A new puffing model for a droplet of butanol-hexadecane blends

A new model was developed to investigate the puffing process of a butanol-hexadecane droplet. The puffing model took into account all the key processes, including the surface evaporation, bubble formation, bubble growth and bubble breakup. The Rayleigh equation was modified to simulate the bubble growth inside a small droplet. The sub-models for surface evaporation and bubble growth were firstly verified against the previous experimental data. Then the droplet puffing experiments of butanol-hexadecane blends were conducted under 1 bar and 750 K condition using the droplet suspension technique to further verify the puffing model. Results showed that the puffing model well simulated three phases of BUT50 (50% butanol and 50% hexadecane by mass). The three phases were the transient heating, fluctuation evaporation and equilibrium evaporation phases. An extremely strong fluctuation and several weak fluctuations were observed during the fluctuation evaporation phase from the experimental normalized squared diameter. Due to the model hypotheses, these weak fluctuations were ignored and only the strong fluctuation was simulated in the present model. Furthermore, a significant turning point was observed in the experimental temperature curve when the droplet diameter had the strong fluctuation. The occurrence of the strong fluctuation was caused by the obvious bubble expansion inside the droplet. The numerical results showed that the significant heat absorption for the bubble expansion led to the turning point in the temperature curve.