Applicability of pulsed 2cLIF-EET for micro-droplet internal thermometry under evaporation conditions

Abstract

The relatively new thermometry technique "pulsed 2cLIF with MDR-enhanced energy transfer" is tested for the first time on micro-droplet streams in a heated air flow. The method allows simultaneous measurements of the droplet internal temperaturefield, droplet size and droplet velocity. Plausibility of the measurement results is evaluated by comparing results of various experimental conditions among each other and by comparison with analytic modeling. Overall, measurement results are plausible. However, measured temperature-fields are biased by the integral fluorescence signal and initial conditions of the models are limited by the Rayleigh jet breakup that creates the droplet stream.

Measuring temperature of emulsion and immiscible two-component drops until micro-explosion using two-color LIF

“…Second, in the case of an emulsion droplet, when the radius of water droplets in the main drop is several microns, all the microdroplets are evenly distributed throughout the drop, which makes it possible to record the luminous When considering the experimental results, we analyzed the possibility of morphology dependent resonances (MDRs) or lasing effect. This phenomenon usually manifests itself either with small droplets (with a radius of under 50 µm) or with relatively high specific power of the laser radiation source [42][43][44].…”

Child droplets from micro-explosion of emulsion and immiscible two-component droplets

“…There is also a limited number of research findings (e.g., [5,10,15,16]) on the integral characteristics of child droplets, because the processes under study are fast-paced and their recording requires complex and expensive recording systems [1,8,9,14,[19][20][21][22][23][24][25][26][27][28], as well as dedicated data processing algorithms. For instance, the key methods for recording the characteristics of child droplets are as follows: Particle Tracking Velocimetry (PTV) [19,20] for the velocities and trajectories of child droplets; Schlieren Photography (SP) [21,22] for their number and size; Laser Induced Phosphorescence (LIP) [23][24][25], Planar Laser Induced Fluorescence (PLIF) [9,26,27], and 2-Color Laser Induced Fluorescence (2-Color LIF) [1,8,14,28] for their temperature. The methodologies for determining the velocities [19,20] and sizes [21,22] of child droplets are robust, while temperatures are recorded in rather sophisticated ways.…”

“…In the case of fast-paced processes, however, even if droplets are relatively large (50-100 µm) [11], the particle concentration may be too low for reliable measurements. Therefore, the LIF technique, where fluorophore is fully dissolved in a liquid, seems a good alternative for child droplet temperature recording [1,8,9,14,[26][27][28]. The PLIF technique [9,26,27] makes it possible to diagnose the liquid temperature provided that the fluorophore concentration and laser radiation power remain constant.…”

“…In addition, since droplets often move erratically on a heated solid surface, the measurement results seem impossible to adjust. In light of the above, the optimal approach to child droplet temperature diagnostics is the use of 2-Color LIF [1,8,14,28]. One of the benefits of this approach lies in its insensitivity to changes in fluorophore concentration and laser radiation power.…”

Fluorescence lifetime measurements applied to the characterization of the droplet temperature in sprays

“…Properly used, intensity ratios can cancel out most of the adverse effects encountered with droplets and thus provide the basis for accurate droplet temperature measurements in sprays. The so-called two-color LIF (2cLIF) technique has been implemented successfully as a pointwise method (Castanet et al 2003(Castanet et al , 2016Perrin et al 2015;Labergue et al 2017;Stiti et al 2019) and more recently as an imaging technique (Düwel et al 2007;Chaze et al 2016Chaze et al , 2017Palmer et al 2020). Whatever the chosen approach (pointwise or imaging), one of the issues is the selection of detection bands and fluorescent dyes.…”