Subcritical and supercritical droplet evaporation within a zero-gravity environment: Low Weber number relative motion

Abstract

A validated comprehensive axisymmetric numerical model, which includes the high pressure transient effects, variable thermo-physical properties and inert species solubility in the liquid phase, has been employed to study the evaporation of moving n-heptane droplets within a zero-gravity nitrogen environment, for a wide range of ambient pressures and initial freestream velocities. At the high ambient temperature considered (1000 K), the evaporation constant increases with the ambient pressure. At low ambient pressure, the evaporation constant becomes almost a constant during the end of the lifetime. At high ambient pressures, the transient behavior is present throughout the droplet lifetime. The final penetration distance of a moving droplet decreases exponentially with increasing ambient pressure. The average evaporation constant increases with ambient pressure. The variation is almost linear for reduced ambient pressures smaller than approximately 2. For higher values, depending on the initial freestream velocity, the average evaporation constant either becomes a constant (at low initial freestream velocities) or it non-linearly increases (at high initial freestream velocities) with the ambient pressure. Droplet lifetime decreases with increasing ambient pressure and/or increasing initial freestream velocity.

Evaporation of Nearly Monosized Droplets of Hexane, Heptane, Decane and Their Mixtures in Hot Air and an Air/Steam Mixture

“…In [15] it is discussed that an internal vortex structure due to the air drag on the surface may reduce the mixing time by a factor of 2.7, which also is in agreement with the findings in [17]. They also discuss a correlation for the maximum surface velocity due to the fluid drag on the droplet, which for the current case results in approximately 1 m/s.…”

“…It should be emphasized that this time scale for heat transport corresponds to a rate of temperature change and after this time not necessarily a constant temperature inside the droplet is achieved. Zhang et al [17] (their Figures 2 and 3) show the time history of the centre temperature of an evaporating stagnant heptane droplet at elevated pressure of 1 MPa with d = 100 µm for a model calculation. Estimating the time scale for internal heat transfer for their situation in the way as described above results in 16 ms, which fits very well with [17].…”

“…A review and test of available numerical models for droplet evaporation can be found in Miller et al [16]. These models have been continuously extended and, for example, Zhang et al [17] developed a model for n-heptane droplet evaporation under high pressures, including the effect of dissolving of the surrounding gases into the droplets.…”

Theoretical analysis on droplet vaporization at elevated temperatures and pressures

“…In numerical simulations, different factors that affect droplet vaporization can be isolated and examined independently. Moreover, the evolutions of droplet temperature and diameter can be studied in simulations in wide ranges of pressure and temperature that resemble the engine operating conditions [8][9][10][11][12][13][14][15][16][17][18][19]. At elevated pressures, various fluid dynamic and thermodynamic non-idealities show profound impacts on the behavior of droplet vaporization [7,8,18,19].…”

Experimental investigation on the rapid evaporation of high-pressure R113 liquid due to sudden depressurization

“…They studied the effect of nucleation and slip at the liquid-vapor-vapor interface, and set up a simple theoretical model to predict the average velocity of the diaphragm fragments after a blowdown. Due to limitations of test equipment and instruments, researches on flash evaporation of high-pressure droplet are mostly based on theoretical study and numerical simulation [12][13][14]. The experimental data of high-pressure droplet flash evaporation during depressurization are rare and insufficient.…”