Experimental and computational investigation on two-phase flow and heat transfer of highly subcooled flow boiling in vertical upflow

Abstract

This study explores subcooled nucleate flow boiling of FC-72 in a rectangular channel having two opposite heating walls at different mass velocities and wall heat fluxes ranging from 42% to 45% of CHF. Experiments are performed in which constant and equal heat fluxes are supplied from the heating walls, with local wall temperatures measured at several axial locations and used to determine axial variations of local heat transfer coefficient. Additionally, detailed information on flow pattern and phase distribution is captured by high-speed video through the channel's transparent sidewalls. Experimental values for key fluid flow and thermal parameters are compared to predictions of 2D computational simulations using ANSYS FLUENT. The computations are based on the multi-phase volume of fluid (VOF) model combined with an appropriate phase change model, and account for conjugate heat transfer along the heating walls. Computed transverse profiles and stream-wise variations of void fraction, flow velocity, and wall temperature are examined. The computed results show reasonable agreement with experimentally captured interfacial behavior as well as heat transfer parameters. Computed cross-sectional temperature profiles for the mixture show non-equilibrium subcooled boiling with steep temperature gradients near the heating walls and low temperature liquid in the core region. This study is concluded by exploring limitations of the 2D model used. (C) 2019 Elsevier Ltd. All rights reserved.