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

Abstract

Here we present the experimental findings of the research into the integral characteristics of secondary droplets produced from the micro-explosive fragmentation of two types of initial droplets. Both types are based on water and tetradecane: an emulsion droplet and a two-component immiscible droplet with water as the core and tetradecane as the envelope. We study the threshold (critical) conditions for the microexplosion of droplets on a substrate heated up to 550 °C. In the course of experiments, we recorded the number, sizes, velocities, temperatures, and component composition of child droplets. It is shown that the parameters of child droplets differ significantly in the case of two-component droplets and emulsion droplets. The decisive impact comes from the heating temperature. Using a combination of Schlieren Photography, Particle Tracking Velocimetry, and 2-Color Laser Induced Fluorescence, we have determined the proportions of the concentration and size of secondary water droplets and combustible component droplets in the emerging aerosol cloud. We have also calculated the kinetic energies of child droplets. When generalizing the experimental findings, we established the conditions for the generation of a high-temperature fine mist aerosol through the micro-explosive breakup of two-component droplets and recorded the typical trajectories of secondary fragments. We show that such conditions are possible for both emulsion droplets and immiscible two-component droplets with a pronounced interface. It is established that much more secondary fragments of water are produced in the second case. This result shows that water separates from the combustible component more intensely in the second case, and the micro-explosion systems relying on water and combustible liquid droplets mixing in the combustion chamber bear more promise.

Physical and Mathematical Models of Micro-Explosions: Achievements and Directions of Improvement

“…Research findings [5,112] show that the heating arrangement of initial droplets has a decisive effect on the number and size of secondary fragments produced in the puff-ing and micro-explosion regimes. The maximum number of secondary fragments was recorded [5,112] in experiments where parent droplets were placed on a heated solid surface (with dominant conductive heat transfer), and the minimum number of droplets were produced upon heating in a tubular muffle furnace (with dominant radiative heat transfer). In experiments with dominant convective heat transfer, the authors recorded the average number of secondary fragments compared with other arrangements studied [5,112].…”

“…The maximum number of secondary fragments was recorded [5,112] in experiments where parent droplets were placed on a heated solid surface (with dominant conductive heat transfer), and the minimum number of droplets were produced upon heating in a tubular muffle furnace (with dominant radiative heat transfer). In experiments with dominant convective heat transfer, the authors recorded the average number of secondary fragments compared with other arrangements studied [5,112]. The aspects outlined in the experiments [5,112] can benefit the mathematical models of droplet breakups by controlling for critical heat fluxes at the droplet surface in contact with the heating environment.…”

Achieving optimal micro-explosions in stable emulsions by adding water-soluble polymers

“…Several studies have shown the potential of this emulsified feedstock technique in chemical production. [8][9][10][11] Due to the great potential of micro-explosion application, a large number of researchers have sought to understand its mechanism and regular patterns by exploring and observing the micro-explosion phenomenon of single droplets [12][13][14] . It has been found that there are at least two different forms of micro-explosion in single droplet micro-explosion experiments, namely "micro-explosion" and "puff" 12,[15][16][17][18][19][20] .…”

“…[8][9][10][11] Due to the great potential of micro-explosion application, a large number of researchers have sought to understand its mechanism and regular patterns by exploring and observing the micro-explosion phenomenon of single droplets [12][13][14] . It has been found that there are at least two different forms of micro-explosion in single droplet micro-explosion experiments, namely "micro-explosion" and "puff" 12,[15][16][17][18][19][20] . In some studies, these two forms of micro-explosion are also called "optimal micro-explosion" and "non-optimal micro-explosion" respectively 6,7,21,22 .…”

Experimental Research on the Disruptive Evaporation and the Motion Characteristics of Secondary Droplets for Emulsified Biodiesel with a Suspended Droplet Configuration

“…The latest experimental studies focused on the relationship between the size of secondary droplets and the temperature of the water core and the influence of additives in droplets on the formation of secondary droplets. − The numerical studies focused on the droplet nucleation temperature of the heating rate and the influence of puffing/microexplosion time. , Meng et al observed secondary droplets caused by the secondary explosion of the jet fuel (RP-3), biodiesel, and ethanol-mixed droplets. The calculation equation of the microexplosion intensity was established to assess the degree of secondary droplet ejection.…”