Numerical analysis of the onset of heat transfer deterioration to supercritical water

In this paper the mechanism of the onset of heat transfer deterioration to supercritical water is elucidated with detailed numerical predictions of flow and heat transfer in the boundary layer. It is shown that for low mass flow rates the buoyancy effects are dominant and the deterioration of heat transfer is caused by the turbulence damping in the vicinity of the heated wall. For high mass flow rates the mechanism of deterioration changes and the triggering factor is the decrease of the thermal conductivity of fluid in the viscous sub-layer. A numerical prediction of this phenomenon requires application of a low Reynolds number turbulence model with y+ less than 1. (authors)