A two-color planar LIF technique to map the temperature of droplets impinging onto a heated wall

This work consists in the development of the planar extension of two-color LIF, usually working as a point-wise technique. This latter has already demonstrated its ability to characterize the temperature of droplets in various situations including droplet evaporation in combusting flows or droplet/wall interactions in the case of point-wise measurements. This technique is based on the measurement of the relative intensity detected on two adequate spectral bands of a single fluorescent tracer. It allows absolute temperature measurement when a reference at a given temperature is known. The two-color LIF system is designed for observing single drop impacts onto a hot wall with a field of view limited to a few square millimeter. In this study, the focus is placed first on the description of the technique development: the selection of a suitable tracer, its temperature calibration, the correction for the non-linearity of the response of the measurement system, and the pixel-by-pixel correspondence of the camera images. After several tests carried out on droplets in temperature-controlled conditions, the feasibility of the method is finally demonstrated in the case of droplets impinging on a heated wall for different impact regimes: rebound, splashing, and deposition of a boiling liquid film.