# Temperature Fields of the Droplets and Gases Mixture
## 2 Experimental Set-Up and Procedure
### LIP Measurement Technique  
The Laser-Induced Phosphorescence (LIP) technique is not new. It is based on the phosphorescence of specialized particles illuminated by near-UV radiation [13; 14; 15; 24; 25; 26; 27], and is actively used to diagnose the temperature of gas media [25; 27], droplets, and layers of liquids [28; 29], as well as aerosol clouds [30]. [PERSON] et al. [31] present the results of temperature measurement using LIP and different luminophores: BAM:Eu, ZnO:Zn, ZnO:Ga, etc. The properties of these particles and their validity ranges were determined. The dependence of phosphorescence intensity on temperature was established. The results from the works in [27; 28; 29; 30; 31] correspond mainly to single-phase flows and media. There are no research findings for the processes, characterized by the mixing of the gaseous and liquid media. At the same time, the stability of some types of particles, both in gas and in liquid, allows us to assume that LIP can be used to diagnose the temperature of multiphase media. To evaluate the temperature distribution of the gas-vapor flow, we used LIP [24; 25; 26]: a non-contact laser thermal mapping technique for gas and vapor temperature diagnostics. We recorded the thermal emission from thermographic particles under the laser excitation by a 355 nm wavelength beam. We used special phosphorescent particles of BaMgAl\({}_{10}\)O\({}_{17}\):Eu powder (BAM:Eu) [24; 25] (particle dimensions 6-8 \(\upmu\)m). The upper operating temperature range of these particles--thermal degradation threshold--is 550-600 \({}^{\circ}\)C [24; 25]. Two CCD video cameras equipped with interference filters (\(420\pm 10\) nm and \(455\pm 10\) nm) were used for recording. BAM:Eu particles absorb laser radiation with a wavelength of 355 nm. The maximum of the BAM:Eu emission spectrum falls between 440 and 450 nm. With a gas medium temperature increase, the maximum of particle emission spectrum almost does not relocate but we observe the left boundary of the spectrum shift towards lower wavelengths (420-380 nm). The right side of the spectrum shifts as well (Figure 3a). The emission spectrum for different temperatures (Figure 3a, left) of the BAM:Eu particles that we used is described in [24; 25; 26]. Here, the temperature of the flow depends on the emission intensity ratio of the left (420 nm) and right (450 nm) sides of the emission spectrum. This ratio increases with a rise in the flow temperature (Figure 3a, right). Thus, the use of optical filters with two different wavelengths 2 (Figure 1) allowed us to register the spectral shift of BAM:Eu particles emission when their temperature changed. Before the beginning of the experiments, BAM:Eu were dried in a muffle furnace at 100 \({}^{\circ}\)C for 120 minutes to prevent the particles from clumping and to ensure a more even seeding of the air flow. To seed the air flow with BAM:Eu particles, we used an air compressor (24 l reservoir, 1.2 MPa maximum pressure). Tracer particles were placed into an elbowed input duct fixed on the side of the channel (Figure 1). The air from the compressor under a pressure of 200 kPa was fed through the duct for 5 seconds, so that all the tracer particles were injected into the air flow. The mass of the BAM:Eu particle sample injected into the air flow was approximately 1.5 g for each event. This is the experimentally defined mass, sufficient for uniform seeding of the air flow. Each experiment involved 3-5 consecutive injection events. An air extraction duct 150 mm in diameter, provided with a fine-mesh filter, able to absorb particles as small as 0.1 \(\upmu\)m, was placed above the gas flow channel. The heated air flow was collected by the extraction fan, and the tracer particles were absorbed by the filter. Figure 3 bshows a typical video frame with BAM:Eu particles moving in an air flow (before it was processed in the DaVis software).