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

Abstract

In this research, we measure the temperatures of the non-combustible component (water) in a fuel droplet by 2-Color LIF before its micro-explosive fragmentation. We use two types of droplets based on water and tetradecane: a two-component immiscible droplet with water in the core and tetradecane as the envelope; a pre-mix emulsion. In both cases, the relative volume fraction of water in a droplet is 9%, and that of the combustible component (tetradecane) is 91%. To provide the micro-explosive dispersion of droplets, we use a scheme with the conductive heating in the range of 250 °C to 550 °C. Using the highspeed 2-Color LIF technique, we observe the coalescence of water micro-droplets in emulsion droplets and intense disruption of the water core in a two-component droplet when heated. The temperature difference may range from 1 °C to 10 °C. Temperature distributions in emulsion droplets are more monotone when heated until micro-explosion. In the puffing regime, the droplet temperature is 1-3 °C higher than in the micro-explosion regime at the same temperatures of the heated metal substrate surface.Within a certain interval of the heating time, the temperatures of water in a two-component droplet and in an emulsion droplet become comparable.

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

“…It was also experimentally established that micro-explosion occurs with emulsions, micro-, and nano-emulsions [4][5][6][7][8], as well as with a heated immiscible two-component droplet (i.e., with one pronounced inter-component interface) [9][10][11]. The use of technologies based on droplet microexplosions affects the economic, environmental, energetic, rheological, and other parameters of the corresponding processing chambers and the processes occurring therein [12][13][14][15][16]. The spraying and secondary atomization of fuel droplets in combustion chambers can be considered the main application [17,18].…”

“…However, despite the abundance of wellknown papers reflecting the research findings on micro-explosive droplet fragmentation [1][2][3][4][5][6][7][8][9][10][11][12][13], most of them determine the critical (boundary) conditions of a micro-explosion with varying key parameters in a wide range, accounting for the decisive effects: component composition of a droplet [13], heating mechanism and scheme [11], external gas medium properties and temperature [9][10][11], original droplet size [9][10][11][12][13], etc. Other popular subjects are the characteristics of micro-explosion, in particular, the atomization mechanism [3,9,13], the duration of micro-explosive fragmentation [10], droplet temperature before the explosion [8,9,14], droplet heating rates [9], etc. In practice, however, the main interest lies in the characteristics of child droplets resulting from the micro-explosion of the parent droplet.…”

“…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.…”