Mechanistic critical heat flux model development for subcooled flow boiling based on superheated liquid sublayer depletion

Abstract

Critical heat flux (CHF) refers to the limit of boiling transfer systems, and crossing this limit may jeopardize system safety. However, a clear understanding of the physical mechanisms of CHF is still lacking. In this study, a new CHF prediction model based on superheated sublayer depletion was established for subcooled flow boiling in an upward vertical tube at low pressure. The model is characterized by its developed determination of the superheated liquid sublayer thickness, net vapor generation location, forced convection heat transfer and liquid supplement caused by bubble turbulent fluctuations. The proposed CHF model was validated by a database covering the low pressure subcooled operational ranging over P = 0.1–2.15 MPa, G = 0.7–35 Mg/m2s, ΔTin = 11–183.16 K, D = 0.7–12 mm, L/D = 4.2–115.55, and xeqout = −0.2673–0.0843. The model can accurately predict the trend of thermal-hydraulic and geometric factors’ effects on the CHF. The prediction results have good prediction accuracy with an root-mean-square error (RMSE) of 15.21%, and overall error of ±25%. The proposed model also shows good adaptation to a non-water (refrigerant 113 and liquid nitrogen) system.