Experimental Study on S-CO2 Forced Convection Heat Transfer in Tubes under High-temperature Condition

Under high-temperature conditions, supercritical carbon dioxide (S-CO2) power conversion systems have significant advantages, which show great potential in improving energy utilization efficiency, reducing environmental pollution, and realizing sustainable energy development. S-CO2, as a high-efficiency working fluid, can achieve high efficiency in higher temperature thermodynamic cycles, which helps to reduce fuel consumption and greenhouse gas emissions. Since the S-CO2 power cycle is significant to energy conversion and utilization, many researchers have conducted experimental studies on the convective heat transfer characteristics of S-CO2. However, existing studies mainly focus on low-temperature condition (10-200 ℃), and experimental data under high-temperature condition (200-500 ℃) are scarce. Most of the research conditions on the heat transfer characteristics of S-CO2 have not reached the optimal temperature range of the S-CO2 power conversion system, in order to master the critical data of the relevant design, it is necessary to carry out experimental research on the heat transfer characteristics of S-CO2 under high heat flux conditions, which holds a crucial significance in the development of associated power conversion systems. This paper first introduced the construction process of the S-CO2 forced circulation test bench, and evaluated the uncertainty of the relevant experimental data. The main temperature range of the experiment is 450-800 K, the pressure range is 7.40-10.22 MPa, and the heat flux range is 20-1 000 kW/m2. The heat transfer characteristics of S-CO2 in a vertical tube under high-temperature conditions were studied experimentally, and the effects of thermal acceleration and buoyancy on heat transfer were analyzed. The results show that the heat transfer trend of S-CO2 is similar to that of gaseous CO2 under high-temperature conditions, but the values are quite different, and the influence of thermal acceleration and buoyancy effect on the heat transfer of high-temperature S-CO2 is negligible. Finally, in order to develop a reliable prediction method of S-CO2 convection heat transfer under high-temperature conditions, this paper collected the empirical correlations of S-CO2 heat transfer in vertical heating circular tubes commonly found in the literature, and analyzed them under high heat flux, evaluated and analyzed their experimental prediction high-temperature conditions. It is found that there are some differences with the existing experimental data. Therefore, this paper proposes an empirical correlation suitable for high-temperature S-CO2 heat transfer. The newly proposed heat transfer correlation has the highest calculation accuracy, which calculates 96.65% of experimental data within ±10% error. It can achieve higher accuracy, which meets the actual engineering needs. © 2023 Atomic Energy Press. All rights reserved.