Effect of buoyancy and flow acceleration on heat transfer of supercritical CO2 in natural circulation loop

In this paper, an experimental study was carried out to investigate the effect of buoyancy and flow acceleration on the heat transfer behavior of supercritical CO2 in the heating section in a natural circulation loop. The experiments were performed for pressure from 7.45 to 10.19 MPa, mass flux from 235 to 480 kg/m2/s, bulk fluid temperature from 21 to 205 °C, and heat flux from 10.5 to 96 kW/m2. Noticeable heat transfer deterioration was found in the test section and the heat transfer deterioration point gradually moved close to the inlet section with the increase of power. Results indicated that heat transfer characteristics of supercritical CO2 in present experiments were affected by both buoyancy and flow acceleration. The flow acceleration effect was less pronounced than buoyancy. The point of heat transfer deterioration corresponded with the maximum value of buoyancy parameter (Bu), while no heat transfer deterioration was found when Bu was less than 2.0 × 10−5. By comparing with experimental data from literature, 94.3% of the new correlation predictions were within ±30% error range.