Determination of the position and characteristics of supercritical heat transfer deterioration

Supercritical fluids (SFs) are widely used in power generation systems using nuclear, solar, geothermal, and fossil energies. The heat transfer deterioration (HTD) phenomenon during heat transfer of SFs is of great importance to the design and operation of the components in supercritical power cycles. The criteria for determining the onset of HTD has been reported in the literature, but the quantitative model to obtain the position of the wall temperature peak during HTD occurrence, and the correlation to accurately predict the heat transfer characteristics at the wall temperature peak, are both missing. In this work, to determine the position and to predict the characteristics of HTD at the wall temperature peak, we developed two correlations based on experimental results for supercritical CO2 (sCO2) in vertical upward tubes with wide range of experimental parameters. The first correlation to predict the location of the peak is developed using experimental data for sCO2, which can accurately determine the dimensionless bulk fluid temperature corresponding to the wall temperature peak. Moreover, a new heat transfer correlation is developed for the Nusselt number at the wall temperature peak, which has a simple form of NuHTD=0.00796Reb0.7215Prb−0.1568K−0.115, where Reb, Prb, and K are Reynolds number, Prandtl number, and supercritical K number, respectively. This correlation shows smaller prediction error compared with five existing correlations in the literature for not only sCO2, but also various other working fluids. It also outperforms the recently proposed K number correlation in predicting characteristics at the wall temperature peak during HTD conditions. The two correlations developed in this work provides the quantitative models for the HTD phenomenon, and can benefit the engineering application of supercritical power cycles.