Numerical analysis of subcooled flow boiling and critical heat flux under variable wall heat flux

This paper presents a numerical analysis of subcooled flow boiling in a vertical pipe through CFD simulation. The study is aimed to investigate the effect of variable heat flux profiles on CHF. To achieve this, a two-phase Eulerian-Eulerian model coupled with the RPI and CHF boiling models is employed for numerical solutions. The variable heat flux profiles examined include linear-increasing, exponential-increasing, and three sinusoidalshaped profiles. The results highlight that when variable heat flux profiles are utilized, the RPI model lacks reliability, and the CHF boiling model proves to be a more suitable choice. Among the profiles studied, the sinusoidal-shaped profile with a peak in the middle of the tube exhibits the highest CHF value, while the lowest CHF value corresponds to the exponential-increasing heat flux profile. In sinusoidal profiles, as the number of thermal peaks increases, the CHF value decreases, its location shifts towards the pipe's end, and augments the risk of approaching CHF. By illuminating the intricacies of subcooled flow boiling under variable heat flux, this study provides valuable insights for the development of more efficient and reliable heat transfer designs.