BUBBLE GROWTH IN FLASH EVAPORATION OF VISCOUS, HIGH SOLID CONTENT BLACK LIQUOR

摘要

This paper presents a new model for the growth of a single vapor bubble during flash evaporation of highly viscous liquids. Model consists of simultaneous solution of heat transfer equation combined with the generalized Rayleigh equation for bubble growth dynamics. A simplified thermodynamical, Raoult-law based equilibrium model describes vapor pressure of water in multi-component solution. By using the new model, unit processes during flashing can be effectively studied and better understood. If was found that when viscosity increases to values close to black liquor, the initial stages of bubble growth are controlled by viscous and surface tension forces. As bubble continues to grow further, heat transfer to bubble surface becomes dominating mechanism.