A molecular-kinetic theory based model for alkali liquid metal boiling incipience analysis

Abstract

Boiling can lead to unexpected heat transfer performance of the components using alkali liquid metal (ALM) as working fluid for high thermal conductivity. Thus study on incipient boiling superheat of ALM is important to the design and safety operation of related components. However, existing data are in large scatter and some important parameter trends are inconsistent, indicating that more research should be done to understand the basic mechanism of ALM boiling incipience. In this paper, the local heat transfer of a wall cavity was investigated and the molecule performance at the three-phase contact line (TPL) was analyzed with molecular-kinetic theory. It was found that during transient process, the liquid temperature distribution near the interface in the cavity may result in considerable unbalanced molecule displacement at TPL and change the contact angle significantly. By estimating the evaporation rate at TPL with interface deformation rate and local temperature gradient, a model which could correlate nucleation contact angle as well as nucleation superheat with heat flux, velocity and interface deformation rate was established. The model was then used to predict the nucleation superheat data involving effects of temperature ramp, heat flux and velocity, and good agreement was gained. Besides, the characteristics of nucleation superheat of different heating methods were also analyzed and the trend of velocity effect was discussed, and some phenomena observed in different experiments were explained.