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Droplet evaporation in sub- and supercritical environments has been studied experimentally under microgravity conditions. A single suspended droplet of n-hexadecane was employed for the experiments. The initial droplet diameter was 0.4 mm. A pair of alumina/silica fibers of 7 µm in diameter was applied to suspend a droplet. The ambient pressure was varied in the range of 1.0–3.0 MPa, and the ambient temperature was set at 773 K. Sequential backlit images of an evaporating droplet were recorded using a high-speed digital video camera. Temporal variations in the droplet diameter were measured using a self-made computer-aided image analyzer. Microgravity conditions were produced by a 50-m drop tower. Temporal variations in the droplet diameter were successfully obtained for droplet evaporations in the supercritical environments. The normalized droplet lifetime increased with the ambient pressure. The evaporation rate constant increased with the ambient pressure, reached the maximum value at an ambient pressure slightly above the critical pressure of the fuel, and then decreased. The initial heat-up period linearly increased with the ambient pressure, reached the maximum value at an ambient pressure of 2.0 MPa, and then decreased. The ratio of the initial heat-up period to droplet lifetime increased with the ambient pressure, reached the maximum value of about 0.6 at an ambient pressure of 2.0 MPa, and then decreased. The droplet evaporation lifetime increased with the ambient pressure at subcritical ambient pressures even though the evaporation rate constant increased because the increase in the initial heat-up period overtook the decrease in the quasi-steady evaporation period. It was found that, in the case of fuels with a high critical temperature, the initial heat-up period determines the ambient pressure dependence of the droplet evaporation lifetime in the environments around the critical point of the fuel. [ABSTRACT FROM AUTHOR]

With the development of large-thrust liquid rocket engines, the behavior of liquid in supercritical conditions arouses increasing public interest. Due to the high pressure and temperature of the combustion chamber, fuel reaches its critical point much more easily, and enters supercritical conditions. Due to the drastic changes in the physical properties of the fluid near the critical point, it is usually difficult to simulate the fluid motion using traditional computational fluid dynamic methods; but molecular dynamics (MD) can simulate fluid motion at the molecular level. In view of the engineering application, the physical properties of a binary system consisting of argon and nitrogen, and the stability of subcritical jets sprayed into supercritical environment, has been studied here using the MD method. First, the molecular dynamic simulation of the equation of state (EOS) of the mixture was put forward. Four conditions, with different mixing ratios of nitrogen, were designed. The results showed that the mixing ratio of nitrogen noticeably affected the results; these results were compared with the Soave-Redich-Kwong (SRK) EOS. Second, a simulation was conducted of subcritical nitrogen jet sprayed into a supercritical argon environment. After analyzing the results, the jet density and temperature distributions were obtained and the disturbance growth rate of the shear layer was analyzed.

The purpose of this study was to examine the structure and composition of the oxide scales formed on Alloy 800HT in a supercritical environment after a relatively short exposure time (circa 500 h) to provide a more complete physical description of the metallurgical factors that influence the protectiveness of the scale formed. This was achieved using transmission electron microscopy and associated techniques on site-specific cross-section samples prepared by focused ion beam milling No physical evidence in support of oxide scale exfoliation was found. Rather, the formation of the discontinuous magnetite (Fe3O4) outer nodular layer is believed to be controlled to a large extent by the underlying microstructure and the presence of ε-martensite plates in particular. The formation of a thin compact corundum-type ([Cr,Fe]2O3) base scale is considered to be sufficiently encouraging to justify an effort to reduce or eliminate the small volume fraction of E-martensite from the starting microstructure of Alloy 800HT as a means to optimize the corrosion resistance. [ABSTRACT FROM AUTHOR]

With the development of large-thrust liquid rocket engines, the behavior of liquid in supercritical conditions arouses increasing public interest. Due to the high pressure and temperature of the combustion chamber, fuel reaches its critical point much more easily, and enters supercritical conditions. Due to the drastic changes in the physical properties of the fluid near the critical point, it is usually difficult to simulate the fluid motion using traditional computational fluid dynamic methods; but molecular dynamics (MD) can simulate fluid motion at the molecular level. In view of the engineering application, the physical properties of a binary system consisting of argon and nitrogen, and the stability of subcritical jets sprayed into supercritical environment, has been studied here using the MD method. First, the molecular dynamic simulation of the equation of state (EOS) of the mixture was put forward. Four conditions, with different mixing ratios of nitrogen, were designed. The results showed that the mixing ratio of nitrogen noticeably affected the results; these results were compared with the Soave-Redich-Kwong (SRK) EOS. Second, a simulation was conducted of subcritical nitrogen jet sprayed into a supercritical argon environment. After analyzing the results, the jet density and temperature distributions were obtained and the disturbance growth rate of the shear layer was analyzed. [ABSTRACT FROM AUTHOR]