Numerical Simulation of Flow and Thermal Field in Supercritical Pressure Carbon Dioxide Flowing Upward in a Narrow Tube

Abstract

A reliable heat transfer correlation valid at a supercritical pressure is indispensible for an accurate estimation of heat transfer in the sub-channel of a fuel assembly of Supercritical Water-Cooled Reactors (SCWR). Despite a number of supercritical heat transfer correlations having been proposed in the past several decades, a reliable one is still missing, since the predictions by the existing correlations show wide discrepancies from each other. In a mixed convection regime, no correlation is able to produce accurate predictions. Under the influence of strong buoyancy, the boundary layer structure is known to deform significantly, when the wall temperature is close to the pseudo-critical temperature; and, therefore, it is suspected to be one of the reasons for the enhancement or impairment of the heat transfer rate. However, a detailed analysis of the boundary-layer transformation process has never been successfully addressed, due partially to difficulty in experimenting at a condition of high pressure and temperature, and to an inadequacy of the numerical tools in dealing with substantial property variations. This paper provides results of the numerical analyses of flow and thermal field in CO flowing upward in a narrow tube.