Experimental investigation on high-pressure high-temperature spray flash evaporation and the characteristic Jakob number

Abstract

Experiments on high-pressure high-temperature spray flash evaporation in saturated vapor environment are conducted on a novel large-scale experimental system. The influence of initial liquid temperature and evaporation pressure on flash efficiency is investigated. These two parameters are thought to affect each stage of the spray flash evaporation process, including nucleation, bubble growth, atomization and droplet flashing. The dimensionless Jakob number (Ja), defined as the ratio between the amount of sensible heat available to the amount of energy required for vaporization, is generally acknowledged to be the characteristic number of flash evaporation, which is a typical finite-rate thermal non-equilibrium process. The larger Ja is, the higher flash efficiency is, and the more violent flash phenomenon is. Meanwhile it is found that flash efficiency is not a single-valued function of Ja. Multiple regression is then carried out and empirical equations of flash efficiency vs. Ja and dimensionless pressure are proposed, which establish coupling between system performance, initial and final states and operating conditions.