Computational prediction of key heat transfer mechanisms and hydrodynamic characteristics of critical heat flux (CHF) in subcooled vertical upflow boiling

• Published in: International journal of heat and mass transfer 2020-11, Vol.161, p.120262, Article 120262
• Main Authors: Lee, Jeongmin, O'Neill, Lucas E., Mudawar, Issam
• Format: Article
• Language: English
• Subjects: Boiling; Bubbles; CFD; Computational fluid dynamics; Conduction heating; Critical heat flux; Energy transfer; Fluid flow; Heat flux; Heat transfer; Mathematical models; Multiphase flow; Subcooled flow boiling; Temperature profiles; Thermal energy; Transient analysis; Two phase flow; Wall temperature
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2020.120262

•A 3-D computational model is presented for prediction of interfacial behavior in subcooled upflow boiling•The model incorporates the important influence of shear-lift force on bubbles•The model is used to predict variations in key flow and heat transfer parameters for three FC-72 mass velocities•Predictions show clear evidence of CHF occurrence for the two lower mass velocities and pre-CHF for the highest The present study investigates extensively the capability of computational fluid dynamics (CFD) to predict two-phase fluid flow and heat transfer characteristics of FC-72 flow boiling in vertical upflow. The computational method performs transient analysis to model the entire flow field and bubble behavior for highly subcooled flow boiling in a rectangular channel heated on two opposite walls at high heat flux conditions of about 81% of critical heat flux (CHF). Transient variations of local vapor fraction, thermal energy transfer and concentration, and wall temperature are estimated through the computational methodology based on the Volume of Fluid (VOF) approach combined with shear-lift modeling to overcome a fundamental weakness in modeling multiphase flows. Detailed information about bubble distribution in the vicinity of the heated surface, thermal conduction inside the heating wall, local heat fluxes passing through the solid-fluid interface, and velocity and temperature profiles, which are not easily observed or measured by experiments, is carefully evaluated. Predictions are compared to the experimental data for three sets of operating conditions. Overall, computationally predicted flow pattern, bubble behavior, and heat transfer parameters (such as wall temperature excursion and thermal energy concentration) clearly represent phenomena of premature CHF which take place slightly earlier than actual operating conditions. But, despite these slight differences, the present computational work does demonstrate the ability to effectively predict the severe degradation in heat transfer performance commonly encountered at heat fluxes nearing CHF.