Heat transfer deterioration in a supercritical water channel

Supercritical water is the working fluid in the supercritical water reactor (SCWR) because of its high thermal efficiency and simplicity. Computational fluid dynamics (CFD) technology has been applied in the studies of supercritical water in circular channels by solving conservation equations of mass, momentum, and energy. Both the renormalization group k-ε(RNG k-ε) and Reynolds stress equation model (RSM) turbulence models were applied with enhanced wall treatment (EWT) for Yamagata's heat transfer enhancement (HTE) experiments. Reynolds Stress turbulence model (RSM) with the enhanced wall treatment (EWT) was used for diagnosis and comparison of the heat transfer deterioration (HTD) phenomena observed in the Shitsman's experiments. The simulations confirmed the heat transfer deterioration (HTD) phenomenon and predicted the associated peak wall temperature and minimum heat transfer coefficient consistent with Shitsman's experiment. Series simulations with various operational pressures and inlet temperatures (T_in) indicated that the increases of both inlet temperature and operational pressure were very effective to relax the heat transfer deterioration. The inclusion of buoyancy effect in the physical model revealed that the buoyancy effect played role on the dramatic increase of the wall temperature, which indicated the important role of buoyancy force on HTD by limiting the convection and turbulence. Dimensionless parameter of Prandtl number, the ratio of momentum and energy diffusion, which changing dramatically near the wall with wide range from 0.8 to 16.6, led to very different patterns of momentum and energy transports in the small region and was another important parameter for the formation of HTD. This study concluded the important roles of buoyancy effect and Prandtl number on heat transfer deterioration of supercritical water inside circular tubes.