Stiti et al 2021b) or phosphorescence (Strizhak et al 2020) which are the consequence of the spontaneous relaxation of molecular species after these have been excited by a type of energy. Laser-induced fluorescence (LIF) offers unprecedented temperature sensitivity and versatility in its applications with a wide variety of fluorescent dyes excitable at various wavelengths and soluble in different solvents.…”