ANALYSIS OF SUBCRITICAL TO SUPERCRITICAL TRANSITION OF N-HEPTANE/ETHANOL BLENDS BY MOLECULAR DYNAMICS SIMULATION

RT He and YP Fu and J He and P Yi and T Li, ATOMIZATION AND SPRAYS, 32, 87-106 (2022).

The transcritical transition of the nonpolar hydrocarbon and highly polar alcohol mixtures from the subcritical to supercritical regime has not been yet well understood. In the present paper, based on molecular dynamics simulation, the nonequilibrium evaporation and transcritical transition processes of the n-heptane/ethanol mixtures are comprehensively investigated under various ambient conditions, and the development of the vapor-liquid interface is deeply analyzed. Under the sub critical condition, the increased ethanol concentration elevates the evaporation rate because of the decreased vapor pressure and increased thermal conductivity. However, under the supercritical condition, the effect of ethanol addition on the mixture temperature becomes slight due to the decreased difference of thermal conductivity between ethanol and n-heptane, but the preferential diffusion of ethanol is observed because of its higher diffusivity. In addition, it is found that the increase of ethanol broadens the vapor-liquid interface at moderately high pressure due to its higher volatility and thermal conductivity. Since the interfacial thickness affects the interfacial resistivities and evaporation characteristics in the hydrodynamic framework, the thickened interface indicates the more significant nonequilibrium effect in the vicinity of interface for the mixtures with large amounts of ethanol. Finally, the transcritical transition time decreases rapidly with the increased ambient pressure, and the descent gradient gradually decreases with the further increased pressure because the thermal conductivity becomes less sensitive to the pressure.

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