Evaluation of identification methods for heat transfer deterioration of supercritical CO2

Abstract

Heat transfer deterioration (HTD) identification is essential for establishing heat transfer correlations and HTD criteria. To assess the accuracy of various HTD identification methods, an experimental investigation of the convective heat transfer characteristics of supercritical CO2 in heated tubes with diameters of 8 and 14.5 mm was conducted. In addition, data from published literature were used as supplements for ranges not covered by this experiment. The evaluation of identification methods was conducted for tube diameters ranging from 2 to 22 mm, pressures from 7.5 to 21.1 MPa, mass fluxes from 50 to 1600 kg/m2·s, and heat fluxes from 6 to 375 kW/m2. Based on these datasets, the accuracy and the appropriate application of each method were determined. The results showed that the Nu/Nudb and Gupta et al. methods are not sufficiently accurate and cannot reflect the heat transfer trend reliably. The Kline et al. method may produce illogical results in cases of a large q/G. The Xie et al. method is not effective in heat transfer enhancement (HTE) cases and HTD cases, where the wall temperature profile changes slowly. Both the Lokshin et al. and Zhang et al. methods require prior addition or adjustment of correction factors.