THEORETICAL MODEL OF BUBBLE GROWTH IN SUPERHEATED ETHANOL-WATER MIXTURE

A novel model was developed to investigate the bubble growth characteristics in uniformly superheated ethanol-water (EtOH-H2O) mixture. The influence of the mass fraction of ethanol was discussed in detail. In the proposed model, the energy equation and the component diffusion equation for the liquid were respectively coupled with quadratic temperature and mass fraction distribution within the thermal and concentration boundary layers. The non-random two-liquid equation (NRTL) was adopted to obtain the vapor-liquid equilibrium ofthe binary mixture at the bubble surface. The comparison between the current calculated bubble radius with the available experimental data demonstrates the accuracy ofthe bubble growth model. The maximum mass diffusion limited growth rate was also proposed to quantibi and illustrate the effect of mass diffusion on bubble growth. The results showed that the later stage of bubble growth in a binary mixture is controlled by both mass diffusion and heat transfer. The bubble growth characteristics strongly depend on the initial mass fraction of ethanol. Within a large concentration range, a higher content of ethanol is adverse to bubble growth at a constant superheat degree. The effect of mass diffusion on bubble growth becomes weaker with an increased initial mass fraction of ethanol.