Experimental study on dynamic evaporation characteristics of free-falling liquefied natural gas droplet: Effects of methane vapor concentration, temperature and initial diameter

Abstract

Many individual liquid droplets are generated in the jet fragmentation following a Liquefied natural gas (LNG) accidental leakage, and the droplets are dynamically evaporated. This work investigates the effects of ambient temperature, methane vapor concentration, and initial droplet diameter on the evaporation of a single free-falling LNG droplet. A droplet evaporation experimental apparatus with an adjustable gas concentration in a low-temperature environment has been designed. The ambient temperature, methane vapor concentration, and initial droplet diameter in the experiments varied from −60 °C to 20 °C, 0 vol% to 100 vol%, and 0.69 mm to 3.3 mm, respectively. The results show that the two-dimensional morphology of droplets undergoes the dynamic process of oblate-sphere-prolate oscillations. High temperatures, high methane concentration and larger droplets have larger Galilei and Eötvös values. The frequency of transient oscillations in roundness is positively correlated with temperature changes and negatively correlated with methane vapor concentration and initial diameter. The droplet equivalent diameter at the corresponding peaks was analyzed by fitting the roundness with the singular spectrum analysis algorithm. Seven typical gas-phase models were evaluated, showing that all models underestimated the decay rate of LNG droplet diameter. Based on 125 sets of LNG droplet experimental data, a multi-factor coupled LNG vapor phase model was established, with R² > 0.77. This provides a theoretical basis for studying the dynamic evaporation characteristics of droplets within the near-field diffusion zone.