Two Phase Flow Interface Dynamic Behavior During CHF Transient

Abstract Due to the absence of detailed two-phase flow interface dynamic behavior in the vicinity of the heated wall during CHF transient, a deep understanding of the boiling crisis phenomenon is not achieved. In this paper, a flow boiling heat transfer facility is designed and constructed. Meanwhile, a transparent test section, which can withstand high temperatures and pressures, is designed and machined. Flow visualization experiments have been conducted in a vertical rod channel with water as the working fluid. Based on visualization experiments of flow boiling crisis, the two phase flow interface dynamic behavior during the CHF transient is analyzed utilizing self-developed image processing programs. The vapor-liquid interface variations characteristics in various operating conditions can be directly extracted through the processed raw images. The two-phase flow interface morphology under different operating conditions exhibits significantly different behavioral characteristics. For vapor layer thickness, the thickness becomes thinner as the inlet subcooling increases, mainly due to the increased condensation effect as the subcooling increases. Furthermore, the mass flux has an extremely pronounced effect on the vapor layer thickness, mainly since the mass flux directly affects the meso-interfacial heat and mass transfer behavior, leading to an increase in the interfacial perturbation, which results in the presentation of smaller vapor layer thickness. In addition, the results show that as the heat flux approaches the CHF, the liquid film thickness is zero in several places, which means that several dry spots appear. The results presented in this paper have important implications for a more in-depth understanding of CHF phenomenon and further support in the development of a mechanistic model for flow boiling.