Advancing the development of supersonic natural gas liquefaction through understanding heavy hydrocarbon crystallization mechanism

Abstract

During supersonic natural gas liquefaction, the solidification of heavy hydrocarbon molecules can be used to improve the efficiency of the liquefaction. This study investigates the supersonic crystallization of n-hexane using an experimental system designed by ourself for precise measurement of liquid heavy hydrocarbon vaporization. The results demonstrate that n-hexane gas condenses rapidly 1.5 cm downstream of the nozzle throat, releasing significant latent heat. The subsequent crystallization of these droplets transitions the substance fully from liquid to solid, and the latent heat released during crystallization is much lower than that during condensation. Under different conditions, we found that higher partial pressures intensify n-hexane crystallization, accelerating liquid phase growth despite slower solid phase mass increase. Furthermore, larger nozzle expansion ratios shorten the time and space distribution of the liquid phase mass fraction. Molecular dynamics simulations reveal n-hexane’s melting and surface crystallization temperatures to be approximately 160 ± 1 K and 158 ± 1 K, respectively, with a supercooling degree of 2 K, explaining the observed crystallization behavior in supercooled droplets.