Experimental study on evaporation characteristics of methyl oleate droplet across critical pressure and temperature environments

Abstract

Droplet evaporation plays a crucial role in many engineering situations involving the transport and computation of sprays. It becomes a challenging issue in fluid dynamics if vaporization occurs in high temperature and pressure environments, especially across critical conditions due to the uncertainty of interactions between droplet and ambient gas. In this study, an experimental system capable of recording droplet morphology and temperature in high temperature and pressure conditions was constructed. The evaporation characteristics of methyl oleate droplet with initial diameters between 0.9 and 1.1 mm was investigated at various ambient pressures (atmospheric to 2.0 MPa) and temperatures (573–873 K). The results revealed that the evaporation process of methyl oleate droplet consisted of three stages: the transient heating stage, steady state evaporation stage, and slow evaporation stage. The third stage occurred due to the gradual decomposition of methyl oleate in the later period of evaporation. The lower the ambient temperature, the earlier the third stage appeared. At lower pressure conditions, the evaporation rate and lifetime of the droplet exhibited a relatively gradual variation with temperature. However, at higher pressure conditions, both the evaporation rate and lifetime changed exponentially with temperature. The influence of pressure on the evaporation rate depended greatly on the ambient temperature and the state of the droplet. In general, droplet across the critical pressure experienced a significant reduction in the evaporation rate. However, this reduction disappears once the ambient temperature is far beyond the critical temperature.